Start of Construction: Frontenac’s Low-Lying Structure

It’s time to talk about the structural ins and outs of Frontenac House.

On a small and rocky lakeside property lined by cedars and cliffs, this project was a really challenging one to build. The property, though beautiful, is incredibly irregular, with cliffs, dips, tree roots, and a large rock outcropping making up most of the buildable land.

To put it simply, rock outcroppings do not lend themselves kindly to the construction of a building.

Building on rock is not always a problem — bedrock acts as a natural building foundation, and a building built on rock will never sink. But when rock is irregular or uneven, the only building options are building the home on stilts, raising the main floor up over the undulating base, filling the spaces between the rock with engineered fill or blasting the irregularities away and building straight on the flattened rock surface.

After very careful consideration, we decided a hybrid approach of blasting some of the highest points of the formation and filling remaining dips and trenches with a compacted engineered fill base. We put a lot of thought into this decision. Blasting is time consuming, expensive, and in this case, puts a permanent scar on a 250 million year old rock formation. However, a small amount of blasting would not only allow us to maintain a smaller envelope which a more energy efficiency building, but it would also allow us to keep the house snug against the ground, which better hides is from view while keeping it completely accessible, so our clients can “age in place” gracefully. It was a tough decision to make, but we were at peace in the end.

Another structural challenge was ensuring there was no step between the garage and the house, an accessibility must. An at grade garage is of course necessary, for cars to be able to drive straight in from the driveway. But building an entire home that low is much more complicated — one has to take into account the depth of the floor joists and the height of the siding so close to the ground. Thankfully, Frontenac’s property slopes downwards, which made building so low just a little easier. The garage is located above the bedrock, and – save for the small area of rock that jutted upwards which needed our attention – the rest of the bedrock falls below the home’s footprint, which made building low possible.

Once our property was level, we laid down a layer of gravel for drainage.

Then, we cast footings which hugged the undulating rock, and placed short ICF (Insulated Concrete Forms) foundation walls onto these footings.  It was strange not to have the typical 48” of coverage over the structure’s footings, but knowing that the house was sitting on solid bedrock quelled our fears.

We erected our wood-framed floor on top of our ICF foundation walls, a change from the conventional slab on grade in most houses without basements. We packed insulation under our floor— we had to be sure it was well-insulated as any temperatures from the bedrock (which is slow to heat up) could seep into the house without proper insulation. Plus, with no basement to allow access to the ground floor’s pipework and insulation from below, all pipes and drains had to be meticulously planned and laid into the gravel base before the floor went in and the walls were erected.

After the floor was framed, we erected our 2×6 wood stud walls with ZIP System wall sheathing (more on that in our next post). And finally came our wood-framed “flat” roof, yet another huge challenge in this complex build.

I say “flat” because no roofs are truly flat.

A completely flat roof would collect far too much snow and rain, and too much additional mass (beyond the roof’s existing weight) would eventually cause the roof to cave in on itself. All roofs need at least a minute slope, to defend against the elements.

Even with a small slope, a “flat” roof still needs to be able to withstand much more weight than the average peaked roof. Snow, leaves, and rain pile up much more than they do on steep roofs, where elements can easily tumble off. But to many, the benefits of a low-lying roof are worth the construction difficulties. Our clients love the modern and fashionable aesthetic of a flat roof, and wanted their home to lie low and blend into the landscape.

We built the flat roof strong enough to handle more than double the normal weight requirements. The roof needed to be able to withstand the weight of solar panels plus the worst possible outcome of snow/precipitation collecting both under and on top of the panels.

Our builders were quick out of the gate on erecting this house, which makes it an exciting project to follow. Next time, I’ll fill you in on the insulation and our air-tight envelope – a serious endeavour!

Here’s a set of time-lapse photos, of site prep and construction. It’s satisfying to see it go up so fast, isn’t it?

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