How much hassle is checking inside a cavity wall?

[Alan_]

I've got back a survey which highlights a problem with some dampness. It recommends checking in a cavity wall from the outside. What's involved with this and how much is this likely to cost? Thanks

With regard to the dampness within the cloakroom area, dampness from saturation of the external brick skin from rainwater and other pipework would not be transmitted to the inner skin unless the cavity was blocked. It is therefore essential to open up the external brickwork and examine the cavity to check for blockages. All blockages or bridging of the damp proof course should be removed and the external brickwork made good.

 

[^woody^]

Is that survey saying that you have a breached cavity? It does not read like that to me - it just reads like a general statement on how moisture can cross through a wall

Has the survey actually determined the cause of the dampness, if not then its a waste of time opening up the cavity?

Opening it up is a case of removing two bricks on one course at DPC level, and one above so you can reach in and remove debris. Then do the same every three bricks

 

[JohnD]

damp wall inside a cloakroom is often caused by basin running over or pipe dripping.

 

[Shytalkz]

I've got back a survey which highlights a problem with some dampness. It recommends checking in a cavity wall from the outside. What's involved with this and how much is this likely to cost? Thanks

With regard to the dampness within the cloakroom area, dampness from saturation of the external brick skin from rainwater and other pipework would not be transmitted to the inner skin unless the cavity was blocked. It is therefore essential to open up the external brickwork and examine the cavity to check for blockages. All blockages or bridging of the damp proof course should be removed and the external brickwork made good.

Presume that, as it's a cloakroom, there's at least a bog and basin in there? Is there a water mains riser? Central heating pipes in the floor screed? I would wager that it's far more likely to be something inside leaking, rather than a blocked cavity and would look into that possibility, before going and cutting bricks out outside and messing around in the cavity.

 

[JohnD]

also, if damp is getting through the cavity above DPC, the outside leaf would also be damp

 

[fastneattrowel]

I've got back a survey which highlights a problem with some dampness. It recommends checking in a cavity wall from the outside. What's involved with this and how much is this likely to cost? Thanks

With regard to the dampness within the cloakroom area, dampness from saturation of the external brick skin from rainwater and other pipework would not be transmitted to the inner skin unless the cavity was blocked. It is therefore essential to open up the external brickwork and examine the cavity to check for blockages. All blockages or bridging of the damp proof course should be removed and the external brickwork made good.

Presume that, as it's a cloakroom, there's at least a bog and basin in there? Is there a water mains riser? Central heating pipes in the floor screed? I would wager that it's far more likely to be something inside leaking, rather than a blocked cavity and would look into that possibility, before going and cutting bricks out outside and messing around in the cavity.

make you right shy

 

[Joe Malone]

You could get a surveyor to check the cavity using a borescope. They even come with cameras attached these days so you can have pictures of anything that might be bridging the cavity. Won't be any cheaper than removing bricks but it's certainly less invasive.

 

[Shytalkz]

You could get a surveyor to check the cavity using a borescope. They even come with cameras attached these days so you can have pictures of anything that might be bridging the cavity. Won't be any cheaper than removing bricks but it's certainly less invasive.

And absolutely useless, if the cavity is full of insulation!

 

[^woody^]

The thing is, the OP has had a survey and dampness has been noted.

He should get the author of the report to clarify if he is actually saying that there is dampness getting from the outside to inside, or if he is saying that there is dampness on the inside and one possibility is that it is coming from the external face of the wall.

 

[booky1]

It's worth checking with the surveyor that he does actually think the damp is originating from the outer leaf and being transmitted inside via a blocked cavity - but it does read that way to me.

I've actually had some experience of this with my last house. Damp patches started to appear on the lower part of the external walls in two west facing rooms (the direction of the prevailing wind in my neck of the woods). The house was about forty years old, of cavity wall construction (brick inner leaf and reconstituted 'ornamental stone' outer leaf) and a bitumen type DPC. The cavity had been retro filled with polystyrene balls about twenty years ago.

I had no reason to believe the DPC had failed and the patches had started to appear after an unusually extended period of heavy rain and high winds that had absolutely soaked the west facing elevation for weeks on end. I could only think that the cavity must be breached and that I hadn't seen it before because the outer leaf of the wall hadn't been soaked all the way through before.

Anyway, I probably would have just left it alone and hoped that it never rained that hard again but it's sods law, I was just about to put the house on the market so I had to to sort it out which meant having a look in the cavity.

I didn't want to remove any of the 'stone' from the outer leaf as I'd probably struggle to get any new mortar/pointing to blend in with the old and it was still not the best weather for working outside. If I opened up the cavity from the inside it would be relatively easy to replace the bricks then just patch up the plaster and hang a few strips of new wallpaper (and I could watch the telly at the same time).

I removed triangles of three bricks from enough sites to give me access to all the damp bits and in every case (except one) the cavity was breached by an ants nest. The ants seemed to think the matrix formed by the insulation was ideal, they had dragged in soil from outside and built nests in the voids between the poystyrene balls. I dug them all out (together with areas of the insulation), put ant poison in and boxed it all back up.

I sold the house soon after (but forgot to mention the ants) but as I only moved a few doors away I'm sure I would have heard if the problem had returned.

Hope this might help or at least be of interest.

P.S. The damp patch that wasn't down to ants was a circular patch at about head height, the classic sign of a dirty wall tie (which it was).