Treating damp and installing wet UFH in Edwardian limestone or sandstone property

[scopnorth]

Hello, nice to be here. I have lurked in these forums for some time and now my time has finally come to post!

I recently purchased a stone built Edwardian home (embarrassingly I am not sure if it is sandstone or limestone). It is in need of renovating and modernising throughout, which I/my builders hope to begin in mid to late October. However, it suffers from some rising damp in a few parts of the downstairs. I had a 'damp specialist' company visit the site and they recommended some work for my builder to do, under a separate contract, as well as 'damp treatment' in the form of chemical damp course etc. From what I have read on these forums, these chemical damp treatments don't really work and can often make damp much worse in sandstone or limestone built properties, so I don't think I will be booking that work in. However, the specialist (and my RICS surveyor, as well as builder) have said that the external ground needs to be lowered by about 15cm in the front and back, and that there is some rendering which is bridging the existing damp course which needs to be removed. However, I'd be so appreciate if someone could share their thoughts on the (long) list of work that I think either needs to be done or should be done to the property before I start working on it.

The damp specialist recommended the following work to be done by his company:

1. Installation of a new chemical damp course to the walls as indicated on the attached sketch (see attached leaflet).
2. Hack off plaster to heights indicated and remove debris. This is necessary due to the fact that rising dampness allows the passage of ground salts to be carried up through
3. the wall which is often absorbed into the masonry and plaster. These salts are usually nitrates and chlorides which are hygroscopic, i.e. they have the ability to draw moisture from the atmosphere.
4. Fit a cavity drain membrane using specialist fixings and replaster as necessary.
5. Carry out waterproofing to the pantry wall/floor joint by cutting back plaster 50mm and applying two coats of waterproof slurry to the exposed brickwork.

He also recommended the following to be done by our builder:

1. Client to remove soil level/gravel to rear elevation to provide better sub floor ventilation to the rear.

There are also a number of areas/things that the specialist didn't pick up on but which I'm certain need fixing to help fix any damp in the property. Cement mortar has been used to repoint the external walls in a number of places - I know this needs to be taken out and redone in lime, so we'll be looking for someone that could do this for us. There is also a section of the back wall where pebbledash has been used to cover the stone all the way from the ground up to the roof - I feel this should be removed but I'd really appreciate any other thoughts?

Separate to the damp, we were hoping to install wet underfloor heating throughout the downstairs but I don't know whether the builder is going about the right approach. I understand that these type of properties need to be able to 'breathe' and am now worried that his plan (which involves using concrete and damp proof membrane) will make the floors less breathable and therefore risk damp issues under the floors? Our builder said he would do the following to install it:
- All downstairs timber floor removed
- excavate the existing sub base out.
- New Floor Makeup of: 150mm compressed hardcore, Visqueen damp proof membrane, 100mm PIR insulation board then 75mm solid screed.
- Tiled throughout downstairs (client supply)
- Wet underfloor heating (UFH), supplied & installed (OMNIE Smart System).

There are two other things I'd appreciate views on - the house has some PVC windows, some sash and some not. Does anyone know whether ideally the windows would be timber sash to help with the ventilation? The previous owners also boarded up some of the fireplaces and, again, I'd be really interested to know whether these should ideally be opened up to allow for better ventilation.

Sorry about the ramble but any advice would be much appreciated. Have attached some photos. Many thanks

 

[malcolm]

For the damp proofing guy stuff - many of us have inherited houses where the interior walls have been tanked as he is suggesting. I bet it hides the problem for a few years, but the problem is more water getting in than can get out and after a few years the wall becomes soaking wet. It gets cold and attracts condensation so still gets damp. Then the water gets above the level of the tanking and you've got the damp up there. You are wise rejecting his contribution.

External ground levels ought to be a good 6 inches lower than internal ground levels and those 6 inches of exposed external wall need to be lime pointed to let the water evaporate away otherwise it will go up into your walls anyway. That's what they did to address damp before they invented damp courses, and for an old building it's best to assume you don't have a damp course.

For the other things I would be inclined to hold back and see if they cause problems. How much do you want underfloor heating? I'm running concrete floors and after introducing lower external ground level and lime pointing they work for me. But huge expense for a fad that's possibly going to get banned in the net zero. If you've just bought the place it's a good plan to live with it for a year or two and find out what your priorities become. Saves a lot of money and is kinder to the house than ripping the thing apart.

 

[Toby Newell]

^^^^ that. +1.

UFH is a fad and generally poor for older houses. Often it is more expensive to run and inefficient as supplementary electrical heating at 3x price is required as unfortunately the system runs at lower temps that cannot sustain comfort levels in less well insulated houses (such as yours)

It is also less efficient in colder weather due to lower delta T temperature difference on which the heat engine runs.

Its a shame it is missold and funds wasted that could be put to better use.

I advise all my clients against it who enquire, unless they are undertaking a complete back to the brick overhaul where installation costs are sonewhat already mitigated.

It is excellent for intelligently designed new builds where the level of increased insulation is built in.

+1 on all the damp / tanking advice too.

 

[malcolm]

I was being stupid and thinking about bricks when thinking about concrete floors once again. Bricks have a load of lime between then that can wick out moisture but stones are bigger so have less lime mortar for the same area. That would mean you can probably get away with less on a stone building than a brick building. A lack of damp is good to have on an old house. A vented underfloor area that nobody is going to bother pointing is a win worth preserving.