Insulating concrete forms are a stay-in-place concrete form that consists of two expanded polystyrene panels (EPS) usually sized 16" in height, 48" long and approximately 2 1/2" in thickness, spaced apart the desired wall thickness. Polypropylene webs (or ties) are spaced 6" or 8" on centre to withstand the concrete pressure and to allow the attachment of wall finishes (damp proof membrane or rainscreen on the outside, drywall on the inside).
Concrete is placed into the cavity between the two panels, with the panels and ties staying permanently with the concrete wall, hence the name "stay in place" concrete form. The EPS panels provide a minimum insulation value of about R24. Increased panel thicknesses can achieve R30 and R40.
Insulated concrete forms (ICFs) can be used for below grade walls (foundation walls) and above grade walls.
The attached report prepared by CLEB Laboritories Inc. comparing the thermal performance of an 8" ICF wall compared with an insulated wood frame wall in accordance with test procedure ASTM C1363-11. The report shows that the ICF wall can achieve up to 60% energy savings with a R-Value 58% higher than the stud wall.
Click on image to see the full report.
Below grade foundation walls are typically formed with 3/4" plywood + metal ties to withstand the concrete pressure. Once the concrete has hardened, the plywood is stripped by breaking each tie on both sides of the concrete and removing the plywood.
Concrete damage to the plywood ultimately leads to the forms being scrapped. The cost of transport, cleaning and storage determine the cost of plywood rentals.
To provide thermal performance and allow attachment of wall finishes, a 2x4 or 2x6 stud wall is built on the inside and fiberglass batts installed between the studs.
With the building code requiring increased levels of thermal performance, ICFs are now a viable economic alternative. ICFs not only form the concrete, but stay in place to provide thermal performance and attachment points for drywall on the inside and damp proof membrane on the outside.
Plywood formed basement walls are notorious for allowing ground moisture to wick in through the concrete (rising damp), leading to the damp musty smell in most basements. ICFs eliminate this problem as long as the footing is protected with a suitable membrane (Fastfoot®).
When the ICF wall is monopoured with the footing (ICF + MP + Helix® method), the ICF MP option is more cost effective that the traditional plywood + stud wall alternative. Click this link to view the below grade cost analysis.
Above grade walls have typically been been constructed with 2x4 or 2x6 studs, plywood (or OSB) sheathing, with fiberglass batts between the studs. With higher levels of thermal performance now been demanded, new wall assemblies are being developed to reduce the thermal transfer through the wood studs, such as the installation of insulation on the outside of the sheathing to reduce thermal bridging.
ICFs are worthy of consideration for above grade walls for the following reasons:
ICFs for above grade walls come at a price: