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Is this unusual? I may have answered my own question as I haven't noticed it on my travels. This is a ground floor lean-to. The roof membrane is visible below the tiles - is this supposed to be the case? The guttering sits at least 2 inch below the tile edge - which is also unusual in...

@mashie did you sort this. What did you go with, I have the same decision to make.

@woody are you saying (from inside out), plasterboard, 25mm PIR, polythene on to joists, 100mm PIR between joists (we then have double OSB, the GRP finish).

@woody, is the VCL not needed behind the plasterboard if using 25mm sheet of PIR on the underside of the joist (there will be 100mm Kingspan between the joists).

@woody thanks, been doing a bit of research on this. The 100mm PIR between the rafters / joist has the foil surfaced ripped off all over the place, loads of 2mm to 4mm gaps, not fastened in place with any expanding foam, and no tape to join cuts of PIR . The second 25mm sheet of PIR has been...

We're in the middle of building a cold dormer (added a couple of posts about it) and wondered if a) Is a vapour control barrier is required (contractor says not) - there will be a house bathroom and an en-suite in the dormers. b) We want to put some 5mm or 10mm thick Acoustic / Soundproofing...

@catlad is that even if fastening 25mm PIR to the plasterboard (was told by contractors - that this would create a foil backed plasterboard as the spec of foil backed is PIR bonded to standard plasterboard).

@catlad I want it to last a long time - we plan to be here at least 15 years. The spec said 80mm insulation between the rafters and 62.5mm foil back PIR. The contractors have said they always do 100mm between the rafters and 25mm on the underside followed by standard plasterboard fastened...

We are in the middle of a large redevelopment - the property has a mansard roof (I didn't know what this was until recently). Long story short, the first floor rooms are kind of in the roof (see example pictures). The builders have put 100mm Kingspan between the rafters, and 25mm PIR on top of...

@oldbutnotdead, thanks - yes, I had a good call with BCO today - they have accepted all changes saying the architect over spec'd - the builder is still proposing minimum or higher than minimum.

@oldbutnotdead, hit the nail on the head. There is a lot of glass so it is all about the SAP... I am PM (and my first go in this trade) - I am an IT PM by trade... This is very different - lots to understand!

no, gaps simply because they had to cut the tongue off as ended up with two types of T & G that did not fit together - one dormer has no gaps - as it was all the same board - the other has loads of gaps - some examples - from smallest to worst.

@sxturbo @Notch7 These are cold dormers finished with GRP (didn't know the difference until recently - too late now as the job is well underway) - the dormers were specified by the architects as part of a bigger job. They will be tile hung fronts and cheeks - they are not finished yet - we...

@RandomGrinch Thanks - I wouldn't mind if they checked in with me first. There are loads of gaps between the boards. Would it be advisable to double board (they said gaps are because they ended up getting board from two different places - and they didn't fit together well so they had to remove...

Hi - you seem knowledgable. I'm in the process of having 2 large (cold) dormers built. They will be GRP, tile hung cheeks and fronts. Builders have used OSB3 instead of ply on the spec, loads of gaps between OSB - minimum 4mm gaps, some larger. They said gaps are because they got OSB from 2...

@woody I thought as much. The spacing is 400mm. Having checked the drawings again, it says roof at 19mm exterior ply, sides at 25mm exterior ply. The gaps are bad - one at the bottom of one one cheeks that runs for at least 50cm - I can fit my hand through. Called the joiner, who said - "don't...

We are in the process of having a huge dormer built. The approved drawings the builder is working from says single layer membrane roof covering bonded to19mm plywood, also sides from 25mm plywood (exterior grade ply). The builder has used 11mm OSB3 board all over (also gaps all over between...

@Doubies How did you get on with this - we have the same challenge. Building Reg drawings say 25mm thick exterior grade plywood. Builder has used 11mm thick OSB3 board (and left plenty of gaps between boards - you can see daylight).