076 RCI 0417

RCI April 2017

ROOFLIGHTS & ROOF VENTS Installation considerations Peter Cherryman, National Domelight Company’s technical sales manager, talks us through the key things to remember when installing a polycarbonate dome with supplied PVC upstand Things to remember about upstands: Remember: Polycarbonate rooflights supplied with a PVC upstand are normally installed on a flat roof or pitches of no more than approximately 17.5º, depending on the manufacturer’s recommendation. Remember: PVC upstands normally come with a splay inward so that the actual dome clearlight size – the amount of sky that you see – will be smaller by approximately 200mm. So, if you want to see 600mm x 600mm area of sky, you need to allow for an 800mm x 800mm roof aperture (hole). If required, vertical PVC upstands can be supplied. Remember: When ordering, the PVC upstand is made to suit a ‘finished’ roof opening size, including plasterwork. Remember: The minimum height for a PVC upstand is 150mm and should be fitted above the roof surface – never below the roof insulation. A 300mm PVC upstand can be used with roof insulation 150mm thick. Remember: If fitted with more insulation than above, a timber spacer should be provided around the roof aperture to raise the upstand to the required level. Remember: Apply the waterproofing (in accordance with the manufacturer’s recommendations) up to the underside of the top flange of the upstand. Things to remember about polycarbonate domes: Remember: To meet current building U-value regulations, a PVC upstand will need to be supplied with a triple-skin polycarbonate dome. Remember: If the polycarbonate dome is to be installed above a kitchen or bathroom, is ventilation required? Remember: All good quality polycarbonate rooflights should be supplied with security fixings. Only use these fixings once you are sure you won’t need to remove the dome. They are called security 076 APRIL 2017 RCIMAG.COM “The minimum height for a PVC upstand is 150mm and should be fitted above the roof surface – never below the roof insulation” fixings for a reason! Remember: Polycarbonate domes are very tough but are easily scratched so don’t use any abrasives to clean them, a soft cloth and soap is all you should need if they get dirty with any site debris. www.nationaldomes.com Polycarbonate dome plus 150mm weathered upstand Polycarbonate dome internal view How to fit a polycarbonate dome: 1. Check the roof opening has been created the right size by placing the PVC upstand over the opening. 2. Apply a generous bead of mastic or silicone around the PVC upstand base and bed down over the roof opening. 3. Screw the upstand to the roof structure through the PVC upstand base using appropriate screws for the roof structure. 4. Apply roofing membrane to PVC upstand to manufacturer’s instructions and recommendations. 5. Once the PVC upstand has been weathered, position the polycarbonate dome over the PVC upstand and affix using the security fixings supplied. Top: Triple dome with upstand Above, left: 300mm upstand with insulation Above, right: 150mm upstand with insulation


RCI April 2017
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