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Design BasicsICF Wall Thickness:
ICF Wall Thickness:
Core Sizes, Total Width and the Floor Space Question
People hear the word concrete and picture a wall like a castle. A standard ICF wall is about 11 inches thick, roughly the same as a 2x6 wall with exterior foam and siding. Here is how the numbers work.
The Short Answer
An ICF wall is the concrete core plus about 2-5/8 inches of foam on each side. With a 6-inch core the wall is about 11-1/4 inches thick before finishes; with an 8-inch core it is about 13-1/4 inches. Cores come in 4, 6, 8, 10 and 12 inches. Most Ontario houses use 6-inch cores above grade and 8-inch cores in the basement, but the engineer or the code tables decide based on height, backfill and loads.
Core Sizes and Total Wall Thickness
| Concrete core | Wall thickness (standard foam) | Concrete per 100 sq ft of wall |
|---|---|---|
| 4 inch | about 9-1/4 in | about 0.9 m³ |
| 6 inch | about 11-1/4 in | about 1.4 m³ |
| 8 inch | about 13-1/4 in | about 1.9 m³ |
| 10 inch | about 15-1/4 in | about 2.4 m³ |
| 12 inch | about 17-1/4 in | about 2.8 m³ |
Thick-foam blocks such as Nudura XR35 use about 4 inches of foam per side, adding roughly 3 inches to the total. Brands vary by a fraction of an inch.
Which Core Goes Where
Basement walls
Usually 8 inches, sometimes 10 for deep basements, high backfill, or walkouts. The flat ICF foundation wall tables in Part 9 of the Ontario Building Code set the minimum by height and backfill.
Above-grade walls
Usually 6 inches for houses up to two storeys. Tall walls, big openings and heavy roof loads may push to 8.
Garage frost walls
Often 6 inches, sometimes 4 where the engineer or the code allows.
Retaining and pools
8 to 12 inches with extra steel, always engineered.
The rule is simple: the code tables or your engineer pick the core, not the salesperson. Our guide to when you need an engineer for ICF explains who decides.
Does a Thick Wall Steal Floor Space?
A little. A 6-inch-core ICF wall is about 11-1/4 inches before drywall and siding. A 2x6 wall with 1-1/2 inches of exterior foam, sheathing, drywall and siding is around 9 inches. The difference is roughly 2 inches per wall.
On a 40 x 30 foot house that is about 23 square feet per floor, the size of a closet. Most designers simply push the outside dimensions out 2 inches so the rooms stay the same. If your lot is tight against the setbacks, tell your designer early.
Bonus
Thick walls give you deep window sills. People who live in ICF houses tend to love them. Cats too.
Get a Real Number for Your Project
Send us your plans or a rough sketch. We price the ICF work from real wall areas, not guesses, and tell you straight if ICF is not the right fit.
Thickness and Windows, Doors and Finishes
- Windows sit in a buck (a frame set in the form before the pour). Decide early whether the window sits to the outside, middle or inside of the wall.
- Doors need jamb extensions to match the wall depth. Order them right the first time.
- Siding and stone attach to the plastic webs or sit on a brick ledge. See how to finish ICF walls.
- Electrical boxes sit in the foam, not the concrete. See wiring and plumbing in ICF.
Get a Real Number for Your Project
Send us your plans or a rough sketch. We price the ICF work from real wall areas, not guesses, and tell you straight if ICF is not the right fit.
Questions We Get
How thick is an ICF wall?+
With a 6-inch concrete core, about 11-1/4 inches before finishes. With an 8-inch core, about 13-1/4 inches. Thick-foam blocks add about 3 inches.
What core size do I need for an ICF basement?+
Most Ontario basements use an 8-inch core. Deep basements, high backfill or walkouts may need 10 inches. The OBC Part 9 tables for flat ICF foundation walls, or your engineer, set the minimum.
Can I use a 4-inch core ICF for a house?+
Rarely for load-bearing exterior walls. Four-inch cores are mostly for garage frost walls, interior partitions and non-structural uses.
Does ICF make rooms smaller?+
By about 2 inches per exterior wall compared with a well-insulated wood wall. Designers usually just push the outside dimensions out so rooms stay the same size.