Advice for lowering the humidity in an old stone basement
I Live in a 19th-century home with a limestone foundation. I don't expect to make the basement into a furnished living space, but I would like to use it for an occasional workshop and for storage.
The grade is fairly flat, but generally slopes away from the house, so we never get bulk water in the basement. But as I have tightened up the rest of the house over the years, the basement has become damper and damper, to the point where mold grows on any organic material left down there over the summer, and the air is uncomfortable to breath. The space is dry as a bone in winter though. I'm not sure of the proportions, but I'm pretty sure the moisture is a combination of air-infiltration condensation and evaporation from the porous walls and the poorly built slab.
Currently, I'm working on cleaning the stone walls, replacing some crumbled lime mortar, and ultimately whitewashing with a lime wash. There are a lot of holes in the mortar where I can feel air coming in, so I hope that patching the mortar will solve a lot of my air infiltration. I'll also look for every other possible air gap and fill with either foam or caulk. Does this sound about right? I'd love to insulate over the limestone, but I'm scared to cover it up and not be able to inspect for spalling or other moisture damage that seems to be ongoing.
Much of my house has a single layer of T&G pine between the basement and first floor, so I plan to do some sort of air-sealing there. Perhaps I will cut sheet goods and fit them between the joists, then air-seal the edges (plywood? high-density fiberboard? rigid foam? painted homosote? or a combination?).
In the short term, my plan is to cover the floor with polyethylene sheeting and cover that with foam anti-fatigue mats (the kind that go together like puzzle pieces that you can buy at Harbor Freight). In the long run, I'd like to tear up the old slab and do a proper drained and insulated slab, but I can't justify the cost right now.
In the spring, I plan to do some grading, run longer gutter downspout pipes, and maybe even install an EPDM underground roof wherever I can get access to the foundation wall.
Finally, I believe I may still need to buy a new dehumidifier. Is there a reliable way to calculate or estimate the expected capacity I would need? The space is about 25-ft x 40-ft with 7-ft. tall walls.
Any advice for this project would be greatly appreciated!
Posted Mon, 01/27/2014 - 17:46
Edited Mon, 01/27/2014 - 23:59
Other Questions in Green building techniques