Seattle Weather and Cedar Siding Cracks

Seattle’s constant moisture is hard on cedar siding: we get 156 rainy days a year, Puget Sound keeps the air damp, and unsealed or aging cedar drinks in water through cracks, nail holes, and worn finishes. Once wood moisture content — the percentage of water held in the fibers — passes 20 percent, the board weakens fast and rot sets in.

Cedar offers natural beauty and some built-in rot resistance, but those qualities only hold up with steady upkeep here. It looks better on a Craftsman than anything else we hang, yet you will also be back on a ladder every few years, and that trade is the whole decision.

Why Seattle’s Weather Damages Cedar Siding

Seattle’s weather is uniquely hard on wood siding, not because of dramatic downpours but because of the near-constant drizzle from October through May, which never lets cedar dry out between rains.

Moisture and Humidity Problems

Seattle gets about 39 inches of rain a year, spread across 156 days, and that steady damp lets water seep into the wood through unsealed edges, nail holes, and worn sealant. Once wood moisture content passes 20 percent, the board grows weaker and open to fungal decay from organisms such as Serpula lacrymans, the dry-rot fungus common in Pacific Northwest walls.

High humidity makes it worse: cedar pulls water from the air, swells, then shrinks back during dry spells, and that repeated movement tires out the wood fibers until stress cracks follow. Marine air off Puget Sound keeps humidity up even on dry days, so your walls stay damp year-round.

Temperature Changes and Wood Movement

The shift from dry summers (July through October) into the wet season makes cedar expand and contract, a cycle that stresses the wood fibers and feeds cracking. South- and west-facing walls take the worst of it because they get the most direct sun, which breaks down sealant and cracks paint.

Over time, that repeated movement leads to splitting, warping, and cracks, and every new crack lets even more water into the wood.

Sun Damage and Surface Cracking

Seattle’s dry summers bring strong UV that dries out the cedar surface and causes small cracks called checking, which weaken the finish so water seeps in more easily once the rains return.

Unprotected cedar can start breaking down after just five years, because wind-driven rain forces water into the cracks and can rot the sheathing — the wood panels under the siding — behind the boards. Finish cedar within two weeks of install, then re-stain every two to three years, or repaint every four to five years, to guard against UV.

How to Inspect Cedar Siding for Cracks

Regular inspections matter here: check your siding twice a year, in spring and fall, and you catch problems before they grow.

What to Look For

Watch for surface cracks, deep splits, warping, buckling, or curling boards. If a board is pulling away from the house, water has likely soaked in and swelled it for good.

Check for peeling, bubbling, or cracking paint, which warns that the finish is failing, and look at the nail heads too, since a nail driven too deep leaves a small hole that lets water in.

Dry rot is hard to catch early, but over time the wood feels soft and spongy when you press it with a thumb or screwdriver, and cedar that has lost its natural oils rots the fastest.

Testing Moisture Levels

A moisture meter is an inexpensive tool that reads wood moisture content in the cedar. Healthy cedar sits at 9 to 14 percent; above 15 percent, the wood holds enough water to feed decay and raise the risk of rot. Test the spots that stay damp longest — shaded walls, north-facing sides, and boards near the ground — because those are the most at risk in our climate.

High-Risk Areas to Check

North-facing walls and shaded areas are the most at risk because they get less sun and stay damp longer, which invites moss, algae, and mildew. The bottom edges of the boards are another weak spot: if those drip edges are not sealed, they wick water up into the wood.

Look hard around the windows and doors, common spots for leaks and seepage, and check the foundation line and anywhere the yard slopes toward the house, since water pools there. Check the flashing and caulk at the joints as well, a frequent path for water behind the weather-resistant barrier (WRB), the water-shedding wrap installed under the siding.

How to Repair Cracked Cedar Siding

The right repair depends on how bad the damage is, with options running from sealing a small crack to replacing whole boards to fixing structural rot in the sheathing.

Fixing Small Cracks

For small cracks under 2 feet, epoxy or wood filler is your best bet because it seals the crack and keeps water out. Clear the loose debris first, then apply the filler per the instructions; once it dries, sand it smooth, prime the wood, and finish with two coats of acrylic latex paint.

Tackle small cracks fast, because if water gets behind the siding it swells the structure and opens even more cracks. Use a flexible caulk between boards so the wood can move with seasonal humidity.

Replacing Damaged Boards

When the damage runs past 2 feet but under 8 feet, replacing the boards beats patching. Cut back to solid wood so the new board fits tight, and before it goes up, prime all its sides and edges. We finish cedar on every face, cut ends included, because the back is where water hits and no coat ever reaches it later.

Seal the nail holes and run a high-grade elastomeric sealant along the seams. Good flashing at the joints is critical here, because wind-driven rain finds even a tiny gap, and a missing kickout flashing — the small diverter where a roof meets a wall — will dump roof runoff straight behind the new boards.

Handling Severe Damage

When damage runs past 8 feet or involves rot, patching will not cut it. Soft, spongy wood, a musty smell, or bubbling paint mean the rot may have reached deeper, into the sheathing or framing.

Remove all the damaged wood, treat the area around it with an EPA-approved fungicide to stop the decay, and check the structure behind it — the studs, joists, and beams — to confirm they are still solid. Then find and fix the water source: bad flashing, overflowing gutters, or poor drainage. If the wall is opened, a rainscreen gap, the vented air space behind the siding, lets any remaining moisture drain and dry before it reaches the WRB.

Major repairs that touch framing or big sections of siding may need permits from the city. Depending on the scope, costs run from $1,200 to over $6,500.

Preventing Cedar Siding Cracks

Preventing cracks in cedar is far cheaper than repairing them. Our climate brings 39 inches of rain a year and high humidity, so staying ahead of the upkeep is the whole game.

Using Water-Repellent Treatments

Water-repellent treatments build a barrier that helps cedar shed moisture. Latex and acrylic paints and sealants work best because they flex with the wood; rigid coatings cannot, so they crack under the strain.

Apply two coats of acrylic latex paint, and work it into the wood grain. Use a brush on the weak spots, like cut ends and drip edges. In our damp climate, pick a coating with biocides or mold inhibitors, which fends off algae, moss, and mildew, especially in the shade.

Routine Maintenance Tasks

Steady upkeep keeps small issues from turning into costly repairs. Wash the siding once a year with a soft brush and mild soap to clear dirt, moss, and mildew, and inspect it each spring and after storms for blistering paint, gaps in the caulk, or swollen boards.

Before the fall rains, clear the gutters and downspouts so overflow does not soak the lower boards, and seal minor cracks and gaps right away with wood filler or good caulk. Repaint or reseal every 5 to 7 years to keep the barrier strong.

Choosing the Right Products for Seattle

For finishes, a semi-transparent stain balances UV protection with showing off the grain. A solid color stain gives the most moisture and UV defense, but it hides the natural wood. Apply any finish on overcast days, when temperatures sit between 50 and 80 degrees, so it does not dry too fast in direct sun.

For caulk, use a high-grade elastomeric sealant on seams, joints, and nail holes, and when staining, back-brush the product into the wood so it soaks in deep. Skip standard exterior paint, which traps moisture and leads to bubbling and peeling. To clean before you recoat, reach for oxygen bleach, which kills mold and mildew without stripping the wood’s natural oils.

Protecting cedar in Seattle’s relentless climate takes regular inspections, prompt repairs, and steady upkeep. Catch cracks early and fix the water source behind them, and you can add decades to the life of your siding.

If you are facing soft spots, extensive cracking, or signs of rot, professional help ensures the problem is resolved completely. Contact our siding repair team for a free inspection and expert guidance on protecting your Seattle home.