Damp coming up through floor in new extension

[Johnharold]

Hi all,
hoping to get some help with a damp problem with a flat roofed extension. The damp is coming up through the floor board. I think it is a beam and block construction. I cut a hole in the floor board to have a look and found the concrete under the dpm to be very rough, possibly puncturing the dpm. Should it be like that? Would it be ok to lift all of the board and tape another dpm on top of the existing one?
I have dug a french drain around the outside and intend to repair the render at the bottom of the wall, taking it down to the concrete base. Could I build it up as a slope so the rain runs down into the French drain? If so should it be a cement mix or concrete, and could I shutter it somehow and fill it to above the missing render?
I'd be very grateful for any advice.
John

 

[freddiemercurystwin]

Some photos from further away might help, what is the exact floor make-up? Beam and block .... then what?

 

[Johnharold]

I think its beam and block then the rough screed in the photo, then the dpm, not entirely sure as I didn't see it being done. I'll get some more photos up tomorrow

 

[Johnharold]

Couple more pics showing exterior walls

 

[Mr Chibs]

Are you aware if there is any insulation in the floor?
I would have thought that the the DPM layer would have been under the insulation or screed (if that's the bumpy stuff in your photo).
That way damp can't reach the floor covering.

Is the damp next to the wall? It could be possibly the cavity is bridged and damp making its way to the inner skin of brickwork and to your floor.
Is the skirting board showing any signs of dampness?

§§Render going to the ground (outside) is never a good idea as this can bridge the DPC.

 

[Johnharold]

Hi, thanks for the reply. es, there is celotex insulation over the dpm. I cut a piece out to get to the dpm.
The skirting does seem damp, but the visible damp patches come through a day or two after rain, mostly away from the wall.

 

[Ivor Windybottom]

Was the soil level above the DPC before you dug it out? It looks that way from the photos. If that was the case then that is the cause, and it just needs some re-landscaping and time to all dry out.

Also have a look while it's raining, check drains and downpipes.

 

[Johnharold]

Hi Ivor, thanks for the reply. The soil level was below the dpc.I dug the French drain last year so it has been taking the water away, but I put some gutter along the bottom of the wall to stop water pooling there. I've only recently pulled the gravel back from the bottom of the wall.
I've just been advised that I should lift the floor board, celotex and dpm, chip off any sharp raised bits of the screed that may have punctured the dpm, give it a coat of tanking slurry, and replace the dpm.

 

[Mr Chibs]

The bumpy surface you posted is presumably the screed?
Where is the celotex above or below the screed?, finishing in chipboard.

 

[Ivor Windybottom]

I just can't imagine that amount of water coming up through celotex, even if there was no membrane at all. Is there any plumbing in the vicinity, e.g. in neighbouring rooms?

 

[Ivor Windybottom]

Also... you say it's a new extension. How long was the concrete left before being floored over?

 

[Notch7]

The damp is coming up through the floor board. I think it is a beam and block construction. I cut a hole in the floor board to have a look and found the concrete under the dpm to be very rough, possibly puncturing the dpm.

if it is block and beam there wont be any concrete

normally the construction from bottom upwards is:

soil
concrete oversite to blind off soil
150mm minimum aid gap
beam and block floor
cement slurry to close gaps and lock blocks i place
DPM
insulation
screed

I cant see any air bricks in the external walls -are there any?

Its rather unlikely for damp to work its way up through the insulation, through the screed to the floorboards

 

[Notch7]

I've just been advised that I should lift the floor board, celotex and dpm, chip off any sharp raised bits of the screed that may have punctured the dpm, give it a coat of tanking slurry, and replace the dpm.

I am a bit confused, normally the screed is above the insulation

where is the DPM that you have shown a picture of -is it just below the flooring?

is this a new extension?

 

[Notch7]

Hi, thanks for the reply. es, there is celotex insulation over the dpm. I cut a piece out to get to the dpm.

are you saying you have a floating floor -ie your flooring is put straight over the insulation

that doesnt make much sense really -unless the building made an error on the heights and had no room for screed

the problem is that the concrete beams are not level they are prestressed and bow upwards -so the floor would not be flat

 

[Mr Chibs]

So it's a floating floor? Working from top down.

Chipboard
Celotex
DPM
Lumpy screed?

If correct, I'd be erring to bridged brickwork as damp perpetrator.