Lethbridge is one of the windiest places in the country, and wind does something to a roof assembly that most insulation conversations never mention. Ceiling spray foam insulation in Lethbridge is very often a response to wind washing rather than to a lack of R-value on paper.
What wind washing actually is
Air entering at the soffit does not politely travel up a vent channel and leave at the ridge. In a strong, sustained wind it is pushed into and through anything porous in its path. Fibre insulation is porous. The wind moves through the outer part of the batt, strips heat out of it, and the assembly performs far below its rated number while the label on the packaging stays exactly the same. It is one of the main reasons a ceiling that measures correctly still feels cold on a windy day.
Why a cathedral ceiling suffers most
In a flat attic the insulation is a deep loose blanket and the wind mostly disturbs its edges. In a vaulted or cathedral assembly the insulation fills a narrow channel with a vent immediately against it and the air is moving along the whole length of the slope. There is no depth for the outer layer to be sacrificial. The wind is in contact with the working part of the insulation for the entire run.
Foam does not care about airflow
A closed cell layer sprayed against the underside of the deck is not porous, so moving air passes over it rather than through it. Its performance on a still day and its performance in a forty knot wind are the same number. In this city that difference is worth more than an extra inch of a material the wind can get into.
Gable ends and the prairie exposure
Houses and shops on open ground around Lethbridge take wind on the gable as well as the soffit. The junction where the ceiling plane meets the gable wall is a common leak, and it is a place a continuous sprayed layer can seal in a way that cut pieces of anything cannot.
Ceiling Spray Foam Insulation Lethbridge: Common Questions
Why does my ceiling feel cold only when it is windy? That is wind washing. Air is moving through the fibre insulation and carrying heat out of it, so the assembly performs below its rated value exactly when the weather is worst.
Does a cathedral ceiling suffer more than an attic? Yes. The insulation sits in a narrow channel with the vent right against it and the air moves along the full slope, so there is no depth to spare.
Does foam solve it? It removes the mechanism. A closed cell layer is not air-permeable, so wind passes over it instead of through it and the number does not change with the weather.
Work out the depth with the R-value calculator, then get a free Lethbridge quote. More on Ceiling Spray Foam Insulation Alberta.