Insulating Concrete Forms
We chose to use Insulating Concrete Forms for both our basement and above grade exterior walls, because of the many advantages they offer.
What are ICF? ICF consists of two polystyrene (hard foam) panels connected together by a metal or plastic web. When glued and stacked together into a wall, the two panels make the two sides of a form into which steel reinforcing bars (rebar) are placed and then a concrete wall can be poured. The major difference between this and a traditional concrete wall is that the form remains in place, you don’t remove it. Even better, the foam form provides your wall insulation right there already. And the metal or plastic webbing that held the forms together also includes furring strips just below the outer foam surface, into which fasteners can be embedded. This allows both your exterior finish (such as siding) and your interior finish (such as drywall) to be directly attached to the ICF. Thus, it’s a one-stop shop for a finished and complete, steel-reinforced concrete wall.
What are the advantages of ICF?
- Increased occupant comfort – An insulated wood frame wall does not have any thermal mass. An ICF wall does. During the hot summer day or cold winter night, an insulated wood frame wall immediately begins to transmit that heat or cold through the wall, no matter how well insulated. The interior wall surface goes up or down in temperature, and the air conditioning system must turn on cooling or heat to compensate. Interior air temperatures go up and down 5°F, in spite of what your thermostat may tell you. With the thermal mass of an ICF wall, however, that day heat or night cold is NOT transmitted immediately. The concrete itself must be heated or cooled first, and it takes several hours to half a day before that temperature change reaches the inside wall. As a result, the interior wall surface stays within a much smaller range of temperatures. The interior air temperature may go up and down as little as 1°F or less.
- Decreased exterior noise – the physical mass of the ICF wall also does a great job of blocking the noise from the neighbors barking dog, or whatever annoying noise comes from outside.
- Lower utility bills – A typical ICF wall corresponds to better than R-50, as compared to a frame wall with R-8 to R-11.5 to R-15 (reference http://www.bhg.com/home-improvement/advice/maintenance-repair/insulating-exterior-walls). This means an ICF house is a Green house. It’s more energy efficient so it costs less to cool and heat. And the R-value doesn’t take into account the energy savings that the thermal mass adds.
- Structurally Strong – I’ve seen photos of a neighborhood after a hurricane or tornado. The only building left standing was the ICF one. I didn’t have any windows left, but it was still standing. Enough said.
About the energy efficiency of ICF, I’d like to mention four more items, relating to temperature transfer:
- ICF blocks heat/cold “conduction”, where a material would otherwise carry heat through its body. Even the metal webbing doesn’t reach the foam surface, so there’s no straight-through conduction path. Wood studs, on the other hand, conduct energy directly through them. You can see it on thermal images of wood frame walls.
- ICF blocks heat/cold “convection”, where little gaps in the structure would otherwise let air blow through the wall. The poured concrete fills every possible opening, without the need for painstaking caulking and sealing, that a builder would otherwise never do.
- ICF blocks heat/cold “radiation”, where electromagnetic waves can go straight through a frame wall, nearly unimpeded. The thermal mass of the frame wall captures those waves.
- ICF taps into the earth as a thermal reservoir. Remember that thermal mass of the concrete inside the wall? This also connects to the concrete footer and the earth as a whole. The earth maintains roughly a 65°F temperature. As the environment tries to heat or cool the wall, some of the excess heat/cool is transmitted to/from the earth, further helping to stabilize the temperature of the interior wall surface.
Below is a photo my glued and stacked ICF wall. You can see the tips of the vertical rebar, as well as the top course of horizontal rebar. Tim is about to cut a form with a hot knife. Cutting is required to match form size of wall length and shape. This is the west corner of the house, with the future garage to the right. Click on the photo to enlarge it.