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constructing a warm roof will not be possible due to the height of the roof. small joists prevent a cold roof. so i was wondering if i could have an empty void with no insulation, moisture plasterboard if it helps. I understand that i may need ventilation, and i would do this via fascia board...

thank you, straight to the point, perfect.

correct and once i lay my sand blinding then the dpm, does this just butt up with the brickwork, as someone said to connect it to the dpc? then i lay my 50mm concrete. thanks

hi @oldbutnotdead, could you help me out with a dpm question. i have posted on here but i am still not understanding. i have a timber raised floor, and am getting mixed answers whether or not to put a dpm between the sand blinding and the 50mm of concrete. A person has said that do put a...

:eek: 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...

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...

sorry @^woody^ exposed the crucial detail that 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...

So you do have to lay a membrane????? which one?

timber ground floors. so a floor with timber, raised or non raised

Timber ground floors: Timber used for suspended ground floors should be treated or naturally durable, in accordance with Chapter 3.3 ‘Timber preservation (natural solid timber)’, and the ground below the floor covered with: 50mm concrete or fine aggregate on a polyethylene membrane laid on...

so just 50mm blinding sand and then concrete underneath? why wouldn’t i need a dpm as damp could rise couldn’t it? would there be any harm in putting one and butting it to the brickwork instead of connecting it to the dpc? is there a diagram you can point me towards?

four screws then, either way i’m asking about penetration of the dpm.

Also you say here that the dpm and dpc are not linked for a suspended timber floor??

ok i understand this. but as i said earlier when the dpm goes up the wall can i penetrate this now and again with 2 screws for joist hangers? if not how else am i going to keep the joists in place?

what if i didn’t. as outside is being rendered.

where would my ventilation go?

in a suspended floor why are these not linked (going up the wall to the dpc). you will still have that small bit where water can get across.

i have added to my diagram shown below. so i know i need a 150mm gap from concrete. my floor level will most likely be around the height of the dpc. is the diagram correct? also say i was going to put joist hangers to the wall, would it be ok the penetrate this with maybe two screws for every...