cat flap installation - breach to dry course

Hi All,

Long time lurker, but first time posting.

I’m hoping on of you guys might be able to advise on some repair work to our damp proof course.

We’ve recently acquired a couple of kittens and have started the installation of a cat flap. We’re on a new-build estate where the final few houses are still being put up so we asked a one of the builders on site if they could drill us a hole in the wall, which I would then insulate and line with plywood.

As you can see in the attached picture, they’ve gone straight through the damp proof course and I’m now trying to work out how best to repair this. Initially I thought laying a new strip of the waterproofing membrane along the base of the cut in the wall might be sufficient, but reading online has revealed you need a 150mm cross over between sheets of the waterproof membrane.

I’m now thinking that some kind of tanking paint might be best – If I paint the inside of the section that has been removed (from the existing waterproof sheet down and round to the other existing section, I’m thinking this might be enough.

Or would I be better getting a builder to repair this so I have some paperwork to show it has been done properly – I’m thinking this might be needed for when we come sell the house.


Any suggestions or feedback would be greatly appreciated!


And to think, I tired getting someone who knew what they were doing to save this hastle!

I cannot be 100% certain but it looks as if the exposed DPC is the verticle part of a cavity tray. In which case your actual DPC is below this and as long as the verticle bit is sound you have nothing to worry about. Perhaps one of the experienced builders on this site will confirm (or rubbish) this opinion.

if a builder done that,i'll be concerned about the rest of the houses there building there

I don't think you have anything to worry about there - its a very small area, and won't cause any issues anyway.

If you're going to ply-line that structure I would wrap your ply 'tunnel' in damp proof plastic and fix the whole thing in place with window mastic.

Personally I would consider inserting a plastic structure instead of ply though, due to the tendency for ply to grow/shrink and eventually need replacing.

If you just buy some PVC sheet you can heat it and bend it into a rectangular tube then solvent weld butt joint on one side. You could then probably mortar this in place rather than using mastic, not that it matters much.

Either way, make sure the tunnel slopes downwards as it goes outwards, so any water on top of it ends up on the outer leaf, and make sure it's bonded on all sides to the bricks/blocks.

Might be worth a read

http://www.heritage-house.org/pages/the-fraud-of-rising-damp.html

Thanks Ben. Quite an eye opener.