The Zebcolm Trench

[a twig]

Might be worth asking some of the posters in this thread how they got on in the end

damp (dare I say "waterproof tanking".....)

Ok. We have recently moved into an old stone house with a big damp and high humidity problem. I know that tanking is a big no no when it comes to traditional stone rubble walls, and I've just spent a couple of weeks removing cement render and gypsum plaster to try and allow my walls to start...

www.periodproperty.co.uk

 

[MBozz]

Wow! Looks stunning!
For me I’d say your best bet is to try and install a geotech membrane on the outside of the wall - something like this https://www.permagard.co.uk/permaseal-8-geodrain-external-waterproof-membrane with a drain at the base to take away the water that is “caught” by the membrane - fair bit of digging to do it but should block and divert pretty much all the water coming down the hill before it can enter your wall, then usual lime etc on the inside to let any moisture that sneaks through out again

Thanks so much for your really helpful reply Twig, and for passing through the link to the other forum. I hadnt come across that membrane, but it looks like a great option in conjunction with the drain. I've posted to see how they got on.

I realise I probably need to speak to a structural engineer, or at least dig some exploratory holes to see exactly what is there, but does the appearance of the wall, with what appears to be bedrock (or perhaps just a giant stone?) suggest that we may have issues digging out? Is it possible the house was originally built in such a way that removing the ground around it (even without going below footings) could endanger it structurally? That's the thing that makes me a tad nervous

 

[Zebra]

This situation, as you have implied, MBozz, is rather different, in that the house was built into a slope. You aren't simply dealing with ground levels which have risen externally over the centuries with road resurfacing, paving, or the accumulation of organic matter. Therefore the excavation could encounter structural issues if the house is structurally dependent on bedrock which is higher than the internal floor level.
The other issue you have here is that the ground is sloping towards the house. In most cases with these trenches, we are only dealing with the water that actually falls inside the trench; there isn't another source bringing water from elsewhere. But in your case there is, so you need to deal with that also.
However, I would think there's much you can do. It looks like much of what is against your walls is earth, on which the house would not be dependent structurally and I think excavation would be a good idea, if a bit daunting, given the enormity of the retaining wall you'd need to build.
But I agree that you may need to deal with the ground water from above in a separate operation - a land drain higher up perhaps, otherwise you'll end up with a moat!
The other thing that occurs to me is that your trench might need to be wider than most, given its depth, otherwise it'll be quite a dank gully where air doesn't circulate very well, and it won't perform as effectively as it might. Good luck though, we look forward to seeing your updates!

 

[MBozz]

Thanks a lot Zebra. Really appreciate the help. We will make sure to provide updates once we get cracking with it.

 

[Also Clueless]

We have a circa 1900 Victorian mid-terrace 2up 2down house. We have a damp, mouldy wall in our kitchen which is the external, garden facing wall. We think its because external levels were raised above the dpc (if there is one) years ago and there is a concrete skirt along the wall outside, all contributing to the damp. We don't know what we will find if we try to lower ground levels and there is a sewer cover (see photos). There is a garage at the end of the garden which is at a very much lower level (maybe 2 feet lower) and it looks like it holds up the garden/patio, much like a retaining wall. Rain water does drain away from the slabs, some will be draining through the gaps between the slabs as they are not mortared. Thought about the Zebcolm trench, but where to start given the pipes and drains in the way. See photos. Any advice is most welcome.

 

[Zebra]

The guttering might be dumping rainwater into the base of the wall if that gully from the downpipe to the drain overflows. It looks like that's not a great system. I think you would be better routing the downpipe straight into the drain.
But also, rainwater will be splashing up from the concrete onto the base of the wall. The base of the wall looks quite wet. It would be good to replace the concrete with a surface that will absorb rainwater rather than splash it up the wall.
But it would be good to go further than that. I think a zebcolm trench would be a good idea.

 

[Also Clueless]

Hi Zebra, many thanks for the reply, very sorry about the delay in responding. The advice about the downpipe and gulley is good, don't know why we haven't thought of it. We will press on with the Zebcolm trench plan, we may come back with more questions of course. Its a bit intimidating for non-builder types. Many thanks again.

 

[Toby Newell]

Holy currumba, yes, what zebra said id great advice, as would be removing everything from the garden. Looks like they raised the entire ground level several courses. Any airbricks should be 100mm + above ground.

 

[Toby Newell]

Glad you have a sense of humour @Also Clueless er, lol. These type of shenanigans are the most common cause of the most pervasive type of damp that I see, at least at ground floor level. Thankfully the area is relatively small and if you have time and a strong back most of it you can do yourself with a wheelbarrow, shovel and cheap SDS drill. If you get into any serious concrete then hiring a big Hilti for the day is preferable to making noise to give yourself blisters.

There are photos on my website homepage of a floor where the seat joists were hollowed out and even the brick piers and mortar had rotted and crumbled and we had to replace the entire floor from the ground up. Prior to our visit the client had removed tens of tons of concrete from the back garden, but that was over a foot high! The mind boggles but effectively it works like putting a large sponge around your house.

I guess the good news is, it's one of the most obvious fixes, I was going to say easy, but rephrased! Removal of concrete / debris always seems tardis like to me, your mind says 'a few rubble sacks' suddenly you are into the dozens and approaching a ton... when you realise one cement lorry holds 18 tons it makes sense but it's so out of our normal frame of reference it never ceases to amaze, or maybe it's just me!.

 

[Rustyoldnail]

Thinking to try this with my rear patio in my end of terrace Victorian/edwardian house where the level has been built up to floor level. Just some debate with my builder who thinks a French drain is necessary but I’m hoping to get away without it.

 

[Zebra]

An open trench is more effective than a french drain.

 

[Rustyoldnail]

The trench has been dug now, ended up being quite wide to allow for the small retaining wall , approx 350mm.
My builder wants to put concrete in the bottom so any rain can travel to the drain, what are your thoughts on this?

 

[Zebra]

If you're only dealing with the water that actually falls in the trench, it really is a very minimal amount and needs no more special rainwater management system than plain unadorned soil would.
Edit: mine is plain soil in the bottom and is fine.

 

[Zebra]

If you're dealing with water that's ending up in the trench from somewhere else, either higher ground sloping towards it or gutter downpipes dumping it there, then yes, but if it's no more affected by rainwater than it would be if it were at the original height, then no special measures are necessary and indeed would be harmful as they would prevent evaporation from wet soil after rain.

 

[Rustyoldnail]

Here are a few photo’s, it will be interesting to see how things go with the heavy rain were having.

Here are a few photo’s, interesting to see how things go with heavy rain.