In Beaverton and Cedar Mill, the safe window for exterior paint is July through about mid-September. NOAA's 30-year normals for Hillsboro Airport average about 3 days with measurable rain in July, and close to 15 in October. Wood siding should read under 20 % moisture before it gets paint, ideally near 12 %. Here's how we handle exterior painting .
What is the best month to paint a house exterior around Portland?
Most advice online says spring or fall. That advice comes from places with humid, stormy summers. Our pattern runs the other way: a long wet season, then a short dry spell that starts late and ends fast.
| Month | Avg high °F | Avg low °F | Days with rain (0.01 in+) | Nights below 50°F | Days 90°F+ |
|---|---|---|---|---|---|
| April | 61 | 39 | 16.0 | 29.4 | 0 |
| May | 69 | 45 | 12.0 | 26.2 | 0.4 |
| June | 74 | 49 | 8.7 | 18.1 | 2.0 |
| July | 82 | 52 | 2.9 | 11.6 | 6.4 |
| August | 82 | 52 | 3.5 | 11.3 | 6.1 |
| September | 76 | 48 | 7.6 | 20.9 | 2.3 |
| October | 64 | 41 | 14.9 | 27.6 | 0 |
NOAA 1991-2020 monthly normals, Hillsboro Airport station (USW00094261), the nearest normals station to the west side. Averages, not a forecast. A "rain day" means at least 0.01 in fell.
July and August are the most dependable months. June and the first half of September usually work if you watch the ten-day forecast. May and October are for small pieces only, like a door or one stretch of trim that can be done and dry in a day .
How dry does siding need to be before you paint it?
Wood finishing research published in the Journal of Light Construction puts the ceiling at 20 % moisture content: above that, don't paint. The target is whatever the wood will average once it's in service, about 12 % for most of the country, with single boards anywhere from 9 to 14 %.
The calendar can't tell you that number. A pin-type moisture meter can. Take readings on several boards per wall, and always include the bottom two courses, the north face, and anything under a roof dripline or a big tree. Firs shade one or two walls of many houses out here all day, and those walls hold water long after the sunny side reads fine. T1-11 and hardboard panels wick water up through their bottom edges, so test low.
How long that takes after a rain or a wash varies a lot by wall . Fiber cement and vinyl don't take a meter reading the same way; their surface simply has to be dry to the touch, joints included.
What temperature is too cold to paint outside, and why do nights matter?
Check the can first. Benjamin Moore's temperature guide lists a span of 35 to 100°F across its exterior products, and wants the surface more than 5°F above the dew point.
Nights are where jobs go wrong. Sherwin-Williams warns that a warm day followed by a night near freezing can keep latex from forming a proper film, and that dew settling at dusk can stain paint that hasn't cured. Out here the nights run colder than the city: NOAA puts September's average low at 47.5°F in Hillsboro and 54.1°F at Portland Airport, and October's at 40.9°F against 46.7°F. Even July averages about 12 nights under 50°F. A warm lunch hour proves nothing.
What about painting at 45 degrees? It dries slowly. Diamond Vogel suggests at least 24 hours between coats once it's under 50°F, but the label on your product has the final word on recoat time .
Can you paint in a Portland heat wave or in full sun?
July and August each average about 6 days of 90°F or hotter at Hillsboro. On a hot wall the paint skins over before it flows out, which leaves lap marks and a weaker bond.
The fix is timing. Do south and west walls in the morning or late afternoon, keep the north and east sides for midday, and skip the worst afternoons altogether .
Is spring or fall a good time to paint outside here?
Spring is tempting, but May still averages 12 rain days, and siding is carrying a whole winter of water. Go by the meter readings, not by how nice Saturday looks.
Fall closes quickly. By October, Hillsboro averages about 15 rain days and lows near 41°F, so in a normal year the outside work wraps up somewhere in the second half of September. One approach that does work: get trim or a covered porch wall done in a dry stretch of late spring, then do the big walls in July. If rain shows up mid-job, stop and let the surface dry fully before going back to it, as Benjamin Moore advises .
When should you book an exterior painter around Portland?
Start in late winter: the dry months are few, and repairs come first. A sensible order:
- Send photos and get a price.
- Fix rot, loose boards and open joints in any dry spell in spring.
- Wash the house and let it dry out.
- Paint between July and mid-September.
For what a repaint costs and why, see our exterior house painting cost guide.
What exterior work can be done before the dry season?
Paint won't hold on soft wood, so the repair list comes first: rotten trim, sills and fascia, split or swollen siding boards, open gaps at corners and windows. We cover that under rot and siding repairs, and most of it can be done in spring.
| Spring or summer job | Basis | Typical | Low to high |
|---|---|---|---|
| Cutting out rot in a sill, fascia or trim board | with materials | $1,500 | $500 to $4,000 |
| Swapping damaged siding boards | with materials | $1,800 | $900 to $6,500 |
| Sealing gaps and joints with caulk | labour only | $700 | $300 to $1,500 |
| Spot painting of trim and fascia | labour only | $900 | $400 to $2,000 |
| Repainting the whole house, siding plus trim | with materials | $3,801 | $2,498 to $5,167 |
Market ranges for the Portland area as read in November 2026; these aren't our quotes.
Caulk and primer have their own temperature and moisture limits on the tube or can, so "before the dry season" means a dry week, not a drizzly one. Stain on a deck or fence wants the same dry stretch, so it's worth planning staining decks and fences alongside the house. We wash the house before painting , though chemical moss killers are on our list of jobs we skip.
How often does a house exterior need repainting?
No honest single number exists. Check each summer instead. Rub the siding: chalk on your palm means the coating is wearing thin. Look for peeling on the lowest boards, grey bare wood on sills, and cracks where trim meets siding. South and west faces usually show it first because they take the most sun.
Bare wood shouldn't sit unprotected for more than about two weeks, according to the same JLC research, so spot-prime those patches the same season you find them .
Can you just paint over old exterior paint?
Over paint that's sound, clean and dry, yes. Over chalky, flaking or mildewed paint, no: it has to be washed, scraped and spot-primed first, or the new coat comes off with the old one.
One line we hold: if the house went up before 1978, its old paint stays put, with no scraping and no sanding from us. Plenty of homes in Cedar Mill and Cedar Hills were built between the 1950s and the 1970s, so check the year first. That's our own policy, and we spell it out with the other work we turn down.