October is the right month to walk your deck with a critical eye. By the time the rains settle in for good — usually mid-November — you've lost your window to make repairs before the wet season does its worst. Seattle averages 38 inches of rainfall annually, and the bulk of it falls between November and March. Decking that enters winter with compromised flashing, soft post bases, or unchecked surface cracks will exit winter in noticeably worse shape. A thorough inspection in October takes about 45 minutes and costs nothing. What it tells you can save you from a much larger bill in the spring.
Why Fall Is the Right Time for a Deck Inspection Seattle Homeowners Often Skip
The logic is straightforward: fall inspection lets you make repairs while the weather is still workable. Structural repairs — replacing a deteriorated ledger connection, sistering a cracked joist, reseating a post base — require dry conditions and open access. Doing them in October means you have a six-to-eight-week window before the rains lock in. Waiting until spring means you're inspecting damage that spent five months getting worse.
There's a second reason specific to Seattle's climate. The temperature swings between October and February — from the low 40s at night to the mid-50s during the day — create repeated freeze-thaw cycles that accelerate cracking and checking in wood decking. Any surface crack that's open in October will be wider and deeper by March. Catching it now, sealing it or replacing the board, prevents that progression entirely.
The 6-Point Structural Inspection
Work through this inspection in order, from the connection to the house outward to the perimeter. Bring a flat-blade screwdriver for probing, a flashlight, and a notepad.
1. Ledger Connection
The ledger is the horizontal board bolted to your house framing that carries the inboard end of every joist. It is the single most structurally critical component of an attached deck, and it is the most common point of failure. What you're looking for: flashing that has pulled away from the house, caulk that has cracked along the top edge of the ledger, any staining or moisture discoloration on the house siding directly above or below. Probe the ledger itself with the screwdriver tip — soft wood that yields under light pressure indicates rot behind or within the ledger. If the flashing has failed or the ledger feels soft anywhere, stop and call a professional. This is not a DIY repair.
2. Post Bases
Get down and look at the metal post bases where the vertical posts meet the concrete footings or deck framing. In the Pacific Northwest, post bases that were installed directly on concrete — without the raised standoff that modern hardware provides — hold moisture between the metal and the post end grain. Look for rust streaking on the hardware, soft or discolored wood at the very bottom of each post, and any play or movement when you push the post from side to side. A post with even minor rot at its base is a structural concern. Post base replacement requires temporarily supporting the beam above while the post is pulled and reset — not a Saturday afternoon job for most homeowners.
3. Joists and Beams
If your deck is elevated enough to access the underside, get under it with a flashlight. You're looking for joists that have cracked along the top edge, any visible sagging between support points, and signs of moisture — dark staining, white fungal growth, or surface checking on exposed beam faces. Pay particular attention to the outer double joist (the rim joist) and any joist that passes over or near a post. Sistering — adding a second joist alongside a damaged one — is a repair that's genuinely within reach for a mechanically capable homeowner, but only if the original joist is cracked rather than rotted. Rotted framing means the wood has lost structural integrity and the full member needs replacement.
4. Decking Surface
Walk the entire surface slowly, stepping on each board. You're listening and feeling for bounce, flex, or a hollow sound that indicates a board has lost contact with the joist beneath it — often because the fastener has backed out or the wood has shrunk away. Look for surface checking (shallow cracks running parallel to the grain), cupping (boards that have curled upward at the edges, creating a channel in the center that holds water), and any end-grain exposure that isn't capped or sealed. On cedar, soft spots under foot pressure are a red flag — probe them. On composite, look for delamination at cut ends and any boards that have buckled or heaved, which typically indicates improper fastening gaps were used at installation.
5. Railing System
Grab each railing post at mid-height and apply side-to-side force. There should be no perceptible movement. Washington State code requires deck railings to resist 200 pounds of lateral force — any post that rocks or wobbles is not meeting that standard, and it's a safety issue. Check the bottom of each post where it connects to the rim joist or deck framing. Loose posts are often caused by hardware that has corroded and lost clamping force, or by blocking behind the rim joist that has rotted away. Also check each baluster: they should not spin freely or pull out with hand pressure. A single wobbly post is enough reason to call a pro — railing failures are the most common cause of deck-related injuries.
6. Stairs
Check stair stringers (the diagonal side members) for cracking along the notch cut lines — this is the highest-stress point in a stair assembly and where stringers fail first. Probe the bottom of each stringer where it contacts the landing pad. Look for stair treads that have pulled away from the stringers, creating a gap at the front or back of the tread. Push each handrail with your palm: it should feel solid and well-anchored.
Repair vs. Replace: How to Read What You Found
If your inspection turned up only surface issues — moss buildup, minor checking on a few boards, loose baluster fasteners — you're in cleaning and maintenance territory. If you found one or two isolated boards with moderate cupping or soft spots, a targeted board replacement is the right call.
The decision shifts toward resurfacing when more than 20–25% of your decking boards show significant checking, cupping, or soft spots. At that point, pulling all the decking and relaying new boards over existing framing (assuming the framing checked out) is more cost-effective than piecemeal replacement. Full demolition and rebuild becomes the right answer when the framing itself — ledger, posts, joists, beams — is compromised. Rotted framing cannot be patched; it has to be replaced, and at that point you're essentially building a new deck.
Cedar vs. Composite: Different Winter Prep
If your deck is cedar, October is when you should be sealing it — not spring. Cedar that goes into winter with dry, unprotected wood absorbs water during the wet months and then loses it during the drier periods in February and March. That repeated cycle causes checking and splitting. A penetrating cedar sealer or oil applied in October, when the wood is still relatively dry from summer, gives you the best penetration and the best protection for the wet season ahead. If your cedar hasn't been sealed in more than two years, it needs it now.
Composite decking doesn't need sealing, but it does need cleaning before winter. Organic debris — leaf tannins, tree sap, pollen — stains composite surfaces and can become nearly permanent if it sits through a wet winter. A thorough wash with a composite-safe deck cleaner (avoid bleach, which can fade some composite colors) and a pressure washer set below 1,500 PSI will clear the surface and prevent winter staining. Pay extra attention to gaps between boards where debris accumulates and holds moisture.
When to Call a Pro vs. Handle It Yourself
Moss cleaning, debris removal, a light scrub of the composite surface, replacing one or two obviously cracked surface boards you can clearly identify and access — these are all reasonable DIY tasks for a homeowner who's comfortable with basic carpentry.
Call a professional when: any railing post has movement, you've found soft wood at the ledger or post bases, any joist or beam shows rot rather than just surface staining, or you're not certain whether what you found is cosmetic or structural. Structural failures on decks rarely announce themselves in advance. The post that feels slightly soft in October can be genuinely dangerous by the following July after a full wet season.
If you found issues during your inspection or you'd rather have a professional set of eyes on it before winter, our team does deck assessments throughout King County. Learn more about our [deck repair services](/deck-repair) or [contact us for a free estimate](/contact).