Painting a House in the Pacific Northwest: Moisture, Shade and the 15% Rule
One of the biggest challenges with exterior painting in the Pacific Northwest isn't the rain itself. It's moisture that sticks around long after the rain has stopped.
We've been painting homes on the Eastside since 2005, and this is something we deal with constantly. A house in full sun can be ready to paint while another house a few blocks away, surrounded by trees, may still have damp siding.
That's why we don't decide whether a house is ready for paint based only on the weather forecast or whether the siding feels dry. We test the wood.
Our rule is simple: If the wood is above 15% moisture content, we don't paint it. We wait.
Why Shade Makes Such a Difference
Anyone who lives in Redmond, Woodinville, Kirkland, Bellevue or Sammamish knows how different conditions can be from one property to the next.
Some homes get direct sunlight for most of the day. Others sit under large firs, cedars and maples and may receive very little direct sun, especially on the north side of the house.
Those shaded areas dry slowly. Gutters, trim joints, cedar siding and the lower sections of a house can hold moisture even when we have had several days without rain.
This is one reason we don't use a fixed rule such as "wait 24 hours after pressure washing." Sometimes that's enough for certain surfaces and conditions. Sometimes it isn't even close.
How Long Should a House Dry After Washing?
Depending on the house and the weather, we may allow anywhere from about 5 to 20 days after washing before certain wood surfaces are ready for primer or paint.
That may sound excessive, but we're not interested in getting paint onto a house as quickly as possible. We're interested in having it stay there.
HardiePlank and other fiber-cement siding generally dry much differently than wood. Cedar can absorb considerably more moisture and may take much longer, particularly when it is shaded.
Rather than guessing, we use a digital moisture meter when there is any question.
The Elegant Painting® 15% Moisture Rule
Wood can look dry and feel dry while still containing more moisture than we want underneath a new coating.
For that reason, Elegant Painting® follows what we call our 15% rule. Before coating wood, we want our moisture meter readings below 15%.
This is especially important after pressure washing and on homes surrounded by heavy vegetation or tree cover.
Painting damp wood creates an unnecessary risk. Moisture inside the siding eventually needs somewhere to go. As temperatures change and the house heats up, that moisture can move through the wood and put stress on a new coating. Over time, excessive moisture can contribute to blistering, peeling and other adhesion problems.
Waiting a few more days is a lot easier than repairing a failing paint job a few years later.
Rain Isn't the Only Thing We Watch
A weather app showing no rain doesn't automatically mean it's a good painting day.
Temperature, humidity, shade, overnight condensation and the temperature of the actual surface being painted all matter.
This becomes particularly important late in the exterior season. A beautiful afternoon can be followed by a cool, damp evening. Surfaces that were dry earlier in the day can develop condensation as temperatures fall.
We pay attention to the forecast, but we also pay attention to what's happening at the actual house.
What We Use on Bare Exterior Wood
When preparation exposes bare wood, our preferred primer is Sherwin-Williams Slow-Dry Oil-Based Wood Primer.
We've used slow-dry oil primer on Eastside homes for years. It penetrates bare wood well and is particularly useful on cedar and other wood surfaces where tannin staining can be an issue.
It takes longer. It's less convenient. And there are faster products available.
We still use it because our priority is the finished paint job, not shaving a few hours off the preparation process.
Our Preferred Exterior Finish: Sherwin-Williams Emerald®
After the preparation and priming are complete, we generally recommend Sherwin-Williams Emerald® Exterior for our premium exterior repaints.
Our typical finish combination is:
- Flat on siding: A low-reflective finish looks excellent on large siding areas and helps minimize the appearance of normal imperfections in older siding.
- Satin on trim: Satin gives trim additional sheen, is easier to clean and provides a subtle contrast against flat siding.
The expensive paint, however, isn't the most important part of the system.
A premium topcoat applied over wet wood or poorly prepared siding is still being asked to do something it wasn't designed to do. Preparation, moisture control and proper priming come first.
Sometimes the Right Decision Is to Wait
A Real Eastside Example
We recently prepared an exterior surrounded by heavy tree cover. The house had been washed and looked perfectly dry from the outside.
Our moisture meter told us otherwise.
Instead of painting, we came back and checked it again. We continued checking until the wood was consistently below our 15% threshold.
That meant losing painting days and leaving the project sitting longer than we originally hoped.
But that's part of exterior painting in the Pacific Northwest. The schedule doesn't decide when the wood is ready. The wood does.
Experience Matters More Than a Weather App
After more than 20 years of residential repainting on the Eastside, we've learned not to fight Northwest weather.
We wash the house thoroughly. We give it time to dry. We check questionable areas with a moisture meter. We prime exposed wood properly. And if conditions aren't right, we wait.
It's not a complicated formula, but it requires patience.
For homeowners, the important thing to remember is that a dry-looking house isn't necessarily a dry house. Before exterior paint goes onto wood siding, especially after pressure washing or extended wet weather, moisture should be checked rather than guessed.
Frequently Asked Questions
How dry should wood siding be before painting?
At Elegant Painting®, we require wood to register below 15% moisture content on our digital moisture meter before we apply primer or paint.
How long should you wait to paint after pressure washing?
There isn't one waiting period that works for every house. Depending on the weather, shade, siding material and exposure, we may allow approximately 5 to 20 days for wood to dry. We use a moisture meter rather than relying on a fixed number of days.
Why does siding under trees take longer to dry?
Heavy tree cover reduces direct sunlight and airflow around a house. Wood siding in those shaded areas can stay damp considerably longer than siding exposed to sun.
What primer does Elegant Painting® use on bare exterior wood?
For bare exterior wood, we generally use Sherwin-Williams Slow-Dry Oil-Based Wood Primer. We particularly like it for cedar and other wood surfaces where penetration and tannin control are important.