BUILDING PRODUCTS

SustainableRainwaterSystemsSpecification & InstallationGuide

The Specifier’s Choice for Sustainable PVCRoofline, Cladding and Rainwater Systems

www.swishbp.co.uk

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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 fixed

Expansion 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

SBP Limited, Pioneer House, Mariner, Lichfield Road Industrial Estate,Tamworth, Staffordshire B79 7TFTelephone: (01827) 317200

Fax: (01827) 317201e-mail: marketing@swishbp.co.uk

www.swishbp.co.uk

© SBP Limited 08/09

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BUILDING PRODUCTS

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