CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 1
-
Daniel Bates
Architectural Venue Design BA, Stage 3.
Faculty of Art, Design and Technology, University of Derby. 2012.
CIAT Student Competition. Technical Report.
Membership ID : 025344
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 2
Contents
Introduction ...................................................................................................................................... 3
Insulation .......................................................................................................................................... 4
External Insulation ......................................................................................................................... 4
Internal Insulation ......................................................................................................................... 7
Airtightness ....................................................................................................................................... 9
Window Strategies ........................................................................................................................ 9
Internal Airtightness Strategies .................................................................................................... 12
Conclusion ....................................................................................................................................... 14
Bibliography .................................................................................................................................... 15
Appendix A – WuFi Moisture Risk Calculation for Party Wall ............................................................ 16
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 3
Introduction
To be able to influence and regulate the environment is a sign of the evolutionary ability to adapt,
from birds creating nests to people building houses, being able to create comfort against the
external environment is an evolutionary gift. Recent developments globally are necessitating a close
look at how we use buildings from an energy point of view. Energy in the construction and use of
buildings accounts for over half of UK energy use. Also, the slow growth of the total housing stock at
less than 1% per annum necessitates a close look at the existing stock for refurbishment (DECC,
2011).
Passivhaus is one of the fastest growing models of low energy design, construction and certification.
Because it is based not upon idealisations of design outside and inside the building shell like in the
Code for Sustainable Homes, but on building physics, it has a proven track record of working. The
completed projects have been shown empirically to perform at a higher level over time than many
other low energy projects (CEPHEUS, 2009). The two standards relevant to this report are Passivhaus
and EnerPHit.
Figure 1 – Criteria for Passivhaus and EnerPHit certifications, including the limiting value of airtightness (air changes per hour).
The primary energy criterion of EnerPHit is the same as Passivhaus. This points to the fact that
120kWh/m2.a is fairly high to begin with and that is it very possible to make significant energy
savings through efficient white goods, lighting and hot water supply.
This report will focus on the numerous challenges of ‘deep’ low energy refurbishment drawing on
the knowledge gained from the study of UK projects that have attempted to achieve either the
Passivhaus or EnerPHit standard, whether the project was finally certified or not. The three main
areas that will be focused on are insulation, airtightness and interstitial condensation issues.
One of the repeated issues found during the case studies has been airtightness. It is difficult to meet
the required levels of airtightness in refurbishment projects due to having to work around an
existing structure. However, what has been shown in the case studies is that it is certainly possible.
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 4
Insulation
The first principle of efficient heating/cooling of buildings is the reduction of heat losses/gains in the
first place. In a UK setting space heating is by far the greatest energy demand in buildings, on
average accounting for 60% of energy use (DECC, 2011).
Therefore a good insulation strategy has to be decided for Passivhaus retrofit, depending on the
planning restrictions of the building. In regards to walls, the two primary insulation methods are
internal insulation and external insulation. Both of these strategies have differing challenges in terms
of buildability. External insulation poses additional challenges aesthetically, whereas internal
insulation poses challenges economically and technically particularly in relation to interstitial
condensation risk. Interstitial condensation issues will be analysed further into this report.
External Insulation
Externally wall insulation was a strategy undertaken in several of the refurbishment case studies,
two methods will be explored:
Foam board and render system (with or without mechanical fixings).
Timber frame with blown cellulose insulation.
A foam board and render system was used in the Passfield Drive and Grove Cottage projects. 3rd
Party installers approved by the suppliers performed the main task of installing the boards; finer
details were left to the general contractors. Details of working with the foam boards largely
consisted of window opening treatment, described in a later section. The fixing of foam boards to
masonry walls can be done with or without mechanical fixings, altering the cost-effectiveness.
Focusing on cost, it is in terms of the required labour and component parts, and focusing on
effectiveness it is in terms of cold-bridging through the fixings (although plastic thermal-bridge
reducing fixings are available).
In essence, the foam boards are primarily fixed by using a cementitious adhesive. This is an
acceptable solution if the masonry wall is bare, i.e. not painted or sprayed. In the case of the wall
having been painted or sprayed there contains risk in that the alkalinity of the cementitious adhesive
could alter the paint chemically, reducing the paint’s adhesion to the masonry wall potentially
resulting in the system detaching from the wall. Flaking of the paint to wall is an issue also, if the
paint has begun to flake this could effect subsequently adhered layers (Permarock, 2012). For both
of these reasons foam boards adhered to painted walls must be installed using mechanical fixings for
added security.
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 5
In the application of boards it is important to restrict air movement behind the board to avoid
thermal bypass. This was done in the Grove Cottage case study by creating an even covering of
cementitious adhesive to the foam boards prior to application.
The design of an external timber frame requires several considerations. The primary ones are
structural; the method by which the frame is held to the wall and supported underneath.
Secondarily, the type of insulation used in the frame to maximise its use. The cost involved in making
a timber frame may be recouped in being able to use cheaper insulation materials. Also, the
aesthetic options available in the cladding system may be preferable to the render often applied to
foam boards.
The Barbrook Passivhaus project utilised a softwood timber frame tied back to the masonry wall
using basalt fibre wall ties and was filled with Warmcel insulation.
Figure 2 – External timber frame. Source: barbrookpassivhaus.wordpress.com, 2012.
The frame was supported at the base with a brick stem wall that was built 150mm above ground
minimum. Between the stem wall and original wall 250mm XPS insulation was used to go below
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 6
DPM level because it is impervious to water ingress, it was capped with a DPM and OSB also. The
wall was entirely sheathed with 18mm OSB to provide a base for fixing subsequent structure onto.
2x3 timbers were used to construct the main frame, and as can be seen supported the window
boxes. The frame was tied back to the wall using Teplo basalt fibre wall ties, resin anchored to the
wall. These wall ties cause minimal thermal bridging with a k-value of 0.7 W/mK (Ancon, 2011).
Figure 3 – Galvanised tube crimped onto basalt fibre tie. Source: barbrookpassivhaus.wordpress.com, 2012.
In appropriate locations such as the
head of the window boxes, the timbers
were doubled up. The frame was sealed
using Gutex wood fibre board, creating
an enclosed timber frame for the blown
insulation.
Crimping of galv. metal
tube onto basalt tie.
Figure 4 - Boxing with penetrations from the blowing nozzle of Warmcel insulation. Source: barbrookpassivhaus.wordpress.com, 2012.
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 7
External wall insulation may involve knock on costs of alterations to roofs typically the extension of
eaves so as to cover the new thickness of walls. This however is an opportunity to replace an old
poorly insulated roof. Two distinct methods of EWI involve either the use of foam boards or the
construction of a timber frame to hold batts. There are pluses and minuses to both. Namely, that the
speed with which foam boards can be placed means a great cost saving. Primary buildability
considerations here are scaffolding, weather, and excavation works for insulating the foundations.
Internal Insulation
Internal insulation is more challenging technically and more costly due to the difficulties in working
around existing structure. It has often been utilised in the case studies because of the aesthetic
value of the façade, which is often of Victorian or Georgian origin in hard to heat homes.
In the Lena Gardens case study the walls were internally insulated with 130mm of phenolic foam
board insulation hung off aluminium spacers, 12mm OSB (airtightness layer), up to 50mm additional
thickness phenolic insulation depending on the presence of electrical or other services, finished with
12mm gypsum plasterboard and skim.
Figure 5 - Aluminium hangers holding the phenolic foam to the wall. Note part of the void has been filled with polystyrene beads, not carried out during the entire project due to moisture related risk. Source: ecohome.tumblr.com, 2012.
The air gap between the masonry wall and first layer of insulation was of critical importance to
minimise interstitial condensation risk. An analysis of this type of risk is held in Appendix A.
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 8
This method of construction was made simple due to the internal joists being cut back and hung off
steel beams, set into insulated wall pockets. These steels and their pockets will be discussed further
on. Not having to make individual joists airtight on a project of this size resulted in cost-effectiveness
in terms of time and ultimately in airtightness and heating costs.
An alternative method of internal insulation utilises
natural materials. This simultaneously addresses
the interstitial condensation issues and embodied
energy in materials. In the St. Luke Street retrofit
project the method involved creating an internal
timber frame to hold batts of sheep’s wool. This
hygroscopic material reduces the risk of interstitial
condensation.
The sheep’s wool was easy to handle, making the
solution buildable on the whole, however in the
locations where the batts had to be cut there were
minor delays due to the difficulty in cutting the
batts (Davenport, 2012).
Figure 6 - Insulation details. Airtightness layer set back from plasterboard to avoid puncturing. Hygroscopic materials used. Source: Anne Thorn Architects LLP, 2010.
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 9
Airtightness
Window Strategies
Referring to the previous section, the construction of the window sub-frames was crucial before the
placement of insulation. 2x6 lengths of treated softwood timber were fixed through the parget coat,
pebbledash and into the masonry wall using Rawlplugs. The intelligent vapour control airtightness
membrane that lined the interior of the building was brought around the front of the sub-frame as
shown in the image below:
Figure 7 - Preparing the window sub-frame for airtightness. Source: towerhamletspassivhausretrofit.retrofitdiaries.org
The sequence of work was to apply the parget coat first, fix the window sub-frames, perform the
required airtightness works, fix windows and make airtight, the 3rd party installers adhere foam
boards to the wall working around window openings where appropriate.
The airtightness interface of the windows to primary layer is often a tricky one to navigate:
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 10
Figures 8 & 9 - The application of 'Rabbit ears' in taped window installation. Allows for the relative expansion of tape and frame, as well as making the installation easier. Source: towerhamletspassivhausretrofit.retrofitdiaries.org
Figure 10 - Expanding foam between the window tape and the external timber frame. Source: towerhamletspassivhausretrofit.retrofitdiaries.org
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 11
Figure 11 - Airtightness tape to the outside. Source: towerhamletspassivhausretrofit.retrofitdiaries.org
Figure 12 - Airtightness tape to the inside. Source: towerhamletspassivhausretrofit.retrofitdiaries.org
An alternative strategy for the construction of windows involves the use of window boxes (shown in
the Barbrook Passivhaus case study above). The comparison of creating a sub-frame versus a
window box has to be looked at in two main ways. Material cost and material function. Functionally
a window box may cause a reduction in the window size, for example a 900mm opening with 18mm
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 12
plywood surrounds will be reduced to 864mm, a 4% reduction. This could be beneficial for north
facing windows to minimise heat loss or may negatively impact heat gains from south facing
windows, often in short supply in refurbishment projects.
The economics of the materials is highlighted in the box below, indicating a more cost effective
boxing method.
Internal Airtightness Strategies
Investigation into the case studies found a myriad of different products and materials used to
achieve airtightness. However, key methods did emerge:
Plastic membrane. Either tough building plastic or intelligent vapour control layer.
OSB taped at the joints. Usually good quality OSB and specialist tape.
Parget coat, using either cement or natural lime based products.
The parget coat method is typically done when exterior insulation methods are employed. For the
sake of depth, a focus on the other two methods will be done here. An intelligent plastic membrane,
first stapled and then taped, costs approximately £4.37/m2. Compared to 11mm OSB at £5.36/m2.
Both are functionally effective in different ways. The intelligent vapour control membrane restricts
the passage of moisture from the interior to exterior during winter and allows it during summer,
theoretically reducing the mean annual moisture content of subsequent layers. OSB taped at the
joints is cost effective and reasonably quick to install, because this method is relatively new time will
tell as to its effectiveness. The Lena Gardens and Balham Passivhaus case studies contained OSB as
their airtightness layer. Lena Gardens achieved the lowest air test result (0.49 ach) of all the 7 case
studies looked at; pointing to its initial effectiveness, especially in a project of its size and complexity
(Open Day Visit, 2011).
900x900 window 0.225 m2 ply per side
0.9 m2 ply box £17.02 per window excl. wastage
8 m treated timber 47x150mm
£25.52 per window excl. wastage
both exclude fixings
prices from buildingmaterials.co.uk
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 13
Post-construction of the internal airtightness layer, be it OSB or membrane, an inspection can be
carried out for the entire airtightness layer. The A blower door test can be run at this stage to check
for any leaks.
Figure 13 - Continuous OSB airtightness layer. Easily visible at this stage of construction. Source: Prewett Bizley Architects.
Joist treatment is one of the most important considerations when choosing
an internal treatment strategy. The main issue is one of interstitial
condensation and the increased risk associated with the application of
internal insulation. One can imagine the theoretical dew point within a wall
moving closer to the interior upon the application of internal insulation
(Little, 2009). Potentially exposing timber joists to increased risk.
There exists a wide variation in the risk factor depending on the wall type,
quality, condition, internal insulation type, joist placement, wall orientation
and microclimate, or wall placement (party or exterior). An analysis of risk
in party wall treatment is analysed in Appendix A.
The option of cutting joists back and hanging them off/on steel or
timber I-beams has been undertaken in several of the case studies. There are a few reasons for
cutting joists back;
Figure 14 – Movement of theoretical dew point due to internal insulation.
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 14
Eliminates condensation risk,
Eliminates cold-bridging through the timber,
Makes much easier the installation of insulation and a continuous airtightness layer.
Improves the load bearing capacity of timber partially decayed at the ends.
The next challenge in designing this option is the structure that’s going to be doing the job of holding
the joists up. Steel was employed in the Lena Gardens case study and was rested in structural
insulated pockets. The build sequence was to chip brick from both party walls, one of the pockets
having brick chipped from the side so as to allow the steel to be swung into position.
Figure 15 - New steel sat in insulated structural pocket. Foamglas blocks employed; thermal conductivity 0.55 W/mk crushing strength 3.5 N/mm2. Source: ecohome.tumblr.com
Conclusion
In conclusion the 7 case studies I’ve looked at, as well as evidence from abroad, shows that it is
indeed very possible to reach EnerPHit or Passivhaus standard in a refurbishment. Payback times,
analysed in more detail in the full version of this report, typically exist around 20 years not including
future fuel price increases.
Thus, there exists a compelling case economically as well as environmentally for deep, low-energy
retrofit.
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 15
Bibliography
Ancon. (2011). Retrieved 6 12, 2012, from www.ancon.co.uk:
www.ancon.co.uk/downloads/s1/l1/ancon%20low%20.pdf
DECC. (2011). Great Britain’s housing energy fact file. DECC.
Little, J. (2009). Breaking the Mould 1 - A study of condensation in single-leaf concrete wall
upgrades. Construct Ireland, 4(6).
Open Day Visit. (2011). Lena Gardens.
Permarock. (2012). Permarock EWI fixing. Interviewer: Daniel Bates.
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 16
Appendix A – WuFi Moisture Risk Calculation for Party Wall
To test the risk of interstitial condensation in an uninsulated party wall: Initial conditions.. occupied
property of high moisture and heat load, unoccupied property of approximate UK climate of RH 20%
in summer, 80% in winter. Two different wall build-ups are tested with these identical initial
conditions.
Fig 1 – Test condition one. Wall buildup in WuFi 5 Pro: 15mm gypsum, 225mm fired clay brick, 15mm
gypsum.
Fig 2 – Test condition two. Wall buildup in WuFi 5 Pro: 15mm gypsum, 225mm fired clay brick,
15mm gypsum, 50mm PU internal insulation on side of occupied property.
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 17
Fig 3 – Initial Conditions in heated property ‘A’ high moisture load. 21C° mean temperature, 1 C°
swing.
Fig 4 – Initial Conditions in neighbouring property ‘B’. 4C° mean value, 5 C° swing.
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 18
Fig 5 – Relative humidity and temperature results in center of brick wall without insulation.
Fig 6 – Relative humidity and temperature results in center of brick wall with insulation.
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 19
The following two results are for external weather conditions instead of the neighbouring property,
involving fairly high levels of rainfall. Weather file - Holzkirchen 1991.
Fig 7 – Solid wall without insulation. Note lowering RH values.
Fig 8 – Solid wall with insulation. Note no discernible difference in RH values. This indicates colder
wall is staying wetter.
CIAT Student Competition Technical Report
Investigation into the buildability and cost-effectiveness of Passivhaus refurbishment - - - Daniel Bates - - - Page 20
Discussion
The party wall showed no significant risk with or without insulation under sine wave test conditions
as noted above. When a high rainfall weather file was chosen as the external environment there was
a significantly higher risk of increased moisture content. The ends of the party wall where exists a
junction with an external wall may be a location of increased risk given the installation of internal
insulation.
Conclusion
It’s possible that breathable insulation materials would promote the passage of moisture out of the
wall during summer and minimise the risks of interstitial condensation, however further testing is
required. It should also be mentioned that a simulation software can’t really predict the results
accurately given the methods of installation of insulation having such an effect on its performance,
i.e. whether foam insulation boards are sealed at their edges with expanding foam sealant or not will
have a great effect on moisture transport and thermal bypass. Also, the orientation of the wall and
local climate are highly relevant factors.
The intuitions of the persons involved in the project through observation of the microclimate,
orientation and condition of the wall is likely to be of value in themselves, the simulation software is
supplementary to these observations.