April 2, 20197 yr I have a warm flat roof which from outside in goes as follows; membrane insulation vcl osb deck furrings metal web joists & associated void plasterboard (& eventual skim) I created upstands for skylights after the deck went on, before vcl etc(as per every and any picture i can find on google). These are 25mm ply sided boxes on 75mm timber framework which are insulated in between. The vcl crosses the deck and climbs the external face of the ply upstand, not to the top but just enough to ensure the membrane joins it to encapsulate the insulation. The membrane does climb to the top. The width of deck underneath the upstand therefore does not have vcl and nor does the internal vertical face which will get plasterboarded. I now think I need vcl lining the skylight void before plaster boarding....but where to terminate this....as I cant seamlessly join to the deck vcl? I dont feel i've created anything unusual and yet cant find any illustration of a comprehensive vcl in this scenario. Minor additional question; at the top edge of the plasterboard which stops just shy of the skylight glass, what should be the approach to finishing this?....i'm imagining it could be the recipient of any condensation that drips off the glass?
November 6, 20205 yr Author Top of plasterboard inside skylight well got a bead which the skim finished neatly too...nothing done about the top edge though. However never seen any condensation (that was suggested by Building Control officer). Fixed a basic vapour barrier to top of skylight frame down to turn under surrounding joists. Best I could do but leaves an unprotected route the width of the upstand where the 2 vapour barriers fail to meet. No immediate problems apparent though.
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