Friday, 6 April 2012

Rooflight dome case study (Lincoln)

The landlord of a residential apartment block invited us to offer our advice on the replacement of a couple of old rooflights on one of his rented properties. The apartment had a bitumen felt flat roof that was much in need of replacement.

Old felt roof with rooflight domes.

The existing rooflights were extremely thermally inefficient; not only were the seals so ineffective that there was a noticeable draft, but there were some serious cold bridging issues. Massive amounts of condensation collected on the glazing, frame and the inside face of the upstand, a sure sign that the cold external temperature was able to travel through the rooflight structure and when the warm air inside the property touched the rooflight surface the moisture in the air then condensates. In fact, these rooflights were so poorly insulated that on very cold days the condensation actually turned to hoar frost!!


Existing rooflights - so poorly insulated that hoar frost can clearly be seen on the INSIDE (click to enlarge).

The plan was to strip the existing roof covering back to the joists, re-insulate the cavity, replace the roof deck and rooflights and then re-weather the roof with a seamless GRP roofing finish. Prior to contacting DVS, the landlord had been speaking with some competitors who had offered to only replace the upper part i.e. just replace the rooflight dome and fix it to the existing upstand. We advised against this, and instead strongly recommended that the entire rooflight structure ought to be replaced, to get the maximum benefit. The fact that the existing upstands were so poorly insulated and the re-roofing works involved stripping back to the joists - we felt it would have been bad practice not to recommend this. We offer our rooflights with a fully insulated (foam filled) GRP upstand, and we know through independent testing that our F100 rooflight dome with upstand exceeds the Building Regulations Part L requirements - our rooflight structure is free from cold bridges.

Our sound advice and quality product secured us the order for the supply of the two F100 rooflight domes supplied complete with our 150mm high fully insulated GRP upstand, both equipped to manually hinge open for ventilation.

Our rooflights being delivered  - securely packaged ensuring they reach site in optimum condition.





Once the roofing contractor had stripped the existing roof, re-insulated and re-boarded - it was time to fix our rooflights. Our F100 rooflight domes are delivered to site completely factory assembled and pre-mounted to their insulated upstand - making site installation very quick, easy and trouble free.

The rooflight is fixed through the upstands "foot flange" into the roof deck at approximately 300mm centres:

The roofing contractor securing our rooflights to the new roof deck.

Once the rooflight has been fixed to the deck, the roofing membrane needs to be applied to the roof and onto the upstands - with the GRP roof covering used on this job it really couldn't be easier as our upstands are manufactured from insulated GRP. Also, because our upstands are manufactured from insulated GRP they are completely seamless (jointless) so they are impregnable to water ingress.

The GRP material seals the upstand to the roof deck
The rest of the roof had the GRP roof covering applied

The finished roof with our thermally optimised rooflight domes - will ensure that the landlord and his tenants have a maintenance free roof for many years to come.


The finish roof with our F100 rooflight domes
Our F100 rooflight dome - internal view

Thanks for reading our article, for more information about our range of rooflights please refer to our website, email us or give us a call on 01284 749051.

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