Damp in a cavity wall both sides of large patio door
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Damp in a cavity wall both sides of large patio door

Post by j0hnone1ll » Sun Nov 21, 2021 2:57 pm


I have a House built in the 1980. It is built on a suspended solid floor and has Cavity Walls. In the dining room there was a large Patio Door. This was converted to some french doors about 10 years ago but I
don't necessarilly think that is relevant as the opening remained the same size.

We have damp both sides of the door towards the bottom. Cant identify as rising damp but it is low down. I must be honest and say this area is tucked away and out of sight beside some cupboards so I cant really say how long it has been damp. It only came to light when we wallpapered the area vs emulsion painting which we had previously.

When we originally had the house (after about a year) we had water literally pouting through the reveal of the then patio door. The builder send a guy along who told us that a drip tray had not been placed above the Patio Door, He installed it and the water stopped pouring in but I am wondering where it then went (or goes now)

Clearly water enters the cavity and has always done so as at that time the wall was brand new so all the pointing etc. would have been perfect. Now I assume it hits the drip tray and gets diverted but to
where ? There are 4 or 5 small holes along the front wall where I assume the drip tray is but I have never seen any water exiting there.

Reading various things on the web I am thinking I should have some weeps at the bottom of the wall somewhere ?

That said there aren't any anywhere else in the house and , as far as I know this is the only damp area .

The wall face house has polystyrene bed insulation.

I suppose the cavity could be blocked by poorly fitted DPC or debris and water building up over the DPC.

I did open the cavity a few years ago and took a load of rubbish out which I thought had cured it but seems not. I am also wondering if at that time I should have replaced all the plaster. Would the plaster just continue to absorb damp ??

I do plan to remove an area of plaster , leave it for a while and then test the blockwork for damp just to make sure it is just not the plaster absorbing condensation.

I am also planning to have some bifold doors installed so I can take the window sills off the French doors and have a look/prod around in the cavity. I guess I could also drill some drainage holes in the front wall and see if I get any water coming out after driving rain.

The wall is South Facing and has polystyrene bead insulation

Any thoughts welcome particularly as to how I could narrow down the causes .

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Re: Damp in a cavity wall both sides of large patio door

Post by stoneyboy » Mon Nov 22, 2021 10:35 pm

Hi johnone1ll,
Suggestions: vertical DPC stops short allowing damp from outside skin to pass to inside skin; debris at bottom of cavity forming a bridge; cavity at bottom of opening filled again creating a bridge. Very unlikely that the plasterwork has become hygroscopic.
Regards S

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