McCracken Posted October 6, 2021 Share Posted October 6, 2021 Hi Folks, I am building a single storey with a pitched roof into a valley at the mo, just working on the parapet and a friend has mentioned I need a line of DPC 6" above the wall plate. the parapet is going 2 blocks high, so that would mean I would have a line of DPC on the last block up. see drawing . I've done one wall, bedded the DPC in but have concerns over binding. Also I'm going to do the valley in fibre glass to come up and seal over the top block. Would that suffice instead of DPC? Is there a standard guide for width of valley, I have a 100mm cavity but thinking of increasing valley size. Any advice welcome Link to comment Share on other sites More sharing options...
PeterW Posted October 6, 2021 Share Posted October 6, 2021 Never seen a DPC at that point - is there not a cavity tray further down..? And what is the roof build up above that wall plate ..? Link to comment Share on other sites More sharing options...
markc Posted October 6, 2021 Share Posted October 6, 2021 Never seen a DPC at that point, same here, can’t think of any good reason for it Link to comment Share on other sites More sharing options...
McCracken Posted October 6, 2021 Author Share Posted October 6, 2021 the rational given was to stop moisture coming down through the top thro the block. As I said, I'm not too comfortable with blocks sitting on plastic up there, and I reckon the fibre glass will do the same. No cavity tray, just DPC at ground level, 155mm up from deck. Prob a bit late for that now. Its 100mm cavity with 80mm PIR. I've not closed with a block, so sealing with insulation and a bit of DPC. I've 6x 2 rafters coming down onto wall plate, so will be creating a valley with OSB and fibre glass. Link to comment Share on other sites More sharing options...
Mr Punter Posted October 6, 2021 Share Posted October 6, 2021 It would be nice to have a coping on the parapet with an overhang both sides and a fall towards the valley. Link to comment Share on other sites More sharing options...
McCracken Posted October 6, 2021 Author Share Posted October 6, 2021 hoping to avoid coping and do it with fibre glass across top with overhang on the out side. any thoughts on DPC at that height? Link to comment Share on other sites More sharing options...
McCracken Posted October 6, 2021 Author Share Posted October 6, 2021 My worry is more that it was just one block sitting up, and wouldn't bond through DPC, but it actually seems sturdy. Link to comment Share on other sites More sharing options...
Dave Jones Posted October 7, 2021 Share Posted October 7, 2021 The problem you may have is that your final roof covering may need the block to be primed prior to sticking to it which will be hard if its dpc. Personally I would use rubber on top, assuming its a warm roof as you show zero ventilation on the drawing should it be a cold roof. Link to comment Share on other sites More sharing options...
MortarThePoint Posted October 7, 2021 Share Posted October 7, 2021 (edited) Could a liquid DPC be an option that gives better bonding to mortar? https://www.toolstation.com/damp-proof-membrane/p10290 Edited October 7, 2021 by MortarThePoint 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