Housing - New Build: Building into a slope

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- CommentAuthorTriassic
- CommentTimeJun 7th 2014 edited
As part of our new build we have permission to build a workshop and wood store, however the location is set into hillside, with the rear wall buried in to the hillside. How do I waterproof the rear wall to stop damp ingress.
- CommentAuthorowlman
- CommentTimeJun 7th 2014
The way I've seen it done in Germany, some time ago mind, was to dig out the wedge lay the suitably insulated DPC'd raft build the blockwork wall,-some distance off the sides of the excavated hole, waterproof/tank the exterior, tied into the raft DPC, then insulate then geotextile then backfill with French drain around. The stuff they tanked the exterior was quite similar to flashband but on 1M rolls it was literally stuck to the primed blockwork. The thick exterior insulation was a type of EPS/EWI but seemed to be impregnated with bitumen. In the UK I'd be tempted to bring in a specialist firm for the job and hopefully with it the guarantee.
The idea of building into a slope is great though, with lots of interesting design possibilities, good luck.
- CommentAuthorCWatters
- CommentTimeJun 7th 2014
If this will be a retaining wall get it all designed by an engineer.
- CommentAuthorTriassic
- CommentTimeJun 7th 2014 edited
As it's a simply shed I'm hoping to keep the design and execution simple, blockwork walls, exterior cladding, slate roof (to keep the planner happy). The ground is mainly limestone with a thin cover of soil so is stable and requires little retaining.
- CommentAuthorNick Parsons
- CommentTimeJun 7th 2014
I distrust tanking and tanking-type solutions so much that I would rather build a retaining wall and then build an 'ordinary building' 'on the flat'.
- CommentAuthorMikeRumney
- CommentTimeJun 9th 2014
<blockquote><cite>Posted By: Nick Parsons</cite>I distrust tanking and tanking-type solutions so much that I would rather build a retaining wall and then build an 'ordinary building' 'on the flat'.</blockquote>

Second that ...
- CommentAuthorowlman
- CommentTimeJun 9th 2014
Posted By: Nick Parsons...............I distrust tanking and tanking-type solutions so much that I would rather build a retaining wall and then build an 'ordinary building' 'on the flat'.

Why is that? Is it from personal experience?
I would agree that many cellars in old UK properties are woeful, and interior tanking with inadequate materials which are applied in and amerteurish fashion can be disappointing. But for a new build with correct materials what's the problem. After all many hundreds of thousands of Continental homes are built with cellars, it doesn't seem to present any problems there.
- CommentAuthordickster
- CommentTimeJun 10th 2014
I guess the water table should be considered, bottom of a clay valley oozing water versus near top of hill in chalk?
- CommentAuthorTriassic
- CommentTimeJun 20th 2014
Posted By: dicksterbottom of a clay valley oozing water versus near top of hill in chalk?
Top of the hill on limestone, very well drained. All I need to do now is excavate the slot into the slope.!
- CommentAuthorJeff B
- CommentTimeJun 21st 2014
Triassic - I did a similar thing about 30 years ago in my previous house. We built a new garage alongside the old one and turned the old one into a utility room and workshop. The LH wall of the new garage was a retaining wall. The garden was mainly clay which supported itself when excavated even though the "cliff face" formed was about 6 foot high! The retaining wall was built of concrete blocks laid on their side as it were, so as to form an 18 inch thick wall and we left about a 6 inch gap between the wall and the clay "cliff face"; a french drain was laid at the bottom of the gap below DPC level; the inner skin was blocks laid in the conventional manner to form a 4 inch thick wall and we formed a 2 inch cavity between the two. We used about 1000 blocks as I recall!

The back of the retaining wall was treated with black bitumen paint as it went up. When at the required height we put corrugated PVC sheets vertically behind the retaining wall and filled the gap with 20 mm gravel. The top of the PVC sheets was covered by lead flashing.

We never had any trouble with damp; note: we lived there for about 23 years after doing this work.
- CommentAuthorTriassic
- CommentTimeJun 21st 2014 edited
Posted By: Jeff BThe back of the retaining wall was treated with black bitumen paint as it went up. When at the required height we put corrugated PVC sheets vertically behind the retaining wall and filled the gap with 20 mm gravel. The top of the PVC sheets was covered by lead flashing.
I like the idea of the PVC sheets and gravel drainage, oh and not forgetting the bitumen.

Just a thought, where does the insulation go in a semi-basement concrete floor and walls - inside, outside, between?
- CommentAuthorJeff B
- CommentTimeJun 22nd 2014
Posted By: Triassic
Posted By: Jeff BThe back of the retaining wall was treated with black bitumen paint as it went up. When at the required height we put corrugated PVC sheets vertically behind the retaining wall and filled the gap with 20 mm gravel. The top of the PVC sheets was covered by lead flashing.
I like the idea of the PVC sheets and gravel drainage, oh and not forgetting the bitumen.

Just a thought, where does the insulation go in a semi-basement concrete floor and walls - inside, outside, between?

Sorry, I don't know what you mean by semi-basement concrete floor and walls?
- CommentAuthorTriassic
- CommentTimeJun 22nd 2014 edited
Sorry, what I mean by semi basement is something built into a slope so that the two sides and the rear wall are buried in the ground but the front is at ground level. So as the basement walls are usually concrete or solid block does the insulation go inside or outside, or in the case of the concrete floor above or below or something else?
- CommentAuthorowlman
- CommentTimeJun 23rd 2014
On all the ones I've seen the insulation is exterior and is part of the overall waterproofing/tanking layer.
- CommentAuthorJeff B
- CommentTimeJun 23rd 2014
Posted By: TriassicSorry, what I mean by semi basement is something built into a slope so that the two sides and the rear wall are buried in the ground but the front is at ground level. So as the basement walls are usually concrete or solid block does the insulation go inside or outside, or in the case of the concrete floor above or below or something else?

Triassic - I think I would internally insulate both the walls and the floor in this scenario. Batten the former and cover with plasterboard and use a floating floor of T&G Weyrock for the latter. Use a vapour barrier in both cases as well.
- CommentAuthorowlman
- CommentTimeJun 23rd 2014
Would this be any good?

http://www.tidl.ie/files/Foamglas_Wallboard_Underground.pdf
- CommentAuthorJeff B
- CommentTimeJun 23rd 2014
Posted By: owlmanWould this be any good?

http://www.tidl.ie/files/Foamglas_Wallboard_Underground.pdf" >http://www.tidl.ie/files/Foamglas_Wallboard_Underground.pdf

Looks good! I think I would still go for an unfilled cavity wall in front of the retaining wall and use IWI. No risk of any water getting at the insulation then. Similarly lay EPS on floor over a vapour barrier and have a floating floor.
- CommentAuthorNick Parsons
- CommentTimeJun 23rd 2014
As someone said to me in another thread, be careful your Floating Floor doesn't become a *floating floor*!

You say EPS over VB. Assume you mean DPM, as the VB would be on the wrong (cold) side.

Nick
- CommentAuthorTriassic
- CommentTimeJun 23rd 2014 edited
Posted By: Nick ParsonsAs someone said to me in another thread, be careful your Floating Floor doesn't become a *floating floor*!
Nick
if my floating floor was to float there would be no hope for the majority of you as I'm 120 foot above sea level, half way up the side of a limestone crag, so no surface water issues dither.
- CommentAuthorJeff B
- CommentTimeJun 23rd 2014
Posted By: Nick ParsonsAs someone said to me in another thread, be careful your Floating Floor doesn't become a *floating floor*!

You say EPS over VB. Assume you mean DPM, as the VB would be on the wrong (cold) side.

Nick

Nick - actually I should have said VB above and below the EPS, which is what I did in our chapel building recently. Belt and braces approach with the benefit of eliminating the possibility of T&G Weyrock squeaking when walked on. It worked!

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