Attic spray foam insulation in St. Albert has a local complication most Alberta towns do not have. The trees here are old and very large, a great many roofs sit in their shade for much of the day, and a roof that does not get sun behaves differently from one that does.
A roof that spends the day in shade
Sun does useful work on a roof. It dries the surface after snow or rain, it lifts the deck temperature enough to move moisture along, and on a clear winter day it takes the edge off what is sitting up there. Under a mature canopy a north or east slope may get none of that for months. Snow stays longer, the deck stays colder, and anything that gets damp stays damp, which is why the shaded slope of a St. Albert roof is frequently in visibly worse condition than the sunny side of the same building.
Frost that accumulates because nothing ever clears it
Vapour pushed up through an unsealed ceiling reaches a deck that is cold and stays cold, freezes onto it, and simply builds through the winter. There is no chinook here to interrupt anything and, on a shaded roof, not even a bright afternoon to help. Owners find it in March when it finally lets go and report it as a roof leak on a day with no rain. That is months of accumulation releasing at once.
Leaves, needles and what they do to an eave
The other canopy problem is mechanical. Mature trees drop a great deal onto a roof, and it collects in gutters and at the eave where the soffit intake is. Blocked intake means the attic cannot vent the way it is supposed to, so sealing the ceiling plane without checking that path leaves the attic worse than it was. On these houses the eave gets looked at as part of the job rather than assumed, because it is frequently the thing that has been quietly failing for years.
Sealing first, depth second, and the order does not move
Insulation slows heat moving through a surface. Sealing stops air carrying heat and moisture through gaps. Over a heating season running the better part of nine months the air path runs continuously, so it accounts for far more than a depth number suggests, and adding depth on top of an unsealed ceiling buries the problem instead of fixing it. That order is not a preference and it does not change because a previous contractor topped the attic up.
Attic Spray Foam Insulation St. Albert: Common Questions
Why did water come through the ceiling in March with no rain? Frost that built on the underside of the deck all winter, releasing when it finally warmed.
Why is one side of our roof always worse? Usually the shaded side. Under a mature canopy it gets no sun to dry it and stays cold and damp far longer.
Ours was topped up years ago. Is that enough? Topping up adds depth without closing any holes. If the sealing was never done, it is still to do.
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