Sunday, 27 January 2013

SENWiEco considers the Durisol CBWF ICF Block for below grade foundations


Anyone who has read my previous blog entries knows by now that I like to verify and do things for myself.  SO it should come as no surprise that I will perform some testing on another ‘new’ product I am considering for my upcoming build.

As mentioned repeatedly on my blog, my focus on this build is a bullet proof and energy efficient building enclosure to lower my impact to this planet.  I am targeting R10/20/40/60 (Slab/Foundation/Walls/Roof) and these are effective values not nominal (so values after taking into consideration all thermal bridging). 

With these targets identified, it makes sense to optimize what ever insulation is installed by placing in locations less effected by thermal bridging.  This usually means putting most/all of the insulation on the interior of the structure or exterior of the wall or roof assemblies.  Now which side you put the insulation on is very important for preventing condensation.  In a Cold-heating-dominated-climate like Vancouver, you want to keep the sheathing above the dew-point potential so that if any interior air leaks into the wall assembly, it will not condense on the back side of the sheathing which can often cause rot and mould. 

Continuous exterior insulation is a great way to prevent thermal bridging (your insulation is firing on all cylinders) and keeps your sheathing, or in this case your foundation walls, warm and dry.  For this reason, an ICF form system makes a lot of sense.  In typical ICF formed walls, there is an interior panel of insulation attached to an exterior panel of insulation with plastic or metal ties.  The concrete is then placed to fill in the gap down the middle. 

From an insulation point of view, the continuous nature of the ICF panels is great and represents a thermal bridge free design.  Your nominal insulation is the same as your effective insulation R values.  However, you do end up with a thickness of insulation on the interior face of the foundation.  This prevents the concrete from acting as a thermal mass that would otherwise allow it to help moderate interior temperatures.  Insulation inboard of the concrete core can also represent a dew-point potential if the concrete pulls away from the foam as it cures and air leakage results.  Finally as the product is made from oil, it can represent strong off gassing potential and a real fire spread and toxic fumes risk if your drywall is not continuous or is damaged and a fire occurs.

But for me, the biggest demerit, against the foam based ICF’s, is that they are made from foam and therefore oil.  If your goal of creating a low energy house is to reduce your impact on the planet, it hardly makes sense to use a product that is the most responsible for human’s impact on the planet today.  We will be no further ahead if we create a demand for foam ICF on a mass scale, as this will just continue the dependence on a product we really need to start considering leaving in the ground.

Now many of you will say the benefits of foam ICF outweigh the use of an oil derived product.  You are at least locking away a lot of the carbon that would be created if the oil was otherwise used for combustion.  At least in a product like this, it will stay buried for probably 50-100 years (and there may even be a potential of recycling the product at the end).  And any increase in insulation decreases the amount of electricity and gas used in homes to provide heat and air conditioning. To an extent, I agree with this rational.  I do not believe you should abandon products just because they are made of oil.  In many categories, the alternative ‘green’ products are not suitable for use and have durability issues.  The regular replacement of an unsuitable component can represent just as large an embodied energy, as using a more suitable oil derived product.  However when you do have a suitable non-oil based alternative, you should do everything possible to incorporate it into your design. It was with this frame of mind, that I started looking at the Durisol ICF block for my upcoming build.

The benefits of a cement-bonded-wood-fibre (CBWF) block are:
  • Made from recycled-wood and cement powder,
  • Places all of its insulation outboard of the slab,
  • Can be left as a final surface within the basement,
  • Can be attached to anywhere in the field of wall (do not need to hunt for hidden plastic tabs to fasten drywall or framing to),
  • Incorporates a drainage plane within the product,
  • Is mold and rot resistant,
  • Is bug and rodent proof, and
  • Best of all – does not burn easily or give off noxious fumes if it does. 

Now for its negatives:
  • Highly air permeable (a benefit of regular ICF is that the concrete core is an air barrier).  The material of these blocks is highly porous and the block has webs that connect the outer and inner panels together THROUGH the concrete core.
  • These webs are not just an air path; they are also possible water and likely a vapour path.
  • There is at least a passing concern that the block could rot in a below grade application.

In researching this product, I was unable to find any comments on-line that the product had ever broken down below grade from decay.  The manufacturer provided an Ontario MOT testimonial that stated they had never had to repair the product due to decay (the product is used extensively above ground, and partially submerged, as a road side noise abatement fences) after 30 years of use. 

The product has been manufactured since 1953, so certainly has been on the market a long time.  If there were significant failures, it would be readily visible on the web. 

So what’s the catch? 

Well the product has not had a huge uptake for below grade installations to date.  The manufactures claims they have a dozen or so projects a year on average in Ontario and I have found 2-3 blogs on the net describing the use of the product.

What’s the risk?

Well, unlike traditional ICF, the interconnecting webs of each block penetrate through the concrete core.  This provides a path for air, vapour, and possibly moisture travel. 

The air barrier is fairly easy to address with a fully adhered membrane outboard of the block (this still leaves some interesting details at the footing level and will probably require some thinking out of the box to seal on the interior face near the basement floor slab - more on this in the future). An airtight drywall approach (ADA) could also be implemented.

The vapour barrier again will be generally dealt with by the fully adhered exterior membrane. Besides, even regular formed concrete foundations have a considerable moisture movement through them from out to in, which is why you should never have a vapour barrier (just a retarder) beneath the drywall in the below grade basement (NO POLY! EVER!!!).

Now for the real issue: What is the danger of liquid water transport through the webs to the interior face of the block, either under hydraulic pressure or capillary action? 

Durisol partnered with the University of Toronto to study the drainage properties of the CBWF ICF block back in the mid to late 90’s.  This UOFT report confirmed the manufacturer’s claims that the product did not support horizontal capillary movement and that liquid moisture drained readily through the material.  In fact the free draining rate of the product was a whopping .5 gpm through a piece of material that was 3.5” Thick, 8” wide and 11.3’ (yes ft) tall.  In another test, where a sample was fully saturated and then allowed to air dry, the retained moisture after 60 minutes was only 38% and the sample had lost a majority of its moisture after just ten minutes.

So far, this all looks great!

Figure 1: Durisol 12” Thermal Block in the R21 configuration (5.5” Concrete Core)
Figure 2: (LEFT) Semi-rigid mineral wool insulation insert on the outboard side of the block. (RIGHT) Product is created with a mixture of recycled-clean-mineralized-wood-fibre and cement powder.   
But unfortunately, I rarely accept others reported results at face value.  I wanted to put the product through a more rigorous testing protocol (in my opinion).  So enter the DBTTC or Durisol Block Torture Testing Chamber!
Figure 3: (Left) 28”l x 19”w x 15”t tub with a selection of Cactus Club takeout containers as standoffs in the bottom.  These support the block without being susceptible to rising damp.  They also isolate the outer and inner webs so that water flowing down the outer web does not flow along the support to the inner web. (Middle) A small water pump is rated for 70 GPH @ 0” head so probably around 40-50 GPH in my configuration. (Right) The containers are 2.5” tall and the water level was set at the halfway point so there is approximately ¾” gap from the top of the water to the bottom of the block (should allow for enough air movement around the bottom of the block so that the humidity does not build up too high and skew the results.
Figure 4: The inboard side of the block surface registered at 11.1% MC.  The block has been sitting in my living room for about a week (which by the way, translates to an indoor air relative humidly of 55% which is what I have the bathroom fan humidistat set to).

Figure 5: I also took the MC of the webs from within the inside journals that the concrete would be placed in.  This will be an easier location to monitor.  I had a reading of 10.4 and 9.3% MC (difference was probably due to a variation in density of the product at the tested location due to the random makeup of the wood fibre).

Figure 6: The Test
Over the next week or so, I will leave the pump on 24/7.  Water flows out of the plastic tube that has been drilled with holes at a regular interval.  The water is draining through the outer panel as fast as it is added at the top where it drips back into the tub and repeats the cycle.

Over time, I will measure the moisture content of the inboard panel exterior face (and the side faces of the internal webs).  The go/no go test will be to see if a piece of paper stapled to the inboard face of the block shows any signs of moisture over time.

I will of course post the results once they have been tabulated.  Here is a video showing the start of the test and another video showing 60 hours into the test.  At this point, there has been no horizontal travel of liquid towards the interior panel, which confirms the testing performed by the University of Toronto.

12 comments:

Zenon Tymosko said...

Sean
Love the blog. Also love the youtubes with the torture testing!

On air movement, I don't think it's a concern, from 2 things I've seen:

1. blower door test from Durisol showing a uniform wall temp. Which wouldn't happen if air was rushing in the webbing (this was a house with just the durisol wall - no finishes yet)

2. A Faswall youtube from a homeowner. http://www.youtube.com/watch?v=Gz9zmXio42A
He said the tech who did the blower door test said it was the lowest readings he'd ever taken. At the 9.12 mark.

He elected to instal an HRV because it was tighter than he expected.

SENWiEco Designs said...

Zenon - Thanks for your comment and video link. Air leakage through the webs of the Durisol is definitely a concern for this style of product but will not be a problem in basements (what I am using it for), because best practice dictates a fully adhered torch-on WRB/AB membrane installed on the outboard side. For above grade applications (I am not using in this application), you would need a air barrier on the inboard or outboard side of the assembly just like any other none ICF wall assembly. Something vapour permeable on the outboard side is best practice in heating dominated climates. It is unfortunate that the video did not get into specifics. Stating "just above code" and "best they have ever seen" really does not say much. Code is actually pretty high. I will be aiming for an ACH50 that is below 1. As for HRV (or ERV depending on climate), they are an absolute must in a high performance well sealed home.

Zenon Tymosko said...

Sean
I'm curious about the torch-on solution. Yes, I understand that it might be a great membrane. But why is it "best practice"?

The people at Durisol said I could use any of a number of solutions. Like cheap parge coat, then spray-on, peel and stick, brushed on, or weaker damp-proofing combined with the dimple membrane.

My proposal is to use cheap parge coat, then Thoroseal foundation coating (brush on), then dimple board, then another couple inches of Roxul Drainboard. I figure there shouldn't be water problems this way.

I also want to stay away from petroleum based stuff (like asphalt based/torch-on), or very "chemical-y" products like the spray-ons. Hence my preference for Thoroseal (relatively "natural").

I'm concerned that with the highly breathable nature of the Durisol, that I would just be encouraging a tar-like smell and off-gassing into my basement.

SENWiEco Designs said...

Fully adhered continuous water proofing membrane is best practice for ANY below grade foundation.

I understand desire not to use "nasties" in a build. However, my philosophy is to use the friendliest product that STILL does the job to a high standard. There is no sense using a 'green' product if it is not up to the job long term and I believe this is a mistake that many eco-builders make. So I will be using membranes in many critical areas of the built to provide 100% water shedding and also in some areas to reduce thermal bridging (will be posting details on blog in upcoming weeks. As far as odours in basement, if present at installation, they will quickly purge during construction and then once the walls are back-filled, they will not ever be 'warmed' up again so should be fairly stable from a VOC standpoint. Once I actually am ready to put drywall down there (10-12 months? - any odours should be long gone.

My assembly will consist of a torch on membrane, 2.38" of ROXUL DrainBoard, followed by dimple board and then back fill.

Zenon Tymosko said...

I tried pricing the 2.38" drainboard today, and the supply place only lists the 1". Have you sourced the 2.38" one yet? You might find it hard to come by. The price I got for the 1" was $0.71/sqft. So 2" would be $1.42 and 3" $2.13.

I agree that full water proofing is best practice. I guess I thought you were saying that torch-on (in specific) is THE best practice. Thoroseal isn't "green". And it is a full waterproofing coating with a long, long history.

I have the extra blessing of being chemically sensitive, so I don't trust any off-gassing product to ever cure/ventilate enough. So I need to eliminate them in the first place. It's much more than just an odour issue for me.

I was planning to skip the drywall and finish the block with clay plaster. That way if there ever is any problem with cracking or moisture, it will be obvious and easy to track. Rather than being hidden behind drywall. It's supposed to be one of the advantages to using Durisol, so I want to preserve that.

SENWiEco Designs said...

I will be getting my DrainBoard directly from Roxul. Contact them and I am sure you will have no trouble getting. Buy this through a wholesaler/distributor - not you local big box store.

Not sure on the price yet as I have not gone out for quote, but insulation products are not factors of the cost of 1". It takes the same labour/energy to make 1" compared to say 3" so you typically only pay the material difference.

Torch On IS specifically the best practice for a porous product like Durisol. A high quality waterproofing spray or roll on sealant may be good enough for a solid concrete assembly but is not best practice for a product that moves moisture so freely. You want something bullet proof in this location as you only get one chance to make it right.


I would be VERY concerned with using a vapour permeable coating for the exterior of a foundation. As the vapour drive is ALWAYS to the interior, you are just inviting moisture into your home with this product. I recommend you re-think.

In order for bituminous products to off-gas, they need to be heated. This just will not happen in an underground application in my opinion. If it somehow became a problem, you could figure out a way to seal the inside of the ICF as a fix.

I too will be leaving portions of the ICF exposed for the look of it.

Zenon Tymosko said...

Ok, I'll check with the Durisol guy again. In all my conversations with him (over the years), I don't recall any mention of torch-on. Of course, they don't dictate waterproofing choices. But he has a bit more experience than me :)!

I'll re-read Swanson's section on waterproofing. He's the one who is keen on Thoroseal on the Durisol/Faswall. I'll let you know.

I hear you about vapour drive. It's definitely important to get this stuff right!

I was all set to use the Henry products, with the fiberglass mesh. I figured that would be pretty bulletproof. Plus I could DIY the application and save $. Same with the Thoroseal. Not so much with the torch-on.

SENWiEco Designs said...

The fully adhered torch on was recommended by my local building envelope roofing expert who works at RDH and has decades of experience. If interested in getting opinions, post of the Building Science forum (not the passive house forum as the experts just don't hang out there).

Regardless of what anybody says, I would not use a product that has a permeance of 10 perms. That is a vapour open product that will cause problems long term for you. This is an area that you just have to bite the bullet and pay someone to do right. It is one of less than a handful of tasks that I will farm out to others on my entire build. This should show how important it is.

Zenon Tymosko said...

I haven't posted this at BSC. For that matter, I can't seem to find a forum at BSC. So I'm not sure what you were referring to. I know I can hire them to consult (for $$$). But I don't know where individuals can ask questions.

Anyways, on the matter of vapour drive through a Durisol foundation wall...

If there is Delta MS wrapped all around the foundation, then how much vapour do you think is going to be driving towards the interior?

Vapour moves from warmer to colder, right? And I expect the basement to always be warmer than the surrounding soil (except perhaps at the very top, where the sun will warm the soil). So why would I expect inward vapour drive?

The only spec I can find on Thoroseal is μH20 of 86-120. I don't know how to convert that to perms. Or if it's measuring the same thing. I did try to convert it. But it seems really complicated, and frankly I didn't want to work that hard this morning.

So I don't see where you get 10 perms. But let's say it is 10 perms. It would definitely not be a great vapour barrier.

I further don't understand how you spent a blog post stating that you didn't really like vapour impermeable walls, but then you are going to use torch-on impermeable on your walls. Is that inconsistent? Are you saying that the vapour drive underground is many times higher than it is above ground? What's the difference between moist air and moist earth? And if I have an impermeable membrane wrapped around the exterior anyways, with an air gap (Delta), then how much ground vapour is reaching the wall in the first place?

I need to understand this a lot better. Because it's not really making sense. I completely understand how one would want to prevent bulk water from penetrating a foundation, through leaks or through capillary action. But vapour drive was not high on my list as a concern in the basement. Especially with using Durisol, Fast-foot, underslab barriers, and at least 2 kinds of waterproofing on the below grade walls.

SENWiEco Designs said...

BSC does not have a forum. The Best place to discuss real building science related issues is on the LinkedIn ‘Building Science’ forum. This is populated by trained professionals (P.Eng. and MASc). There are also individuals like me, and the pro’s are very tolerant of questions that may be more junior than they typically deal with on a day to day basis, and quick to steer the likes of me back on track when I get off the rails. The PassiveHaus community tends to be full of well meaning, but untrained professionals that often do not understand why assemblies work or do not work, and only know how to regurgitate what has been handed down from on high.

You will see that all my comments state 'vapour permeable TO THE LOW PRESSURE SIDE'. The last part is important. You do want a VB, but it should only be installed on the high pressure side so the wall can perspire to the low pressure side.

Vapour drive is based on VP or vapour pressure. This is based on both temperature AND moisture. For heating dominated climates (you and I), there is a HUGE difference in the conditions between above grade and below grade. Above grade, the VP is almost always to the outside (except when reverse solar vapour drive occurs), where in below grade installations, the VP is ALWAYS to the inside because the ambient RH of soil is maintained around 100%. This is why it is very poor practice to install Poly on the inside of basement walls but it works just fine above grade (just do not use as an AB).

SO you want your VB control layer to the exterior of the foundation and the interior of the above grade walls.

The primary purpose for the below grade exterior of foundation barrier is water control, but this also forms the VB in your assembly.

Above grade, you are often better off with a vapour retarder over a vapour barrier (allow some diffusion under high loads so that walls in distress –leak- can also dry to the inside).

This is why I will use a VB paint on the above (and below grade) walls. The paints typically have a perm in the 1-2 range.

The 10 perms for Thoroseal came from http://goo.gl/YRy6Rt I actually mistyped – it is 12 perms (see bottom of pg 2). I would not use this product for below grade installation on the exterior of a foundation unless it was covered with a full vapour barrier – so then why waste your money.

Anonymous said...

We have a durisol block house built in 1961. Stucco on exterior and plaster on interior. No vapour barrier, no cavity.

House was very tight and heated well.

SENWiEco Designs said...

Thanks for your post - where was the house built.