G and J Posted September 10 Share Posted September 10 I need a recommendation for a fire resistant board for our upstairs walls. We are within a metre of our boundaries on both sides. We have a rendered blockwork skin on the ground floor, but not upstairs. Upstairs we are having fire retardant treated vertical wood cladding, so we need a fire resistant layer between the frame and the cladding. We are assuming this layer will go on battens on top of the breather membrane. I did look seriously at Magply, which it appears can be the frame sheathing too, but then discovered that warranty companies really don’t like magnesium based boards. Our architect has proposed 15mm Supalux, and whilst it’s rather whizzy it’s also eyewateringly expensive, so we need an alternative, kinda pronto. Help! Link to comment Share on other sites More sharing options...
stu w Posted September 10 Share Posted September 10 STS, never had a problem on TF properties Link to comment Share on other sites More sharing options...
G and J Posted September 10 Author Share Posted September 10 Fab, ta. Will investigate Link to comment Share on other sites More sharing options...
LnP Posted September 10 Share Posted September 10 I've discussed this in detail with the timber frame suppliers we're getting quotes from. If the off site fire risk assessment using the STA methodology indicates mitigation is required, the expectation all of them described is to replace the 9mm OSB external sheathing with cement board on the relevant elevation. The membrane will go on top of the cement board in the same way it would have gone over the OSB. The additional cost will just be the difference in price between OSB and cement board. I guess you'd have to wait and see what the risk assessment says though. Link to comment Share on other sites More sharing options...
G and J Posted September 10 Author Share Posted September 10 We’re talking to a timber frame kit supplier (who do not erect) who provide circa 8’ x8’ panels sheathed with 9mm OSB. So the architect is simply suggesting the fire resistant layer goes straight onto the OSB with the breather membrane over that. But I’m not keen on paying for Supalux! Link to comment Share on other sites More sharing options...
Alan Ambrose Posted September 11 Share Posted September 11 Thinnest cement board then which will give the fire rating? 6mm I’m guessing. £16 a sheet. Link to comment Share on other sites More sharing options...
G and J Posted September 11 Author Share Posted September 11 2 hours ago, Alan Ambrose said: Thinnest cement board then which will give the fire rating? 6mm I’m guessing. £16 a sheet. I wonder if two staggered layers of 6mm are better than one layer of 12mm. Can imagine 6mm cement board sheets being quite fragile to handle. Link to comment Share on other sites More sharing options...
Alan Ambrose Posted September 12 Share Posted September 12 >>> Can imagine 6mm cement board sheets being quite fragile to handle. They're really quite tough, although you can shatter them. Also heavy. You need proper carbide tools to e.g. cut a 100mm hole for a pipe. I have some bits of board around if you want to experiment. Link to comment Share on other sites More sharing options...
Roundtuit Posted October 12 Share Posted October 12 On 11/09/2024 at 07:38, Alan Ambrose said: Thinnest cement board then which will give the fire rating? 6mm I’m guessing. £16 a sheet. My local BM is coming in at twice that price for 6mm 2400 x 1200 sheets; any tips on sourcing cheaper please? 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