Help & Advice

ICF Design

The question of whether an ICF wall needs to be reinforced does not have a straightforward answer. The project structural engineer decides this. Generally, most ICF homes do not require any steel reinforcement in the walls when built above ground. Of course, above any openings (such as doors and windows), there is a need for reinforcement. However, when building a basement or a retaining wall, there will always be reinforcement. 

Curved basement construction with reinforcement
Polarwall curved basement with reinforcement

The project structural engineer will specify the size and the amount of steel required. He bases this on his load calculations and the design.

There is a British Standard for steel tying – BS7973-2 2001 Part 2 – Fixing & Application of Spacers & Chairs and Tying of Reinforcement. This needs to be followed as Building Control will be checking your reinforcement.

Reinforcement is used where the concrete is in tension. Concrete, like stone, is a material is very strong in compression but very weak in tension. Concrete is great for columns (in compression) but weak when used as a beam (in tension). Wherever the concrete is in tension there is a need for reinforcement within the wall. 

Reinforcement in ICF Lintels

Above openings, in the lintel area, it is usually designed to have two or four reinforcing bars. This is because the lintel is a beam and it is being put into tension with the load from above. The reinforcing bars size and number of bars required, depends upon the opening size, and the loadings. Your project engineer will decide the sizing and spacing of the bars.

When the beam is shallow, such as when the top of a window is too close to the the eaves, then instead of a cast in-situ beam being used, a steel section can be used. The sizing of all lintel reinforcement or steel beams will be decided by the project’s structural engineer.

Reinforcement in ICF Basement Retaining Walls

To the question “does my ICF basement wall need to be reinforced”, the answer is always an emphatic “YES”!. Two layers of A393 welded wire meshis the usual specification for a Polarwall basement, (or retaining wall). These steel sheets are usually fastened to an “L” shaped bar coming up from the concrete raft foundation and fastened to the reinforcement steel in the raft. 

Structural engineers like to specify welded wire mesh reinforcement, rather than loose bar. This is because there is less room for builder error with mesh reinforcement. Mesh reinforcement saves lots of time over the tying and the fixing of the loose individual reinforcement bars.

Other ICF systems, being moulded blocks, have to rely upon loose reinforcement bar which is tied in place. Of course, we can do this with Polarwall, but why would you if you can use mesh?

A bad practice

A common practice of many ICF builders, is to fasten horizontal to the ICF blocks as each course is built. When the wall is built, the builder then inserts the vertical bars from the top of the built wall all the way to the bottom with it tied only at the top. This not acceptable. The previously mentioned BS7973 states that bars of 20mm or less need to be fastened to alternate horizontal bars. At perimeters it needs to be fastened to every intersecting bar.

It needs to be built with the vertical bars in place, as in the Polarwall curved basement wall above, and horizontals to be fastened as you go. Dropping vertical bars in is not good practice!

Eagle eyed BC officers have spotted this on more than one occasion. This then needs a takedown and rebuild. The reinforcing steel provides the structural integrity. So not putting it in properly is extremely reckless. Make sure that your builder is fixing the steel properly. Also check that there is proper overlap on all bars – this should be a minimum of 40 times the steel bar diameter. The reinforcement needs to have adequate concrete cover.

Reinforcement between ICF Wall and Concrete Floor

Sometimes the ICF Wall needs reinforcement bars to fasten the connection between walls and floors. This is especially true at the top of basement walls, in apartment blocks, or when there is a large sideways wind load on a wall. Such a connection improves the structural integrity by creating a “reinforced box”.

The reinforcement in a cast in-situ concrete floors is invariably connected the the wall reinforcement, usually with L-bars

Pre-cast concrete floors, such as beam/bock or hollow-core are often connected to the wall reinforcement in a variety of methods, but this is not always deemed necessary.