When choosing a foundation your options are typically a site formed and poured concrete wall or some form of insulated concrete form (ICF) wall. Early on in the process I gravitated to an ICF wall because it would eliminate the need to hire forming crews and rent and fabricate forms.
When looking at ICF, the traditional product is made from some form of
EPS foam which has a very high embodied energy, lots of off-gassing, and
is made from non-renewable components. The foam industry (EPS and XPS)
will try to 'green-wash' this by stating the foam, as an insulation,
reduces heat loss and reduces carbon output over the lifespan of the
dwelling. Yes this is true for ANY insulation, so choosing an
insulation with a starting lower embodied energy will put you that much
further ahead on your reduction goals. So again, early in the process I
looked for a product that on the surface was friendlier to the planet.
One of the benefits of all ICF walls is that they typically require a
smaller concrete core than a standard foundation. The code allows for a
5.5" core on ICF walls where a standard site formed wall generally
start at 8". The reason for this escapes me because the ICF product
itself is not considered structural so why would all walls not be
allowed to be only 5.5" regardless of forming method. If someone knows
the answer to this please post a comment. The smaller core of the ICF
significantly reduces the concrete needed and therefore the cost and
embodied energy of the overall wall.
One of the other downsides to a typical ICF forming material (foam), is
that you end up with too much insulation on the inboard face of the
core. This decouples the core from the interior environment and can
lead to condensation in some isolated cases, but more importantly it
limits the walls ability to be a moderating force to the homes inside
environment. An exposed concrete wall can buffer the temperatures by
acting as a thermal mass.
The further downside to foam style ICF blocks is that just about
everyone loves them from rats to ants. They burrow and nest in the
product creating holes in your thermal blanket. They are also quite
fragile and can be easily damaged during construction and require
significant blocking during pouring to prevent blow-out.
My quest for the perfect block led me to the Durisol product.
It is made with virgin but scrap wood (manufacturing waste and tree
tops). This wood is chipped and then through a patented process, the
organics are removed to create a mineralized wood fibre (think petrified
wood). This is then added to a cement slurry and formed into the ICF
block. This process and product would help meet my goals to dramatically reduce the embodied energy of the foundation.
There is another similar product made by Faswall, but my research
indicated that this product utilized non-virgin wood sources like used
pallets and had a lot more dimensional tolerance issues with the block
itself. I also was informed that Faswall was initially going to be a
licensee of Durisol but ended up swiping the formulation and heading out
n their own. This did not sound like the right fit for me so I focused
on Durisol even though it meant I would have to freight them from back
Once I decided to seriously consider Durisol, I then wanted to ensure it
was suitable for the task. My immediate concern was that the blocks
would rot. But the product has been used for decades as sound abatement
walls on highways (where some of the wall is always buried) and I
received a letter from the Ontario Ministry of Transport advising that
they have never had to repair a wall due to decay (just traffic accident
My next concern was how would this wall act from the point of view of
air and moisture movement. It was made clear from the beginning, that I
would need a independent air barrier as this product was air permeable
(it has webs that penetrate through the concrete core so the core is not
continuous). So this was a negative against the product when compared
to foam, but as I wanted a bullet proof building enclosure, I had
always planned on an robust WRB (water resistant barrier) on the
exterior of the foundation. I think the idea of 'damp-proofing' a
foundation wall in a rain forest climate is ludicrous and had always
planned on Water Proofing my wall. And a waterproof membrane is almost
always also an air barrier.
My next concern was how the blocks would act if subjected to regular
wetting. The manufacturer claimed the product was unable to support
capillary action and had some university testing to support. But I was
not satisfied and so set out to torture test the product over 16
months. I started the experiment in Jan of 2013 (Begin experiment). At the eight month mark I posted the status) Status at 8 months) and then altered the block to also contain the concrete core. The experiment concluded on June 1, 2014.
All off my testing supported the manufactures claims. This was a free
draining assembly that did not support moisture movement from the
outboard to inboard face. I will also be preventing moisture movement
through the footings via a FastFoot mebrane and also using a touch-on or
self-adhered AB/WRB mebrane on the outside face of the foundation and
so will have a very durable and forgiving assembly. I now felt
confident using this product on my project and have now received the
product on site. Once the excavation is complete, I will post some
videos on the installation of the product (visit my project journal for the tribulations in getting these goods to site).
As I have time (may be at end of construction, I will also try to post
some cost comparisons between the various options and the embodied
Thanks for visiting.