Clark Kent Posted July 1 Share Posted July 1 Looking for a bit of guidance on the flat rood=f of our kitchen extension. Our rear extension is underway, we decided to go with SIP's and it was to be the full envelope. Roof, walls just bosh it up and off you go. The SIP supplier has doubts about the flat roof, they want to ensure that there is a fully ventilated cavity and now want to change the construction to a warm roof. At this point I must admit that I have done all the design drawings and naively had not considered this to be a cold roof and the intricacies of this system. I don't have an overall section of the roof build up but basically the build up (from inside to ou) is- Plasterboard, SIP, Firing, 18mm OSB, EPDM. It's to have a parapet running all the way round and this is the reason that makes me think I've gone completely down the wrong track, I don't see how this roof can be ventilated. Any advice would be greatly appreciated. Link to comment Share on other sites More sharing options...
Iceverge Posted July 1 Share Posted July 1 I'm guessing that this part of the roof can't get any higher? Is the steel in place? Is it overall thickness of the roof or slope you're mainly concerned about? Link to comment Share on other sites More sharing options...
Clark Kent Posted July 1 Author Share Posted July 1 Basically the overall height is supposed to be 3m maximum (as stated by the permission). If I move to a warm roof this will need to be increased to 3150-3200mm Steel isn't in place, basically we're only just out of the ground. Trying to finalise the drawings from the SIP suppliers. The drawing you have referenced is their one, even if I used the batons and ply as they suggest I'm guessing I'd have to bring this void up the parapet and exit under the coping strip to allow ventilation? Link to comment Share on other sites More sharing options...
Clark Kent Posted July 1 Author Share Posted July 1 I'm thinking maybe I would be better looking at a warm roof as it appears to be lots of cold bridges with the supporting timbers Link to comment Share on other sites More sharing options...
SteamyTea Posted July 1 Share Posted July 1 As this is really about ventilation, can mechanical ventilation be fitted that removes the problem. Don't change the cold bridge and parapet issues. Link to comment Share on other sites More sharing options...
Clark Kent Posted July 1 Author Share Posted July 1 I guess there's always more than one way to skin a cat, are you suggesting some sort of fan to blow air through the vented cavity? Link to comment Share on other sites More sharing options...
Iceverge Posted July 1 Share Posted July 1 A warm roof is exactly the same as a SIP. Typically Insulation sandwiched between layers of PLY or OSB. I'm unclear as to why you can't just apply EDPM straight on top of the SIP. maybe with one layer of OSB to bridge the joints if it was necessary. Rest the SIPS on a beam or exposed glulam internally to to maximise the ceiling height. Dispense with the parapet if you can. It's a recipes for leaks or troublesome cleaning duties. To ensure a slope just support one side of the SIP higher than the other. Link to comment Share on other sites More sharing options...
SteamyTea Posted July 1 Share Posted July 1 16 minutes ago, Iceverge said: I'm unclear as to why you can't just apply EDPM straight on top of the SIP Why not get it sheathed in GRP (in a workshop). Then install and get the joints GRPed in situ. Is SIPs considered vapour impermeable? Link to comment Share on other sites More sharing options...
Clark Kent Posted July 2 Author Share Posted July 2 The parapet is a part of the design I need really as the cladding runs level all the way round, I don’t want to see the flat roof. I could probably just lay EPDM over the SIP if I were to be able to install it with a fall. I’m wondering if building the roof traditionally would be cheaper though as I could frame it out myself. I don’t believe SIPS is vapour impermeable, the SIP company specify a robust vapour barrier. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now