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Community and Q&A

Choice of foundation wall: on Faswall and Durisol

J Chesnut | Posted in Green Products and Materials on

I recently made a statement on another thread about my opinion of Faswall and Durisol ICFs as a poor choice for walls particularly in a cold climate. Like most of my opinions I’m usually failing to see all aspects of the issue.

For a foundation wall Faswall and Durisol ICFs seem like appropriate choices because of the amount of concrete they displace compared to foam ICF forms including the T-Mass wall. Also for a comparable core width you get some embedded R-Value were you get very little R-value from the concrete cores of the foam ICF forms, including the T-Mass wall (in fact the T-Mass wall seems to represent the most quantity of concrete). While foundation wall thickness is not a limiting factor with Faswall and Durisol you can still add insulation layers and achieve a higher R-value for a given width.

For the exterior a parge coat finish above grade seems sufficient.

The Durisol and Faswall forms are manufactured through some vague “mineralization” process of wood chips. I’m sure this has an embodied energy ramification and I wonder how it compares to concrete embodied energy.

It is still my opinion that because unit sizes of these ICFs can’t be manufactured with smaller tolerances of dimensional difference that stacking them and maintaining level courses can be a challenge. A slight wonky wall below grade is easily hidden, but maintaining a level sill plate may be made difficult.

I’d be curious to hear others take on this.

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  1. Chris Koehn | | #1

    I recently constructed a timber frame on a project with a Durisol foundation built by carpenters on Salt Spring Island, BC. Speaking with the carpenters, the height of the product was consistent enough to result in a very level mud sill. There may have been more variability in length, but they are usually cut to length each course, so that doesn't matter so much. CMU's offer more height adjustability via mortar joints. ICF's require a dead level and smooth footer.
    I have no idea as to the energy involved in "mineralization" of the wood fibre but I too would be interested to learn.

  2. Matthew Amann | | #2

    The tolerances I have experienced with total height Durisol walls are no harder to deal with than the usual "less than perfect" stem walls I see and build on. Mortar leveling of the first course is recommended. The Durisol blocks are made at slightly tighter tolerances than the Faswall IMO. The most challenging aspect in my experience was bracing of these walls, given the small size, which can create a sort of "saw tooth" stagger from block to block vertically. Designing a space around the block increments is critical for cleanly laid walls.

  3. Vipul Acharya | | #3


    I work with Durisol and can offer the following:

    While I can't comment (without bias) about the tighter tolerances with Durisol, I believe others have seen the difference. Because of longer history with Durisol and combined R&D with all 14 manufacturing locations worldwide, I do believe that our products tend to offer the state of the art with respect to cement bonded wood fiber (medium density).

    Our North American facility is in the process of further upgrades that will bring the height tolerances even tighter than current and at the same time, really address the other dimensions in a more concentrated effort. I have no doubt that our tolerances are better and will only continue to be even more so.

    With respect to mineralization, while it is a proprietary process and therefore necessarily "vague", it is a completely benign, subtractive (not adding anything to the wood) and extremely low in embodied energy. It is a process that is not endothermic (i.e. it does not require energy like the manufacture of cement).

    Hope this helps.

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