Rigid Insulation Under Basement Slab

When slab insulation is provided a sheet polyethylene vapor barrier should be located over the rigid insulation and in direct contact with the concrete slab.

Rigid insulation under basement slab. Dupont styrofoam brand extruded polystyrene foam insulation is an ideal solution for under slab installations offering the following advantages. Insulation located below grade as required in climate zones 4 through 8 should extend the length specified in the table by any combination of vertical insulation insulation extending under the slab or insulation extending out perpendicular to the building insulation extending perpendicular away from the building should be protected by pavement or by not less than 10 inches of soil. R 7 7 rigid foam insulation model 310891 18 35 18 35. Evenly spread the base gravel under the basement slab keeping it 1 inch lower than the conventional method.

Tape the joints between the boards with builder s tape. Additional insulation is applied along the edges of the slab because that is a primary surface for heat loss. For installation on concrete foundations and under floor slabs the rigid foam insulation you choose can make a difference of tens of thousands of dollars on a project. Place a 1 inch layer of 4 x8 extruded polystyrene foam board over the gravel covering the entire floor area.

4 10 2012 3 climate zones e301 1 6 5 8 4 slab r value table 402 1 1 insulation and fenestration requirements by component e402 1 1 climatezone slab r valued 4 10 2 ft 5 10 2 ft 6 10 4 ft 9. If the foundation is on frost susceptible soils install a layer of impermeable insulation horizontally in the soil at a slope ratio of 1 5 for at least 1 m 3 ft. As the slab will only be able to dry upward the slab should be allowed to dry before finishes are applied. Insulation is applied to houses with slab on grade foundations exactly as you would insulate the outside of a full basement see section 6 1 insulating the basement from the outside.

Reduces energy loss between ground and concrete slab reduces potential for condensation and moisture damage high compressive resistance can sustain heavy loads without damage. A careful evaluation of these materials performance attributes against the project s needs can dramatically shrink labor and material costs. You want to create a tight insulation layer.