dpc or what

29 Aug 2010
Reaction score
United Kingdom
I am in the process of building an extension.
Problem, dpc level then wooden floor joists in old house

new extension want to do a concrete floor, but it would be starting at above dpc to be same height as existing floor

what to do?

I have built b4 but floor level was the same in old and new extension, dpc ran straight across.
I will have a floor, starting at dpc, 50/75 insulation, 100 mm concrete floor, 50mm for UFH battens and oak flooring

below that will be 100mm ballast, 50mm sand and then dpc

but this will make my new floor against unproduced brickwork.

need a piccy to see what I should do!!!

Sponsored Links
Do you pay per word for internet bandwidth? :rolleyes:

Floors can be higher than external DPC, as long as the DPC and DPM are continuous

The old house has standard dpc at 2 bricks above external ground 150mm, dpc then floor joists 200mm approx, internal about two bricks 73mm.

The existing external wall the joist level bricks, will now be above dpcas this is where I need to put my concrete floor, at this level.

how do I join DPC old to new DPM ?
and will it will have to go up the external wall (old house)? as like I said the dpc to top of floor is 2 bricks lower

so as not to breach dpc

not ppw for internet access btw lol:cool: :D
You wont be breaching the DPC. It does not matter if the concrete floor touches the wall above the DPC

The DPC stops moisture coming up the wall, and then the DPM under the floor laps over the wall DPC to form a continuous barrier to ground moisture

You don't have to guard the floor from moisture coming across the wall from above DPC
Sponsored Links
cheers Woody

I am under the impression that the dpc to dpm where they actually touch will be the weak point. Due to the fact that the dpc is usually not proud of the brickwork therefore, the very edge of the dpc to dpm will leave a small void.

Thinking that void will be able to, by capillary action transmit water/damp.

would I be better using some kind off dpm adhesive to use against the wall where the dpm will cross the dpc at 90 degrees? if they make something like that.

Brick D.....conrete floor..........D Brick
Brick P.....conrete floor..........P Brick
DPC XM"""""""""void"""""""""""M DPC
Brick D"""""""""void"""""""""""D Brick
Brick P"""""""""void"""""""""""P Brick
~~~~ M dpm dpm dpm dpm M Brick

point X in the above is my issue with damp

the void is to be filled as per first post

btw hope this makes sense
hello - not to be rude or anything, but i have a damp problem i've posted about on another thread and i wondered if woody you would have time to have a look at it. i only ask because i have enjoyed some of your posts to other people on damp issues in the past. b ut of course if you don't have time i completely understand.
many thanks
ps - also hope you sort this one out!
Sorry, I can't understand that list.

The actual DPC/DPM joint only becomes a problem if you have a high water table or damp ground. Otherwise no moisture tends to get though the joint as the ground under the building stays relatively dry.

But if you want to, you can add a coating of liquid waterproofer such as RIW or Marley Superprufe to the area around the joint
cheers woody

I am probably looking at it too hard.

I am going to stick the dpm to the existing wall and stardard fit to the extension wall, cavity tray down to exisiting external dpc and fit weep stuff

cheers and thanks for the advice

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links