Fiberglass Rebar in ICF Walls: What Ontario Builders Should Know

Fiberglass (GFRP) rebar can be used in ICF walls in Ontario, but not under the code's prescriptive ICF rules. Sentence 9.3.1.1.(4) of the 2024 Ontario Building Code requires the reinforcing in Part 9 flat ICF walls to conform to CSA G30.18 with a minimum yield strength of 400 MPa, which describes steel bar. A GFRP-reinforced ICF wall therefore needs an engineer's design and the building department's acceptance, and ICF manufacturers say the same thing: GFRP works when the wall has been engineered for it.

This guide covers what the prescriptive ICF rules require, what changes with GFRP, and how to order it so the job doesn't stall on site. For the standards behind GFRP, see does fiberglass rebar meet code.

What the Ontario code requires for ICF walls

Part 9 has prescriptive rules for flat insulating concrete form walls in houses and small buildings. Under Sentence 9.3.1.1.(4), they apply to flat ICF walls in buildings of light-frame construction up to 2 storeys in building height, with a maximum floor-to-floor height of 3 m. In those walls, unless designed under Part 4:

• Concrete must conform to CSA A23.1 with a maximum aggregate size of 19 mm.
• Reinforcing must conform to CSA G30.18, have a minimum specified yield strength of 400 MPa, and be lapped at least 450 mm for 10M bars and 650 mm for 15M bars.
• The ICF units themselves must conform to CAN/ULC-S717.1 (Article 9.15.4.1.).

The bar layout then depends on where the wall is:

Foundation walls also need cold joints reinforced with at least one 15M bar at no more than 600 mm o.c., embedded at least 300 mm on each side of the joint, and vertical bars interrupted by openings placed within 600 mm of each side. Our guide to foundation wall rebar in Ontario covers the vertical bar tables, and concrete wall rebar spacing covers spacing more generally.

Every number above was written for steel. The bar sizes, the spacing and the lap lengths all assume steel's stiffness and bond, which is why GFRP can't be dropped into these tables.

The engineered route for GFRP in ICF

To use GFRP, the wall is designed rather than taken from the tables. In practice:

1. An engineer designs the wall for GFRP, usually using CSA S806, the Canadian standard for building structures with fibre-reinforced polymers, with bar made to CSA S807.
2. The design is submitted with the permit as an alternative solution, since the Ontario Building Code doesn't reference the FRP standards. The building department decides whether to accept it.
3. The ICF manufacturer's guidance is checked. Nudura, for example, states that GFRP bars can be installed in place of conventional steel as vertical and horizontal reinforcement in its ICF walls, provided the structure has been engineered specifically for GFRP. Check the technical literature for the form system you're using.
4. The bar list follows the design, not the steel tables.

Nudura also cites a 2018 University of Nebraska-Lincoln test in which GFRP-reinforced ICF walls had flexural capacity comparable to a steel-reinforced ICF wall, even with a smaller area of reinforcement. That's useful background, but one test doesn't replace a design for your wall, your backfill and your loads.

Vertical GFRP bars in foundation walls

"Can fiberglass rebar be used vertically?" is one of the most common questions. In an ICF foundation wall, the vertical bars do the main structural work: they resist bending from soil pressure between the footing and the floor framing. GFRP can do that job in a designed wall, but its lower stiffness changes how the design is checked:

• Crack width and deflection usually govern GFRP walls rather than strength. That can mean more bars, larger bars, or a different position in the wall than steel would need.
• The bar position matters. The prescriptive rules put foundation wall vertical bars in the inside half of the wall because that face goes into tension under soil pressure. The GFRP design will set its own position and cover.
• Laps and embedment are different. The 450 mm and 650 mm laps in Sentence 9.3.1.1.(4) are for steel. GFRP laps come from the GFRP design.
• Footing dowels are bent shapes. The L-shaped dowels that connect the footing to the vertical wall bars have to be factory-bent GFRP or another material the design allows.

Our GFRP vs steel rebar comparison covers the strength and stiffness differences in more detail.

Corners, openings and site handling

ICF walls have a lot of bent bars: corner bars to make horizontal reinforcement continuous, bars around openings, dowels at the footing, and ties into floors. With GFRP:

• Nothing is bent on site. Nudura notes that GFRP bars can't be bent in the field but pre-bent corner bars are available. Every bent shape has to be on the order before the forms go up.
• Cutting is limited to straight bars, typically with a saw, and bent bars shouldn't be cut in a way that removes the bend.
• Lighter bars are easier to lift into the form webs and to carry around a site with limited access, which is one of the reasons builders like GFRP.
• Ties and chairs should be what the specification calls for, usually coated or non-metallic.
• Bar diameter vs web clips. GFRP bar diameters don't always match steel exactly, so confirm the bars sit properly in the form's web cradles at the positions the design requires.

When GFRP is worth it in an ICF house

GFRP's main advantage is that it doesn't corrode. In a typical ICF basement, the steel sits inside concrete that is itself inside foam, so corrosion isn't usually what limits the wall's life. The cases where builders and designers weigh GFRP more seriously include:

• Walls exposed to de-icing salt, such as ICF garage walls, frost walls beside driveways, and exposed stem walls
• Projects where handling weight matters, like tight urban sites or remote builds
• Owners or designers who want non-metallic reinforcement for other reasons, such as non-conductivity

If none of those apply, a steel-reinforced wall built to the prescriptive tables is usually the simpler path through permit and inspection. If your footing is also being designed with GFRP, see fiberglass rebar in footings and foundations.

Ordering rebar for an ICF job

For a steel ICF wall, we can take the bar sizes and spacing from your drawings or the code tables and produce a bar list with straight bars, corner bars and dowels, cut, bent and tagged by wall. For a GFRP wall, we need the engineer's design, the bar standard and grade, nominal areas, and every bent shape, because bent GFRP is made to order.

We supply GFRP rebar alongside steel bar from 10M to 55M, with detailing and bar lists prepared from your structural drawings. Send us your ICF drawings for a take-off and quote, or see our rebar products.