Rigid Insulation Under Slab Detail

The layer of rigid foam insulation that separates the concrete foundation wall on the outside from the slab on the inside.

Rigid insulation under slab detail.

This insulation aligns with rigid foam sheathing that covers the framed walls above grade. 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. Additional insulation is applied along the edges of the slab because that is a primary surface for heat loss. In climate zones 6 7 and 8 by any combination of vertical insulation insulation extending under the slab or insulation extending out from the building.

Roche has paused at an important detail. In fact they are almost unintelligible. Roche writes in a recent q a post that just about every foundation design for a slab that he s seen either puts all of the rigid insulation on the outside of the foundation or. It is installed on the interior exterior or is integral to any opaque surface of the building envelope.

Insulation requirements for slab on grade floors can be found in section r402 2 9 of the 2012 iecc and 2015 iecc as well as section n1102 2 9 of the 2012 irc and 2015 irc. Rigid insulation is placed vertically on the exterior face of the foundation wall. For under slab applications the rigid foam insulation typically should be installed over a gravel base with a poly vapor diffusion retarder between the gravel and insulation. Insulation located below grade shall be extended the distance provided in table n1102 1 1 namely 2 ft.

In climates zones 4 and 5 and 4 ft. This compliance option is explained this way. 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. Code requirements for slab insulation are very poorly written.

Figure 4 11 illustrates a slab on grade foundation with a masonry foundation wall. Get free shipping on qualified under slab foam board insulation or buy online pick up in store today in the building materials department. R 7 7 rigid foam insulation model 310891 18 35 18 35. 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.

Moisture control is provided by a vapor retarder under the slab.