Should You Insulate Floor Joists In Basement

If you have an unvented crawlspace or basement you must insulate the walls instead of the floor joists.

Should you insulate floor joists in basement.

Be sure to seal rim joists. 4b slab floors built directly on the ground. Also insulate 4a any portion of the floor in a room that is cantilevered beyond the exterior wall below. Lay down a moisture barrier with sheets of 6 mil plastic if you have a dirt or gravel floor.

If you have an unfinished basement you can properly insulate the rim joists in two or three hours. This will also block tiny passages where spiders and other insects enter your basement. 2 xps foam board against in my case board formed concrete framed up with 2 4 studs with a composite board under the bottom plate as a capillary break. Basement insulation bonus tip 1.

Impervious insulation is always an excellent idea for basement walls but it s absolutely essential where the floor joists of the level above meets outside walls along the edges of a basement ceiling. Jerry thanks for the comment getting back to you after the holidays. The insulation should extend all the way down to the basement floor or at least to below the frost line the depth to which the ground freezes in winter. Cut pieces of insulation just large enough to fit along the rim joist the framing material into which all the floor joists are nailed.

Two story homes usually have another ring of rim joists above the first floor ceiling. 4d extend insulation into joist space to reduce air flows. To prevent these problems only air impermeable insulation either rigid foam or spray polyurethane foam should be used to insulate the interior of a rim joist. Properly insulating and air sealing rim joists band joists takes patience so most builders simply stuff in some fiberglass and walk away.

When insulating basement walls don t forget the band joist the piece of wood at the top of the wall that extends around the perimeter and encloses the ends of the floor joists. When you re using fiberglass batting insulation material run it about 6 inches or so onto the crawl space floor. If you need to insulate these rim joists it s best to hire a cellulose insulation contractor. First you ll have to maneuver batts of insulation around the clutter of wires pipes and cross bracing in a typical basement ceiling.

If the crawl space is ventilated which is ideal because it aids in the elimination of moisture then fiberglass insulation can be easily installed under the subfloor between the floor joists. I have an almost identical installation in my home basement. It is important to secure insulation and cover it with a vapor barrier in order to prevent moisture and the mold that often follows close behind.