Floor Slab Insulation Detail

If the insulation is going below the slab the damp proof membrane dpm is laid next followed by the insulation a polythene separating layer and the concrete slab.

Floor slab insulation detail.

In this insulation detail at the perimeter of the slab a total of 6 inches of rigid foam insulation separates the interior slab from the outdoors. This technique can limit inward vapor movement when the sun shines on damp bricks. A plywood bottom plate helps to stabilize the double stud wall. In new hampshire chris roche is pulling together plans for a new energy efficient home.

Illustration by chris roche. Slabs lose energy primarily as a result of heat conducted outward and through the perimeter of the slab. The codes are silent about whether above grade slabs need to be insulated. Any cooler surface in contact with the slab will try to steal its heat.

These codes do not require any insulation for slabs that are more than 12 in. 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. Such spaces typically have a sound level concrete slab floor but lack sufficient floor insulation to achieve the thermal performance targets for new habitable rooms. Installing slab insulation around the perimeter of the slab will reduce heat loss and make the slab easier to heat.

Below grade need vertical insulation at the slab perimeter. Otherwise both codes require that slab on grade floors with a floor surface less than 12 in. Depending on the use of the building the slab can then be finished ready for use or receive a screed suitable for a floor finish. Rigid insulation is placed horizontally under the slab perimeter and vertically in the joint at the slab edge.

Continuous insulation is applied directly to the underside of the slab and extends inward horizontally from the perimeter for the distance specified or continuous insulation is applied downward from the top of the slab and then extends horizontally to the interior or the exterior from the perimeter for the distance specified. If headroom is tight then the only option may be to break up the existing slab dig further down and build up an entirely new floor. Remember that your slab will be about 75 degrees f.