Best Insulation For Floor Joists

If you want to insulate a floor assembly by leaving the joist bays empty and installing rigid foam on the underside of the joists here are a few things to keep in mind.

Best insulation for floor joists.

Floor joists on new construction. 4d extend insulation into joist space to reduce air flows. Also insulate 4a any portion of the floor in a room that is cantilevered beyond the exterior wall below. Less than the height of the rim joist.

We chose 2 in thick r 10 extruded polystyrene don t use expanded polystyrene which is a less effective air and moisture barrier. Cut the foam into 8 ft long strips 1 8 in. In some cases if the floor is accessible from below it may also be possible to partially insulate the joists from underneath which offsets thermal bridging through timber members but this is not often the case. Fiberglass insulation works as an insulator because it traps air in the fibers of the insulation and slows the collision of warm and cold air.

The best insulation material for crawl spaces is rigid foam insulation board. Trim pieces of fiberglass insulation using a utility knife so the pieces fit into joist bays along the rim joist. If the fiberglass insulation gets wet or very damp it will begin to collapse get heavy and fall from the floor joists rendering it useless to trap air and be an insulator. Rigid foam is the best insulation for rim joists.

The floor joists are all fastened to the rim joist which runs along the. Any compromised floorboards or joists can also be replaced as part of the retrofit project. Second i have foundation vent all around the house should the remain unblock or do the need to be covered. Instead of installing the foam insulation between floor joists in the crawl space the foam board is installed against the crawl space foundation walls.

4b slab floors built directly on the ground. In attics aluminum sheeting is often used for insulation and this same method can be used for insulation for floor joists but this will not be the most efficient method for retaining heat within the home. Fiberglass insulation batts or rolls are the most economical and easiest diy choice for insulating between the floor joist in a crawl space. Department of energy recommends r 11 3 insulation under floors in warm climates and an r 25 6 to 8 in cold climates.

According to the 2012 irc the minimum r value for floor assemblies is r 13 in zones 1 and 2 r 19 in zones 3 and 4 r 30 in zones 5 and 6 and r 38 in zones 7 and 9.