Best Insulation For Floor Joists

4c as an alternative to floor insulation foundation walls of unvented crawl spaces.

Best insulation for floor joists.

4b slab floors built directly on the ground. 4d extend insulation into joist space to reduce air flows. Department of energy recommends r 11 3 insulation under floors in warm climates and an r 25 6 to 8 in cold climates. We chose 2 in thick r 10 extruded polystyrene don t use expanded polystyrene which is a less effective air and moisture barrier.

Clarification for march 23rd e mail. Less than the height of the rim joist. Floor joists on new construction. 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.

Fiberglass insulation batts or rolls are the most economical and easiest diy choice for insulating between the floor joist in a crawl space. First insulation will be going between the floor joist i only filled gaps with foam. Instead of installing the foam insulation between floor joists in the crawl space the foam board is installed against the crawl space foundation walls. 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.

The floor joists are all fastened to the rim joist which runs along the. Cut the foam into 8 ft long strips 1 8 in. Rigid foam is the best insulation for rim joists. Trim pieces of fiberglass insulation using a utility knife so the pieces fit into joist bays along the rim joist.

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. 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. Any compromised floorboards or joists can also be replaced as part of the retrofit project.

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.