Renovating a basement into a healthy, energy-efficient living space


Renovating a basement space is a great way to increase the living area of your home. However, transforming a Maine basement into a living area should only be considered after all moisture and soil gas concerns have been addressed. Use this checklist as a guide. If in doubt, hire a qualified professional, or contact the Maine Indoor Air Quality Council (; 207-626-8115) for answers to questions.

  • Prevent soil gas intrusion. A third of Maine homes have radon levels above the recommended thresholds. And radon is the #1 cause of lung cancer in nonsmokers and the #2 cause of lung cancer nationwide. Be sure to test your home for radon and fix it if necessary before starting basement renovation. Seal all sump units to prevent radon, sewer gas, and moisture intrusion.

  • Keep rainwater outside where it belongs. Maine has a very wet climate, with a lot of rainfall each year. Make sure exterior grading and drainage slopes out and away from building (4 inches of pitch for every ten feet). Make sure gutters and downspouts direct water away from the building. Seal all foundation cracks to prevent air and water leakage prior to renovation, and use crack injection if exterior excavation is impractical.

  • Insulate for energy efficiency and to prevent condensation. Maine has a cold climate. And the soil under and around your home stays cool all year long. Warm, moist air from May-October will condense on any cold, uninsulated surface, causing mold growth and building rot.

  • If the basement floor is not already insulated under the slab, insulate it with rigid foam on top of the slab if headroom is sufficient and stairs can be reworked. If unable to insulate the basement floor, use dehumidification during the summer months to prevent condensation and mold growth. Consider a commercial grade dehumidifier that is both more energy efficient and more effective at removing excess moisture. Insulate the walls using rigid foam over block and concrete or spray foam over field stone. (Note: all foams must be covered with a fire preventive barrier—special paint, drywall, or plywood. Refer to local building codes for detail). Allow proper drying to both the inside and outside: do not use a vapor barrier or a product that acts as a vapor barrier over the foam insulation.

  • Always keep relative humidity in a basement between 30-50%. Even a well-insulated basement can suffer from too much moisture. Cold water pipes, well pressure tanks, and HVAC ductwork can be cold enough to cause condensation.

  • Expect the unexpected. Floods, plumbing leaks and system failures can and do happen. Use construction strategies that minimize damage, property loss, and mold growth when the unexpected occurs.

  • Wallboard should never touch the floor – leave at least a 4” gap covered by a removable baseboard. Avoid fiberglass insulation in stud cavities. Use fiberglass-covered wallboard instead of paper-covered wallboard. Avoid wall-to-wall carpets in basement spaces. Use concrete floor paint or vinyl composition or ceramic tile instead. Use only small area rugs that can be removed and cleaned on a regular basis. Avoid a drywall ceiling: install a suspended ceiling, or paint the exposed ceiling above.

  • Living spaces are for people, and people need fresh air. Ventilate your new space to let fresh air in and exhaust stale air and pollutants out. For basement spaces, balanced mechanical ventilation is recommended.



This article is reprinted from the fall 2015 issue of Green & Healthy Maine Homes. Subscribe today!