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BUILDING PRODUCTS
SustainableRainwaterSystemsSpecification &
InstallationGuide
The Specifier’s Choice for Sustainable PVCRoofline, Cladding and
Rainwater Systems
www.swishbp.co.uk
UniclassL7314:P7114
CI/SfB(52.5) Xn6 0809
recycledcontent
carbonsaving
KM508760
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General Swish Rainwater systems are designed forapplication in
most domestic propertiesthroughout the UK.
The following information is given to helpspecifiers determine
the basic requirements of a gutter system. Swish Technical Services
canprovide further information and guidance asrequired. Tel: 01827
317238
System PerformanceTo determine the elements of the guttersystem
the designer must calculate the likelyquantity of rainwater run-off
from the roof asfollows:–
• Decide on the local rainfall intensity that thesystem must
cope with.
• Calculate the effective roof area (m2) to bedrained.
To meet these requirements, the designer willneed to:
• Choose a gutter with sufficient flow capacity(litres per
second)
• Decide on the system layout including the fallof gutter and
the number and position ofoutlets required to maximise the
flow.
Rainfall IntensityBS EN 12056 suggests likely rainfall
intensitiesfor different areas of the UK, which may beexperienced
as unusual events of 2 minutesduration, once every 1, 5, 50 and 500
years. Thevolume of water involved in these eventsincreases as they
get rarer, but because of theirrelative infrequency, it is
suggested that domesticgutter systems should be designed for a
stormevent that is likely to occur once a year. Theintensity of
such an event will vary across theUK, but it is sensible to design
a system for aminimum intensity of 75mm/hour per m2 or aflow rate
of 0.021 litres per second.
Roof AreaThe area of roof that drains into any one
gutter(effective roof area : m2) can be calculated intwo ways (see
diagram):–
• (H/2) + W x L
• L x W x Pitch Factor
A selection of pitch factors is shown in table A.For other pitch
factors please contact SwishTechnical Services. Table A
Roof Pitch Pitch Factor
10º 1.088
20º 1.182
30º 1.288
40º 1.419
Flow CapacityIn general terms the most efficient section of
gutter runs from the outlet, for a distance of 50 times the maximum
height of water thegutter can hold when level. In the case of Swish
Round gutter this is approximately 2.4m (ie. 48mm x 50). The
capacities shown forSwish gutter systems have been
independentlyassessed on a flow rig in accordance with BS EN
12056:2000 and are based on thefollowing:–
• A ‘short’ run of gutter (ie 50 x height ofwater the gutter is
capable of containing).
• The gutter is set straight and level (ie a fall of up to
3mm/m).
• A storm event running at 75mm per hourper m2 or 0.021 litres
per second.
• Capacities are reduced by a ‘safety factor’ of 10%. Table
B
Short Gutter Flow litres* Max. areasystem per second drained
m2
Round 0.9 43
Square 1.6 76
Ogee 2.2 105
Deepflow 1.5 71
*Outlet positioned at end of run
System LayoutIt is at once obvious from the flow capacitytable
that different gutter shapes have differentflow and area drainage
capabilities.
The roof area to be drained should becompared with the maximum
area that a guttertype is able to drain (Table B: right column). If
the figure in the table is too low the designerhas the following
options:
• Select a system with a higher capacity
• Increase the fall on the gutter. With a longergutter this has
its limitations, as water comingoff the tiles is more likely to
overshoot thegutter at the lower end. With a shallow fasciathis may
not even be an option. In additionthe greater volume of water in a
long gutterwill tend to reduce the speed of flow.
• Move the outlet point to a central position to significantly
increase the gutter drainagecapacity.
For further guidance please consult SwishTechnical Services.
Other Notes on Layout• If an end outlet is located around a
corner
flow rates should be reduced by 15%.
• Larger valleys may require a dedicated outletat the
corner.
• Where the roof is likely to discharge waterrapidly eg. long
slopes or where low frictionroof coverings are employed, a larger
guttermay be required to avoid water overshootingthe gutter.
Swish Roofline &Cladding Systems
Swish Cellular PVC is suited to the exposedconditions
encountered on clad facades andat the roofline. Situated in
elevated positionsand subject to extreme weather conditions,these
areas are difficult and costly to accessand maintain. Cellular PVC
requires nomaintenance; it will last the life time of thebuilding
and can be fully recycled at the endof its service life.
New build - The BRE Green Guide (June2008), which underpins the
Materialssection of the Code for Sustainable Homes,recognizes the
sustainability of PVC buildingproducts which can help developers
achievehigh materials ratings under the Code.
PVC cladding over timber framework isclassed as an A+ external
wall system; thehighest rating available. In addition,
SwishCellular PVC cladding and roofline systemsqualify as Tier 3
products under ResponsibleSourcing.
Refurbishment - Swish Cellular PVC offersthe potential of a 60
year, maintenance freeworking life, minimising lifetime costs
forlandlords of social housing and privaterented accommodation.
This may free upthe maintenance budget for the purchase ofCO2
reduction materials such as insulation.
Specification Guidance
W
H
L
Effective roof area
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Installation Guidance
PreparationEnsure that fascias are straight and true and ingood
condition. Swish recommends thattimber roofline components are
replaced withSwish cellular PVC fascias, soffits andbargeboards for
longevity, lower lifetime costsand a reduced carbon footprint over
theservice life of the building.
PositionThe gutter should be fitted as high as possibleup to the
edge of the roof and fixed at a fall ofbetween 1mm/m and 3mm/m. In
areas wheresnow is likely to accumulate on the roof, ensurethat the
outer edge of the gutter does notproject above the line of the
roof. Neithershould the roof covering project far over theinner
edge of the gutter. Down pipes shouldbe located directly above the
drain opening.
GutterFix the end fascia bracket to the fascia boardwithin 75mm
of where the stopend or cornerwill be located. The gutter can
finish flush withthe end tile or extend beyond it by no morethan
half the depth of the gutter.
Tie a plumb line to the end bracket and feed itthrough the
outlet. This allows the installer toposition the outlet accurately
above the drainpoint and ensure the correct fall from the endfascia
bracket before securing the outlet.
Fit the intermediate fascia brackets and gutterjoints in place
using the plumb line as a guide.
Feed the back edge of the gutter fully underthe back clips of
all the fascia brackets, unions,corners etc. Ensure that the gutter
ends line upwith the markings on the inside of each unionor outlet
unit (to allow for thermal movement)and push all front clips firmly
and fully over thefront edge of the gutter. Swish gutter seals
arepre-treated with silicone but installers areadvised to apply a
spray of silicone prior toassembly.
PipeThe offset in the pipe is formed by using two1120 bends to
return the pipe to the wall. Ifthe soffit is small and the two
offset units needto be close to one another they will still
requirea small section of pipe between them to makethe joint fit
properly.
It is important to allow for expansion of themain pipe. This is
best concealed in the offsetor a pipe socket. Allow 10mm expansion
gapper 5m of pipe.
CompatibilitySwish Rainwater Systems are compatible withsome
elements of other guttering systems.Designers and installers should
consult SwishTechnical Services for guidance.
Specifications
Last fasciabracket
Fasciaboard
Drainpoint
Plumb line used toset correct fall and
outlet positionabove drain
Outlet
Gutter Round Square Ogee
Distance between fascia brackets – Standard 1m 1m 800mm
Distance between fascia brackets – Conservatories 500mm 500mm
500mm
Distance between top hung fascia brackets - - 800mm
Distance between corner/stopend units and next fascia bracket
75mm 75mm positively fixedExpansion gap at joints Marked on
moulding
Screws for brackets and positively fixed components 25mm No10
s/s round head
Quantity of screws per fascia bracket 2 2 3
Quantity of screws per positively fixed component As per number
of fixing holes
Pipes Round/Square
Vertical distance between pipe brackets 1.8m
Expansion gap per 5 metres 10mm
Handling & StorageSwish gutters and pipes are supplied in
polyethylene sleeve wrapping. They will withstand generalsite
handling, however, the following guidelines should be
observed:–
• Loading and unloading should be carried out by hand.
• It is advised that products are stacked on a flat, firm base,
to no more than 1m high andprotected from the elements. Wherever
possible a dedicated racking system is stronglyrecommended with
side supports at intervals not exceeding 1m.
• Set aside off cuts and store carefully for re-use.
• Contact with solvents and organic based compounds such as
bitumen products, paint orcreosote should be avoided.
• Boxed fittings should be stored under cover away from damp
surfaces to retain the integrity of the box.
• Please recycle packaging where possible.
BUILDING PRODUCTS
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SBP Limited, Pioneer House, Mariner, Lichfield Road Industrial
Estate,Tamworth, Staffordshire B79 7TFTelephone: (01827) 317200
Fax: (01827) 317201e-mail: [email protected]
www.swishbp.co.uk
© SBP Limited 08/09
A604
BUILDING PRODUCTS
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