builder DPM disaster

[falconxxx7]

hi, i had an extention built and the builder put a dpm under the concrete raft foundation and did not bring it up the wall thus serving no purpose and there was a lot of surface water on the concrete slab. the architect noticed and adv ised that he need to lift the flooring up and staple the dpm on the underside of the joists or raggle a channel on the brick and tuck it in there and mastic in.
can you please advise the best way to lay the dpm and fix it properly.
since then the builder bogged the dpm with gaffer tape and some staples it looks a mess and dont trust the longevity of the gaffer tape also there is excess dpm and not neat ....so much for the federation of master builders approved builder. its been one nightmare after another
attached is picture of the spec , that was not followed

Untitled

• falconxxx7
• 9 May 2012
• 1

 

[freddiemercurystwin]

You shouldn't need a dpm on top of the slab though it would not do any harm to fit one. Any damp that penetrates the void through the slab (no idea why its a raft anyway) will evaporate away and be extracted through the air bricks or if actual standing water it should be able to drain out though this should be designed out if at all possible. Just a dpc 150 above ground level in the wall is all that should be required. Provided your joists are above the dpc level then that should be all the protection that is required.

Besides if you did bother with a dpm on top of the slab you would need an oversite or screed to hold it there or it'll just float which your architect's not drawn. But to reiterate the finished level of this oversite should either be sloping to allow water to run off or be above the surrounding ground level so standing water cannot occur.

Your builder and your architect do not appear to have a good grasp of what they are trying to achieve.

The only reason you would really need to link the slab dpm to the wall is if a Radon barrier was already incorporated in the existing house. But if your existing house does not possess this there is no point trying to achieve it in the extension.

 

[falconxxx7]

hi, thansk for the reply .there is no question wheter i need a dpm or not because thats the way it has been designed and approved by planning/building control. my exisitng house is on raft so extention needed the same.
My quesstion was regards the best way to lay and secure to the building since it has been missed and kit roof joists are in now.

 

[freddiemercurystwin]

If you ain't gonna listen then I'll bow out.

 

[falconxxx7]

hi, thansk for the reply .there is no question wheter i need a dpm or not because thats the way it has been designed and approved by planning/building control. my exisitng house is on raft so extention needed the same.
My quesstion was regards the best way to lay and secure to the building since it has been missed and kit roof joists are in now.

 

[TonyW2]

You could leave the joists & floorboards out and fill the paddling pool that is being created so you have a leisure feature instead of a room.
Your drawings are mixing up two intentions for using a DPC membrane.

 

[falconxxx7]

@ tonyw2 that is as much help as a chocolate ashtray ...explain your comments or don't bother commenting and acting smart

 

[TonyW2]

Sorry---I guess I would be feeling teed off too.
By turning up the membrane, you are creating an under floor area that is just the same as a lined paddling pool. (Think of the effect of a burst or flood above it) . It will not have ventilation, nor any water exit.

The membrane would have been retained by the wall plate;
this arrangement would have provided protection to the joists and wall plate from any moisture in the inner blockwork, but why not just insert the wall DPC at a level below the wall plate and joists?

The membrane will sit on the raft; the raft has standing water on it, so where will that go? The membrane will just sit on a bed of water. The membrane is serving no purpose except to protect the joist ends.

If you have already fitted the joists and wall plate, then turning up and attaching the membrane will be ineffective, as you cannot get it under the wall plate and join into the wall DPC so the joist ends will not be protected by the membrane.
(If the joists are in hangers, then they are already isolated from the wall)

Your main concern should be the removal arrangements for the surface water. If there is a run off or enough ventilation available, it would work better without the membrane.

Was that detail as originally drawn, or has it been adapted when it was decided to raise the floor? Was the original just a solid floor?