DPC height

[Paukel]

I've seen builders putting the dpc at subfloor height which seemed to make sense to me as it was at the right level to achieve a good overlap with the dpm under the finished floor. Now I've noticed that architects seem to show the dpc at finished floor height which seems a lot more akward as, in order to achieve the overlap, the dpc would have to be bent down the inside of the wall. Then what happens at the corners. You would have to cut it in order to bend it down both sides of the corner so then there would be no overlap unless you stick another piece around the corner. Very fiddly. It seems to me that there would be a good chance of dampness at the corners.
The only disadvantage I can see with the first method is that you would need a minimum of 15 inches from the ground level to the finished floor level (6 inches to the dpc plus 9inches for the finished floor) which I don't think would be a problem, two steps up to the door.
Can anyone explain to me the proper way to do this to satisfy building control, especially the problem at the corners?
Thanks.

 

[jeds]

There's no one way to do it. Standard method is dpc at finished floor but circumstances sometimes dictate otherwise. Look up the Visqueen website. The publish some good guides and technical details.

 

[^woody^]

Now I've noticed that architects seem to show the dpc at finished floor height

Which it has been like for decades.

It's not cut or fiddly or a problem at the corners either. You just fold it and lap it

 

[Paukel]

I'm not with you Woody. Are you talking about the dpm or the dpc. There's no problem folding the dpm up the walls, but if you have a dpc built into the wall so that it extends inwards 5 or 6 inches then at the corner it's going to stay horizontal unless you cut it surely.

 

[^woody^]

DPC stays within the wall. DPM laps the DPC within the wall.

 

[Paukel]

I can't see how that would work. In order for it to be lapped within the wall the dpm would have to be laid before the wall was built. So you would be walking over it, dropping blocks on it etc the whole time while the house was being built. I don't think I'll be doing that.
I found this on a website called civil construction tips. It seems to support my thinking.

"A cavity wall is built as two leaves separated by a cavity. The purpose of the cavity is to act as a barrier to the penetration of rainwater to the inside of buildings. It is practice to build a cavity wall directly off the foundation so that the cavity extends below ground. A requirement of the Building Regulations is that the cavity should be carried down at least 150 mm below the level of the lowest dpc.

A dpc in external walls should ideally be at the same level as the clpm in the concrete oversite for the convenience of overlapping the two materials to make a damp-proof joint.

Where the dpcs in both leaves of a cavity wall are at least 150 mm above outside ground level and the floor level is at, or just above, ground level, it is necessary to dress the dpm up the wall and into the level of the dpc. This is a laborious operation which makes it difficult to make a moisture tight joint at angles and intersections.

The solution is to lay the dpc in the inner leaf of the cavity wall, level with the dpm in the floor, as illustrated in Fig. 37".

Here is the URL if you want to check it out:
http://civilconstructiontips.blogspot.co.uk/2011/06/damp-proof-courses-in-cavity-walls.html

 

[^woody^]

I can't see how that would work.

It's worked since they swapped quarry tiles for polythene back in the 50's

The trick is to lay the floor slab before building above DPC level. Or hang some skirts out and put the slab in later.

 

[noseall]

I can't see how that would work. In order for it to be lapped within the wall the dpm would have to be laid before the wall was built. So you would be walking over it, dropping blocks on it etc the whole time while the house was being built. I don't think I'll be doing that.

You haven't done a lot of building work, have you.


As Woodscrew says - you lay the DPM then lay your floor slab concrete whilst you have the easiest access.

There are few reasons why you would not lay the floor slab prior to building any walls. Prolonged cold weather could be one, but the cold temp's would also would prevent you from building any (masonry) walls in any case.

 

[Paukel]

I'm not getting through to you at all. Let me try and explain the way I would do it. You build the walls up to subfloor height. Then you lay the subfloor concrete or slabs or block and beam as the case may be. Then you put the dpc down on the outer and inner leaves of the walls so that the dpc in the inner leaf sticks out about 5 inches over the subfloor concrete. Then you build the house, and plaster the walls. Then you put down the damp proof membrane so that it overlaps the dpc sticking out from the inner leaf. Then you lay 5 inches of thermal insulation and FINALLY the finished sand and cement floor.

 

[^woody^]

I'm not getting through to you at all

No. And you never will with that method.

 

[noseall]

I'm not getting through to you at all.

Eh? Someone say summat?

I wouldn't patent your idea if I were you. Be sure to pre-empt BC about your methods. A confused BCO is not good for building projects.

 

[Paukel]

Just a wee update on this. Since my last post I've been talking to a lot of other builders in my area (Northern Ireland) and I haven't come across any who put the dpc at finished floor level. They all do it my way. I've checked with building control as well and they're happy with it. So I will continue to do it my way as described in the Civil construction tips link which I posted earlier which obviously no one here bothered to read. And yes Nosesall I have done plenty of building over the last 30 years with no complaints so far.

 

[^woody^]

30 years with no complaints

Same as Jimmy Saville ... and then wallop

 

[tomfe]

The solution is to lay the dpc in the inner leaf of the cavity wall, level with the dpm in the floor, as illustrated in Fig. 37".

Lots of builders do this around here but this is not the way you are describing with adding an dpc to the internal skin and over lapping the dpm and dpc 300mm mid floor.

The way we do it around here is to make sure the external dpc is greater than 150mm above ground the internal dpc is the dpm which is at the subfloor level as long as the levels are correct for any infill in the cavity this is the same as the link you provided not the method you are describing.