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Sunday, 10 August 2014

SENWiEco concludes testing of DURISOL ICF Block

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 east.

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 damage).

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 energy numbers).

Thanks for visiting.


Anonymous said...
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SENWiEco Designs said...
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Jake Vierzen said...

In the States, all walls are allowed to be only 5.5" thick below grade; provided they meet the structural requirements. So the structural requirements are identical for poured walls and ICF. In fact, the 5.5" thing came about not because of ICF, but because that is the size of a 6" wall tie for aluminum forms. An 8" wall tie is 7.5", etc. Their corner panels are set up this way too; in fact, one would have to invest in special corner forms to pour a true 8" wall.

Jake Vierzen said...

Sorry, I couldn't help one more comment!
Nudura is an all foam product, and always has been. I have been using them for many years. I won't link their sites here, but you will be able to verify that Faswall is whom you are really referring to.
Regarding the possibility of insect and rodent damage to a foam-based ICF; I will readily grant you that Durisol is superior in this regard. However, I have installed foam based ICF's on over 150 ICF's in the last 11 years without a (known) problem. I don't want your readers to forget that a foam-based ICF is superior to most wood framed assemblies out there.

SENWiEco Designs said...

Thanks for the info Jake. Is the 5.5" regardless of wall height? What reinforcement does your code call up then?

SENWiEco Designs said...

Thanks Jake - I rechecked and then rechecked the ref. You are right, it is not Nudura, it is Faswall. I have updated my blog accordingly.

SENWiEco Designs said...

Jake came back privately with a reply on the code requirements for the 5.5" foundation core (because I accidentally deleted this posting and had to restore). I am posting his response here along with my follow up.

Jake (re the US Building Code requirements): The foundation thickness and rebar requirements have several variables: height of unbalanced backfill, overall wall height, and backfill type (soil pressure). Once these inputs are selected, you can choose from a thicker wall with less rebar, or thinner with more rebar. And definitely there are times you can't use 5.5" concrete. Particularly once you get to over 8' of unbalanced backfill in anything heavier than clay.

My Reply: There is the difference between the US and Canadian code. The ONLY rebar allowed in a foundation if following the Part 9 Building code is that part of the code relating to ICF foundations. You cannot build a conventional site formed concrete foundation with Rebar in at least BC UNLESS you have that foundation engineered. There is no provision for rebar in the code except for when installing ICF.