DPM where should it go and when

nfk

Hi,
This is an Excellent forum, I have a question about the DPM.
The situation is as follows.

The building has all the walls completed.

It has the following buildup:

Compacted 3 inch down
Randon Barrier
Steel
Raft Concrete slab

The external leaf is concreteed to the low step of the raft with a block, then a soap bar and then DPC laid on top

The internal leaf has DPC laid on top of raft, then a soap bar then dpc again.

Is the DPM laid on top of the raft and folded up around by the edges of the internal walls?
Then the insulation laid, UFH pipes and then screed.
How high up the walls should it go?

When is this part normally done, before windows and roof or after?

Thanks...

Poor Uncle Tom

The DPM should lap underneath the DPC on your internal leaf of the external wall all around creating a complete unbroken membrane throughout the entire footprint of the ground floor. Traditionally it is positioned a block below the DPC level and, as said, is lapped up the side of the last block and under the DPC on the inner leaf. Since the introduction of the Radon Barrier it is possible to get a membrane which will act as a DPM and a Radon Barrier but this is not always the case. If one barrier is used as both, its positioning is very important. It sounds as though your external finished ground level will be about 200mm below the Radon barrier level, if this is the case check if the barrier is meant to double as a DPM and also check that it is designed as a non liquid permeable membrane. Otherwise it is not possible with the walls in place to position a full DPM sucessfully, imo.

nfk

Hi Tom,
I'm not sure what type the Radon barrier is, its red in colour, fairly thick and not very flexable, I'll have to look at the packageing it came in to know for sure, it comes up to the top step where the first row of outer bricks sits.
I think this will be just at ground level in my case.

Has anyone just laid the DMP in each room with out having it under the DPC, was it a success?

muffler

nfk wrote: »

Has anyone just laid the DMP in each room with out having it under the DPC, was it a success?

DPMs and DPCs must overlap at internal and external (inner leaf) walls.

RKQ

Can you upload a few photo's?

Its preferable that the dpm laps the dpc in the inner leaf of blockwork.
It is still possible to lap the floor dpm up at least 150mm in each room. Its not ideal but its better than no dpm.
If water enters the cavity at least it can't enter the side of the floor.

Who designed or is certifying this construction?
Have you discussed your concerns with your Certifier?

nfk

Thanks RKQ,

I have no way of transferring photos at the moment. I guess I'll make the best of the situation and lap the DPM up the height of the finished floors around by the edges and overlap it 150mm through the doors.