The wall panels ...

Over the years I’ve come to appreciate the benefits of wrapping the outside of a wood-frame wall with a layer or two of foam insulation - the most obvious of which is the effect it has on thermal bridging. In a typical wood-frame wall, one with no exterior insulated sheathing, thermal bridging through the studs and plates accounts for a 20%+ decrease in the nominal thermal resistance rating of the wall (i.e. R-20 is actually R-16 or less).

There are other important benefits too, such as ease of air-tightening the structure and reducing the potential for exterior moisture making it further into the wall. We’ve made insulated sheathing a feature of our panelized walls for many years, in part because it's a “universal” approach that works just as well in hot humid climates as it does in cold dry ones, something that fits neatly with our commercial strategy for conquering the world. In a place like southern Japan where it gets unbearably hot and humid in the summer, a closed-cell insulated sheathing like polyisocyanurate (call it poly-iso), not only helps to keep the heat out, it acts as a vapour barrier, preventing exterior moisture from making its way in and condensing somewhere in the wall - say on the back of the drywall that has been cooled by air conditioning.





























In a cold climate like we have in Ottawa the vapour drive for most of the year is in the other direction, from inside where we are cooking, doing dishes and bathing the dog, to the outside. So in our climate we are required by code to install a “vapour diffusion retarder” (aka vapour barrier...) on the warm side of the insulated wall (or ceiling, or floor) to prevent moisture from condensing somewhere in the wall - say on the back of the OSB sheathing that has been cooled by the winter winds.

In cold climates most builders install a layer of polyethylene sheeting (call it poly) immediately before installing the drywall to do this job of controlling vapour diffusion. Where this can get confusing is that most northern builders also rely on this poly as an “air barrier”, going out of their way to seal around electrical boxes, laps in the poly, plumbing stacks and any other place where unwanted air can leak through the membrane.

I’ll get back to why air-leakage is so bad in a moment but in the mean time it is useful to know that there are other ways - more simple ways in fact - to control air-leakage than by sealing up a poly vapour barrier. The downside of sealing the vapour barrier on a wall in a cold climate where you’ve installed exterior insulated sheathing is that you create a kind of moisture trap, where any moisture that does find its way in - like on a rainy day during construction - has a difficult time drying out and can contribute to mould growth. The key is to maintain what is called “drying potential” which is exactly what it sounds like, the potential for the wall to dry out if it does happen to get wet. Given that our local codes require a vapour barrier, and yet we want desperately to use vapour-proof exterior insulated sheathing, our approach has been to turn the polyiso into the air barrier and allow a wet wall to dry slowly to the interior by simply not sealing the joints and penetrations in the poly barrier... make sense?

If you’ve stayed awake during this explanation you may be wondering about the vapour diffusion that occurs through the unsealed laps and holes in the poly. It turns out that the amount of moisture that moves into the assembly this way is so insignificant as to be completely inconsequential. The key to all of this lies in doing a great job of the air barrier, and we have developed a set of details and techniques for turning our foam sheathing into a continuous air-tight membrane.

Now back to why air-leakage is bad. The single biggest contributor to energy consumption in an average building is the leakage of untempered air - hot in the summer, cold in the winter - from outdoors because of the work the mechanical system has to do to bring it to the temperature and humidity level deemed comfortable by the occupants. As air leaks through the building fabric it carries with it moisture that can condense on surfaces within that are below the dewpoint temperature. In fact, when compared to vapour diffusion as a mechanism for pumping moisture into the fabric of the building, air leakage turns out to be a much more significant culprit - dramatically more significant (see diagram below). Air leakage also brings with it outdoor noise, dust, and airborne pollutants - pollen for example - that can compromise the health and comfort of the occupants.















While that sort of makes sense, most people intuitively feel that sealing up a house will be bad for their health, that they will be “stewing in their own juice” as it were, which would be true if it not were for the other side of the healthy house coin - mechanical ventilation. When air leakage is controlled and a properly sized mechanical ventilation system is installed the occupants are suddenly in charge of their domestic lives like never before. If the humidity level in the house gets too high, the ventilator can automatically lower it. If it’s pollen season and the kids are wheezin (sorry), the windows can be closed and the pollen filtered out of the ventilation air with a low-cost washable filter. If fear of burglars, the noise of a nearby road, or plus/minus 30 deg. C temperatures conspire to keep the windows closed, the ventilator can magically lower CO2 levels and eliminate the memories of last nights fish dinner. Like in so many things, it’s all about control. People who live in airtight, mechanically ventilated houses have it, those who don’t, don’t.

While I’m at it, the main criticism leveled at the “airtight / ventilate right” strategy described above - beyond paying for the ventilator in the first place - is the cost of operating it. While there are several ways to mechanically ventilate a house, we are big fans (sorry again) of “Heat Recovery Ventilators” (HRV’s), machines that bring fresh air in from outside, exhaust stale indoor air, all the while transferring thermal energy from one airstream to the other using a simple heat exchanger. In the winter an HRV takes incoming fresh cold air and pre-heats it with the outgoing stale warm air without mixing the two air-streams. In the summer the outgoing stale air not only cools the incoming fresh air, it also dehumidifies it, further reducing the need for air conditioning. HRV’s typically recover 50-70% of the outgoing thermal energy, which may seem low-ish but far better than cracking open a window and switching on a bathroom fan when it’s minus 20. Many HRV’s now come with EC motors (Electronically Commutated) which draw very little power - usually in the 40-70Watt range (think of a light bulb) in low-speed operation depending on size and make. For those who feel that buildings should be “passively” ventilated, somehow breathing on their own without the aid of expensive energy consuming equipment, don’t bother, it doesn’t work.

Sorry for the tangents, but all of these things are related... You now know that the wall panels we built for the Snye House were clad with insulated sheathing but how much polyiso is enough was the subject of some debate during the design charrette (see earlier blog posting) we held back in March.

Before we convened for the charrette we put the house through two types of computerized heat-loss simulations - two types so that we could compare the results for consistency. Tools like this allow building designers to test the energy implications of a wide range of factors, including insulation levels, window size and placement, roof overhang shading, air leakage values and a host of other things. Using the software we looked at the energy benefit of adding more insulated sheathing relative to its cost, which sounds rational and scientific and does produce some useful insights. One of these is that adding more and more insulation follows the “law of diminishing returns” maxim, where the first bit gives you the greatest benefit and beyond a point it is hard to rationalize the economic sense of adding more. That’s fine, but there are two variables in this equation that can dramatically alter the result: 1 - predictions about the future cost of energy, and 2 - the inclinations of a guy in the energy efficient housing business who wants bragging rights about how well insulated his house is and given that I’m only going to insulate this building once, how much insulation is going to make me feel like I’ve done enough.

It’s worth mentioning at this point that there is a basic truth behind much of the thinking that went into the design of the Snye House. In the world today conserving energy turns out to be cheaper in the long run, more reliable, and less harmful to the environment than buying it or even using bolt-on technologies like wind-power or pholtovotaics to generate it. While such “renewables” are clearly useful in reducing dependence on fossil fuels they make little sense on drafty, poorly insulated buildings. The oft-used illustration of this truth is the leaky bucket analogy... If you have a leaky bucket, you have two ways of keeping it full of water - go get more water or plug the holes in the bucket.

At first I looked at building a 2x4 wall at 16” centres with rockwool batt insulation in the stud cavity and 3” of polyiso on the exterior for a nominal R-value of 36 (U=0.16). Before long I’d graduated to a 2x6 wall at 24” centres with Icynene (www.icynene.com) stud cavity insulation and 4” of exterior polyiso (www.atlasroofing.com) for a nominal R-value of 50 (U=0.11), which is where I stuck. (Note: these thermal values include the radiant barrier effect of the foil-faced polyiso sheathing). My chums at the charrette pointed out that at todays energy prices this uber-wall made little economic sense but were all agreed that with these prices trending wildly upwards there was an argument for buying as much insulation as I could afford.















Footnote: Those in the know about insulation might be wondering why I would use Icynene - a 1/2 lb. density foam - instead of a higher performance 2 lb. foam in the stud cavity. The answer is that 2 lb foam is more expensive and I was bumping up against the limit of what I could reasonably afford. I wanted to use some type of spray foam because it does a more reliable job of filling the stud cavity than site installed batts while simultaneously adding to the air-tightness of the structure. Also, the chemical constituents of Icynene - like those of the polyiso we use - have no ozone depletion potential and contribute no discernible chemical burden to the indoor air, not the case for many 2lb foams.

Before moving on I’d just like to mention one other important feature of the Snye wall panels - the rain-screen. Regardless of what you clad your building with - brick, rendered block, cedar shingles, clapboard siding, cement board with stucco, anything at all - the rain's gonna get through. When it does, you’d better have a way for that water to drain back to the outside before it gets any further into the structure and does some real damage. The accepted best practice in this regard is to treat the exterior finish as a “rain screen” by providing a cavity behind the cladding, flashed in such a way as to lead any wind-driven rain back outside. In our case, with a plan to use horizontal wood siding as an exterior finish, we installed 1x3 vertical wood battens on the surface of the polyiso as a nail base, fastened back through the foam to the studs with 7” screws. The battens create a 3/4” gap between the back of the siding and the surface of the rigid foam, an air-space that becomes pressurized in a driving rain, preventing moisture from jumping the gap. Any water that gets through runs down the back of the siding and out at the bottom. The air space also promotes balanced drying of the siding after a storm. When wood siding is nailed tight to another surface rather than on battens the front surface dries and shrinks more quickly in the sun than the back, causing the material to cup.















The panels were built in our Carp shop in June. As this was my house and not that of a valued Client the June time slot had more to do with a gap in our shop schedule than it did with being ready for the panels on site. In another “low man on the totem pole” decision we used borate-treated framing material, not from any concern about moisture affecting the wood, rather we had some left over from a UK job where they are (overly) worried about moisture affecting wall framing and where treated material is thus a de facto requirement. The borate treating colours the wood and for some reason the batch we had on hand varied from green to lavender. With no UK jobs on the horizon we felt it better to use it up rather than get into a complicated discussion with a Client about why we use multicolored wood.















Before erecting the panels on site we were anxious to sheathe the top of the timber frame with 2x6 Douglas Fir decking and cover it with a waterproof membrane. The DF decking, which acts as structural sheathing and the ceiling finish for the living and dining rooms, was pre-stained on the exposed face with a single coat of white stain to give more visual prominence to the timbers. On top of the decking we installed a layer of Ice and Water Shield (www.grace.com) to protect the decking and timbers from the rain and to serve as a vapour barrier in the final insulated roof assembly.


















Some of the wall panels went up before we’d finished sheathing the timber frame because of a special arrangement we had with our crane operator. Bill Gardiner of Gardiner Tree Removal is one of the most experienced and skillful crane operators around and our preferred choice for any work we do in the area. It also happens that his shop is about fifteen minutes from our site so we worked out a deal where Bill would drop around at the beginning or end of his day for an hour or so to help move us along without charging the four hour minimum that is typical in the crane business. We brought our wall panels to site a bit ahead of schedule to take advantage of this arrangement and managed to get a few of the ground floor panels installed one morning even though we hadn’t finished sheathing the timber frame.







































































































Erecting panels is always an exhilarating process. The building takes shape very quickly, the spaces and views imagined at the design stage emerging into the real world with every panel that is set. With the ground floor exterior walls up in less than a day Jesse and George took the next two days to install and sheathe the pre-cut second floor framing. Another part day of second floor exterior walls and we were suddenly ready for trusses, very exciting for all of us, but especially for the carpenters who had labored for so long in the trenches.

The Timber Frame ...

The first post-and-beam (or Timber Frame) structure I remember seeing was in a ski chalet in Vermont where I was billeted as a teenage ski-racer. It made a big impression. The timbers were beautiful, the workmanship was evident and the quality of the cathedral-like space was awesome. I also remember being attracted by the “honesty” of the structure - important to a kid struggling with the duplicitous world of adults - where even an inexperienced eye could follow the loads as they traveled down from the roof to the foundation.

Timber frames clearly have their place. Looking back, that Vermont frame felt right not just because of its intrinsic beauty and the inspiring spaces it traced, it somehow managed to reflect the character and quality of the place where it was built. It felt like it grew there on those wooded slopes, that it belonged, less obviously imposed by human will.

Over the years my ardor for timber-frame buildings cooled a bit as I came to recognize that all that exposed structure had more to do with beauty than function, where the insulated skin that clad the frame was in fact capable of holding the roof up, but my love of the aesthetic and my appreciation for a well-crafted frame remained.

That we would have a timber frame in this house was an early design decision, which unlike many others I never went back to reconsider. My experience in Vermont had shown that a frame could echo everything I loved about the site - the trees, the river, the change of the seasons, the need for protection from the elements. Along the way Alison quite rightly raised the issue of cost and “is it really necessary”, but I knew that more than any other aspect of the design the frame would define the house so I fumbled through my awkward explanation but stuck to my guns.

Deciding who to get to do the frame was easy. Andy Cobus had built a traditional mortice and tenon timber frame for a project we did in Korea a couple of years back and had done an outstanding job. No CAD software or numerically controlled milling equipment for Andy, just graph paper, sharp chisels and an uncanny ability to visualize complex joints in three dimensions. Andy and his business partner Tim run a small shop with only two or three employees which means that their output is limited, so as with George I began the conversation many months ahead of time.

One of the first decisions to make was what species of wood to use. From a sustainability perspective it made sense to use pine, our watershed being one of the pre-eminent pine growing regions of the world. I struggled with that one because I’m not a big fan of pine, far preferring the colour, grain and more refined appearance of Douglas Fir which only grows on the west coast many thousands of kilometers - and tons of transport carbon - away. I also ended up with some spans that would have been hard to engineer in pine, it being much weaker than Douglas Fir. In the end the aesthetic and engineering concerns trumped the environmental ones, something I’m not proud to admit because it exposes an obvious contradiction to my stated green building objectives.

Now that I’ve brought it up... in case you haven’t noticed there are many other such contradictions in this project, one of the most glaring is that I’m building on a two acre, pristine natural site down the end of a long dirt road that demands a fairly lengthy car ride to pick up milk. It could be argued that if I were truly committed I would be building on an urban in-fill site with existing infrastructure, within a stone’s throw of a bus stop. Add to that, I’m using some patently non-renewable and energy intensive materials - concrete and foam insulation for example. Some of these choices are easier to rationalize than others, such as the foam insulation that will conserve many times more energy in the 100+ year life of the house than it took to manufacture and transport it to my site. Are there less energy and resource intensive insulations I could have used to achieve the same result? There are, but all of them give rise to other costs and complications that in my decision-making matrix ultimately outweighed their environmental benefits. Building on a remote natural site is harder to justify, but given that I was bound and determined to do so it made sense to build the most energy conserving house I could possibly afford. Moving on...

The original schedule had Andy erecting the timber frame in early July so he wanted the timbers on hand in April to minimize his stress. With all the work we’ve done in Japan over the years (lets not talk about the environmental implications of shipping houses to Japan...) I’ve developed a network of suppliers in Vancouver including a source for timbers who was prepared to personally select the ones for my house, so when the truck finally arrived in Andy’s yard I was keen to see what he’d picked. Even Andy was impressed with what showed up, and with that concern out of the way we got down to the business of confirming dimensions and fine-tuning details of the frame.



















I visited Andy and Tim’s shop a couple of times in the intervening weeks (months actually) to see how things were progressing. It was a bit like those visits to the doctor, staring at the ultrasound screen to see how the baby was coming along. We even pinned photos of the developing frame to the fridge just like we did before the kids were born (I doubt that my wife will appreciate this comparison) so by the time the slab was finally poured and we were ready for the frame to show up excitement (at least mine) was at a fevered pitch.
















































































Back to the slab for a minute. When we last left the site all of the sub-slab prep was done - plumbing drains in, electrical conduit, poly membrane, 4” of foam, radiant tubing, the whole bit. I had a promise from Adbro - the guys who were pouring the slab - that they would be ready to show up on a Wednesday. On Tuesday the weather forecast was for rain the following day so we put the pour off till Thursday. Thursday morning I called Adbro to learn that they had nobody available to pour the slab that day - a real problem because Andy was set to bring the timbers to site on Friday, set them on the slab and begin to erect Saturday (you got all that?). When I heard the bad news from Adbro Thursday morning I decided to become the King of England, demanding that they put off whatever else they were planning to do that day and get my damn slab poured. This technique works surprising well in the construction industry - mind you, like the boy who cried wolf you don’t want to make a habit of it - and lo and behold the lads showed up.

The plan all along was for Adbro to use a pump to place the concrete. Of course with their sudden schedule change there was no pump available so they arrived with three guys and a wheel barrow. The guys looked at all the radiant tubing they would have to push their wheel barrow over and decided it would be best to put down some OSB sheathing to avoid crushing the pipe - a thoughtful gesture. We had a pile of scrap OSB nearby so they began to toss it up onto the floor at which point George yelled out to be careful because some of the pieces had nails in them. With the words barely out of his mouth, a spikey sheet of OSB landed on the floor and punctured one of the radiant lines, producing a heart-stopping hissing sound as the pressurized tubing gave up its charge of air. As luck would have it our plumber was working on a site about twenty minutes away so he quickly dropped what he was doing, raced over and replaced the now quiet line. All tubes were then re-pressurized and the business of pouring the slab resumed - whew! There was no other drama - other than the concrete truck driver spearing his shovel into the wet concrete, narrowly missing another radiant line - no drama that is until it was time to do the final troweling of the slab.











































The slab crew disappeared after the concrete was placed and leveled, the crew boss promising to return in two hours, “once the concrete has set”, to do the final finishing. Three and a half hours later it was now dark, the temperature dropping steadily, and still no finisher. All I could think of was that he’s been in an accident or he stopped at the bar and I’m going to end up with the slab from hell.

Around 8:00 p.m., after making numerous unanswered phone calls, with the temperature now unseasonably close to zero deg. C, feeling faint from stress and a lack of food, I raced home for a bite to eat. By the time I returned 45 minutes later, hallelujah, the guy was there busy troweling the slab as his shivering girlfriend (can you believe) held one of those articulated desk lamps for him to see by - quite the scene. I blessed him for returning, surprising him with the earnestness of my thanks, then raced back into Arnprior to get to Canadian Tire before they closed so I could purchase some proper floodlights. The pimply kid at Canadian Tire, stunned by the speed of the sale, watched in bewilderment as I grabbed the lights, my change, spun on my heel and raced back out into the dark from whence I’d come, the sound of screeching tires giving him one final jolt. Back on site, with the slab now lit up like a football stadium, my blood pressure slowly returned to normal. After some chit-chat with the still shivering girlfriend about the quality of life with her nocturnal slab-troweling boyfriend I slunk back home for a restless night’s sleep, resigned to deal with whatever slab the morning light would reveal.

As things turned out the slab was pretty good - not perfect - but better than I expected. Andy, Tim and the lads arrived as promised around 11:00 a.m. and began spreading out the heavy timbers on the newly minted surface. We had originally planned to have Adbro back out to cut control joints but I put them off to the following week so as not to interfere with the erection of the frame. It was a perfect sunny fall day, ideal for sorting timbers, doing the layout and the final cutting of post heights. As I watched them work, the weeks of drudgery - the foundation, well & septic, and other seemingly two dimensional aspects of the job - gave way to the promise of seeing the three dimensional form of the building finally revealed.







































































During the brief spell between the completion of the sub-slab work and the arrival of the timbers on site George and Jesse had managed to frame the second floor of the garage. This provided the ideal vantage point to watch the timber raising, so it was with great anticipation that we climbed up to that floor, lawn chairs and coffee mugs in hand to witness the arrival of the crane and start of the festivities that sunny Saturday morning.





























What a day! With a steady stream of observers joining us on our perch Andy, Tim, George, Jesse and the rest of the crew went about the business of fitting, pegging and hoisting the various members into place. I’d purchased a digital still camera with a time-lapse feature that took pictures every three minutes and set it up in an attempt to capture the process. In the morning’s excitement I failed to set it up properly and realized to my deep disappointment around lunch time that the damn thing wasn’t working. I quickly re-read that section of the manual and managed to capture the second half of the day.









































































By eight o’clock that evening the lads were in the garage drinking beer and sharing the satisfaction that only comes from a hard day’s work where everything went well. The fruits of that particular days labour came in the form of a beautiful timber structure - a magnificent testament to skill and craftsmanship. As the frame went up there were many references made to a traditional barn raising and while I’ve never had the pleasure, I doubt there could be any greater sense of camaraderie and good will than we all shared that day.

When carpenters are masons...

I knew from the early going that the ground floor of the house would have to be elevated in order to achieve the necessary slope to the septic system. The trouble was that the rock prevented digging down and the elevated floor wouldn’t be high enough to create a basement or even a useful crawl space without creating grading problems around the house. It was the realization that there would be no below-grade level that led me to the idea of pouring an elevated concrete slab - great for radiant heat and solar storage... but how to support it?

The options were really to pour a concrete stem wall or use some form of block that would support the slab edges while containing the stone backfill necessary to support the slab itself. Ultimately I decided to use block instead of pouring concrete because I wanted more precision than I was likely to get from a concrete foundation contractor. In my line of work - panelized buildings - close foundation tolerances are key to ensuring a fast and pain-free panel setting process. Ideally I wanted to use something the carpenters could install, that way I would be assured of precise work and I wouldn’t have to find, schedule and pay for a mason. For a while I considered using a polystyrene ICF (Insulated Concrete Formwork) but the less than ideal environmental profile of the product, along with the need to finish the exterior surface left me lukewarm.

Instead I chose “Durisol” (www.durisol.com), a concrete block made of cement and waste wood fibre. I’d used the product for a foundation a few years earlier and had been very pleased with its ease of installation and appearance. Durisol blocks are meant to be laid up dry - no mortar joints - then reinforced with re-bar and poured full of concrete, much like a styrofoam ICF. The blocks can be cut with a circular saw, and are generally friendly to all types of woodworking tools and fasteners - and thus to carpenters. They come with semi-dense rockwool inserts to increase their thermal resistance and the exterior offers an attractive textured surface that the manufacturer assures me won’t suffer from exposure to the elements.

































In keeping with my desire to perfect the layout I called Tim Rowe, my favorite surveyor, to come and lay out the building corners on the footing. If the footing had been level - i.e. the top surface all at the same elevation - and the footprint less complicated (fewer corners) - I would have been comfortable having George and Jesse lay it out because it’s easy to confirm square by checking diagonal dimensions on a flat surface. But this footing had several 12” steps in it (12” is the height of a Durisol block) as it marched up and down the site, so the potential for error was higher. Tim defined his starting point by driving a nail through a piece of orange surveying tape at the corner of the garage footing closest to the lot line, and set up his “Total Station” (a computerized surveying instrument) on that point. An hour later all the corners of the house were bang-on and we were ready to start laying block.

































While part of the plan was to avoid the hassle of finding a mason to do the foundation, George thought it a good idea to set the first course in mortar to iron out any discrepancies in the top of the footing. Luckily my first call produced results. Nick Deritis, a mason I’d worked with twenty years earlier on the very first house we built in Ottawa, was available and keen to help. Nick, now retired and without a truck, needed some help getting his mixer and other tools to the site but once we got over that he got down to business. Being of the old school, Nick was pretty sceptical about our wood-fibre concrete blocks but ultimately the light weight and ease of cutting won him over. A solid twelve hour day of mixing mortar and laying block finished off the first course for both the house and garage. The stage was now set for Jesse and George to install the horizontal and vertical re-bar and lay up the remaining courses.

























































At the lowest corner of the building the height of the foundation wall would be 6’ - or six courses of block. This scheme of backfilling behind the block with stone worried me because of the potential for shifting the block wall during the process of compacting the stone. I actually hired an engineer to think about this, and their recommendation was to do what I’d been planning all along, which was to simply brace the tallest and longest lengths of wall prior to backfilling - advice that scarcely warranted the five hundred bucks they charged me... They did also recommend tying the top of the Durisol wall into the edge of the concrete slab with pieces of 90 deg. angled rebar to permanently connect wall to slab and eliminate the possibility of the foundation wall ever shifting - a good idea that made me feel slightly better about their invoice.

The folks at Durisol also suggested that a thicker wall would be helpful in resisting backfill pressure so we used 12” block for all but the top course, where we switched to 10”. The narrower top course allowed us to move the slab edge, and the 1-12” thick strip of polystyrene that serves as a thermal break between foundation wall and slab, closer to the interior surface of the wood-frame wall where the joint between block, polystyrene and slab edge will be hidden by baseboard and won’t interfere with the final floor finish. Actually the 10” block wasn’t even quite narrow enough to achieve the desired detail so I had George and Jesse cut back the top inside wall of this top course a couple of inches to get the slab edge where it needed to be.