Masonry Walls ~ U-Values and the building Regs

masonry walls and beam-and-block floorsU-values and building regulations

sean doran, bre scotland

special digest SD 42007 edition

this digest is a revision of special digest 4 published in 2003. it explains how the requirements of the building regulations for conservation of fuel and power may be satisfied using aggregate concrete blocks. it gives information on the relevant regulations, showing various approaches to compliance, together with a number of worked examples. it is written for the concrete block industry, for designers, architects and builders who may be considering using masonry, and for enforcers of the regulations who are assessing applications.some of the terms used in this digest are explained in box 1 on page 2.Revised building regulations for the conservation of fuel and power have applied from 6 April 2006 in England and Wales and from 30 November 2006 in Northern Ireland. Similar revisions have applied from 1 May 2007 in Scotland. These new regulations are markedly different in their approach from the previous regulations in their criteria for compliance, by making a requirement in terms of overall CO2 emissions in addition to performance requirements on individual elements. The regulations implement part of the EU Energy Performance of Buildings Directive (EPBD), which calls for a calculation methodology for assessing the energy performance of buildings and for regulations to be set based on that methodology.

For new buildings, the Elemental Method and the Target U-value Method are no longer applicable and instead compliance is now assessed by using SAP 2005 for dwellings[1] or SBEM[2] for buildings other than dwellings. The compliance calculations take into account a combination of factors, including level of insulation, airtightness, efficiency of the heating system and heating controls.

In England and Wales, Conservation of fuel and power is covered by four new Approved Documents, L1A, L1B, L2A and L2B[3], which respectively cover new dwellings,

existing dwellings, new buildings other than dwellings and existing buildings other than dwellings. Section 1 of the documents concerned with new buildings sets out the process for demonstrating compliance in terms of overall energy performance. Section 2 gives guidance on assessing the construction ‘as built’ and contains provision for post-construction testing, including commissioning and mandatory airtightness testing.

New buildings must attain a target CO2 emissions rate where the target rate is determined by the size and shape of the building. The Regulations include guidance on replacement heating systems and replacement windows, doors and rooflights, while recognising that special consideration may be needed for cases such as historic buildings.

In Northern Ireland, requirements for the conservation of fuel and power are described in Technical Booklets F1 (Dwellings) and F2 (Buildings other than dwellings)[4]. In Scotland, Energy is covered by Section 6 of the Scottish Building Standards Technical Handbooks[5].

� masonry walls and beam-and-block floors – SD 4

The Approved Documents L1A, L1B, L2A and L2B for England and Wales and Technical Booklets F1 and F2 for Northern Ireland are supported by the Government’s Accredited Construction Details (ACDs)[6], which cover junctions between elements and detailing around windows and doors. For Scotland, Accredited Construction Details (ACDs) are given on the Scottish Building Standards Agency website[5].

the five key criteria for compliance for dwellings (england, wales and northern ireland)For compliance with the Regulations for England, Wales and Northern Ireland, there are five key criteria which all need to be met.

criterion 1: show that the dwelling (co2) emissions rate (der) does not exceed the corresponding target emissions rate (ter) To obtain the TER, the CO2 emissions rate for a notional dwelling of the same size, shape and ‘living area fraction’ as the proposed dwelling is first calculated using SAP 2005[1]. This notional dwelling has a fixed set of criteria for the fabric heat loss, building services and air permeability, as set out in Appendix R of the SAP 2005 document[1]. The principal values are shown in Table 1.

The notional dwelling corresponds to a dwelling heated by mains gas which complies with the Part L Elemental standards for 2002[3] as set out in Appendix R of the SAP 2005 document[1]. To obtain the TER, the CO2 emissions rate for the space heating and water heating in the notional dwelling is first adjusted by a fuel factor (see Table 2). The CO2 emissions rate for the notional dwelling is then reduced by 20% (to reflect the new standards to be achieved). The result is the TER (Target Emissions Rate).

The emissions calculation is then repeated for the actual dwelling (again using SAP 2005) and if the DER from the proposed dwelling does not exceed the TER then Criterion 1 is satisfied. BRE-approved SAP 2005 software incorporates a function that automatically generates the target CO2 emissions level when the characteristics of the actual dwelling have been defined.

The calculations require information about the efficiency and controls of heating systems (see Box 2 for information on secondary heating). To assist in the calculations, a list of SEDBUK boiler efficiencies is available at www.boilers.org.uk.

The results of the above calculation should be regarded as the ‘design’ DER as it is based on some assumptions (such as air permeability performance, adoption of and adherence to Accredited Construction Details[5,6]) which have to be reviewed post-construction. If any of the ‘as built’ characteristics of the design are worse than initially assumed, the DER calculation must be repeated to ensure that the ‘as built’ DER remains lower than the TER (see Criterion 4).

Box 1: Glossary of terms

Accredited Construction Details A list of examples of typical constructions (used in dwellings) in which the thermal bridging effects are limited to a reasonably low level.

Air permeability The physical property used to measure airtightness of the building fabric at a pressure difference of 50 Pa. It is expressed in m3/(h.m2).

BER The building (CO2) emission rate, equal to the annual rate of emission of CO2 from a building (or building premises) per square metre of floor area.

CHP Combined heat and power.

DER The dwelling (CO2) emission rate, equal to the annual rate of emission of CO2 from a dwelling per square metre of floor area.

Living area fraction The living area, including any room not separated from it by doors, divided by the total floor area of the dwelling.

SAP The Government’s Standard Assessment Procedure.

SBEM Simplified Building Energy Model, used for regulatory purposes as a calculation tool for assessing buildings other than dwellings.

SEDBUK The seasonal efficiency of domestic boilers in the UK. Information on SEDBUK is available from www.boilers.org.uk.

TER The target (CO2) emission rate against which the DER or BER is compared for the purposes of satisfying building regulations.

Thermal bridge A region within a building element where transfer of heat is higher compared with other parts of the same element.

Thermal conductivity (λ) The heat flow in watts per square metre of surface area for a temperature difference of 1 K per metre thickness of material. It is expressed in W/m.K.

Thermal resistance (R) The ability of an element or layer within an element to impede the passage of heat. It is expressed in m2K/W.

U-value (thermal transmittance) The rate of heat transfer in watts through 1 m2 of a structure when the temperatures on each side of the structure differ by 1 ˚C. It is expressed in W/m2K.

Table 1: Specifications for the notional building (for calculating the TER)

U-value of roofs 0.16 W/m2.K

U-value of windows and doors 2.0 W/m2.K

U-value of walls 0.35 W/m2.K

U-value of floors* 0.25 W/m2.K

Efficiency of mains gas boiler 78 %

Airtightness 10 m3/(h.m2) at 50 Pa

*Refers to ground floors and exposed floors.

� SD 4 – masonry walls and beam-and-block floors

criterion 2: design limits should be satisfiedIn addition to limits on overall performance as described above, the Approved Documents give limits for various parts of the dwelling (or building). These limits are intended to ensure that each element of the design plays a part in limiting overall CO2 emissions.

Maximum permissible U-values are shown in Table 3. They give limits for area-weighted U-values of elements and a limit to the allowable U-value of any part of any element. No part of any element may exceed the design limits shown. The documents also give minimum acceptable criteria for the following: • air permeability [which should be no worse than

10 m3/(h.m2)],• heating and hot water systems, • insulation of pipes, ducts and vessels, • mechanical ventilation and cooling,• lighting.

criterion 3: the design should include provision to prevent high internal temperatures in summer due to excessive solar gainsAppendix P of SAP 2005[1] enables designers to calculate an indicative risk of solar gains resulting in high internal temperatures. The risk can be reduced by changing window size and orientation, or by introducing shading devices, increased ventilation or through the use of thermal mass. Further guidance on avoidance of overheating can be obtained from the Energy Saving Trust’s publication CE 129[7].

criterion 4: the performance of the dwelling, ‘as built’, should be consistent with the der

Quality of construction and correct commissioningThe quality of construction and the correct commissioning of building services needs to be demonstrated with reference to the proposed building design. If any assumptions made at the design stage fail to carry through to the final construction, the SAP calculation should be repeated and the ‘as built’ DER calculated and compared with the TER limit.

building servicesA notice should be provided by a suitably qualified person declaring that the building and its services have been inspected, tested and commissioned, and that they are in accordance with the proposed building design.

accredited construction detailsSite inspection and checking is required to confirm that the insulation has been installed satisfactorily to minimise thermal bridging.

air permeability

An air permeability test must be carried out to show that the design air permeability standard has been achieved and that the permeability does not exceed the limit of 10 m3/(h.m2) at 50 Pa. Air pressure testing is required to be carried out to an approved procedure by an ATTMA member or similar accredited tester. The design, construction and operation of dwellings should always recognise the importance of adequate ventilation provision to avert risk of condensation. As a general rule, an increase in controlled ventilation is typically required with increasing airtightness. Guidance is given

Table 2: Fuel factors (for calculating the TER)

Mains gas 1.00

LPG 1.10*

Oil 1.17*

Grid electricity (for direct acting, 1.47* storage and electric heat pumps)

Solid mineral fuel 1.28*

Renewable energy, including 1.00 bio-fuels such as wood pellets

Solid multi fuel 1.00

*In Northern Ireland these figures are multiplied by 1.14.Note: Simply achieving the conditions in Table 1 will not lead to compliance because a further 20% improvement is required and is built into the TER calculation.

Table 3: Maximum permissible U-values (W/m�K) (applicable in England, Wales and Northern Ireland)

Element Maximum Maximum U-value area-weighted for any part U-value of any element (W/m�K) (W/m�K)

Roofs 0.25 0.35Glazed openings 2.2 3.3Doors 2.2 3.3Walls 0.35 0.70Floors 0.25 0.70

Box 3: Air permeability

Air permeability is determined by the air leakage rate (m3/h) per unit envelope area (m2) at a test reference pressure differential across the building envelope of 50 Pa. The envelope area of the building is the total area of all floors, walls and ceilings bordering the internal volume that is subject to the test (including the volume of party walls and floors). Overall internal dimensions are used to calculate this area and no subtractions are made for the area of the junctions of internal walls, floors and ceilings with exterior walls, floors and ceilings.

Box 2: Secondary heating

Approved Document L1A requires that all dwellings are assumed to have a secondary heating system that supplies 10% of the heating demand. In the calculation of the TER, the secondary heating is assumed to consist of electric room heaters and this assumption must follow through to the DER unless a different secondary heating system, capable of supplying at least 10% of the overall requirement is specified.


in Approved Document F[8] for England and Wales or Technical Document K[9] for Northern Ireland.

Where Accredited Construction Details are not used, air pressure tests should be carried out on each dwelling type in the development in accordance with Table 4.

If the test result is greater than 10 m3/(h.m2) at 50 Pa, or greater than the value assumed at the design stage to the extent that the dwelling fails to achieve a compliant DER, the required action is set out in the regulations. This includes remedial measures to reduce air leakage, re-testing of the dwelling to show compliance and an additional test of another dwelling of the same type. It is in the builder’s interests to ensure that the quality of construction, particularly the sealing of air leakage paths, is to an adequately high standard to achieve the limiting value of 10 m3/(h.m2) at 50 Pa. For developments of no more than two dwellings, the need for air pressure testing can be avoided if a dwelling of the same type has been tested elsewhere in the previous 12 months, or alternatively if an air permeability rate of 15 m3/(h.m2) at 50 Pa is used in the calculation of the DER. The latter choice would usually mean having to make significant improvements elsewhere in the design to attain the TER.

calculating the ‘as built’ derOnce all of the above ‘as built’ data have been determined, the dwelling emissions rate (DER) should be recalculated to reflect any changes between the design assumptions and the actual performance and actual details of the construction ‘as built’.

The heating and hot water systems should be commissioned and a notice issued by a competent person to the local authority to confirm that commissioning has taken place.

criterion 5: the operation and maintenance information should be provided to the owner to enable the building and its services to be operated in an energy-efficient mannerThe owner of the building should be provided with a set of simple operating and maintenance instructions explaining how to use the installed heating and hot water system to achieve economy in use.

compliance in scotlandSection 6 of the Scottish Building Standards Technical Handbooks deals with energy[5]. The basis is similar to that adopted for England & Wales, by setting an overall carbon emissions target, but for dwellings the target is established in a slightly different way. The guidance document gives specifications for notional dwellings (of the same size and shape as the proposed dwelling) that define the target CO2 emissions rate, but without application of improvement factors or fuel factors. Instead of applying fuel factors, as is done in England & Wales, the differences in carbon intensities of different fuels are taken into account by the definition of a notional dwelling for each fuel category (gas, LPG, oil, electricity, solid mineral and biomass). It follows that if the dwelling is constructed to specifications at least as good as the notional dwelling it is not necessary to perform calculations to demonstrate compliance.

For buildings other than dwellings, the target emissions level is set in the same way as in England and Wales (the target is slightly lower (ie slightly more demanding) because the notional building is based on the 2002 Elemental U-value standard of 0.30 W/m2K, rather than 0.35 W/m2K, for walls).

In addition to the requirement for CO2 emissions, there are requirements for U-values of elements, heating efficiency and controls, insulation of pipes, ducts and vessels, summer overheating, commissioning and provision of information. The maximum permissible U-values are shown in Tables 5 and 6. Further information, including guidance on Accredited Construction Details and discrete thermal bridging around openings, can be found on the SBSA website at www.sbsa.gov.uk[5].

In Scotland, the dwelling can comply if its performance is at least as good as the notional dwelling, as defined in Table 6. In Scotland, the notional dwelling would be considered to satisfy the requirements. In England, Wales and Northern Ireland, the notional dwelling would not satisfy the requirements.

boiler efficienciesTo assess compliance with Regulations, it is necessary to provide information such as the efficiency of the heating system and the types of controls. SAP 2005 software incorporates a database of boiler efficiencies which is automatically accessed by approved SAP software. To assist in providing this information, a list of seasonal

Table 5: Maximum permissible U-values in W\m�K (applicable in Scotland)

Element Maximum area- Maximum U-value weighted for any part U-value of any element (W/m�K) (W/m�K)

Roofs 0.20 0.35Glazed openings 2.2 3.3Doors 2.2 3.3Walls 0.30 0.70

Floors 0.25 0.70

Table 4: Requirement for air pressure testing

Number of instances Number of tests to be carried of the dwelling type out on each dwelling type

Four or less One test on each dwelling typeMore than 4 Two tests of each dwelling type but not more than 40

More than 40 At least 5% of each dwelling type unless the first five units of the type tested achieve the design air permeability in which case the sampling can be reduced to 2%

Table 6: Specification for the ‘notional dwelling’ in Scotland

Element Mains gas LPG Oil Electric Heating Solid fuel or system heating heating heating heating by biomass heating (see Note 1) (see Note 1)

Walls U = 0.25 W/m2K U = 0.25 W/m2K U = 0.25 W/m2K U = 0.25 W/m2K U = 0.25 W/m2K U = 0.20 W/m2KFloors U = 0.22 W/m2K U = 0.22 W/m2K U = 0.20 W/m2K U = 0.22 W/m2K U = 0.22 W/m2K U = 0.20 W/m2KRoofs U = 0.16 W/m2K U = 0.16 W/m2K U = 0.16 W/m2K U = 0.16 W/m2K U = 0.16 W/m2K U = 0.16 W/m2KOpenings U = 1.8 W/m2K U = 1.8 W/m2K U = 1.7 W/m2K U = 1.8 W/m2K U = 1.8 W/m2K U = 1.5 W/m2K (see Note 2) Area is 25% Area is 25% Area is 25% Area is 25% Area is 25% Area is 25% of floor area of floor area of floor area of floor area of floor area of floor areaAllowance for 0.08 × total 0.08 × total 0.08 × total 0.08 × total 0.08 × total 0.06 × total thermal bridging exposed surface exposed surface exposed surface exposed surface exposed surface exposed surface (see Note 3) area (m2) area (m2) area (m2) area (m2) area (m2) area (m2)Open flues None One One None One OneHeating system Gas boiler LPG boiler Oil boiler Air to water HETAS-approved HETAS-approved (pump in room-sealed, room-sealed, room-sealed, heat pump wood pellet anthracite boiler heated space) fan flued, fan flued, fan flued, boiler with autofeed in with 90% with 90% with 93% heated space efficiency efficiency efficiencyHeating system Programmer, Programmer, Programmer, Programmer, Programmer, Programmer, controls room thermostat, room thermostat, room thermostat, room thermostat, room thermostat, room thermostat, TRVs, boiler TRVs, boiler TRVs, boiler TRVs TRVs interlock interlock interlock, weather compensationHot water system Stored HW (from Stored HW (from Stored HW (from Stored HW by Stored HW (from Stored HW by (not applicable if boiler) with boiler) with boiler) with electric boiler) with dual electric combination boiler) separate time separate time separate time immersion separate time immersion and control for space control for space control for space control for space solar and water heating and water heating and water heating and water heatingSecondary space 10% electric 10% closed 10% closed 10% electric 10% electric 10% electric heating wood log-burning wood log-burning room heater room heater (see Note 4) (see Note 4)Solar panels, None None None None None 4 m2 panel evacuated tube, between SE and collector efficiency SW, not more η = 0.6, a1 = 3 than 45° pitch, no overshadingArea of windows, doors and rooflightsOrientation All glazing oriented east/westShading from sun Average overshadingNumber of

2

sheltered sidesChimneys NoneVentilation system Natural ventilation with intermittent extract fans, 4 for dwellings with floor area more than 80 m2, otherwise 3Air permeability 10 m3/(h.m2) at 50 PaHot water cylinder (for solar water heating a combined 150 litre cylinder insulated with 50 mm of factory-applied foam cylinder with solar (cylinder in heated space) store 75 litre, Cylinder temperature controlled by thermostat no solar-powered pump) Primary water

Primary pipework insulated

heating losses

Low energy 50% of fixed outlets light fittings

Notes:1 The biomass column should be used not only where biomass fuel is used but also for biogas, large scale waste combustion from boilers and waste heat from power stations. It does not, however, include dual or multi-fuel which should be taken under the ‘solid fuel’ column.2 U is the average U-value of all openings (windows, doors, rooflights) based on one opaque door 1.85 m2 of U = 1.8 W/m2K, any other doors fully glazed. For windows, doors, etc. a frame factor of 0.7, light transmittance of 0.80 and solar energy transmittance of 0.72 for U ≥ 1.7, 0.63 for U < 1.7 are assumed.3 Construction using ‘Accredited Construction Details’ (Scotland) is considered to correspond to the default figure of 0.08 for thermal bridging.4 Under secondary heating, the closed wood log-burning room heater is capable of burning wood only, not multi-fuel.5 If total exposed façade area is less than 25% of the floor area, the total exposed façade area.

Total of 25% of total floor area



boiler efficiencies (SEDBUK), together with additional information about SEDBUK, is given on the website www.boilers.org.uk.

workmanshipGood workmanship and appropriate site procedures are necessary to achieve the design thermal performance and airtightness. Achieving this in practice is likely to depend on a combination of good site management, training and monitoring. Key points for achieving this are:• continuity of the insulation layer,• continuity of vapour barriers,• sealing of services penetrations.

Management of all contractors concerned with constructing the building fabric need to be aware of the requirements to ensure that insulation materials of the correct specification are installed as directed and with the specified degree of continuity. They also need to be aware of ensuring that the fabric is constructed to be airtight. Contractors (such as plumbers and electricians) responsible for installing services which penetrate the building fabric need to be aware of the need to restore or replace any insulation that has been disturbed and to ensure that service penetrations are made airtight.

effective detailing at jUnctions At junctions between walls, floors, roofs and openings it is important to avoid excessive thermal bridging, which can lead to increased heat loss, unwanted condensation or mould growth. For example, a junction between two adjacent walls and a ground floor can be particularly prone to low surface temperatures, leading to risk of mould at the corner. A series of junction details that are deemed to be of low risk are published in the Accredited Construction Details document[6]. For junctions not covered in Accredited Construction Details, see Box 4.

The increased heat loss attributable to a junction (which is not accounted for within the U-values) is indicated by its linear thermal transmittance value, or Ψ-value, and this is expressed in watts per metre per degree (W/m.K). A low Ψ-value indicates a good detail, while a high Ψ-value indicates a poor detail (as far as heat loss is concerned). A Ψ-value cannot be evaluated using simplified calculation procedures and has to be calculated using detailed thermal modelling procedures in accordance with BRE’s report Conventions for calculating temperature factors and linear thermal transmittance[13].

Table 7 gives default linear thermal transmittance values for junctions[10]:

The reduced surface temperatures caused by thermal bridging at junctions is indicated by an f-factor, where a high f-factor indicates a slight reduction in surface temperature and a low f-factor indicates a severe reduction in surface temperature and an increased risk of mould growth or condensation. An f-factor of 0.75 or above is considered acceptable for dwellings. More information on the definition, calculation and interpretation of f-factors is given in reference [10] as well as an indication of minimum acceptable f-factors. Accredited Construction Details are deemed to have an acceptable f-factor.

In cavity walls, particularly at wall–floor junctions where the insulation layer is interrupted, it is important to maintain a sufficient overlap between the floor insulation and the wall insulation and guidance is given in Accredited Construction Details[6] and the SBSA website[5]. For an internally insulated structure, where it abuts other construction details, the insulated layer needs to be kept continuous around the perimeter of the building. At window reveals it is important to maintain an overlap (typically 30 mm) between the frame (including packers) and the wall insulation.

A decision not to follow Accredited Construction Details (or details which are certified as being of satisfactory thermal performance) may lead to poorer dwelling performance. If a particular detail is not an Accredited Construction Detail then it should be dealt with by following the guidance in reference [10]. If details other than Accredited Construction Details are used it is necessary to show that the detail will not lead to unacceptably low surface temperature factors, as junctions with low surface temperature factors will

Box 4: Thermal bridging

Discrete thermal bridging that is not covered in Accredited Construction Details[6] needs to be accounted for and this may be done using the method in BRE’s Information Paper IP 1/06[10]. For additional information about risks associated with thermal bridging, see BRE Report Thermal insulation: avoiding risks[11]. For information about detailing in cladding constructions, reference is made to MCRMA Technical Paper no. 17[12].

Table 7: Default ψ-values for junctions in Accredited Construction Details[�]

Junction detail Default linear in external wall thermal transmittance (W/m.K)

Steel lintels with perforated 0.50 steel base plateOther lintels (including 0.30 other steel lintels)Sill 0.04Jamb 0.05Ground floor 0.16Intermediate floor within a dwelling 0.07Intermediate floor between dwellings* 0.14Balcony within a dwelling† 0.00Balcony between dwellings*† 0.04Eaves: insulation at ceiling level 0.06Eaves: insulation at rafter level 0.04Gable: insulation at ceiling level 0.24Gable: insulation at rafter level 0.04Corner (wall–wall junction): normal 0.09Corner (wall–wall junction): inverted -0.09Party wall between dwellings* 0.06

* Half of the linear thermal transmittance is assigned to each dwelling. † This is an externally supported balcony (not a continuation of the floor slab) where the insulation is continuous and is not bridged by the balcony slab.

� SD 4 – masonry walls and beam-and-block floors

have an increased risk of surface mould growth or condensation.

assessing carbon emissions for a bUilding other than a dwellingFor buildings other than dwellings SBEM[2] can be used for calculating the Building Emissions Rating, BER. Additionally, other approved software, as detailed on www.ncm.bre.co.uk, may be used.

For buildings other than dwellings the BER must be shown to be no higher than the Target Emissions Rate (TER) for the building. A preliminary calculation is done as part of the design submission, based on plans/specifications and must be done using an approved calculation tool (eg SBEM). Once the building has been constructed, a final calculation is carried out incorporating any design changes and including results for actual air permeability, ductwork leakage and fan performance as commissioned.

Box 5: Dwelling data for Example A

Ground floor area 40.0 m2

Area of windows 16.30 m2

Glazed door 1.85 m2

Opaque door 1.85 m2

Wall area (net) 70.0 m2

Roof area 40.0 m2

Fuel type mains gas

Secondary fuel electricity

Boiler type combination

Secondary heating electric room heaters (10%)

foUr examples of constrUctions

To illustrate the requirements of the regulations, compliance is assessed for the following four constructions, each of which uses aggregate blocks. All of these four examples pass the requirements.

example a: semi-detached (or end-terraced) houseA typical two-storey semi-detached house has blockwork cavity walls, a pitched roof with insulation at ceiling level and is glazed with low-emissivity windows. It has a total area of 80.0 m2, and is to be heated using a gas boiler serving radiators and controlled by a programmer, room thermostat and thermostatic radiator valves (TRVs). The summary specification is given in Box 5.

calculation of target (co2) emissions rate (ter)Taking into account the dwelling size and shape, the carbon dioxide emissions for the ‘notional dwelling’ are calculated using SAP software on the basis of the fixed performance assumptions shown in Table 1 of this Digest. This gives a TER of 23.22 kg/m2.yr. Figure A1: A floor plan of the dwelling

5.2 m

7.7 m

7.7 m

Door

First floor

Ground floor

Door


calculation of dwelling (co2) emissions rate (der)The DER for the notional dwelling is 29.02 kg/m2.yr. Clearly, the notional dwelling design will not satisfy the requirements; to satisfy the requirements various improvements are needed. The schedule given in Table 8 shows a series of ‘improvement measures’. These are listed together with their respective CO2 emissions savings (calculated relative to the notional dwelling performance).

No specific secondary heating system is provided for the proposed dwelling so the default setting (electric appliance meeting 10% of the space heating demand) is carried through from the TER to the DER calculation.

The total CO2 emissions rate when all of the above energy-saving measures are applied is less than the TER of 23.22 kg/m2.yr and the dwelling therefore complies, subject to subsequent confirmation that the actual dwelling characteristics as constructed are no worse than assumed at the design stage.

Since the DER is not more than the TER this improved specification satisfies the requirements. Table 9 shows alternative designs which comply.

Table 8: Improvement measures for Example A

Adjustment Resulting to DER DER (kg/m².yr (kg/m².yr of CO�) of CO�)

Unimproved (notional dwelling) 29.02 with values as in Table 1Improvement measure (compared with the notional dwelling) 50 mm tank insulation (instead of -0.78 28.24 38 mm) and primary pipework insulation Use of Accredited Construction -0.87 27.37 DetailsSEDBUK boiler efficiency -2.8 24.57 of 90% instead of 78%Air permeability of 8.0 m3/(h.m2) -0.39 24.18 at 50 Pa instead of 10.0 m3/(h.m2)Floor U-value of 0.18 W/m2K -0.42 23.76Wall U-value of 0.30 W/m2K -0.52 23.24Window & door U-value -0.51 22.73 of 1.8 W/m2KTotal adjustment -�.�9Improved (proposed dwelling) 22.73

Table 9: Variations to the house design for Example A

Examples which comply Case 1 * Case � Case �Boiler efficiency 90% 91% 90%Airtightness 8 m3/(h.m2) 7 m3/(h.m2) 10 m3/(h.m2)Wall U-value 0.30 W/m2K 0.35 W/m2K 0.30 W/m2KFuel Mains gas Mains gas Mains gasFloor U-value 0.18 W/m2K 0.18 W/m2K 0.18 W/m2KTime–temperature zone control No No Yes

* As in detailed schedule.

Lighting

Pumps and fans

Water heating

Space heating (secondary)

Space heating (main system)

45%

4%

41%

2%

8%

Figure A2: Pie chart showing typical distribution of fuel use (based on SAP calculations)

9 SD 4 – masonry walls and beam-and-block floors

example b: detached houseA two-storey detached house has masonry cavity walls and a pitched roof with insulation at ceiling level. It has a total floor area of 100 m2. The summary specification is given in Box 6.

calculation of dwelling (co2) emissions rate (der)The DER for the notional dwelling is 32.12 kg/m2.yr. Clearly, the notional dwelling design will not satisfy the requirements; to satisfy the requirements various improvements are needed. Table 10 gives a schedule that shows a series of ‘improvement measures’. These are listed together with their respective CO2 emissions savings (calculated relative to the notional dwelling performance).

Examples of changes to the design which would lead to further improved performance are given in Table 11.

Box 6: Dwelling data for Example B



Glazed door 1.85 m2

Opaque door 1.85 m2

Wall area 125 m2

Roof area 50.0 m2

Fuel type mains gas


Boiler type regular


Hot water cylinder 150 litres

Table 10: Improvement measures for Example B

Adjustment Resulting to DER DER (kg/m².yr (kg/m².yr of CO�) of CO�)

Unimproved (notional dwelling) 32.12 with values as in Table 1Improvement measure (compared with the notional dwelling) 50 mm tank insulation (instead of -0.54 31.58 38 mm) and primary pipework insulation Use of Accredited Construction -2.49 29.09 DetailsSEDBUK boiler efficiency -2.99 26.10 of 90% instead of 78%Air permeability of 8.0 m3/(h.m2) -0.43 25.67 at 50 Pa instead of 10.0 m3/(h.m2)Floor U-value to 0.22 W/m2K -0.18Wall U-value of 0.30 W/m2K -0.77 24.90Window & door U-value -0.48 24.42 of 1.8 or 2.1 W/m2KTotal adjustment -�.��Improved (proposed dwelling) 24.24

calculation of target (co2) emissions rate (ter)Taking into account the dwelling size and shape, the CO2 emissions for the ‘notional dwelling’ are calculated using SAP software on the basis of the fixed performance assumptions shown in Table 1 of this Digest. This gives a TER of 24.25 kg/m2.yr.

Figure B1: A floor plan of the dwelling

6.2 m

8 m

8 m

Door

First floor

Ground floor

Door

10 masonry walls and beam-and-block floors – SD 4

It is proposed to build a small single-storey office near Manchester. The office, which has a total floor area of 250 m2, consists of a reception, an open-plan office, cellular offices, a meeting room and washroom/toilets. The open-plan office is conceptually divided into two zones, an east zone and a west zone, according to the conventions given for SBEM. The summary specification is given in Box 7.

The areas and U-values for the construction are given in Table 12.

The total CO2 emissions rate (BER) when all of the above specification items are applied is 30.54 kg/m2.yr, which is less than the target emissions (TER) rate of 31.30 kg/m2.yr so the building therefore complies.

Z0/03, Open-plan office,

west side, 72 m2

Z0/04, Cellular offices,

54 m2

Z0/02, Open-plan office,

east side, 36 m2

Z0/05, Meeting room,

36 m2

Z0/01, Reception,

36 m2

Z0/06, Toilets, 18 m2

Figure C1: A floor plan of the office

Table 11: Variations to the house design for Example B

Change to design Change in DER Resulting DER Result (kg/m�.yr) (kg/m�.yr)Improving air tightness from 8 to 6 m3/(h.m2) and -0.04 24.20 Pass increasing wall U-value from 0.30 to 0.32 W/m2KUse of time/temperature zone control and -0.06 24.18 Pass increasing wall U-value from 0.30 to 0.34 W/m2KImproving airtightness from 8 to 6 m3/(h.m2) and, -0.24 24.00 Pass using temperature/time zone control and increasing wall U-value from 0.30 to 0.35 W/m2K

example c: small office (not air-conditioned)

Lighting

Pumps and fans

Water heating



52%

5%

34%

2%7%

Figure B2: Pie chart showing typical distribution of fuel use (based on SAP calculations)


Box 7: Building data for Example C

Air permeability 6 m3/(h.m2)

U-value of roof 0.13 W/m2K

Thermal capacity per 8.8 kJ/m2K unit area for roof

U-value of wall 0.35 W/m2K

Cm of wall 80 kJ/m2K

U-value of floor 0.2 W/m2K

Cm of floor 60 kJ/m2.K

U-value of window 1.8 W/m2K

Dead-leg length in toilets 1 m

Room height 3 m

Type of boiler LTHW

Seasonal efficiency of boiler 90%

Heating distribution central heating using water to radiators

Table 12: Areas and U-values for Example C construction

External element Net surface area U-value Details (m�) (W/m�K)Ground floor 250 0.22 Z0/01 (Reception), 36 m2 Open plan, east side, 36 m2 Open plan, west side, 72 m2 Cellular offices, 54 m2 Meeting room, 36 m2 Toilets, 18 m2

Windows and glazed doors 1.8 Opaque doors 1.8 External walls 270 0.3 Z0/01 (Reception), north wall, 9 m2 Z0/01 (Reception), east wall, 18 m2 Z0/02 (Open Plan, east side), east wall, 18 m2 Z0/02 (Open Plan, east side), north wall, 18 m2 Z0/03 (Open Plan, west side), north wall, 36 m2 Z0/03 (Open Plan, west side), west wall, 18 m2 Z0/04 (Cellular offices), south 27 m2, west 18 m2 Z0/05 (Meeting room), south 18 m2 Z0/06 (Toilets), east 9 m2 Z0/06 (Toilets), south 18 m2 Z0/06 (Toilets), west 9 m2

Roof 250 0.16 Z0/01 (Reception), 36 m2 Open Plan, east side, 36 m2 Open Plan, west side, 72 m2 Cellular offices, 54 m2 Meeting room, 36 m2 Toilets, 18 m2

Total —

Lighting

Pumps and fans

Water heating



59%

0%

2%

22%

17%

Figure C2: Pie chart showing typical distribution of fuel use (based on SAP calculations)

1� masonry walls and beam-and-block floors – SD 4

example d: ground floor flatIt is proposed to build a ground floor flat with blockwork cavity walls, low-emissivity windows and a mains gas boiler serving radiators. The summary specification is given in Box 8.

No specific secondary heating system is provided for the proposed dwelling so the default setting (electric appliance meeting 10% of the space heating demand) is carried through from the TER to the DER calculation.

The total CO2 emissions rate when all of the above energy-saving measures are applied is less than the target emissions rate of 26 kg/m2/yr and the dwelling therefore complies, subject to subsequent confirmation that the actual dwelling characteristics as constructed are no worse than assumed at the design stage.

Since the DER is not more than the TER this improved specification satisfies the requirements. Table 14 shows how the DER is affected by various changes to the design.

Table 14: Changes to the house design for Example D

Case 1* Case �

Boiler efficiency 90% 86%Wall U-value 0.35 0.30Pass or Fail Pass Pass

* As in detailed schedule.

Box 8: Dwelling data for Example D



Door area 1.85 m2

Wall area (net) 125 m2

Type of heating system gas boiler to radiators

Main heating fuel mains gas


Boiler type regular


Water tank volume 117 litres

Figure D1: A floor plan of the dwelling

6.2 m

8 m

Door

Ground floor

Table 13: Improvement measures for Example D

Adjustment Emissions to DER DER emissions (kg/m²/yr) (kg/m²/yr)

Unimproved (notional dwelling) 32.25 with values as in Table 1Improvement measure (compared with the notional dwelling) Use of Accredited Construction -0.81 31.44 DetailsBoiler efficiency of 90% -3.29 28.15 instead of 78%Air permeability of 8.0 m3/(h.m2) -0.40 27.75 instead of 10.0 m3/(h.m2)Floor U-value of 0.20 W/m2K -0.55 27.20 instead of 0.25 W/m2KWindow & door U-value -0.49 26.71 of 1.8 W/m2K instead of 2.0 W/m2KTank insulation of 50 mm -0.23 26.48 instead of 38 mmPrimary pipework insulation -0.81 25.67

calculation of target (co2) emissions rate (ter)Taking into account the dwelling size and shape, the CO2 emissions were calculated on the basis of the fixed assumptions in Table 1, giving a TER of 26.10 kg/m2.yr

calculation of dwelling (co2) emissions rate (der)The DER for the notional dwelling is 32.25 kg/m2.yr. Clearly, the notional dwelling design will not satisfy the requirements; to satisfy the requirements various improvements are needed. Table 13 shows a series of ‘improvement measures’. These are listed together with their respective CO2 emissions savings (calculated relative to the notional dwelling performance).

1� SD 4 – masonry walls and beam-and-block floors

calcUlating U-valUesAssessment of compliance with regulations requires U-values to be provided for all the elements and components making up a building, dwelling or premises. U-values of masonry constructions, together with most roofs and floor decks, can be assessed using the method in BS EN ISO 6946[15], also known as the Combined Method. U-values of ground floors can usually be assessed using the method in BS EN ISO 13370[16]. Inexpensive software to calculate U-values according to these standards is available commercially.

U-value calculations should take account of the conventions given in BRE’s Conventions for U-value Calculations[14] (www.bre.co.uk/uvalues). They should include allowances for any repeating thermal bridges, but should not make any allowance for non-repeating thermal bridges, as these are dealt with separately.

Tables of U-values are given in this Digest which are based on typical constructions. The underlying assumptions used in the calculations are given below.

assumptions on mortar fractionsTable 15 indicates appropriate mortar fractions for various options, based on guidelines in reference [14].

Outer leaf concrete blocks with a sand–cement render are treated as exposed, and outer leaf mortar is assumed to have a conductivity of 0.94 W/m.K. Blocks with a polymer render and inner leaf blocks are treated as protected and mortar is assumed to have a conductivity of 0.88 W/m.K. Conductivities of exposed and protected concrete blocks are taken from Table 3.1 of CIBSE Guide A (2006 edition)[17]. Typical conductivities of other materials are obtained from CIBSE Guide A and BS EN 12524/(ISO 10456)[18]. If the difference in the thermal resistance of a block and its associated mortar

is less than 0.1 m²K/W the effect of the mortar may be disregarded in the U-value calculation (as has been done in preparing the tables later in this Digest).

A conductivity of 17 W/m.K is generally considered appropriate for stainless steel wall ties. Guidance on wall ties for masonry walls is given in BS 5628[19]. The effect of wall ties may be disregarded if the total of the corrections to the U value is less than 3% of the overall U-value of the wall (as permitted in BS EN ISO 6946[15]), and this has been done in the calculations in this Digest.

wall tiesBS 5628[19] requires that the leaves of a cavity wall be tied together by wall ties and gives guidance on the number and type of wall ties which should be provided. The choice of the type of wall tie and spacing depends on the cavity width and the widths of the leaves of the cavity wall.

Typical wall tie types and densities are shown in Table 16.

Examples of constructions, together with their U-values, are given in this Digest. They are based on standard-sized insulation products and they show how suitable U-values may be achieved for a variety of constructions. The construction solutions are based on the rules for declaring thermal conductivity values for insulation products as given in the applicable standards[20] taking account of product variation (90% percentile values) and aged values. Guidance on the conductivities of other materials can be found in references [14, 17, 21].

Guidance on discrete thermal bridging is given in reference [10].

For additional information about risks associated with thermal bridging, refer to BRE’s Report Thermal insulation: avoiding risks[11].

Resistances of air cavities and other airspaces within cavity walls are calculated according to the method in BS EN ISO 6946[15] and conventions in reference [14], taking account of the dimensions of the airspace, ventilation level and emissivity of bounding surfaces. Table 17 gives resistances of airspaces in walls for some typical dimensions. BS EN ISO 6946[15] also gives guidance for assessing resistances of airspaces in other types of walls, roofs and exposed floors. Guidance on the treatment of airspaces in suspended ground floors is given in BS EN ISO 13370[16]. Further information on airspaces can be found in Section 3.3.8 of CIBSE Guide A[17].

The U-value of a solid or suspended ground floor varies depending on the size and configuration of the floor plan. In the ground floor examples, the U-values

Table 15: Mortar fractions

Option Mortar fractionStandard 440 mm × 215 mm 0.067 (ie 6.7%) concrete blocks with a mortar width of 10 mmBlocks laid flat such that the 0.112 (if 10 mm horizontal 100 mm dimension is the height and vertical mortar joints are used) or 0.131 (if 10 mm vertical mortar joints and 12.5 mm horizontal mortar joints are used)

Table 16: Typical wall tie specifications for cavity walls

Cavity width Minimum thickness of the Tie material Cross-section Ties per inner and outer leaves (mm�) square metre of the cavity wallUp to 100 mm 90 mm or more Stainless steel 12.5 2.5101 to 150 mm 90 mm or more Stainless steel 50 2.5151 to 300 mm 90 mm or more Stainless steel 80 2.5

These values are based on typical ties compliant with BS 5628[19], taking into consideration conventions in reference [14]. Wall tie types are defined in Annex C of BS 5628-1[19].


have been calculated for a typical small detached house with a perimeter to area ratio of 0.57 m-1 (ie floor area ÷ floor perimeter = 1.75 metres). Large floor areas will generally lead to lower U-values (ie lower heat loss) due to their more favourable perimeter to area ratio.

References [14] and [15] give guidance on how to allow for air gaps between and around sections of insulation. In particular, reference [14] gives guidance on the use of appropriate air gap correction levels.

For calculating U-values of constructions other than those presented in this Digest, the conductivity values given in Table 18 may be regarded as typical. They take account of insulation ageing and 90% percentile values. Additional information on insulation materials can be obtained from www.timsa.org.uk.

Table 18: Conductivity values for insulation materials

Material Conductivity (W/m.K)Phenolic foam 0.021–0.024Rigid polyurethane 0.022–0.028Polyisocyanurate 0.022–0.028Mineral wool (including batts 0.032–0.044 and blown fibre)Expanded polystyrene (including boards 0.030–0.038 and injected beads)Grey expanded polystyrene ca 0.032Extruded polystyrene 0.029–0.039Plywood, chipboad or oriented 0.13 strand boardPlasterboard (standard wallboard) 0.21Acoustic or fire-resistant plasterboard 0.25Outer leaf brick 0.77Timber roof or floor joists 0.13Timber rafters 0.13Dense aggregate concrete block, 1.22 1800 kg/m3 (protected)Dense aggregate concrete block, 1.31 1800 kg/m3 (exposed)Low density block (protected)* 0.30Blocks with furnace bottom ash 0.46 aggregate (protected)*Blocks with furnace bottom ash 0.49 aggregate (exposed)Blocks with other lightweight aggregate 0.57 (protected)*Blocks with other lightweight aggregate 0.61 (exposed)Cement/sand external render 1.00Mortar (exposed) 0.94Mortar (protected)* 0.88

* ‘Protected’ refers to blocks that are not exposed to wetting, such as inner leaf blocks or blocks that are protected by a polymer render.

Table 17: Thermal resistances of airspaces in walls

Thickness of Resistance for Resistance if airspace surfaces of one surface (mm) normal has an emissivity emissivity of 0.� or less 5 0.11 0.17 7 0.13 0.2210 0.15 0.2915 0.17 0.3720 or more 0.18 0.44

Note: These figures are based upon standard ambient temperatures where one surface has an emissivity of 0.9 and the other surface has an emissivity of either 0.9 (first column) or 0.2 (second column).


U-valUes for masonry wall constrUctionsThe following examples give tabulated U-values (W/m²K), for various types of ‘new-build’ constructions.

example 1: cavity wall fully filled with insulation, having brick outer leaf, blockwork inner leaf and internal plaster finish

102 mm external brickwork, λ = 0.77 W/m.K

Cavity insulation bridged by stainless steel wall ties

100 mm concrete blocks bridged by 6.7% mortar, λ = 0.88 W/m.K

13 mm dense plaster, λ = 0.57 W/m.K

Notes

• Refer to manufacturers’ test information for further information on conductivities of insulation materials.

• Final U-values should be rounded to two decimal places.

• To obtain intermediate values, linear interpolation may be used.

U-values (W/m�K) for a range of fully filled cavity wall designs

Block type

Cavity *Af Conductivity Correction Low- Medium- Medium- High- width (mm) of insulation level density density density density (mm) (W/m.K) blocks blocks blocks blocks λ = 0.�0 Wm.K λ = 0.�� Wm.K λ = 0.�� Wm.K λ = 1.�� Wm.K 75 12.5 0.032 0 0.336 0.348 0.352 0.363 75 12.5 0.032 1 0.336 0.348 0.363 0.375100 12.5 0.042 0 0.332 0.343 0.348 0.358100 12.5 0.039 0 0.313 0.323 0.327 0.336100 12.5 0.036 0 0.293 0.302 0.306 0.314100 12.5 0.032 1 0.276 0.284 0.287 0.294100 12.5 0.032 0 0.266 0.273 0.276 0.283125 50 0.042 0 0.286 0.295 0.298 0.306125 50 0.039 0 0.270 0.277 0.280 0.287125 50 0.036 0 0.253 0.260 0.262 0.269125 50 0.032 1 0.238 0.243 0.246 0.251125 50 0.032 0 0.230 0.236 0.238 0.243150 50 0.042 0 0.246 0.252 0.255 0.260150 50 0.039 0 0.232 0.237 0.239 0.244150 50 0.036 0 0.217 0.222 0.224 0.228150 50 0.032 1 0.204 0.209 0.210 0.214150 50 0.032 0 0.197 0.201 0.202 0.206

A correction level of 0 corresponds to a situation where no air gaps exceeding 5 mm penetrate the insulation layer and is applicable where insulation materials have high dimensional tolerances. A correction level of 1 corresponds to a situation where tolerances can be more than 5 mm but where air is still unable to circulate on both sides of the insulation.* Af is the cross-sectional area of each wall tie (mm2).Factors influencing the U-value are indicated in blue.Values which do not meet the limit in Table 1 are shown in red.

Table of adjustments to be applied to the U-value for specific design variants

U-value of wall before adjustment (W/m�K)

Variation 0.� 0.� 0.� 0.�Lightweight plaster (λ = 0.18 W/m.K) instead of dense plaster –0.002 –0.004 –0.008 –0.01212.5 mm plasterboard on 15 mm plaster dabs –0.005 –0.012 –0.021 –0.032 with well sealed joints, instead of 13 mm dense plaster12.5 mm plasterboard on 22 mm battens (12%) –0.008 –0.018 –0.032 –0.049 with well sealed joints, instead of 13 mm dense plasterExternal render (19 mm thick) –0.001 –0.002 –0.003 –0.005Dense blockwork outer leaf +0.002 +0.005 +0.009 +0.014No internal plaster finish +0.001 +0.002 +0.004 +0.006


example 2: cavity wall partially filled with insulation

102 mm external brickwork, λ = 0.77 W/m.K, over 50 mm clear unventilated wall cavity

Insulation bridged by stainless steel wall ties



Notes




U-values (W/m�K) for a range of partially filled cavity wall designs

Block type

Total Insulation *Af Conductivity Low- Medium- Medium- High- cavity thickness (mm�) of insulation density density density density width (mm) (W/m.K) blocks blocks blocks blocks (mm) λ = 0.�0 Wm.K λ = 0.�� Wm.K λ = 0.�� Wm.K λ = 1.�� Wm.K100 50 12.5 0.023† 0.308 0.318 0.322 0.331110 60 50 0.023† 0.291 0.299 0.303 0.311125 75 50 0.032 0.329 0.340 0.345 0.355125 75 50 0.023† 0.249 0.255 0.258 0.264150 100 50 0.042 0.313 0.333 0.337 0.348150 100 50 0.036 0.289 0.297 0.301 0.309150 100 50 0.032 0.265 0.272 0.275 0.281150 100 50 0.023† 0.202 0.206 0.208 0.211175 125 50 0.042 0.272 0.280 0.283 0.290175 125 50 0.036 0.242 0.248 0.251 0.256175 125 50 0.032 0.221 0.226 0.228 0.233175 125 50 0.023† 0.170 0.173 0.174 0.177

* Af is the cross-sectional area of each wall tie (mm2).† An air gap correction level of 1 and foil facing (emissivity 0.2) are assumed for materials of conductivity less than 0.03 W/m.K.Note: In some instances in the above Table, the rules in BS EN ISO 6946[15] permitted the effects of wall ties to be ignored.Factors influencing the U-value are indicated in blue.Values which do not meet the limit in Table 1 are shown in red.



Variation 0.� 0.� 0.� 0.�13 mm lightweight plaster (λ = 0.18 W/m.K) –0.002 –0.004 –0.008 –0.012 instead of 13 mm dense plaster12.5 mm plasterboard on 15 mm plaster dabs –0.005 –0.012 –0.021 –0.032 with well sealed joints, instead of 13 mm dense plaster12.5 mm plasterboard on 22 mm battens (12%) –0.008 –0.018 –0.032 –0.049 with well sealed joints, instead of 13 mm dense plasterExternal render (19 mm thick) –0.001 –0.002 –0.003 –0.005Dense blockwork outer leaf +0.002 +0.005 +0.009 +0.014No internal plaster finish +0.001 +0.002 +0.004 +0.006


example 3: cavity wall with clear cavity and external insulation and thin coat polymer render

External insulation with 6 mm polymer render

50 mm clear unventilated cavity bridged by stainless steel wall ties



Notes




• The conductivity figure of 1.22 W/m.K for dense outer leaf concrete blocks is based on a 3% moisture content, appropriate for sheltered or protected blocks.

U-values (W/m�K) for a range of external insulation options

Block type

Insulation Conductivity Low- Medium- Medium- High- thickness of insulation density density density density (mm) (W/m.K) blocks blocks blocks blocks λ = 0.�0 Wm.K λ = 0.�� Wm.K λ = 0.�� Wm.K λ = 1.�� Wm.K100 0.039 0.300 0.309 0.312 0.321100 0.036 0.282 0.290 0.293 0.300100 0.032 0.257 0.263 0.266 0.272100 0.023 0.195 0.199 0.201 0.204125 0.039 0.251 0.258 0.260 0.266125 0.036 0.236 0.241 0.243 0.249125 0.032 0.214 0.218 0.220 0.224125 0.023 0.161 0.164 0.165 0.167

Factors influencing the U-value are indicated in blue.



Variation 0.� 0.� 0.� 0.�Lightweight plaster (λ = 0.18 W/m.K) instead of dense plaster –0.002 –0.004 –0.008 –0.01212.5 mm plasterboard on 15 mm plaster dabs –0.005 –0.012 –0.021 –0.032 with well sealed joints, instead of 13 mm dense plaster12.5 mm plasterboard on 22 mm battens (12%) –0.008 –0.018 –0.032 –0.049 with well sealed joints, instead of 13 mm dense plasterNo internal plaster finish +0.001 +0.002 +0.004 +0.006

100 mm dense concrete blockwork, λ = 1.22 W/m.K


example 4: cavity wall with clear cavity and internal insulation

102 mm external brickwork

50 mm clear unventilated air cavity with wall ties

22 mm unventilated airspace, R = 0.18 m2K/W, bridged by 12% timber battens, λ = 0.13 W/m.K

Internal insulation

Notes




U-values (W/m�K) for a range of internal insulation options

Block type

Insulation Conductivity Low- Medium- Medium- High- thickness of insulation density density density density (mm) (W/m.K) blocks blocks blocks blocks λ = 0.�0 Wm.K λ = 0.�� Wm.K λ = 0.�� Wm.K λ = 1.�� Wm.K 50 0.023† 0.289 0.297 0.300 0.308100 0.039 0.278 0.286 0.289 0.297100 0.036 0.263 0.270 0.272 0.279100 0.032 0.241 0.246 0.249 0.254100 0.023† 0.177 0.181 0.182 0.185125 0.039 0.236 0.242 0.244 0.249125 0.036 0.222 0.227 0.229 0.234125 0.032 0.203 0.207 0.208 0.212125 0.023 0.149 0.151 0.152 0.154

† Foil-facing (emissivity 0.2) is assumed for materials of lower conductivity. Airspaces adjacent to foil-faced insulation boards are assumed to have a thermal resistance of 0.44 m2K/W.Factors influencing the U-value are indicated in blue.



Variation 0.� 0.� 0.� 0.�External render (19 mm thick) –0.001 –0.002 –0.003 –0.005Dense blockwork outer leaf –0.002 –0.005 –0.009 –0.014


12.5 mm plasterboard, λ = 0.21 W/m.K, with vapour control layer


example 5: solid wall with polymer-rendered external insulation

6 mm thin coat polymer render

Insulation

Notes




• For the U-value calculations an airspace correction level of 1 is used for the insulation.

• For guidance on technical risks associated with single-leaf external walls, refer to BRE’s Thermal insulation: avoiding risks[11].


U-values (W/m�K) for a range of insulation options

Block type

Insulation Conductivity Low- Medium- Medium- High- thickness of insulation density density density density (mm) (W/m.K) blocks blocks blocks blocks λ = 0.�0 Wm.K λ = 0.�� Wm.K λ = 0.�� Wm.K λ = 1.�� Wm.K100 0.039 0.295 0.312 0.320 0.339100 0.036 0.277 0.293 0.299 0.316100 0.032 0.253 0.266 0.271 0.285100 0.023 0.193 0.201 0.204 0.211125 0.039 0.242 0.258 0.264 0.279125 0.036 0.228 0.241 0.247 0.260125 0.032 0.207 0.218 0.223 0.233125 0.023 0.160 0.165 0.167 0.172

Factors influencing the U-value are indicated in blue.



Variation 0.� 0.� 0.� 0.�12.5 mm plasterboard on 15 mm plaster dabs –0.005 –0.012 –0.021 –0.032 with well sealed joints, instead of 13 mm dense plaster12.5 mm plasterboard on 22 mm battens (12%) –0.008 –0.018 –0.032 –0.049 with well sealed joints, instead of 13 mm dense plaster13 mm lightweight plaster instead of 13 mm dense plaster –0.002 –0.004 –0.008 –0.012No internal plaster finish +0.001 +0.002 +0.004 +0.006



• The 13 mm internal plaster finish is based on relatively tight dimensional tolerances. Where tolerances are such that thicker plaster is necessary to address rough facing, the U-value will be slightly less (ie slightly better) than that given here.

�0 masonry walls and beam-and-block floors – SD 4

example 6: rendered solid wall with internal insulation

6 mm external polymer render

215 mm (exposed) concrete blocks, bridged by 11.1% mortar, λ = 0.88 W/m.K

22 mm unventilated airspace, R = 0.18 m2K/W, bridged by 12% battens

Insulation

Notes





U-values (W/m�K) for a range of insulation options

Block type

Insulation Conductivity Low- Medium- Medium- High- thickness of insulation density density density density (mm) (W/m.K) blocks blocks blocks blocks λ = 0.�0 Wm.K λ = 0.�� Wm.K λ = 0.�� Wm.K λ = 1.�� Wm.K 50 0.023† 0.292 0.309 0.316 0.335100 0.039 0.277 0.293 0.299 0.316100 0.036 0.262 0.275 0.281 0.296100 0.032 0.240 0.251 0.256 0.268100 0.023† 0.179 0.185 0.187 0.194125 0.039 0.235 0.246 0.251 0.263125 0.036 0.221 0.231 0.235 0.245125 0.032 0.202 0.210 0.213 0.222125 0.023† 0.150 0.154 0.156 0.160

† The insulation is assumed to be foil-faced with a foil of emissivity 0.2.Factors influencing the U-value are indicated in blue.



Variation 0.� 0.� 0.� 0.�2 sheets of 12.5 mm plasterboard instead of 1 sheet –0.002 –0.005 –0.009 –0.014Insulation mounted on 15 mm plaster dabs instead of +0.003 +0.007 +0.013 +0.021 22 mm timber battens

12.5 mm internal plasterboard, λ = 0.21 W/m.K

�1 SD 4 – masonry walls and beam-and-block floors

example 7: profiled steel sheet (or cladding system) with inner leaf blockwork

Cladding panel/system incorporating insulation

Unventilated air cavity (25 mm or more)

140 mm concrete blockwork bridged by 6.7% mortar, λ = 0.88 W/m.K

Notes




U-values (W/m�K) for a range of external panels

Block type

R-value of Low-density Medium-density Medium-density High-density external panel inner leaf inner leaf inner leaf inner leaf (m�K/W) blocks blocks blocks blocks r = ��0 kg/m� r = 1�00 kg/m� r = 1�00 kg/m� r = 1900 kg/m� λ = 0.�0 Wm.K λ = 0.�� Wm.K λ = 0.�� Wm.K λ = 1.�� Wm.K2.5 0.303 0.316 0.321 0.3343.0 0.263 0.273 0.277 0.2873.5 0.232 0.240 0.243 0.2514.0 0.208 0.214 0.217 0.2234.5 0.189 0.194 0.196 0.2005.0 0.172 0.177 0.178 0.182



Variation 0.� 0.� 0.� 0.�No internal plaster finish +0.001 +0.002 +0.004 +0.00613 mm lightweight plaster (λ = 0.18 W/m.K) –0.002 –0.004 –0.008 –0.012 instead of dense plaster 12.5 mm plasterboard on 15 mm plaster dabs –0.005 –0.012 –0.021 –0.032 with well sealed joints, instead of 13 mm dense plaster12.5 mm plasterboard on 22 mm battens (12%) –0.008 –0.018 –0.032 –0.049 with well sealed joints, instead of 13 mm dense plaster


�� masonry walls and beam-and-block floors – SD 4

U-valUes for beam-and-block floor constrUction

example 8: beam-and-block suspended ground floorThe U-values have been calculated on the basis of level access.

18 mm chipboard, λ = 0.13 W/m.K

Insulation

100 mm concrete block, λ = 0.46 W/m.K

Notes

• Figures assume a perimeter/area ratio of 0.57 and an underfloor ventilation level of 0.0015 m2 per metre perimeter length. Figures assume a beam fraction of 0.14 (ie 14%). In this example, the insulation is continuous (ie not bridged). The U-values are calculated using the method in BS EN ISO 6946[15] and BS EN ISO 13370[16].


U-values for a range of insulation thicknesses and a beam conductivity of 1.9 W/m.K

Insulation thickness U-value (Wm.K)

(mm) λ = 0.0�� λ = 0.0�0 λ = 0.0�0 80 0.191 0.227 0.267100 0.164 0.197 0.236120 0.144 0.174 0.211140 0.128 0.156 0.191160 0.115 0.141 0.174

Values which do not meet the limit in Table 1 are shown in red.



Variation 0.10 0.1� 0.�0 0.�� 0.�0Ventilation level of 0.0030 m2 instead of +0.002 +0.003 +0.007 +0.011 +0.015 0.0015 m2 per metre perimeter length Lighter concrete blocks, –0.001 –0.002 –0.003 –0.004 –0.006 λ = 0.30 W/m.K (r = 850 kg/m3)

Concrete beam, λ = 1.9 W/m.K (2200 kg/m3)

Underfloor space

�� SD 4 – masonry walls and beam-and-block floors

windows, doors and rooflightsU-values of window frame sections and door frame sections may be calculated using BS EN ISO 10077 Parts 1 and 2[22]. Part 1 offers a simpler calculation procedure but leads to more conservative results. Part 2 sets out a more detailed calculation procedure, involving numerical modelling techniques, but usually leads to a lower U-value being obtained.

BS EN ISO 10077-1[22] and the Glass and Glazing Federation Data Sheet 2.2 (March 2002 edition)[23] give procedures for combining frame section U-values and glazing U-values to obtain indicative U-values for windows and doors of standardised dimensions. Further guidance on the calculation of window and door U-values is given in reference [14].

references and fUrther reading [1] BRE. SAP 2005. [The Government’s Standard Assessment Procedure for Energy Rating of Dwellings.] Available as pdf and software. www.bre.co.uk/sap2005 [�] BRE. Simplified Building Energy Model (SBEM). [A national calculation method]. Available at www.ncm.bre.co.uk [�] Communities and Local Government (CLG). The Building Regulations 2000. Approved Document L: Conservation of fuel and power. L-1A: Work in new dwellings, L-1B: Work in existing dwellings, L-2A: Work in new buildings other than dwellings and L-2B: Work in existing buildings other than dwellings. 2006 editions. Available from www.planningportal.gov.uk [�] Northern Ireland Office. Building Regulations (Northern Ireland) 2000. Technical Booklet F: Conservation of fuel and power. F1: Dwellings, F2: Buildings other than dwellings. London, The Stationery Office. Available from www.tsoshop.co.uk [�] Scottish Building Standards Agency (SBSA). Technical standards for compliance with the Building (Scotland) Regulations 2004. Section 6: Energy. Available from www.sbsa.gov.uk [�] Communities and Local Government (CLG). Accredited Construction Details for limiting thermal bridging and air leakage. Available from www.communities.gov.uk [�] Energy Saving Trust. Reducing overheating: a designer’s guide. CE 129. 2005. Available from www.est.org.uk/best practice [�] Communities and Local Government (CLG). The Building Regulations 2000. Approved Document F: Ventilation. 2006 edition. Available from www.planningportal.gov.uk [9] Northern Ireland Office. Building Regulations (Northern Ireland) 2000. Technical Booklet K: Ventilation. London, The Stationery Office. Available from www.tsoshop.co.uk[10] Ward TI. Assessing the effects of thermal bridging at junctions and around openings. Information Paper IP 1/06. Bracknell, IHS BRE Press, 2006[11] BRE. Thermal insulation: avoiding risks. BR 262. Bracknell, IHS BRE Press. 2002 edition[1�] Metal Cladding and Roofing Manufacturers’ Association (MCRMA) & Engineered Panels in Construction Limited (EPIC). New guidance to the Building Regulations: Conservation of energy. Technical Paper 17. Available from www.mcrma.co.uk[1�] Ward T & Sanders C. Conventions for calculating linear thermal transmittance and temperature factors. BR 497. Bracknell, IHS BRE Press, 2007[1�] Anderson B. Conventions for U-value calculations. BR 443. Bracknell, IHS BRE Press, 2006 edition[1�] British Standards Institution. BS EN ISO 6946:1997: Building components and building elements. Thermal resistance and thermal transmittance. Calculation method [1�] British Standards Institution. BS EN ISO 13370:1998: Thermal performance of buildings. Heat transfer via the ground. Calculation methods [1�] CIBSE. Environmental design: CIBSE Guide A. 7th edition. London, CIBSE Publications, 2006[1�] British Standards Institution. BS EN 12524 (ISO 10456): 2000: Building materials and products. Hygrothermal properties. Tabulated design values [19] British Standards Institution. BS 5628: 2005 Code of practice for the use of masonry. Part 1: Structural use of unreinforced masonry. Part 2: Structural use of reinforced and prestressed masonry. Part 3: 2005 Materials and components, design and workmanship

[�0] British Standards Institution. BS EN 13162:2001: Thermal insulation products for buildings. Factory made mineral wool (MW) products. Specification BS EN 13163:2001: Thermal insulation products for buildings. Factory made products of expanded polystyrene. Specification BS EN 13164:2001: Thermal insulation products for buildings. Factory made products of extruded polystyrene foam (XPS). Specification BS EN 13165:2001: Thermal insulation products for buildings. Factory made rigid polyurethane foam (PUR) products. Specification BS EN 13166:2001: Thermal insulation products for buildings. Factory made products of phenolic foam (PF). Specification BS EN 13167:2001 Thermal insulation products for buildings. Factory made cellular glass (CG) products. Specification BS EN 13168:2001: Thermal insulation products for buildings. Factory made wood wool (WW) products. Specification BS EN 13169:2001: Thermal insulation products for buildings. Factory made products of expanded perlite (EPB). Specification BS EN 13170:2001: Thermal insulation products for buildings. Factory made products of expanded cork (ICB). Specification BS EN 13171:2001 Thermal insulation products for buildings. Factory made wood fibre (WF) products. Specification

[�1] British Standards Institution. BS EN ISO 10456:2000 Building materials and products. Procedures for determining declared and design thermal values [��] British Standards Institution. BS EN ISO 10077: Thermal performance of windows, doors and shutters. Part 1:2006: Calculation of thermal transmittance. General. Part 2:2003: Calculation of thermal transmittance. Numerical method for frames [��] Glass and Glazing Federation. Data Sheet 2.2 (March 2002 edition)

acknowledgementThe author acknowledges the support provided by the Concrete Block Association (CBA) in the preparation of this Digest.

BRE is committed to providing impartial and authoritative information on all aspects of the built environment for clients, designers, contractors, engineers, manufacturers and owners. We make every effort to ensure the accuracy and quality of information and guidance when it is published. However, we can take no responsibility for the subsequent use of this information, nor for any errors or omissions it may contain.BRE is the UK’s leading centre of expertise on the built environment, construction, energy use in buildings, fire prevention and control, and risk management.BRE, Garston, Watford WD25 9XX Tel: 01923 664000 Email: [email protected] www.bre.co.uk

BRE Digests are authoritative summaries of the state-of-the-art on specific topics in construction design and technology. They draw on BRE’s expertise in these areas and provide essential support for all involved in design, specification, construction and maintenance. Digests, Information Papers, Good Building Guides and Good Repair Guides are available on subscription in hard copy and online through BRE Connect. Details at www.breconnect.com BRE publications are available from www.ihsbrepress.com, orIHS BRE Press, Willoughby Road, Bracknell RG12 8FB Tel: 01344 328038; Fax: 01344 328005; Email: [email protected] to copy any part of this publication should be made to:IHS BRE Press, Garston, Watford WD25 9XX Tel: 01923 664761 Email: [email protected] www.ihsbrepress.com

�� masonry walls and beam-and-block floors – SD 4

SD �© BRE �00�

October �00�ISBN 9��-1-��0�1-9�0-�

Masonry Walls ~ U-Values and the building Regs

Documents

repeating thermal bridges

british standards institution

technical booklets f1

hot water systems

specific design variantsu

discrete thermal bridging

primary pipework insulation

water heating pumps