The short answer
In Ottawa, exterior painting usually runs from late spring to early fall. The exact window changes from year to year with the weather, and it depends on the paint, because every exterior paint lists its own minimum temperature on the can.
Temperature, day and night
Paint doesn't dry and cure properly when it's too cold. For many exterior paints the minimum is about 10°C. Some newer paints are made for cooler weather and can go on at about 2°C. The minimum applies to the surface as well as the air, and it has to hold while the paint dries, which takes longer in cool weather. That's why a cold night can spoil paint that went on during a warm afternoon. In spring, and again in late September and October, Ottawa often has mild days and cold nights.
Rain, dew and humidity
Surfaces have to be dry before painting, and fresh paint needs time to dry before rain hits it. Morning dew on siding has to dry off first, and dew that forms after sunset can settle into paint that hasn't set. Ottawa's humid summer days slow drying, so a good painter watches the forecast and the time of day, not just the date.
Sun and heat
Strong, hot sun can make paint dry too fast and leave lap marks, where one stroke overlaps another that has already dried. Painters often work their way around the house with the shade for this reason.
Why booking early matters
Most people want their house painted in the same few months. If you want the work done in late spring or early summer, start getting estimates in winter or early spring.
What you can do in the off season
Interior painting works all year in a heated house. The off season is also a good time for a consultation and an estimate, so your exterior job is booked before the rush.
Sources: Sherwin-Williams: exterior painting temperature FAQ
Written by Carleton Prime Painting, Ottawa. Last updated October 23, 2026.