Damp cottage. French drain

shugy · 17-03-2016 12:49pm #1

We've been doing up an old cottage in Leitrim for few years. The walls, roof are in good order however were getting rising damp which is a major concern. 2 year ago we striped everything out, retired it. Plumbed it last spring and drylined/plastered out in winter. Didn't go near it until 2 weeks ago and one side of the house, the floor is soaking! It's created a lot of moisture in the house and some moody spots appearing on plasterboard at that end of the house.

We've ripped up the floor and have went down 6 inches below bottom plate of drylined walls. We're going to fill this in, lay sheet DPC and screed however were still worried about damp riding in the walls and creating moisture behind the drylined walls.

Someone mentioned a frenchdrain and saying this should solve the rising damp problem. Has anyone on here ever installed a French drain and been successful in removing the damp. This house and the land its on is sitting above all the surrounding fields which I own. I've googled French drains but not getting much on them about solving damp in cottages. What I'm thinking, dig a ft wide trench Down below or level with stone foundations, fill with percolation stone and install drainage pipe at a fall of 1inch per 10ft. If this is correct, I can do this all around the house and drain away into the field Facing my front door.

If a French drain and newly screened floor won't solve this damp, what else could be done.

Johnnyhpipe · 17-03-2016 10:44pm

It wont solve your problem. Sounds like you'd need an injected DPC qnd possibly replace ground floor slab with insulation/DPM. Why not contact a damp proofing specialist to inspect and prescribe remedial works.

French drain is simply a stone filled trench that will help relieve local drainage issues (depending on ground conditions) - but certainly will not solve your particular problem.

dubber · 18-03-2016 11:28am

Speaking from personal experience injecting "DPC" into walls does not work. I would also recommend not contacting a damp proof specialist, or at least ones that recommend injecting walls. It's a great way to keep moisture in the walls. Unfortunately I can't recommend a solution, although a French Drain might very well be part of the solution. Also, assuming the walls are single leaf, your dry lining might be part of the problem. Have a read of this:

https://warmupbristol.co.uk/sites/default/files/Final%20-%20A%20Bristolian's%20Guide%20SME522_Bristol%20wall%20insulation_PRINT%20AW02.pdf

Dudda · 18-03-2016 12:03pm

I’ve installed a French drain on several buildings over 100 years old including churches, old stone schools, old army barracks, and other protected structures. The options available to you are electro osmosis, injecting DPC and a French drain and in my experience the perimeter French drain is the best.

Electric osmosis is when holes are drilled into the wall at DPC height and rods inserted. The rods are connected in a loop and a small current passed through it. The electric field of the small current stops the water rising. It means you have to have it turned on all the time.

Injecting DPC varies a lot depending on the type of wall. The best test is to take a section of the wall and have it injected it with a strong coloured die. Knock the wall and then check how far the die penetrated. Usually it’s not very far and only small areas of the wall end up getting treated so the problem isn't fixed but you've spent a lot of money. We have never had a wall fully protected by injecting DPC.

The French drain is usually around 750mm deep and 300m wide around the full perimeter of the building and has a 100mm dia perforated drain connected to a surface water or soak pit. It needs to be wrapped in a gotextile and I’d advise a weed protection layer just under the surface. You’ll need a drainage channel under doors or other similar areas. You can get gravel made from recycled glass which you can use instead of regular gravel. I haven’t yet used this due to cost but I have looked at it as it’s better than gravel for water abortion and has good insulation properties which will help an old stone building.

Personally I’d go for the French drain and electro osmosis.

shugy · 24-03-2016 11:59pm

Dudda wrote: »

I’ve installed a French drain on several buildings over 100 years old including churches, old stone schools, old army barracks, and other protected structures. The options available to you are electro osmosis, injecting DPC and a French drain and in my experience the perimeter French drain is the best.

Electric osmosis is when holes are drilled into the wall at DPC height and rods inserted. The rods are connected in a loop and a small current passed through it. The electric field of the small current stops the water rising. It means you have to have it turned on all the time.

Injecting DPC varies a lot depending on the type of wall. The best test is to take a section of the wall and have it injected it with a strong coloured die. Knock the wall and then check how far the die penetrated. Usually it’s not very far and only small areas of the wall end up getting treated so the problem isn't fixed but you've spent a lot of money. We have never had a wall fully protected by injecting DPC.

The French drain is usually around 750mm deep and 300m wide around the full perimeter of the building and has a 100mm dia perforated drain connected to a surface water or soak pit. It needs to be wrapped in a gotextile and I’d advise a weed protection layer just under the surface. You’ll need a drainage channel under doors or other similar areas. You can get gravel made from recycled glass which you can use instead of regular gravel. I haven’t yet used this due to cost but I have looked at it as it’s better than gravel for water abortion and has good insulation properties which will help an old stone building.

Personally I’d go for the French drain and electro osmosis.

House is old stone and plastered walls. very damp

wayoutwest · 25-03-2016 9:14am

Shugy - A stone walled building without dpc needs to have breathable coatings (internally and externally) which help to transfer the rising damp as well as coping with moisture caused by living (steam etc)
Diagram of migration of moisture through stone/breathable lime mortarAttachment not found.
A french drain is usually always a good idea with these old buildings
What is the outside ground level compared to the inside finshed floor level (put spirit level across window cill and measure down) ?
Is ground around house very wet?
Does ground fall away or into the house?
Hopefully some of your damp is the result of plastering followed by period of non-ventilation and no heating, if you've not been there.

rnaylor2012 · 30-01-2022 6:47pm

Hi, my Wife and I are just starting restoration of an old farmhouse. Solid stone wall construction.

Just wondering what approach did you end up taking and how have the results been?

rnaylor2012 · 30-01-2022 6:48pm

https://www.boards.ie/discussion/2057573912/damp-cottage-french-drain

Hi, my Wife and I are just starting restoration of an old farmhouse. Solid stone wall construction.

Just wondering what approach did you end up taking and how have the results been?

theboss80 · 31-01-2022 1:55pm

Is the land outside the walls affected high or low? We had a similar issue and dropped the land and that solved it. 140yr old house with stone (****) walls

Markcheese · 10-02-2022 2:07pm

https://www.boards.ie/discussion/comment/118559274#Comment_118559274

That's what I was thinking ,, but remember those old rubble walls don't have foundations as such , so be aware of undermining your wall ...

kildarejohn · 12-02-2022 7:41pm

Just a couple of points not mentioned by other posters about dampness in stone walls - it might not be rising damp at all. Generally rising damp does not rise more than 500mm or so. Dampness higher up can be either Condensation or Penetrating damp.

As rising damp as such is only at the bottom of the walls, one solution which can work is applying a tanking compound to the inside of the walls up to c. 500mm.

Condensation is due to lack of ventilation and non-vapour permeable (not breathable) internal lining or external cement render. So the dry lining could be making dampness worse if causing condensation. Penetrating damp is due to driving rain and/or leaking gutters, in old buildings can be caused by cracks in hard cement render, water gets in but cant evaporate out.

Shoog · 12-02-2022 8:23pm

Helped renovate an old cottage recently, similar construction with very little foundations and no damp proof course. Something many people will not be aware of is that in Leitrim air humidity runs between 80-100% much of the time. At these humidities even a small change in air temp can produce significant condensation and the floors will sweat copiously to the point where you would be convinced that there was an active water leak. Once the house was sealed up from the outside and had a regular fire to raise the temp this mostly disappeared. These old floors tend to always sweat even in a heated house because the floor is at a fairly constant temp similar to the ground outside and the floor becomes the main dew point for the house, and if there is any rising damp at all this will make things worse. Best to either put in a DPC and insulation and a new concrete floor to allow the surface to heat up or not cover them at all. You will notice that all the door frames are rotten at the bottom and this is due to this condensation primarily.

I would say a french drain is an excellent idea for helping dry out the underhouse space but don't expect it to solve these condensation issues which will have to be resolved seperately. I know of a friend who built one around his parents old two story house and he would swear by it.

An injectable DPC would be the absolute last thing I would try - they are only ever going to be successful in a brick or block house and even then only if applied from both sides.

Damp cottage. French drain

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