Saturday 7 September 2013

Designing walls that are not vapour permeable - A good idea?

I have been having a discussion on a LinkedIn Passive House forum regarding the choices one can make in regards to insulation and the effects of these choices.

http://goo.gl/1vGTyI


The poster was asking for experiences within the building community with Wood Fiber vs. Cellulose insulation and I suggested that neither may be desirable depending on your climate conditions and instead suggested continuous exterior mineral wool fibre insulation.  This then morphed the conversation towards what constitutes a durable high performance wall.

I posted my thoughts on the perfect wall (which just happens to match my walls in my upcoming build) and other who are builders of PassivHaus (PH) structures posted their perfect wall details.  This led to a discusion about the merrits of designing a wall that is vapour open to the low pressure side, where one of the posters stated:

"I've been indoctrinated with the Bau-biology "Breathable Wall" idea with nearly 10 years now and spent many years preaching that gospel. But then I found the Spokane and Tsong studies where they opened the walls of 250 houses, that were built wrong in terms of 5:1 breathability but no decay was found.  The walls had no membranes, no decay was found, its the same for SIPs houses, ICF houses and most other construction methods, the walls don't breathe as per the 5:1 rule and the houses aren't falling down."

The two studies can be found here:
1) http://www.viking-house.ie/downloads/Tsong79.pdf
2) http://www.viking-house.ie/downloads/Spokane.pdf

I read the two studies the poster provided and was somewhat shocked at the jump in logic that is represented by the statement that we do not need to make walls permeable and that impermeable walls will not rot. This is such an important subject, I though I would reproduce my comments here to a larger readership.

The Tsong study is discussing the lack of VB, and not a wall that is vapour tight. A wall that does not have a VB is by definition VERY vapour open and in fact most of the assemblies studied were quite vapour open (poorly insulated wood frames).  It is also important to note that the study occurs in 1979 and the levels of insulation discussed are far below what we are talking about in today's high performance homes (the study does not state the R value but we are talking about poorly filled 2x4 walls, so probably an effective average of below R7). Therefore these walls all had a lot more drying potential due to thermal bridging than high performance homes of today and certainly a lot less drying potential compared to a PH. It is also important to note that these houses had an average ACH50 of 16.2, which is more than enough to also help dry the assembly when it was experiencing very high RH levels. I have been unable to locate the permeability of Urea Formaldehyde insulation so do not know how permeable those walls were if detailed perfectly – but per the study, these foam walls had a lot of air leakage due to foam shrinking and cracking. The average foam shrinkage was 8% and the report states that as a result of the shrinkage of this foam, there was a 70% increase in heat loss (heat loss dries walls, so even these walls could dry easily).

It should also be noted that areas of high moisture content were found at many locations on these homes where bulk water entry was occurring (in other words control layers regularly fail and you should design your assemblies for such to the extent possible).

What I do love about this study is their remark at how the mineral wool insulation had an ‘extremely low average moisture content’ when compared to the other insulation (in no case was the moisture content of the mineral wool above 2%). The study went on to say this is “probably attributable to the fact that mineral wool is not hygroscopic, whereas the cellulose and U-F foam both tend to retain moisture”. Go ROXUL!

I then went on to say that relying on this dated research to state that a wall should not be vapour permeable to the low pressure side is grossly flawed in my view, does not come close to lining up with the current recommendations of the building science community and their experience in repairing failed structures, and in my view also miss-interprets the studies results and compares conditions that are grossly miss-aligned with the high performance structures we are building today.

All this study can really claim is that there was no significant moisture damage associated with diffusion observed on any of the homes that generally had no or minimal insulation and high levels of thermal bridging. And as we know today, this results in assemblies with built in drying safety factors. The study was also was clear to specify that these results could not be related to colder climates.



The second study was by the same author but took place in a colder climate.  The same arguments above apply.  It should also be noted that colder climates generally have less problems with moisture damage to wall assemblies than milder climates.  In climates with cold winters and hot summers, the moisture typically exists as frost all winter and then quickly dries out in the late spring as the temps rise. In a location like the Pacific North West (3000 DD), moisture will stay in liquid form for months at a time as is able to cause a LOT more damage as the moulds take hold and flourish.

Can you build vapour tight assemblies that work in the Pacific North West?  Yes, but you then need to sweat the details.

An ICF IS a wall that works.  It is often quite vapour tight but because there is no air movement through it at any point in the structure, there is generally no opportunity for condensation to occur (I have heard of isolated events where condensation has occurred between the foam ICF and concrete core leading to mould build-up).  The typical foam materials of the ICF are also highly resistant to vapour diffusion, all but eliminating that risk as well. From a building science standpoint a typical foam ICF structure makes a lot of sense, but where it fails in my view is the very high embodied energy that it represents both in terms of the volume of concrete used in these homes and the foam used in the typical ICF blocks.

As far as SIP construction (structural insulated panels), which are typically fabricated with OSB sandwiched on each side of a foam block, I personally feel that the jury is still out.  There is a multitude of reports of SIPs failures across North America and once again, this style of construction represents a high embodied energy.

For me, I will stay true to my stick frame, plywood sheathed structure wrapped in a nice continuous warm blanket of highly vapour permeable and fire/rodent/bug proof Roxul mineral wool insulation thank you very much.

18 comments:

Unknown said...

Have you seen the study by Durisol of a comparison of one of their assemblies versus a standard stick-frame house? They had moisture/Relative Humidity sensors placed in the wall cavity, and for a 6 month heating season, they tracked the RH.

The Durisol wall had a average daily range of 2.6%, where the stick framed wall ranged by 15%. The stick wall frequently exceeded 70% RH, where the Durisol wall only exceeded it once. The Durisol chart is a relatively smooth line compared to the spikes and troughs in the stick framing. I imagine SIPS and the like would also be "spikey".

It's on their site. http://durisolbuild.com/iaq-shtml/

It has me wanting to go all the way to the roof with the Durisol. I assume you aren't doing that because it would be crazy expensive to ship that much block to you?

SENWiEco Designs said...

Yes I reviewed the study back when deciding to use their product.

Yes it would be silly expensive to ship that much product to the West Coast but their is a much more important reason I chose to not go with ICF above grade. It has a much higher embodied energy than most other wall systems. Cement requires huge amounts of energy to produce and adding fly ash does not really reduce this aspect of the product. A stick frame house is much cheaper to build AND has a much lower embodied energy. Durisol does not have this problem, but the other issue with traditional Foam based ICF is the massive embodied energy the foam itself has. Then you have to take into account that much of the foam (insulation) is on the wrong side of the assembly. IN a cold climate, you want as much of the insulation as possible outboard of your control layers.

Unknown said...

About Roxul DrainBoard... and it's use below grade as a foundation drainage plane. I understand the principle that they are saying. That the stuff is free draining, and if water hits it, the water would percolate its way down to the drain tile. It's a great theory. And I suppose if it's free draining in the same manner that gravel is free draining, then it would indeed conduct water away before it hit the wall.

But something about it just doesn't sit right with me. I have some drainboard here, just sitting in my yard, and when it rains, the stuff gets saturated. And it stays wet for what seems like a long time. And of course when it's wet, it's a pretty useless insulator.

So how can I trust it to provide insulation value AND to be a great drainage plane. When what I expect is that it will get wet with ground water, and just stay wet.

Remember from the GBA site that I'm planning to use the FastFoot/gravel under footings/ drain tile below footings approach. So I'll have lots of capacity to drain whatever gets down there. But I just can't get my head around how this stuff is supposed to sit in constant contact with earth, and still provide drainage as well as insulation value.

I'm trying to think of ways to put something in front of it - like another membrane, or even plywood. But that's counter to it's claim that it's a great drainage plane on its own.

Can you think of a torture test (that you do so well) that would illustrate how well it works or doesn't work? Or do you accept Roxul's claims at face value? Help!?

SENWiEco Designs said...

Zenon - is your piece in the yard sitting flat or is it vertical. I believe this makes a big difference.

I can say that the piece of mineral wool inside the Durisol ICF block was never saturated and stayed free draining even after 8 months of wetting from the top. That is a pretty good torture test. However, the piece was open to the ICF cavity. I have now filled this with concrete and will need to setup the torture test again to see how it performs.

I believe it also does not loose a lot of thermal resistance when it is damp like other insulation do.

At a seminar I was just at that discussed below grade ROXUL, the common experience in the room was that the outside 1/4" or so got wet and de-rated that thickness of R Value but the rest was just fine.

In my installation, the product will NOT sit against back fill. I will still cover over with dimple board. Not only will this keep the ROXUL dry, it will also keep the fines out of it and the drain rock below.

IS this dimple needed - maybe not, but in my wet region, I do not want to take any chances. I had even considered installing a granular layer outside of the dimple and then Geo-textile, but I really need to look at cutting costs and build time and have been told, this just is not necessary with all the other controls I have.

Unknown said...

The piece in my yard is "sort-of" vertical. It's probably on a 20 degree angle off of fully upright. If you look at it on rainy days, the bottom seems saturated. To be honest, I haven't looked at the backside of it after the rain. Which I will remember to do next time. So my test is not at all scientific, nor is it representative of how the product would be installed anyways.

It's good to hear about your 1/4" reports from people in the field. That corroborates the Roxul sales letter that says they tested a bunch of drain-board-like product installed in the ground in 1976. They dug it up and found it wasn't noticeably compressed or wet. Which is great.

I told you I was pricing out the DrainBoard here. And the local distributors only have the 1". I called Roxul, and they said the 2 3/8" is pretty much exclusively a US product. Probably because of codes in the US, and the R-10 rating. In Ontario, the last 2 3/8 that they sold was in 2011. But I'm welcome to buy as much 1" as I want and apply it in layers (possibly even a better thing, as I can stagger the joints).

And I asked if one could buy it direct from Roxul - especially in Vancouver, and they said no. That all sales go through the Ontario office, and you gotta buy from a distributor. So she had no idea how you were getting (a) the 2 3/8 product at all and (b) buying direct from Roxul.

They WILL make up a batch of 2 3/8 for me if I want (through a distributor), but I have to buy a minimum of 17 skids, which is enough to do 7,344 sqft of foundation walls. My walls are only 1,800 sqft. So I'm stuck with the 1".

Now, you say that you will put a dimple membrane on as well. Which I also was planning on. It seems like relatively cheap insurance. But I'm not sure where to put the dimpleboard. If you place it outboard of the Roxul, the dimples are just going to compress into the drainboard, and not give that gap. Kind of defeating the purpose of the dimples. If you get the drain sheet material with the dimples-OUT, and the geotextile-OUT, then maybe. But then you are relying on a thin geotextile to stay unclogged forever and to perform perfectly. Which somehow doesn't sound like a safe bet to me.

I think it's safer to put the dimples-IN right on the waterproofed durisol wall, and then put as much Drainboard as you want overtop of that. And backfill with anything, because the chances of water getting through all that is pretty low.

I wonder if waterproofing the Durisol, and putting 2 or 3" of Drainboard is enough. I love overkill. But let's say the dimple board is around $0.35 /sqft. And that an additional layer of 1" drainboard is $0.71. If given the option, would it make more sense to put the money into another layer of drainboard? The insulation value of DeltaMS is zero. But you get another R-4ish with 1" more DrainBoard. And how much water is ever going to make it through 3" of drainboard?

Your thoughts?

SENWiEco Designs said...

I will be able to provide more comment re the availability next week. I am communicating with ROXUL at their executive level (I recently met with the VP of Business Development and other executives). In my communications, there has not been any mention of 2.38" logistical issues. Note that the product is ALL made in Canada. They do not yet have any plants in the USA (soon to change). Most of the product is made at their heavily automated Milton plant. SO I am not sure why the person you talked to had that response. I have asked my contacts for someone to contact in the Ontario area and will pass on this info once I have it.

You have made a good point about the orientation of the dimple. I do not believe it will be a problem because the DrainBoard is dense enough, and the dimples spaced close enough, that compression of the dimples into the insulation will be mostly resisted. Will definitely research and test prior to installation.

I would not waste it beside the Durisol as it really will not do anything there. Should go outside of ROXUL or not at all in my opinion.

Unknown said...

I'm sure the person at Roxul was talking about generic buyers like me. And not people who have connections to VPs and executives. I'm sure if you are connected well, that you can get whatever you want, directly or otherwise. Lucky you!

I called Cosella-Dorken about where to place the Delta product. And their tech people weren't there today. But the lady I spoke with said she'd recommend the Delta Drain product, which is the dimples-OUT-with-geotextile product. She would put it outside of the Roxul, like you are thinking.

I have my doubts that the Drainboard would withstand backfill pressure at all the dimple spots with the regular Delta MS. I just don't think it's going to retain a gap. Maybe that's not important. I wouldn't even expect XPS or EPS to stand up to the dimples. So I can't see how a comparatively fluffy product like Drainboard is going to fend off hundreds or thousands of pounds of backfill pressure.

But switching to Delta Drain would also cost a lot more, and get me closer to just putting another 1" of DrainBoard on, and getting another R-4.3 out of it.

If the sole purpose of the drainboard in this assembly is to provide $700 worth of "insurance", then what's wrong with putting it directly against the Durisol? It's not going to hurt. Am I missing something?

SENWiEco Designs said...

Some quick comments because I need to get some design work done.

- DO not rely on vendor advise for product use. If unsure, ask questions at the Building Science LinkedIn forum or GreenBuildinAdvisor site. Often vendor reps due not have the building science knowledge to provide the right advise.

- Have you felt the DrainBoard product? Like the ComfortBoard IS, it is a semi rigid product with compression strengths similar to EPS/XPS.

- A fully adhered torch on membrane does not need any other defence. The dimple is just to provide protection to the ROXUL.

Unknown said...

Drainboard compressive strength at 10% deformation: 17 kPa

XPS at 10%: 210 kPa, and up to 689 kPa

They aren't even in the same league. That's why they aren't recommending RockBoard for use underslab. Because the compressive strength just isn't there (yes, they may still test and find it ok).

I worked with DrainBoard last year on a Habitat build. And I have the leftovers from that job in my yard. So I have first hand experience with it. I spent a couple days installing it. If you fiddle with it in your fingers for long enough, it will fall apart.

Last year I also put a bunch of ComfortBoard in my house. Pretty much the same story as the DrainBoard. Actually, it felt more rigid.

If you are under the impression it has similar compression strengths to EPS or XPS, you need to check your numbers. Because one of us is way, way out. Unless you are referring to something else as "compressive strength".

I really hope YOU are right about this. Because I would LOVE for it to have similar strength to XPS.

Roxul's digging up of the 1976 test sample would suggest that the drainboard doesn't need any other defence either. Hmmm.

Unknown said...

Oh, and I'm also a bit leary of the GBA site. I think it could also be called the "FoamBuildingAdvisor" site. Because according to Martin, there isn't a problem around that enough foam can't solve. Which isn't very "green" in my opinion. Nor is it necessarily healthy.

They seem to pursue R-values as the ONLY goal worth talking about. But a structure should be healthy and resistant to mold, and many other things that the over-use of foam just can't provide. Again, IMO.

I have to build a house that I have to live with for 50 more years. I don't want to find out down the road that foam WASN'T the Holy Grail that "people in the 2010's thought it was". I could go on about this, but I'll restrain myself.

SENWiEco Designs said...

Zenon - I will post and comment on your latest comments soon. I am under the gun to get my drawings finished and off to the engineer.

In the meantime - please contact Trudy Puls at ROXUL for your 2.38" DrainBoard requirements.

trudy.puls@roxul.com

Unknown said...

Sean: I'm in no rush on my design, so take your time. Good luck with your deadlines!

SENWiEco Designs said...

Your right that DrainBoard is only 17kPa (355 psf). I thought it was similar to the ComfortBoard IS (product I have worked with) which is 35.6 kPa (743 psf). Typical wall XPS is 2160 psf and EPS is 1460 psf. So yes, as you pointed out – there is a difference. In the filed, ComfortBoard IS 'works' very similar to the typical XPS and EPS put on walls regardless of the psf differences.

You are also right in that you do not use mineral wool below a slab. You can only use the higher densities ($$$) XPS or EPS (I am starting a test shortly that will compare the ages R value of both when in a moist environment). You can also use Foam Glass ($$$$) below a slab.

As far as durability, even the board EPS and XPS start to break down when repeatedly handled, although they are more resistance than mineral wool. However, mineral wool's benefits far out way any challenges, as I am sure you will agree. As long as you are careful, you can apply without any problems.

As to the dimple compressing into the board, I met with an engineer earlier in the week who advised this is a problem even for the XPS & EPS over time. SO you use the dimple board that has a second sheet of plastic on the dimple side. These style of membranes maintain the air gap. As soon as I get specs on the product I will post. I have often seen at job sites, but cannot find on the net at the moment.

Agree with you re GBA to a degree. There are many foam friendly posters. This is where it is important to separate good building science from additional environmental concerns. Foam insulation (spray or rigid) make great thermal barriers. And if installed on the right side of the assemblies, meet building science best practices including the reduction of mould risk. (just don’t use spray foam as an air barrier). But these products are poor from an environmental standpoint and should not be used in a low embodied energy dwelling unless there are no other practical/durable options (below slab). Fortunately, there are much better solutions for foam insulation in the majority of cases (mineral wool being one of the best).

Unknown said...

Is "Delta-Drain" the 2-ply product you are talking about? It has the geotextile fused to the dimples, and is applied with dimples facing out.

But you said 2 layers of plastic.

SENWiEco Designs said...

No it is a product with a second rigid plastic sheet fused to the top of the dimples. It is probably a commercial product. I will ask at the BCBEC conference on Wednesday.

SENWiEco Designs said...

Zenon - You were close, it is DELTA
®-DRAIN 6200 HI-X that has the second rigid layer to prevent it compressing into insulation. Comes in 4ft x 6 ft sheets.

Unknown said...

Sean - thanks for that. I'll check it out. I still wonder about putting 2-4" of Drainboard, and then this Delta-Drain outboard of that. That means the Drainboard will stay dry (hopefully) and provide R-value. But it also means there will be no air gap right at the wall.

I ordered a cheap pond pump from ebay, and I'm going to set up my own test of the drainboard, with various thicknesses. I'm curious about how deeply the water will penetrate if it's given a path down to a drain tile. If we're only talking about the outer 1/4" getting wet (like you suggested), then maybe it's not necessary to protect the Drainboard with the Delta. I just have this sense that the best place for the dimpled product is right outboard of the wall itself.

I'll keep you posted.

SENWiEco Designs said...

Look forward to your results.

The insulation itself is a drainage plane, so Delta against the foundation would just be wasted. Delta outboard of the insulation may be over kill, but would help keep it dry and help keep fines out of it. These will both help preserve its R value.

I am not worried about the foundation itself because I will have a torch on membrane which will fully block vapour or liquid moisture (plan to use a Siplast torch on).