Rear wall & floor damp tanking / DP'ing / insulating etc

[CornishPaasty]

Hello there,

I have an old stone cottage which is in need of some renovation and I would appreciate a bit of advice on the best way to ensure a dry house.

To set the scene, the cottage is built on the side of a steep bank/cliff and the rear of the ground floor of the cottage is cut into the cliffside, the front is level with the ground which slopes away downhill.

Inside there is obvious damp in the rear wall (ground floor only) and also coming up through the floor. The rear wall is plaster and lining paper at present, I would assume there will be a stone wall and render of somesort behind. The floor is an old lime-style floor - hard on the top but a chalky crumble not far below the surface. Clearly there is water moving slowly through the cliff rock and over time it has affected the house. If the property had not been concrete rendered externally in the past then perhaps the house would have breathed it away, but what with more modern methods having been used in the past, its somewhat suffocated now.

Anyway. I want to cure this problem in a modern manner so that I can improve the thermal efficiency of the house and get the walls straight etc at the same time. The rear wall is my main concern and the floor needs sorting anyway as it has cracks etc across it. I think the floor was probably flagstones at some time in the past which have been removed as the level seems to be about 75mm too low.

My plan is to strip the back wall off and tidy up the stonework, then membrane it and I am thinking that if I lay membrane directly on top of the existing floor I can then concrete screed directly over the top of that (might add underfloor heating at this point too) to seal that too. I'd run the floor membrane up to overlap the back wall membrane and use sealant tape on the gap. I was then thinking I'd add 2" of kingspan/celotex foam in front of the wall membrane for insulation and then top/bottom fixed batten in front of that so that I could add a modern plasterboard to give the final wall finish. I can afford to lose 3-4" at the back to take up the products and the floor can come up too.. what have i not considered..? how could I do this better ?

The only other thing I am thinking of is that I could add a gully drain from the back wall under the floor (I'd channel it into the existing floor) and out of the front wall so that rather than just relying on the permeable rock taking the water at the back away, it could come out through the pipe also.?

Any more thoughts and any specific product recommendations for this lot? (currently considering using Construction Chemicals products ?)

Many thanks in advance.
Matt.

 

[pinenot]

In essence you have a good grasp of the old way of construction versus the new, as far as porous/breathability v waterproof materials is concerned.
The crux of the problem appears to be that the house imposes a virtual dam of the water flow on the hillside.
Have you tried clearing any silt build up of the drains away from the property, silting can cause intermittent drain water backup which can be difficult to detect, and whilst drains on the property can be clear and free flowing, those away from it can cause the problem. A good scrape out of these drains would be my first suggestion.
Traditional builds wouldn't rely solely on evaporation to shed the water, but would link this to specific ground drainage, this may not be instantly visible and if it's damaged damp will ensue. So before you start throwing modern remedies and materials at this problem look first for the existing solution would be my best advice...pinenot

 

[pred]

A few years ago I renovated an old cottage in Badminton similar to yours, first we removed the flagstones, excavated about a foot, backfilled with half to dust, compacted with a wacker plate, poured in 4" of concrete and then a 2" screed, not forgetting the DPM, nowadays you would also put 100mm kingspan under the concrete for insulation.

 

[CornishPaasty]

In essence you have a good grasp of the old way of construction versus the new, as far as porous/breathability v waterproof materials is concerned.
The crux of the problem appears to be that the house imposes a virtual dam of the water flow on the hillside.
Have you tried clearing any silt build up of the drains away from the property, silting can cause intermittent drain water backup which can be difficult to detect, and whilst drains on the property can be clear and free flowing, those away from it can cause the problem. A good scrape out of these drains would be my first suggestion.
Traditional builds wouldn't rely solely on evaporation to shed the water, but would link this to specific ground drainage, this may not be instantly visible and if it's damaged damp will ensue. So before you start throwing modern remedies and materials at this problem look first for the existing solution would be my best advice...pinenot

Excellent advice, sadly when the property was built there was not a road laid up against the rear of the property (parallel to the rear) or the mains water/drainage/services etc put within it, so the water flow dynamics of the localised area will have changed a lot in the last 300-400 years. Ultimately there will be a lot more run-off water in the surrounding area as there have been many properties built around and above this one (whole streets worth) so the run-off characteristics are now completely changed. That aside I do appreciate your point and will see if there are any remnants of ancient drainage around. Seemingly the property in its current standing dates back to the late 1500's so I do not hold up a huge amount of hope, we will see however !

 

[pinenot]

You might want to check vertical drainage (also known as wick drains) which would involve placing a geosynthetic sheet material against your back wall. This effectively gathers the water, that would otherwise soak your ground contacting walls, diverting it down to a field drain/perf pipe and allowing it to divert to your drainage. Would both solve your problem and retain the old build properties with a modern slant on a very old concept. Here's a very good read on the subject if your interested - http://www.ejge.com/Bouquet08/Palmeira/Palmeira_ppr.pdf ...pinenot