What is ICF construction?
Insulated Concrete Forms are hollow blocks made of rigid foam insulation, stacked and filled with poured concrete to form a wall's structure. The concrete provides strength. The foam layers on both faces provide continuous insulation, with no wood framing or thermal gaps in between.
Every Fuller home is built on a Fox Blocks ICF foundation with a six inch concrete core, on custom builds and on the Deerhurst Townhomes alike, with 2x6 framing and R22 batt insulation above grade.
What that is worth, in numbers
Fox Blocks publishes a steady-state R-value of R-23 for the block, calculated to ASHRAE 90.1, and it is the same figure across core widths because the foam thickness does not change with the concrete. Whole-wall calculations, which account for the absence of thermal bridging, put the assembly at around R-24.
The manufacturer also cites a dynamic equivalent above R-32 once the thermal mass of the concrete is factored in. That is a different kind of measurement than a steady-state R-value and is worth understanding rather than just quoting: it reflects how the wall behaves through a real day of temperature swings, not how it performs in a lab at a fixed temperature.
For a builder or an official who wants the paperwork, Fox Blocks holds a CCMC evaluation, which is the Canadian construction materials assessment most building departments here will recognize.
How does ICF compare to standard framing?
Because the foam runs continuously around the concrete core, an ICF wall avoids the small gaps and thermal bridging points that occur between studs in framed construction. Every stud in a framed wall is a slightly colder line running floor to ceiling. An ICF wall does not have them.
There is a code point that reflects this. SB-12 treats specified ICF assemblies as deemed to comply with certain compliance packages, which means the wall does not need separate energy modelling to satisfy the requirement. Some building officials will still ask for product literature or third-party thermal testing, which Fox Blocks supplies.
Beyond raw R-value: airtightness and thermal mass
ICF has two performance benefits that do not show up in the R-value number at all.
Airtightness. Poured concrete walls have far fewer air leakage points than framed walls, which reduces drafts and the energy lost to uncontrolled air movement.
Thermal mass. Concrete absorbs and releases heat slowly, which evens out temperature swings between day and night and reduces how hard a heating system has to work to hold a steady temperature.
On a Fuller home, both work hardest in the basement, where the ICF wall, the poured slab and the in-floor hydronics sit in the same assembly. The basement is the part of a house most people expect to be cold. Here it is the part built to hold heat best.
What else helps, beyond the walls?
R-value in the walls is only one part of a home's envelope. A few other factors carry real weight.
Roof and attic insulation. Heat rises, so a wall assembly cannot address that category of heat loss on its own.
Air sealing. At windows, doors, and every penetration through the envelope, since small gaps undo a meaningful share of the benefit high-R walls provide.
High-performance glazing. Windows are the weakest point in any wall assembly, regardless of how well insulated the wall around them is. That is the next article.
Mechanical ventilation. A tightly sealed home needs controlled fresh-air exchange to manage humidity and indoor air quality. Every Fuller home has an HRV, as does every other new home in Ontario, because SB-12 requires a heat recovery device on ventilation equipment in each dwelling unit.
Why this matters for a Muskoka build specifically
Given the length of the local heating season and the real swings in winter weather, investing in envelope performance up front tends to pay back more visibly in this climate than in a milder one.
Part two of three. Back to what R-value measures, or on to windows and heat in the floor.