ICF 101

ICF stands for Insulated Concrete Forms. There are many companies that make the blocks - the one we are using is Nudura. These blocks are 18" tall and come folded in packages of 3. Each of the straight blocks is 8' long:


Here is a corner block - it's smaller than the straight blocks, presumably so that it ships smaller. This block has not been pulled apart yet - the center pieces fold for shipping, so that the two sides of the block are stacked. Some of the other blocks do not, which makes shipping more difficult.


The blocks have plastic studs, spaced 8" apart. These are what the siding and sheet rock will be attached to, using screws. The plastic pieces that hold the two sides together (the same ones that fold) are shaped so that the horizontal rebar locks right in. Some of the other blocks use ties to hold the rebar, which makes the installation more costly (at least in theory - seems like they all charge the same!). There is also some steel mesh that runs along the length of the block, stiffening it in that direction.


Here's a view looking down the blocks at a corner. There is vertical rebar every 24" coming out of the footings, and horizontal rebar every block high (18"). Our contractor uses 5/8" rebar, although 1/2" could be used. The rebar are overlapped by 24" at the ends. The strength of the ICF walls can be increased by using wider blocks, more rebar, and larger rebar. The literature says they can be designed to withstand up to 300 mph winds. I believe ours will be rated for 150 mph. The blocks they are using for the foundation will have 8" of concrete (width), and the main part of the house will be 6" wide. The overall width of the walls include the 2 5/8" of foam that makes up each side of the block, for a total wall width of 13.25" for the foundation and 11.25" for the house.


Ideally, the rebar is supposed to be a embedded in the concrete, so is installed a couple of inches from the sides of the foam. The rebar from the footings on one of our walls touches the foam, but this wall will have dirt compacted on either side, so is not a big deal.


They have placed a couple of pieces of rebar for where the center footings will be dug into the fill dirt. Notice that there is a vertical seam to the left of the rebar. Most of the blocks are staggered, like bricks in a wall, but there are two vertical joints in our wall. I think this is unavoidable unless the size of the house is made to conform exactly to the available lengths of the blocks.


The installers used a gun to inject foam at the base of the blocks. It's not a complete seal, but will be sufficient to hold the concrete in.


After the concrete is poured (they have to use a pump truck to get it in the walls), and while it is still wet, they will place rebar that will tie into the parking slab.

Next update Tuesday night after the concrete pour, if I have time...

Happy Easter!