Being underground, basements tend to be damp. Whether or not you plan to convert your basement to a living space, it’s crucial to identify and resolve all moisture problems. Moisture can damage stored items and interior finishes, and mold or mildew can form on damp surfaces.
Proper drainage and maintenance on the outside of your house will minimize moisture intrusion. Keep gutters clean, downspouts clear, and rainwater flowing away from the foundation. Subterranean drainage cures, such as perimeter or French drains, can be more expensive, but may be well worth it to avoid moisture damage. A sump pump may also be helpful. If you have a high water table or an adjacent stream, it may be difficult to control basement moisture enough to convert basement space to living space.
To remove moisture from inside the basement, focus on controlling potential moisture sources. Check that there are no plumbing leaks from the floor above. Moisture could be coming from a poorly exhausted shower, so install a fan to increase air circulation. If your dryer is in the basement, make sure its exhaust vent doesn’t leak and has a direct path to the outside. If you have an energy-saving switch on the exhaust, use the outdoor setting.
Finally, any basement should be insulated and have sufficient lighting installed.
Converting a Basement to Living Space
Basements can be ideal for remodeling into usable space. They are quiet, private, and cool—and often already have plumbing and HVAC equipment. Insulating, air sealing, and moistureproofing are vital, and it’s important to identify potential problems with basement HVAC equipment.
Air Sealing Your Basement
A seamless barrier keeps moisture and soil gases from entering the new basement living space. In the United States, radon hazards are prevalent throughout mountain zones and the upper Midwest. Check the EPA map and guidelines (Resources), and test for radon if you think it may be a hazard. You can purchase a radon detector at most hardware stores, and there are radon remediation contractors in most parts of the United States.
Before adding finish materials to the floor and walls of your basement, make sure all cracks in the concrete are caulked. You may also want to build up the floor, as described under “Garages,” to keep the finish floor from being in contact with the damp, cold concrete floor.
Is there peeling paint on the inside of the basement walls? That indicates moisture seepage from outside. If you’re not in a position to excavate around the basement and improve the drainage from outside, masonry sealer and paint may help. If seepage is frequent, the entire wall may need to be resurfaced with a concrete coating. If you plan to add interior wall finishes, apply a rigid foam moisture barrier to the concrete walls before adding framing, to minimize condensation from interior humidity.
Because basements can be damp, the best materials for interior basement insulation are rigid foam with sealed seams or sprayed polyurethane foam (SPF). Both can provide unbroken air and vapor barriers that won’t be damaged by moisture.
Although SPF is expensive, it has several advantages over rigid foam: it controls moisture better, saves more energy, and makes a basement more comfortable—and it may allow you to downsize the mechanical system. It also provides more design flexibility, since the necessary R-value is fitted into small framing cavities. Note that SPF can’t be installed without sufficient access. The applicator must be able to get close enough to the sheathing to spray from 16 to 24 inches away as straight on as possible.
Your home performance assessor can check your basement’s current insulation values and identify areas that need attention.
Basements can be dark, so lighting is an important factor. First, maximize natural light; if the basement is at least partly aboveground, add windows. If you add window wells, make sure they have waterproof covers to avoid leaking. If you’re concerned about break-ins, install glass bricks rather than windows.
For electric lighting, recessed lights can create a more open feeling than light from surface fixtures. As long as the basement is part of the conditioned space, there won’t be a problem with disturbing ceiling and floor insulation. You may want to use occupancy sensors to turn on lighting for hands-free ease when carrying objects downstairs.