I have a 150 yr old cornish granite cottage, with moderate damp issues which I am going to try to address by improving the guttering and lime pointing. I do however also want to lower the floor level to a) create more headroom and b) install some underfloor heating in parts of the ground floor. There are no foundations for this house and at the moment the floor is a layer of 1" of concrete on top of bare ground.
My concern is that if i dig down approx 1 1/2 feet and then damp proof before re laying concrete/insulation etc any damp will simply be 'pushed out' towards the walls, exacerbating the problem.
Any thoughts from the damp gurus amongst you?
Tony
posted on 01-11-06
How will the damp move through the granite? Where does it go now? what floor coverings do you have?
honeyguide
posted on 02-11-06
I'm planning to DPC the ground then concrete and insulate on top of this. After this I will put small joists and floorboards for the main body of the house and ufh/tiles in the kitchen.
The internal walls will be a mixture of exposed granite and lime rendered.
Tony
posted on 02-11-06
Sounds like no problems then.
Kit
posted on 07-11-06
hg,
If I understand correctly it sounds like you are planning to excavate 1 1/2 ft below the bottom of the existing walls, since you say there are no foundations. No foundation is quite common in old properties. Be aware that lime mortar and random rubble granite walls are VERY weak in tension (good in compressive loads) and, if you are not careful you will lose considerable portions of your external wall. The ground the walls are standing on will move inwards to the excavated area under the weight of the walls, and will therefore need serious shuttering to support it whilst you pour all that environmentally unfriendly concrete. If you are going to dig floor levels below wall foundations you should really underpin the walls first. A very time consuming business. Additionally you will need to tank the inside of the new vertical area around the perimeter of the lowered floor.I once restored a property in warwickshire where the previous owner had dug a garden path along the outside of one gable end, 6 inches below the existing 6 inch foundation. The gable end parted company with the rest of the house - still it was cheap to buy!
Can you not live with the existing headroom? It's a lot cheaper and you are proposing quite difficult work to gain your extra height.
Kit
Phil
posted on 13-11-06
I have lived in Cornwall all my life and worked on countless properties of this type and Kit is right your biggest issue will be that of supporting the masonry and the ground, I would normally expect to see this type of structure on to shellet base (thin slatey type stone that will cleave very easily)which is more than capable of supporting the load of a building and yes underpinning can be carried out but it will involve a lot of work. Whilst tanking could be option to seal the ingress of water in such situations please don't look at this as the be all and end all for curing damp in buildings where works such as you are describing will be carried out. All too often tanking is looked at in isolation and the main points that need factoring in are overlooked.
