Converting basements into a livable area of your home must be done with caution. Finishing a basement can be a risky proposition, and getting the details right is a challenge. Moisture, radon, and fire and gas safety are all factors that can influence whether or not your basement is suitable for a transformation, and they cannot be fully addressed in all basements. If these issues have been addressed and your basement is suitable for refinishing, sealing, insulating, and selecting proper finish materials will transform the space into a safe, livable area designed to last. A newer home with poured concrete, a capillary break between the footing and foundation wall, and that is properly waterproofed with good drainage is a less risky basement to finish.
Radon is a radioactive gas common in Minnesota soil that can lead to lung cancer. The naturally occurring gas is a result of continual mineral decay, specifically, uranium and radium. The gas penetrates a home's foundation and is a common issue in Minnesota because of our cool climate and heating requirements. To describe it simply, as heated air rises through our homes, it creates a vacuum that pulls radon from the soil, through the foundation, and into the lowest level of a home, so concentrations are usually highest in basements. Learn more
Construction strategies in newer homes can reduce (although not totally prevent) moisture infiltration, but in some older homes that lack moisture protection, basement remodels are strongly discouraged and may be nearly impossible. Finishing a basement without moisture management will ruin finishes and foster mold growth which leads to poor indoor air quality and possible structural problems.
To address moisture issues, it is important to understand the four basic ways moisture travels through our homes. All four mechanisms occur everywhere in a home, but basements generally experience all four mechanisms, and frequently to a greater degree than other parts of the home. The mechanisms are:
a) Bulk water enters as leaks through cracks, joints and holes.
b) Capillary wicks water into and through the pores of concrete and masonry. It can move in all directions, including up through a foundation floor or across through a foundation wall.
c) Air and the moisture evaporated in it moves from higher air pressure to lower pressure. As it moves it can carry significant quantities of water vapor. This is common in basements as warm air escaping up through your roof or other leaks in the house create negative pressures in the basement and draws in saturated air from the soil.
d) Vapor moves by diffusion from a higher vapor concentration to a lower concentration, and this can be inward or outward in below-grade spaces. Air conditioning or dehumidifying lowers vapor concentration, drawing vapor in, and winter humidification will be drawn out.
You can use a simple but very rough screening tool to begin assessing the risk of moisture in your basement. Tape a sheet of plastic film covered with a rug or some rigid insulation to the wall and/or concrete floor at least 16 hours and preferably several days when exterior conditions are quite wet. Visible moisture condensation means you may have significant moisture penetration and should follow up with a test to determine the actual rate of transmission. A better test is the vapor emission test, something almost all manufacturers require before installing carpet vinyl, or wood flooring.
Reducing bulk moisture penetration begins at the exterior of your home. Establish proper drainage around your home by sloping landscaping away from the house by one foot in the first 10 feet. Consider installing drain tiles to direct stormwater away from your home. Seal foundation cracks and holes with hydraulic cement (available at home improvement stores) and use an ENERGY STAR dehumidifier to remove excess moisture and control humidity levels. In cases with severe moisture penetration, an interior drainage system may be needed. This involves removing a perimeter portion of the floor slab and installing drain pipes. Learn more
Construction practices can help manage the impacts of moisture. Air sealing the whole house will minimize air pressure differences. Moisture-resistant construction practices can help manage moisture moved through capillary action and diffusion, as well as air pressure differences.
Interior Insulation & Air Sealing
After you've determined that your basement has safe radon and moisture levels; interior insulation and air sealing are the first steps towards creating a comfortable and efficient finished basement. Since ensuring moisture resistance is key to the longevity of your refinished basement, hire an experience contractor if you're not familiar with the insulating practices described below. Beginning with the exterior of your home, you'll need to insulate and flash your foundation wall to 6" below grade. This will reduce water and air infiltration. Refinishing the exterior of your home is a good opportunity to do this but it can be done independently as well. On the interior, seal and insulate around rim joists (where the floor structure above meets the foundation wall).
Because of the difficulty with moisture management, a safer interior finish is to avoid insulation which could trap moisture and uses systems that minimize moisture movement into walls as well as allowing it to dry. Use studs with a bottom plate on treated spacers, paper drywall held 3/4” off the floors, and finishes the walls with vapor permeable, low- or no-VOC, flat latex paint.
Fire & Gas Safety
Talk to local code officials to understand how to make your basement compliant with egress (routes of exit in case of emergency) and fire code. A challenge of egress windows is that they are a very common source of moisture entry problems, adding water to the adjacent soil or as a source of leaks into the wall surround or directly into the basement. If utility rooms are in the basement, make sure combustion appliances have proper ventilation. Install a carbon monoxide detector since basements can be a trap for carbon monoxide gas created by combustion equipment. Learn more
Basement wall and floor materials should be moisture tolerant and installed to avoid direct contact with concrete. Walls should be insulated and framed out to receive finish materials. Avoid finish products like wood, carpet, and paper which can absorb moisture easily. Carpet and carpet padding in basements can trap dirt and moisture and create perfect conditions for mold growth and dust mites. If carpet is an absolute must, choose area rugs that can be easily removed and replaced if there is a moisture problem, and that are easy to take outside to air at least once a year. Vacuum frequently to prevent build-up of dirt. See these expert discussion of carpet in basements for ideas of how to create a comfortable space.
See Interior Finishes for recommend finishes