DPM External Flap - what to do with it?

[AppleDown]

Hello everyone. I’m doing a few ‘keep busy’ jobs over the next week until my crew are back on site. One of them is tidying up the DPM flaps that are hanging everywhere.

 

My build is timber frame, over blocks on slab. DPM is between blocks and soleplate as per usual - and currently extends out anywhere from 15cm to 40cm.

 

What should I do with this? Original idea was to lap it up the breather membrane on the OSB (DPM flaps cut to a uniform length first) and then tape. Is that just the standard detail?

[Nickfromwales]

10 minutes ago, AppleDown said:

Hello everyone. I’m doing a few ‘keep busy’ jobs over the next week until my crew are back on site. One of them is tidying up the DPM flaps that are hanging everywhere.

 

My build is timber frame, over blocks on slab. DPM is between blocks and soleplate as per usual - and currently extends out anywhere from 15cm to 40cm.

 

What should I do with this? Original idea was to lap it up the breather membrane on the OSB (DPM flaps cut to a uniform length first) and then tape. Is that just the standard detail?

Have you got some pics of the ‘affected’ areas?

 

Lapping it up may harbour water so we need context for some better answers   

[AppleDown]

6 minutes ago, Nickfromwales said:

Have you got some pics of the ‘affected’ areas?

 

Lapping it up may harbour water so we need context for some better answers   

Will grab some better ones tomorrow but here’s a hastily cropped and zoomed version. The buildup on top of this includes Actis BoostR Hybrid - for insulation and airtightness. So ideally the DPM gets lapped up, taped, BoostR stapled and taped, battened, and then clad / render depending on area.

[Russell griffiths]

Water works with gravity everything travels downwards ( apart from a bit of capillary action ) so lap everything downwards, just sit and look, pretend your a water droplet where will you get trapped, how would you run under that sole plate and into the house. 
 

lap everything down and out. 

[saveasteading]

18 minutes ago, Russell griffiths said:

pretend you're a water droplet

You've given away the secret of good design.   Water droplets, units of force, whatever.

Then express it on site in dance.

[AppleDown]

2 hours ago, Russell griffiths said:

Water works with gravity everything travels downwards ( apart from a bit of capillary action ) so lap everything downwards, just sit and look, pretend your a water droplet where will you get trapped, how would you run under that sole plate and into the house. 
 

lap everything down and out. 

My thinking was more along the lines of keeping a sealed envelope. If I lap down, the opening between the DPM and soleplate is exposed. If I lap up (and do it properly) then the envelope is sealed - better airtightness and less chance of water ingress. Double sided tape (butyl) between DPM and mebrane, staple through, then tape fully over the top of DPM to form a complete seal.

[saveasteading]

I would say that tape or staples are a temporary fix but a sensible way to prrp and tidy for now. Is there a designed  detail?

[Bramco]

4 hours ago, AppleDown said:

My thinking was more along the lines of keeping a sealed envelope. If I lap down, the opening between the DPM and soleplate is exposed. If I lap up (and do it properly) then the envelope is sealed - better airtightness and less chance of water ingress. Double sided tape (butyl) between DPM and mebrane, staple through, then tape fully over the top of DPM to form a complete seal.

 

I'm pretty sure this was how ours were done - the join then site behind any cladding.   Do make sure that you get them 'permanently' fixed. We had one bit that wasn't that well fastened up and in time started to vibrate in high winds (albeit from a very specific direction) but it took a while to work out what the heck was going on.

[AppleDown]

7 hours ago, saveasteading said:

I would say that tape or staples are a temporary fix but a sensible way to prrp and tidy for now. Is there a designed  detail?

The detail just shows what most do - DPM just ‘finishes’ directly after the soleplate.

[Dunc]

+1 to lapping down. Our breather membrane is not 100% watertight. If I'd lapped up behind it it the dpm could have collected the small amounts of water that sometimes penetrate in high winds (no cladding yet).

Trimmed DPM off about 50mm below sole plate. Left the breather membremane long enough to cover this. Used the stainless steel mesh that is at the base of the cladding battens to stop it flapping about.