XPS and EPS board for basement walls, under slabs and continuous exterior insulation on new builds across Toronto and the GTA. Cut tight, adhered, taped and detailed by CNG crews so the board works as insulation and as a moisture and air layer.
Rigid foam is insulation in sheet form: extruded polystyrene (XPS) or expanded polystyrene (EPS), in boards from half an inch to four inches thick. Because it goes on as a continuous layer over the face of a wall, a slab or a foundation, it insulates across the studs and joists as well as between them, and that is the whole point. A framed wall loses a quarter of its rated R-value through the framing; a continuous board on the outside puts it back.
Below grade the same boards do double duty. Foam does not absorb water, does not rot and is not bothered by being buried against a damp foundation, which is why it is the product for foundation walls, under basement slabs and anywhere else a batt would eventually fail.
Both are closed-cell polystyrene boards installed the same way. They differ in R-value per inch, compressive strength, water absorption and cost, so the right one depends on where in the building it is going.
The dense pink or blue board. High compressive strength, very low water absorption and a long-term R-4.8 per inch that it holds in the cold, which makes it the default below grade: under slabs, on basement walls and anywhere the board will be damp or carrying a load.
The white bead board: lighter, cheaper per R and made in thicker sheets, with a rating that does not drift over time because it holds no blowing agent. Type 1 is the sheathing grade; Type 2 and 3 are dense enough for slabs and foundation walls.
XPS below grade and under slabs, where compressive strength and water resistance matter most. EPS where you want continuous exterior insulation at the lowest cost per R, or a thick board on a foundation wall. We will mark up the drawings and price the assembly each way.
Often it is the vapour barrier. Closed-cell board of sufficient thickness with taped seams acts as a vapour retarder and, detailed properly, an air barrier. Where foam is on the exterior of a batt wall, the assembly has to be checked so moisture is not trapped; that is a drawing question we will answer before we quote.
No. The Ontario Building Code requires foam plastic insulation on the interior to be covered with a thermal barrier, normally half-inch drywall. Our crews frame and board over it as part of the same contract, so the inspection sequence is straightforward.
Usually 2½ inches of Type 2 EPS or just over 2 inches of XPS to reach the R-10 the code asks for under a heated slab, over compacted granular and under the poly and the slab. More where there is in-floor heating. It is cheap insurance for a warm, dry basement and it cannot be added later.
Cap fasteners or adhesive to the sheathing, seams taped, then strapping or the cladding manufacturer’s fastening schedule through the foam to the framing. Thickness and fastener length are set with the framer and the siding installer before anything goes on the wall.