Every now and then we field questions about ICF (insulated concrete forms). We thought it was high time we did a blog post about it!
Given that the folks who come to us are interested in building a super, energy efficient home, it’s not surprising that we sometimes get asked about ICF or insulated concrete forms. There is no question that ICF is superior when compared to a conventional wall assembly, for these two key reasons:
1. Thermal bridge free design. Any low energy home requires thermal bridge free design and ICF accomplishes this with continuous EPS styrofoam on both sides of a concrete core. The insulation value of a standard ICF is the same (R22) as conventional 2 x 6 construction, however the 2 x 6 frame has a technical thermal bridge every 16” – 24” depending on the stud spacing.
2. Air-Tightness. Since the walls are continuous poured concrete, it is considered an airtight system. The roof frame connection to the ICF walls is very important to maintain the air tightness, however. Most ICF homes are usually less than 2 ACH (air changes per hour) without any special interventions, whereas most conventional homes have twice the air leakage.
For newly built passive homes, including EkoBuilt ones, the ACH rate is 0.6 and the retrofit standard is 1.0.
Does EkoBuilt Use ICF?
Although we do use a modified ICF for a super-insulated foundation, we do not use ICF for above ground walls. This is for a number of reasons:
1. Sustainability – ICF uses styrofoam which is a petroleum-based product. For this reason alone, we do not entertain using ICF above grade. We believe styrofoam should be used only where it is beneficial, which is below grade (where it stands up well against moisture), not above grade.
2. Affordability – A passive house in most areas of Canada requires an insulation value in the walls of near R75. The cost of adding more than triple the standard amount of styrofoam to an ICF would be cost prohibitive and instantly make the home unaffordable to the majority of the market.
3. Health – Although the styrofoam is covered in drywall, ultimately it is indirectly exposed to the inside of the home, potentially sacrificing indoor air quality. A home that has an air exchange system should take care of these impurities, but the point to make here is why risk sacrificing indoor air quality if there are better alternatives?
4. Non-renewable materials – Styrofoam is a non-renewable resource (being petroleum-based) and we prefer renewable alternatives for building sustainable healthy homes. The EkoBuilt wall assembly is 100% renewable with double wood frame wall assembly/cellulose insulation.
5. Non-renewable resource – An extension of point 4, we consider the concrete core of an ICF structure to be a great waste of a non-renewable resource since it’s simply not required. To be planet-friendly, we believe ICF should only be used where it has unique benefits. In this case, being in contact with moisture in below grade foundation systems, is a very appropriate use.
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