Depth Insulation Under Concrete Floor

Foamular does not absorb water like other types of foam board which makes it ideal for below grade and under slab installations.

Depth insulation under concrete floor.

Home depot does sell the right solution for residential concrete slab insulation. Insulation is laid on the concrete and covered with a screed. The math is pretty simple the thicker the concrete floor insulation material the deeper the slab will have to be. Excavate the area under the slab to 12 inches below the planned level of the top of the slab.

There will be a damp proof membrane under the insulation and possibly a second membrane on top depending on the type of screed. Phenolic foam is a popular choice to get around this issue as it s able to achieve strong levels of insulation for less depth. If the slab has hydronic tubing the minimum r value of this insulation increases to r 15. In this scenario a rigid foam insulation is usual and as you d want the same u value in the roof we need the same thickness of insulation 180mm.

In cold climates it is advisable to use a minimum of 2 inches of extruded polystyrene under the slab. In climate zones 4 and 5 the code requires certain slabs below grade slabs that are less than 12 in. Many increase the under slab insulating foam board thickness to 3 or 4 inches at the outer 2 to 4 feet of the slab. Foamular provides r 5 per inch of thickness winter and summer.

Designers generally insulate both directly under the slab and around the perimeter as well. Many builders will baulk at this figure it was not long ago that installing 50mm of insulation in the floor was considered fairly advanced. This stops any thermal bridging across the walls leading to cold spots. Where the heating is likely to be turned on and off such as in new build domestic properties and a faster thermal response is required the floating floor arrangement of insulation above the slab can be more appropriate.

This allows an area for insulation and fill material under the slab. Insulation below the slab suits continuous low level heating gradually warming the thermal mass of the concrete and sustaining it at a consistent temperature. On the other hand if you are laying insulation on top of the existing slab than you will need to make sure that there are no construction. Namely if you are only digging the slab you will need to take into account the thickness of the insulation since it will affect the depth of the slab.

Foamular 250 foam board. The first important thing to pay intention to is the depth of the floor slab. Below grade to have r 10 vertical insulation at the slab perimeter extending downward from the top of the slab to a depth of at least 2 ft.