Three places on a Pacific Northwest home get hit hardest by dry rot: siding, decks, and window frames. They share wind driven rain, splashback, full sun exposure, freeze and thaw cycles, and the difficulty of keeping caulk and paint perfect for years. They are also where most dry rot repair work in Portland and Vancouver WA actually happens.
This guide breaks each one down: where the rot usually starts, how to identify it, how a real repair is done, and what it costs in 2026. The goal is to give you enough information to know whether to grab a screwdriver and look closer, or just call a contractor.
If you want a free dry rot inspection in the Portland or Vancouver WA metro, you can call NW Reliable Home Services at (360) 713-8022.
Why Siding, Decks, and Window Frames Take the Hardest Hits
All three see consistent exposure to wind driven rain, but more importantly they all rely on multiple layers of protection that need to stay perfect: paint, caulk, flashing, and sometimes building wrap behind the visible surface. When any one of those layers fails, water finds its way to the wood, and PNW wood does not stay dry long.
Dry Rot in Siding (Cedar, T1-11, LP, Fiber Cement)
Where it usually starts
Siding rot usually begins at the bottom edge of a board, where water sits longest, or behind fasteners where moisture wicks in. It also commonly starts under windows, at horizontal trim, and anywhere two siding sections meet without proper flashing. Cedar shingle siding tends to rot first at the butt edges and along the keyways. T1-11 plywood siding rots at panel edges and around nail penetrations. LP smartside rots where paint and caulk have failed. Fiber cement is the most rot resistant material, but the wood trim around fiber cement panels rots like any other.
How to spot it
Look for soft spots when you push gently on the siding with your thumb. Look for paint peeling or bubbling at edges and seams. Look for dark stains running down from horizontal trim. Probe suspect areas with an awl or screwdriver. Healthy wood resists. Rotted wood gives in.
How a real repair is done
Remove the affected siding sections and any rotted trim. Inspect the building wrap and sheathing behind the siding (rot frequently extends here, especially when paint has been failing for years). Replace any rotted sheathing and any damaged or torn building wrap. Treat surrounding sound wood with a borate fungicide. Install new siding, primed on all six sides before install, with proper flashing at all horizontal terminations. Caulk, prime, and paint.
Cost range
| Scope | Typical 2026 cost |
|---|---|
| Single small siding area (4 to 8 square feet) | $600 to $1,500 |
| Full wall siding section with sheathing repair | $2,500 to $7,500 |
| Full elevation siding replacement | $8,000 to $25,000 |
| Cedar to fiber cement upgrade (one wall) | $4,000 to $12,000 |
Dry Rot in Decks
Where it usually starts
Deck rot starts in three predictable places. First, the ledger board (where the deck attaches to the house), if flashing was missed or installed wrong. Second, deck posts where they meet the ground or concrete pier. Third, joists and beam tops where water sits between decking boards and the framing below.
The ledger is the dangerous one. A failed ledger does not announce itself. A deck full of people loads it dynamically and a rotted ledger can pull away from the house with no warning.
How to spot it
Check the underside of the deck for soft spots in the joists where they meet the ledger or sit on the beam. Check posts at ground level by pushing with a screwdriver. Look for cracking, bulging, or staining at the ledger where it meets siding. Walk the deck and listen for soft underfoot spots or boards that flex more than they should.
How a real repair is done
Temporarily support the deck load. Remove decking in the affected area. Replace rotted joists, beam sections, or posts with pressure treated lumber sized to current code. For ledger rot, this often means cutting back siding to install a new ledger with proper Z flashing and through bolts (lag screws into rotted framing are a code and safety issue we see frequently). Re install decking, repair siding, recheck attachment hardware.
Cost range
| Scope | Typical 2026 cost |
|---|---|
| Replace 2 to 4 deck boards over rotted joist | $650 to $1,800 |
| Single post and footing replacement | $700 to $1,800 |
| Joist replacement (several joists) | $1,800 to $5,000 |
| Ledger board replacement with proper flashing | $2,500 to $6,500 |
| Full deck framing rebuild | $8,000 to $20,000 plus |
Dry Rot in Window Frames and Sills
Where it usually starts
Almost always at the bottom corners of the exterior sill and at the head flashing if any has failed. The combination of paint that has cracked at the corner joint, caulk that has split, and water that sits during PNW rain produces rot inside the sill and into the adjacent trim within a few years.
We also see rot in older wood windows where the bottom rail of the sash has failed, which then drops water into the sill.
How to spot it
Push gently on the exterior sill with a thumb. Probe the corners with an awl. Look for paint that is bubbling, lifting, or flaking at the bottom rail of the sash or the top of the sill. Open the window and inspect the interior sill and stool for staining or peeling.
When to repair vs. when to replace the window
If the rot is confined to the exterior sill and trim, repair makes sense. If the rot has reached the jamb, the rough opening framing, or the bottom rail of the sash itself, full window replacement is often cheaper and more durable than a sash and frame repair.
How a real repair is done
Remove exterior trim, sill, and any rotted material back to sound wood. Inspect the rough opening framing and replace any damaged material. Apply borate treatment to surrounding wood. Install a new sill, properly sloped and flashed. Replace trim. Caulk all joints with a high quality polyurethane or hybrid sealant. Prime and paint.
Cost range
| Scope | Typical 2026 cost |
|---|---|
| Single window sill and trim repair | $400 to $1,500 |
| Multiple windows on one elevation | $1,500 to $4,500 |
| Single window full replacement (mid range vinyl) | $900 to $2,500 |
| Single window full replacement (wood or clad) | $1,800 to $5,000 |
Preventing Dry Rot From Coming Back
Every dry rot repair is also a chance to remove the cause. The same maintenance habits keep new rot from starting.
- Inspect caulk at windows, doors, and siding terminations once a year. Replace any that has split or pulled away.
- Repaint or restain exterior wood on schedule. Most PNW homes need exterior paint refreshed every 7 to 10 years.
- Keep gutters cleared and downspouts extended at least four feet from the foundation.
- Keep landscaping plants and irrigation off siding and trim.
- Maintain six inches of clearance between soil or splash zones and the bottom of siding.
- Ventilate attics, soffits, and crawlspaces.
When to DIY vs. Call a Pro
Small areas of cosmetic rot that have not reached structural framing can be a reasonable DIY project for an experienced homeowner. Anything that involves the deck ledger, structural framing, siding sheathing, or window rough openings should be handled by a contractor. The cost of getting it wrong (failed repair, safety issue, larger second repair) is much higher than the cost of the first repair done correctly.
How NW Reliable Home Services Handles Dry Rot in Siding, Decks, and Windows
We have spent more than a decade fixing PNW dry rot. Our process is the same on every job: probe to find the full extent of damage, cut back to sound wood, treat the surrounding wood, replace with proper materials, address the moisture source, and finish so the repair blends. We are licensed and bonded in both states (OR CCB# 255838 and WA NWRELRH777) and serve Portland, Beaverton, Hillsboro, Gresham, Tigard, Lake Oswego, West Linn, Oregon City, Milwaukie, and Tualatin, and Vancouver, Camas, Washougal, Battle Ground, Ridgefield, La Center, Brush Prairie, and Hazel Dell.
To schedule a free dry rot inspection, call (360) 713-8022 or visit nwreliablehomeservices.com.
Frequently Asked Questions
How do I fix dry rot in siding?
Cut back to sound wood, inspect the sheathing behind the siding, replace any damaged sheathing and building wrap, treat surrounding wood with a borate fungicide, install new primed siding, and address the moisture source (usually flashing, caulk, or gutter issues). Painting over rotted siding does not fix it.
Can a rotted deck post be replaced without rebuilding the deck?
Yes. The deck is temporarily supported, the post is removed, the footing is checked or replaced, and a new pressure treated post is installed. This is one of the more common deck repairs we do in the PNW.
Is window dry rot expensive to fix?
Single sill repairs run $400 to $1,500. When the rot extends into the jamb or rough opening, full window replacement at $900 to $5,000 is often more cost effective.
How often should I inspect my siding, deck, and windows for rot?
Once a year is the right cadence in the PNW, ideally in spring after the wet season. Walk the perimeter, probe suspect spots, check caulk and flashing, and address small issues before they become structural ones.
Will insurance cover dry rot repair on my siding or deck?
Usually no. Insurance treats dry rot as a maintenance issue. Coverage is possible when the rot was caused by a sudden covered event such as a burst pipe or wind damaged flashing that you reported promptly.
If you have soft spots in your siding, decking, or window sills, call NW Reliable Home Services at (360) 713-8022 for a free inspection in the Portland or Vancouver WA metro.
