dpm

[^woody^]

The membrane is for weeds, not damp

 

[A Trowel]

For my sanity I quit, I suggest you don’t do this on a building notice but get approval first then you will have a drawing to follow or better yet just pay someone to do the work.

 

[electrified]

The membrane is for weeds, not damp

ah i see i see. isn’t polyethylene a dpm material though, so i still need to lay this, and i’m guessing i can butt it up to the brickwork as i don’t need to join it to the dpc.

also see diagram below: if i didn’t lay this membrane which is the same material as a dpm, could damp come up from below the black onto my green beam?

 

[electrified]

For my sanity I quit, I suggest you don’t do this on a building notice but get approval first then you will have a drawing to follow or better yet just pay someone to do the work.

sorry @^woody^ exposed the crucial detail that the membrane is for weeds not damp.

 

[A Trowel]

sorry @^woody^ exposed the crucial detail that the membrane is for weeds not damp.

SUSPENDED TIMBER GROUND
FLOORS (MOISTURE FROM
THE GROUND)
4.13 Any suspended timber floor next to the ground will meet the requirement if:
a. the ground is covered so as to resist moisture and prevent plant growth; and
b. there is a ventilated air space between the ground covering and the timber; and
c. there are damp-proof courses between the timber and any material which can carry moisture from the ground.

Approved Document C, Building Regulations

 

[electrified]

So can you just respond with YES if this is right:

sand blinding, dpm to resist “moisture and plant growth” ( this will be butted up against the blockwork not connected to the dpc), then 50mm of concrete goes on top of this dpm, which then i will leave a 150mm gap so i can have a suspended timber floor.

 

[A Trowel]

No

 

[electrified]

No

could you at least tell me why i have done wrong. @^woody^ is telling me to put a membrane down which “stops weeds” but it is the same material as dpm. but then i’m told i don’t need a dpm as it is a timber raised floor. just tell me what i need to put down instead of the reg lingo please many thanks

 

[A Trowel]

If you had read to the bottom of NHBC 5.2.10 you would have seen that 150mm is a minimum dependent upon the subsoil, so just to say needs 150mm is incorrect, and the “ regs lingo” is for fact checking and reference

 

[^woody^]

There is no problem with damp under a suspended timber floor as the ventilation deals with that. You do not need a DPM

There is a potential problem with vegetation growing in the ground though

So, you either lay a concrete oversite which stops anything growing though, or you lay gravel and beneath that you put down something that stops anything growing though. That something can be made from polythene, polyethylene, whatever you if you like, as long as it forms a barrier and wont rot away.

It is not a DPM, and does not need to be installed like a DPM, even if its made of the same stuff a DPM might be made from.