Insulating basement walls and the basement ceiling as part of a basement finishing project can help walls keep heat in a basement during cold months and prevent heat from entering a basement in warmer months.
Before insulating basement walls, there are important tasks that should be completed and considerations that can prevent future damage to your finished basement. Moisture issues should be resolved before insulating basement walls, as moisture can seep into insulation, wood, drywall, and other materials, causing irreparable damage.
Consider the type of insulation materials that will be used to insulate the basement walls. There are several types of insulation, and while fiberglass insulation is common for other projects, it is not best to use for basement walls as it can retain moisture, leading to potential mold, mildew, rot, and water damage.
The best insulation for basement walls in terms of moisture resistance, cost, quality, and ease of installation is rigid foam board insulation, which is available in sheets that are easy to measure, cut, and install. Another installation consideration is the method for installation, which usually includes furring strips or a standard 2×4 wall system. Furring strips can be used to secure insulation to the wall, while a 2×4 wall system involves framing out the wall over the insulation.
To prevent condensation, gaps in insulation should be sealed with tape, caulk, or spray foam. Small cracks, gaps, or holes in insulation can create cold spots along the basement wall which can cause condensation when in contact with warm air.
Most building codes require a thermal barrier when insulating basement walls from the interior. Foam plastic insulation (including polyisocyanurate, polystyrene, and polyurethane) must be separated from the building interior with an approved thermal barrier, which is typically a ½-inch or greater piece of gypsum wallboard, drywall, or an equivalent material.
Learn about basement insulation types and considerations when installing insulation materials.