Hello all, I have a small worry with next door. We’re building an extension out to party wall (victorian terrace) at the back. Next door are doing the same build in a couple of months so we agreed party wall agreement not an issue. Party wall used to be large garden wall and part lean to outhouse on each side. Next door thought it needed rebuilding as there was damp in the lean to part on both sides.

My builder thinks its fine to build on with tanking/dry proofing but mortar is a bit crumbly so neighbours still think it needs rebuilding. My side has been re-mortared where need be, tanked, rendered with tanking render and ready to go. Next door are still worried that tanking isn’t enough and the middle of the wall may remain moist if tanking both sides.

All build is going through building regs and within the law.

My question… does a wall dry out from the inside if you tank both sides and top is sealed (no rising damp). Are my neighbours too concerned with what they can see now before the lads are anywhere near finishing? Who should relax, me or them?

Cheers

I’m surprised the building inspector is happy using the existing wall. Does it have proper footings? I’d tend to rebuild it. Not that much cost to save a lot of potential hassle.

Yea theres fproper footings that have been there for yonks

Building Surveyor here. I’d be concerned, looks like one for me in 5 years time.

APF

so we agreed party wall agreement not an issue.

Yeah, right! 🙄

Is it double skinned with cavity? If not the sound attenuation will be poor and it won’t conform to regs.as it’s not insulated.

I’d build a new one.

This garden wall is very unlikely to have any type of DPM or as was used, slates to stop damp being sucked up so I would expect it to still be damp,

Yea theres fproper footings that have been there for yonks

Footings for a modern extension and a old garden wall are two different things. I presume someone must have dug down to inspect the footings?

Best to replace it easier for both sets of tradesmen and customers to have a nice new wall to look at and work from.

But then being a tradesman, some customers always want the cheapest job, without looking at the consequences of future costs in latter years

It did have dpm at the lean to. The dpm was decayed hence damp. Cavity being built when next door do theirs.

Yea they dug down and will be concreting floor around footing

Personally I would build a new cavity wall with Kingspan in between. Then the only thing you will share is a few tiles.
It could save a load of Ball ache further down the line if you want to sell.

What about damp wall? If it’s tanked will it dry out considering damp came from my rubbish lean to?

Knock it down and do it properly. It’ll save you all manner of grief in the long, and not so long, run, not least with your neighbour.
You haven’t even started yet, and already you’re disagreeing on a vital detail…

MOre to the point – why aren’t you sharing a builder? Surely cheaper than two goes at it?

Next door want theirs to go out to tender. Agree would have been so much easier and cheaper if they had ours.

Is it double skinned with cavity? If not the sound attenuation will be poor and it won’t conform to regs.as it’s not insulated.

This will be your neighbour’s problem not yours. You’re building out first then they’re adding onto your build (as long as your build stays ahead). Relatively easily solvable from their side with a secondary stud wall to create a cavity

Dmorts – thanks. That’s what I was thinking. My builders offered to put a stud wall in on my side because of my worries but he still doesn’t think it’s needed. Can I add that my builder has a 10 year guarantee on things and he literally said to me it’s more than his reputation is worth to cutcorners. He’s confident and he offered to get a surveyor around for my peace of mind this week. He’s confident. I’m not a builder. He said there’s no big weight on the wall it’s all taken by rsj in the house that they are putting in.

Did I say he’s confident haha

If you wrap the existing wall in rubberised plastic, where do you think the damp will evaporate to?

Your existing builder sounds like a cowboy if they are happy to tank it, rather than start afresh.

Does damp always evaporate?

I was brought up on the motto “if a jobs worth doing, it’s worth doing well”.

Stop trying to penny pinch and knock the damn thing down and rebuild it properly with proper footings. It will only cost you half the actual cost if you are sharing it with your neighbours so will be tiny in the grand scale of things. I won’t have any DPM, I doubt any kind of footings it has are sufficient once you add in the weight of roof, internal render etc

If you don’t you will end up with damp problems forever. Tanking is a solution to a problem that can’t be avoided and should be avoided when possible by design.

The builder is probably confident as he doesn’t want the hassle of knocking down and rebuilding, or he has another job lined up and doesn’t want to over-run etc, etc

Funny reading some of the above. What happens in a refurb? Do we knock all walls down and start again?
Fwiw, as part of a big refurb I’m currently on we used an existing boundary wall to the school playing field to build the gable of a garage off. Even though it’s possibly late victorian it does actually have a 3/4 inch old fashioned concrete found and the usual “spread” of brickwork at the base.
Re the damp, salts may be an issue as well as the damp so it’s worth salt stabilising as well damp proofing via tanking etc.

It seems there’s more than one way to skin a cat then.