gavztheouch Posted October 19 Share Posted October 19 This is a hard one to explain with just words. So I made a model to represent the problem. This flat roof dormer connects to a 35 degree roof clad in metal. I am having a hard time work out how to waterproof the area where the upstand for the parapet meets the sloping roof. Open to changing the roof material and design. Would much rather not have these flat roof dormers but I am here now and need to make the best job I can. World appreciate any ideas and thoughts Link to comment Share on other sites More sharing options...
BotusBuild Posted October 19 Share Posted October 19 I think the sticky EPDM is the answer, but not in one piece. A piece over the batten first, which goes up the slope say 10-15 cm, and also across the flat board by the same amount. Then a piece that comes down the slope and overlaps the first piece. Where it gets to the batten, overlap as far as you can, probably only 3-4 cm, molding it round as best you can, getting it to stick as well as possible. Finally, slap some of our favourite sealant, CT1, across all the joins of both pieces. HTH 1 Link to comment Share on other sites More sharing options...
BotusBuild Posted October 19 Share Posted October 19 An alternative is to use GRP (fibreglass). Messy, but will mold round that batten nicely. You could go all the way along the join, making it one continuous seal. Thinking about it, this probably the better solution in this situation 1 Link to comment Share on other sites More sharing options...
SteamyTea Posted October 19 Share Posted October 19 If you do go the GRP route, you need to make sure that there is a large radius on any up stands. Glass fibre matt does not like bending too much. 1 Link to comment Share on other sites More sharing options...
gavztheouch Posted October 20 Author Share Posted October 20 Having a go at this in resitrix epdm. I think I need to cover both upstands in one go across the whole width of the dormer. Maybe GRP is the way forward, getting it dry enough at this time of year for GRP could be an issue. I try again with the resitrix and see if I can get it better. Link to comment Share on other sites More sharing options...
gavztheouch Posted October 26 Author Share Posted October 26 157.414_DormerDetail.pdf Link to comment Share on other sites More sharing options...
gavztheouch Posted October 26 Author Share Posted October 26 (edited) 157.414_DormerDetail.pdf Just received the details from the architect. First thoughts are it is very complicated for 4 very small dormer roofs and will be a lot of work. I don’t think the circular outlet has enough area around it to weld/glue too. There are also a lot of varying surfaces/angles and junctions in a small space. It’s annoying details like this are taken through the simplest part of the roof and do not take into consideration the more complicated areas like the upstand corners transitioning into the top of the upstand area. The upstand corners need to be detailed with a pigs ear or a remolded epdm piece this would be right in the way of the outlet. Then we have the issue of the area in the video where the pitched/flat and in upstand meet. A lot of these issues could be solved with grp. How does glass fibre cope with movement? Edited October 26 by gavztheouch Link to comment Share on other sites More sharing options...
scottishjohn Posted October 26 Share Posted October 26 (edited) On 20/10/2024 at 21:52, gavztheouch said: Maybe GRP is the way forward, getting it dry enough at this time of year for GRP could be an issue. start with polythene sheet under where you going to grp it will set fine will take about 2hrs to go off or less depending on how much accelerator you use then copper nail it in place when set that might be a good fix for that complicated area Edited October 26 by scottishjohn Link to comment Share on other sites More sharing options...
gavztheouch Posted October 31 Author Share Posted October 31 Currently leaning toward these Modified PU liquid rubber roofs. A very similar method to GRP but less sensitive to rain and temp during install and flexible once set. Looks like a better option than GRP. https://www.bmigroup.com/uk/ultima/ Link to comment Share on other sites More sharing options...
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