Portland gets around 43 inches of rain a year, most of it concentrated in a long gray window from October through May. That calendar fact is the single biggest reason exterior paint fails prematurely here — not the paint brand, not the application, but moisture in the substrate that was there before the first brush stroke.
Wood siding absorbs and releases moisture constantly. After a wet spell, the outer few millimeters of a board can be saturated while the surface looks dry to the eye. Apply paint over that and you've sealed water in. It warms up, expands, and presses outward. You'll see blistering and peeling within a season or two, usually on north-facing walls first, and the failure will look like a paint problem when it's actually a scheduling problem.
What the moisture meter actually tells you
A pin-type or pinless moisture meter reads the water content of wood as a percentage. For latex paint on wood siding, the standard threshold is 15% — above that and the paint can't bond correctly. In practice, we check moisture content on every wall before any exterior job, and we look specifically at north and west exposures, under eaves and gutters, and around windows where caulk has failed and water has been infiltrating.
Most of the time, a week or two of dry weather following a wet stretch will bring a wall down from 18–22% to a workable 12–13%. The solution is not magic; it is patience and a schedule built around the forecast. We book exterior work in the window between showers, check the ten-day forecast before we send a crew, and leave if readings come back above threshold.
The honest Portland painting season
The reliable window is mid-May through late September — three to four months where you can consistently find stretches of low humidity, temperatures between 50°F and 90°F, and no sustained rain in the immediate forecast. We can work opportunistically in March and April on good stretches, and occasionally in October, but the risk of a moisture-check failure is much higher at the margins.
If a painting contractor quotes your exterior in March and makes no mention of moisture readings or weather windows, that is a red flag. It either means they're painting regardless of conditions, or they've never thought about it — and both outcomes end the same way: paint peeling off your house within a couple of years and a contractor who is nowhere to be found.
Prep is 70% of the job, and moisture is the single most important variable in that prep. A homeowner who understands this will always get better results, even if it means waiting an extra few weeks to start.