Foundation Construction Details

Slab and foundation/basement walls with insulation and frost skirt

With the slab poured and the ICF well under way, I thought I would write a quick post with visuals explaining the construction methods and materials being used. I've created some images to go along with all the photos we've been posting to hopefully add some clarity to what you've been looking at so far!

The images above and below show the concrete foundation and foam insulation as it will be once completed. The image below has labels calling out the various layers. 

Components of the foundation

The biggest difference between our foundation and a typical residential foundation is the lack of concrete footings.  A typical foundation would pour strip concrete footings right onto undisturbed soil, then pour the concrete walls, and finally pour the slab inside the walls. In our home, the slab is poured before the walls and will actually support them, which is why it is so much thicker (8" instead of the standard 4") and has so much steel rebar in it. It is also completely contained within the foam insulation tray, eliminating any thermal bridging through the concrete to the ground. The end result of this is a concrete floor that will retain the heat it absorbs from the house above, rather than simply dumping it through into the ground. 

The walls on top of the slab are made up of three layers. First is the ICF (insulated concrete forms) from Nudura. These are like Lego for grow ups. They snap together to form the walls and are held apart by integrated webbing. The cavity is 6" wide and on Friday we will be pouring it full of concrete. Watch for photos this week showing the alignment system that will ensure the walls are straight and true as the concrete is poured. 

Once the concrete is poured and the walls straightened, we will be adding two more layers of foam from Styrorail to the exterior to build up the insulation value of the walls. The first layer has horizontal wood strapping embedded, and the second layer will cover this wood and effectively embed it in the middle of the wall. The foam will be glued in place using PL 300 glue, which is specifically formulated not to deteriorate the foam over time. The horizontal wood strapping gives us something to tie back into when we go to install our siding above grade. 

The slab poured and the first layer of ICF in place. 

Now let's talk about the big white elephant in the room: why so much foam? The amount of insulation is one of the trade offs required to achieve passive house performance on such a challenging site. Because of the limitations of orientation and south-facing window areas, we have to compensate by beefing up the thermal envelope more aggressively than you might find in other passive house projects. The final thickness was determined after several rounds of refinement of the energy model (using PHPP for those keeping track). The really nice thing about this configuration is that all of the concrete is on the warm side of the thermal envelope, where it will hold its warmth, and is protected from expansion and contraction. This alignment becomes especially important when we get to the design of the framed walls above...more on that soon. 

ICF at the end of 1 day's work.  

ICF at the end of 1 day's work.  

Soil bearing capacity test


I was expecting something more high-tech — maybe a glass box that would be filled with soil and mechanically compressed and measured for PSI. Nope. The engineer went into the hole with a hammer, scraped it in a few places, touched some dirt and said ‘yep, good to go!’. We have a report stating our dirt is comprised of glacial till, silty gravel with clay, cobbles at a bearing capacity of 100 kPa. I guess he just knows. Who knew?

My dad


So I came across my dad's thesis in our storage locker last week. "Towards an architectural co-existence with the sun". I'm guessing this was around 1977 (?). He was always ahead of his time. Writing about passive principles and solar voltaics. 

He was a strong voice. One could argue, the father of green building in Canada, as we know it today. One of his first employees, Oliver, worked on the Saskatchewan House, renown in Passive House circles. In the early 90s, he was responsible for Ottawa's Minto-built Innova House, one of the country's first R-2000 houses and the first that contributed electricity back to the grid with its solar panels. He also brought the Energy Star program up to Canada and wrote the first iteration of the program. These programs, and their ease of adoption for developers have had large-scale impact on the quality and energy efficiency of the housing industry overall. One off homes, like ours, are great, but if we want real impact, it's made through existing channels and large developers, like Minto

When you're a kid, your parents are just your parents. What, they had lives before you came around? Only later in life were we getting glimpses at who my dad was before we came along and what he actually did 9 to 5. I'm so proud. Sure wish he was around to see us through our build. Miss you dad. 


Trees and doors (and a whole lot more)

The jungle

The jungle

We have yet to break ground and shrubbery is quickly taking over. Our windows and doors are already on the shipping container, headed over from Euro-ville. When we ordered them, we thought we’d be waiting for them to arrive and not the other way around. Cut us a break would ya??!! It’s our first time building a house…

My grandmother would always tell us kids, as we impatiently asked about dinner, “good things come to those who wait”. Argh. It killed me then and it’s killing me now. I keep channelling Granny as things keep getting delayed. It will be worth it. 

I’m beginning to realize that there is a direct correlation between my blog writing and my emotional and mental state. When I’m excited, and progress is being made, there’s an influx of posts. When the opposite is true, things remain somewhat stagnant. It is my full intent to write as frequently as possible, reporting on all house happenings, and not just when I ‘feel’ like it. There’s just not a whole lot to report yet.

Last week, Mark prepped more drawings (electrical and plumbing) and distributed them to multiple trades for estimates. He accidentally wrote 145 Bayswater on the plans (instead of 105) and has caused some confusion. Our neighbours at 145 have just started building a house on an adjacent empty lot as well. Imagine the surprise of the excavator trade showing up at 145 to see there was already a hole in the ground. Our neighbour texted me to say someone was there scratching his head about the drawings the architect sent him. Du-oh! 

I have been consulting with several tree service teams so we can get the lot cleared and ready to build on. It’s always more complicated than at first thought. There are some trees at the front (closer to the sidewalk) that we have to get permission from the city to cut. And there are some growing over the electrical lines on the alley that we have to get Ottawa Hydro to cut. Then we bring the tree team in. 

Our wonderful orange house neighbours have gone ahead and started some of the clear cutting for us. The large apple tree is down! They want to burn some of the wood in their fireplace. I have requested that they leave some of the larger diameter portions as I would like to mill it and turn it in to something for the house. What that something is, remains to be seen. A powder room counter top? A stair landing in the dining room? TBD. It’s beautiful old-growth apple tree and was in the centre of our lot for 100+ years. It’s a part of the land and needs to be a part of the house.

El stump'o

El stump'o

Good news on the silver maple front: it’s healthy! There is a bit of a concern that we’ll do some damage to the root system when we excavate. The house is far enough back, though, that any damage will be kept to a minimum (we hope!). We’ll probably just do some deep root fertilization to help it get through the year, and look at cosmetic trimming in the future. The canopy is good as-is. No need to unnecessarily add stress to the tree at this stage.

What else? We are meeting someone from Ottawa Hydro at the lot tomorrow morning to discuss how we will connect to the main line. And we are making some big decisions on the backend that we hope to share soon enough. Oh, and did I mention we ordered blue doors? Reflex blue. The bluest of the blues. Couldn’t expect us to go entirely neutral with neighbours as colourful as ours, could you?

That's blue baby! 

That's blue baby! 

Pre-fab no more

We’ve thrown the towel in with our pre-fab builder. The red flags have been flying for a while now. We’ve finally decided that we would feel more comfortable building the good old fashioned way — with site framing. 

Despite this setback, we're feeling much more comfortable with where the build is headed. With tried and tested techniques and builders. We’ve got several enthusiastic and experienced builders anxious to join our team. Mark has had to redesign our wall panels so that they can now be built on site (rather than the factory), using updated modern framing methods. His new wall system is pretty exciting. One in which he might actually like even more than before! He will write a post about it, because it’s worth writing about. Something new that can open up the doors for blah blah blah… (I say blah, but it’s very fascinating. Blah is because I’m not sure how to explain it.)

Now the ball is back in our court. We’ve got structural engineer looking at the new wall system. He should be giving us his feedback and stamp this week so we can finally get the city all of the drawings it needs to issue our permit. Quelle relief that will be.

This is what comfort looks like

Mark has been doing ‘thermal bridge calculations’ on our house. With Passivhaus, the goal is to make the building as air-tight and insulated as possible. Weaknesses often lie in the details —where differing materials connect or gaps occur. Obviously we don’t want any weaknesses. We want a fortress of thermal resistance, which is exactly what Mark’s models are showing.

The image above is a thermal bridge calculation on where our walls meet the slab. By all accounts, it looks excellent. Uniform heat distribution throughout. The inside sits at a comfortable 20•C and the outside at 0•C. If we had any gaps or weaknesses you’d see the warmer colours leaching their way out to the exterior. Instead, we have magical, rainbow coloured walls :)

Going off-grid in the city

Elon Musk announcing the Tesla Home Battery. Image courtesy of GeekyGadgets.

Elon Musk announcing the Tesla Home Battery. Image courtesy of GeekyGadgets.

There are three utilities that conventional urban homes take advantage of: electricity, gas and water/sewage. Going completely off-grid would imply ditching all three. But primarily, when the term “off-grid” is thrown around, it addresses the electrical grid.


It’s incredibly frustrating to open up a hydro (electricity) bill. Half the cost is for delivery and fees alone. We already pay some seriously high rates for electricity in Ontario, which are only set to skyrocket in the near-future by as much as 40%. So much of our energy is nuclear, supplied by ageing power stations and is delivered via grids and infrastructure established half a century ago. There’s no shortage of uncertainty. Sure would be nice to go completely off-grid — to smugly sigh and sit back as the politicians and utility companies mess about. 

Alas. We will be plugging in to the grid. For the following reasons:

  1. Capital costs. The grid is right at our door step and so the costs to connect are fairly minimal compared what they would be if we were to set ourselves up off-grid. If we were in the country, going off-grid would be a no-brainer, since the cost to connect would be significantly higher.
  2. Space. Even though our energy requirements will be 80-90% less than an average home, we would still require a decent-sized array of solar panels to power it. This can be tricky on a small, urban site.
  3. Storage. Solar panels only produce energy when there’s sun. But we often demand energy when there is no sun. The supply does not always keep up with the demand, and visa versa. So there has to be a storage solution. From what I understand, the storage process is inefficient— lots of energy gets lost in the process. 

Planning for the future.

There is hope that we will be able to go off-grid (or at least become partially self-sustainable) in the near future. Tesla is set to announce their home battery technology at the end of the month. We are anxiously awaiting the details. According to

“The technology promises to store things like solar energy or potentially a mix of that and cheap electricity during off-peak hours, helping keeping state power grids balanced and trim bills by 20 to 30 percent for some customers.”

That would solve our storage issues. The space for our solar panels has been ear-marked for the roof of the garage that Mark has designed in to the master plan. The capital costs would definitely be the largest obstacle to overcome. Government incentive programs would go a long way here. 

Mark has been coveting a Tesla car since its debut. And now the Tesla house.

What about those other utilities?

Gas. We will be fossil-fuel independent. Hooray! We won’t be bringing a gas line in to our house. We won’t need gas for heat or hot water. For water, we are going with an efficient electric heat-pump hot water tank. 

Water and sewage. It just makes sense to connect to water and sewage in the city — to guarantee clean drinking water and treatment of waste water. I don’t think that the building code, nor the city, would even permit otherwise. What doesn’t make sense is that we flush our toilets and water our lawns with clean drinking water. Our house will be grey-water-ready. We don’t have the capital to get it going yet, but we don’t want to preclude it. What this means is that one day, we will be able to flush our toilets with used bath water instead of clean drinking water.

In short, we won't be going off-grid. We'll be 1/3, with a lofty potential for 2 out of 3. We’ll take it. And do everything we can to future-proof our home against rising energy prices.