Reduce moisture intrusion from the outside to assist with your dry basement.
As a general rule, unless you live in the desert, basements should not be finished. Why? Because foundations are not waterproof. Moisture can penetrate through concrete, even though you may never see actual water on your basement floor. Elevated levels of moisture in a wall cavity are sufficient to contribute to the growth of hidden mold. Even if this mold doesn’t penetrate into room air, the gases produced by mold growth can penetrate. Mold gases are biologically active and can harm your health. Many individuals who think they have a dry basement really don’t, because of the elevated levels of relative humidity due to water vapor penetrating through foundation walls and the floor slab.
Question: But I run a dehumidifier.
Response: A dehumidifier will protect the contents of the room it is in but will not dehumidify the wall cavities. In addition, there could be wicking of moisture through the foundation to wood surfaces in contact with the foundation and then to the paper backing of drywall.
Question: Couldn’t I waterproof the basement?
Response: Of course waterproofing would be a big step towards a dry basement, but waterproofing is better done at the time of construction. Even if you had the walls waterproofed from the exterior, moisture could come up through the slab. Here’s what true waterproofing looks like: put a moisture barrier down before the slab is poured. Then, after the walls are up but before backfilling, put wet-dry tar on the exterior walls and wrap in polyethylene sheeting, overlapped to allow for expansion and contraction of the walls. Apply silicone beading inside where the wall meets the floor.
Reduce moisture intrusion from the outside
Meanwhile, whether your basement is finished or not, there are steps you can take to reduce moisture intrusion from the outside, thus promoting a dry basement.
- Walk around the foundation during a heavy rain to monitor if gutters are doing their job and downspouts are directing water away from the foundation (10’ if possible).
- If gutters are overflowing, have them cleaned. If they are still overflowing, check out any clogs (a roto router company) in underground lines. Sometimes the gutter run is too long for the amount of water, and you need to run another downspout midway.
- Keep shrubs cut back to 1-2’ from the foundation, to give the house a chance to better dry out after rain.
- If possible, maintain a 15-degree slope away from the foundation wall, but avoid soil-siding contact or termites might have an easy path to pass behind siding.
- Keep branches from rubbing against the roof.
- Install window well covers as needed.
- Apply a least-toxic sealant such as from www.decoproducts.com to above-ground concrete, brick, and stucco is advised, to help rainwater run off the foundation and not be absorbed into the concrete. Check with their representative to get the right product for your situation.To see if a sealant is needed, throw water against the foundation wall. The water should run off, not be absorbed into the foundation. One of the worst mold situations I saw was a Cape Cod house where water was absorbed through soft brick at every rain. When the drywall was opened up, the plywood sheathing was black with Stachybotrys mold.
- If waterproofing is needed, approach it from the exterior, not the interior. Keep water from entering the basement rather than recycling it once it is there. In other words, be skeptical of a waterproofer who wants to install a subterranean drain in the basement (unless there is a high water table, and then such a drain may be necessary). Waterproofing may involve digging down around the foundation, brushing off the concrete, applying a thick coat of wet-dry tar, and then wrapping the foundation in polyethylene sheeting and installing a French drain before filling the trench. This is done in sections, not the whole foundation at once.
- Intercepting water running downhill may be needed. Depending on the situation, a trench, a swale, drywells, drainage system, or other methods to divert the flow may be called for.