RooflightsContinued from page 363Watertightness and water run-offAnother major cause for complaints hasbeen leaking rooflights causing damage toroof structures and interior decorations. NARMhas been contacted regarding instances wherethe glazing frame has been poorly designed, orthe rooflight has been installed poorly and/orwithout sufficient pitch to allow water run-off,resulting in water building up on the glazing andeventually penetrating edge seals.Most high quality glass rooflights incorporate aglass unit factory bonded into a fully thermallybroken aluminium frame, which includes a dripdetail to ensure the unit is fully watertight assoon as it is fitted onto an upstand. They shouldbe sealed to the upstand on site (for airtightnessas well as watertightness), but the seal is only asecondary seal, rather than the primary means ofpreventing water ingress. In some more economicdesigns there is no frame, and the glass is simplysealed to the upstand on site. The absence of anydrip detail on a frame means water can easilytrack back on the underside of the glass, andwatertightness of the units becomes entirelydependent on the quality of the site-applied seal(often onto an upstand which is not flat and level,after the upstand itself has been weathered),which can cause leaks: this style of rooflightshould therefore be avoided.Glass is not completely rigid and any glass rooflightwill bow slightly under the effect of gravity. Flatglass rooflights should therefore always beinstalled at a slight pitch to avoid ponding (whichwould otherwise occur if the bow created anegative pitch). Typically, smaller rooflights shouldbe installed at 3 degree pitch, and larger flat glassrooflights should be installed at 5 degree pitch. Youshould always make sure that the contractor whois building the upstand is aware of this pitchrequirement, to avoid the unsightly problemsassociated with ponding (including rapid dirt buildup,and potentially water ingress).Some rooflights are offered with “self-cleaning”glass, which is misleading: true self-cleaning glass“We’re aware ofrooflights beingsupplied for domesticuse with no mention ofPart Q”(such as Pilkington Activ) works best at pitchesabove 30 degrees, with a minimum pitch of 10degrees so is not suitable for flat glass rooflights.Some grades of low maintenance or easy cleanglass can be used, but still require regular cleaning.4Security For domestic properties, Part QBuilding Regulations states that rooflightsdeemed as easily accessible need to beproven to resist criminal attack or incorporatefeatures that are proven to reduce crime. We’reaware of rooflights being supplied for domesticuse with no mention of Part Q. Even rooflightssupplied with a laminated inner pane may notpass Part Q testing as the outer could be brokenand then the inner pane just lifted out of the hole.5Thermal performance It’s important thatmanufacturers state ‘whole product’ U-values to ensure thermal performancewhich will allow compliance with Part L BuildingRegulations. Some manufacturers are quoting‘centre pane’ U-values which do not take intoaccount edge spacers and frame construction.The thermal performance of a rooflight must beconsidered for the whole assembly, because whileglazing may be compliant, poor frame design canaffect thermal performance. This can result inhigher energy bills for building users andsubsequent unwanted higher CO2 emissions.Above left & inset: The glazing on this rooflight was notproperly fixed, resulting in it being blown off in windyweather and ending up in a nearby garden. Luckily, no onewas injured in this instance.Remember: a great looking rooflight isn’tnecessarily a great rooflightNARM has noted that in many cases wherecomplaints have occurred, the manufacturer istargeting homeowners with sophisticatedwebsites and literature focusing heavily on theaesthetics of the product and often claimingexcellence in quality standards. Some have evenreferenced NARM documents on their marketingmaterials; beware!In a crowded marketplace, where somemanufacturers are making confusing or untrueclaims, careful consideration needs to be given torooflight choice if problems of water ingress,ponding or worse still, inadequate safety, are tobe avoided.The good news is that there are many excellent,trustworthy UK suppliers of properly designedrooflights which will offer years of safe andreliable service. One simple and certain way toensure you’re dealing with such a company, is toestablish whether your supplier is a NARMmember company. NARM has stringentmembership criteria, a key part of which is thatany product supplied by a member company isfully compliant with Building Regulations andmeets all required specification and safetystandards.Contact NARMwww.narm.org.uk@_NARMUK38 TC SEPTEMBER 2020
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