Rim joist spray foam insulation in Cochrane has an extra dimension that flat-ground towns do not, and it follows directly from how this town is built. On a hillside, houses step, and every step adds a band.
A walkout has more than one band
A conventional house has the band where the main floor structure lands on the foundation. A walkout has that, plus a second where the floor structure lands partway along a wall that is above grade on one side and below on the other. On a bi-level or a split stepping down a slope there may be a third. Each of those is open framing behind the finish, each is typically filled with a friction-fit batt that seals nothing, and together they add up to a considerable length of unsealed perimeter.
The extra band is the exposed one
The band on a conventional foundation sits at the top of a wall surrounded by ground. The extra band on a walkout sits in a wall with outside air on the other side of it, which means it is exposed on far more of its surface and is not benefiting from the stable ground temperature that makes a normal rim joist tolerable. It sits directly under living space, and on most Cochrane walkouts it is the coldest line in the house.
Wind makes an unsealed band worse than the numbers suggest
In still air a gap loses heat by convection at a modest rate. Under the sustained pressure Cochrane sees off the foothills, air is driven through it continuously, so the same detail performs far worse here than the same house would somewhere sheltered. That is why cold floors along an outside wall are a more common complaint in this town than the age of the housing would predict.
Reach it while the lower level is open
Where a walkout's lower level is unfinished, all of those bands are accessible now and the work is quick and clean. Once the level is developed, reaching the same framing means opening and closing finished walls at a cost that routinely exceeds the insulation itself. On a Cochrane house about to have its lower level completed, this is the cheapest hour available and the material cost is identical either way.
Rim Joist Spray Foam Insulation Cochrane: Common Questions
How many of these bands does a walkout have? At least two and sometimes three, depending on how the house steps down the slope. Each is open framing behind the finish.
Which one matters most? The one in the above-grade section of wall. It is exposed on far more of its surface and gets no help from stable ground temperature.
Should we do it before finishing the lower level? Considerably cheaper. Once finished walls stand in front of the framing, reaching it costs more than the insulation does.
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