A spring inspection takes two to three hours and requires no special tools beyond a screwdriver and flashlight. The screwdriver test — pressing the tip firmly into wood to check for resistance — is the most reliable field method for identifying rot. Solid wood resists; rotted wood gives way. Work systematically through each area below, noting anything that warrants closer attention.

For each finding, this guide rates severity in three levels: Watch (monitor, address before next winter), Address Soon (repair within the current season), and Address Now (potential structural or safety concern, get a specialist assessment promptly).

When you find damage that needs professional attention, the St. Louis wood rot repair specialists in the Wood Rot Experts network can be matched to your specific findings—whether it's a deck joist, a window sill, or a fascia board.

1. Deck

The deck is typically the highest-priority area for spring inspection. St. Louis winters are hard on deck wood, and damage that is caught now is far less expensive than what it becomes by fall.

Deck boards

Check every board

What to look for: Discoloration (gray, black, or brown), checking (surface cracks running with the grain), soft spots underfoot, paint or sealer failure, cupping or warping.

How to test: Press the screwdriver tip into the end grain of each board and into any discolored areas. Walk the entire deck surface in a grid pattern — soft spots underfoot indicate joist issues more than board issues, but compromised boards reduce the warning you get.

Watch:Checking (surface cracks) without soft wood underneath. Seal these before summer.Address Soon:Soft spots on 1–3 boards, screwdriver penetrates 1/4 inch or more. Replace affected boards this season.Address Now:Multiple soft boards, screwdriver penetrates through board thickness, or boards that flex significantly when walked on.

Deck railings

All posts and rails

What to look for: Wobbly posts, soft top rails (horizontal surfaces collect water), discoloration at post bases where they connect to the deck frame.

How to test: Apply lateral pressure to each post — they should feel solid. Probe the post base connection and the underside of top rails. Test the top rail along its length for softness.

Address Soon:Soft top rail section that still has structural integrity. Surface rot on post base.Address Now:Any wobbly post or rail is a safety concern. Do not use a deck with railing failure until repaired.

Joists

Structural priority

What to look for: Requires getting under the deck. Look for discoloration, fungal growth (white strands), and any sagging. Check joist tops (the surface closest to the deck boards) and joist sides near the ledger.

How to test: With a flashlight, inspect joist tops between boards where accessible. Probe any discolored areas. Tap joists with the butt of the screwdriver — hollow sound vs. solid thud.

Watch:Surface discoloration without softness. Keep debris cleared from joist bays this season.Address Soon:Soft spot on one or two joists. Repair before the joist is further compromised by summer humidity.Address Now:Multiple soft joists, any visible sagging, or joists that flex when pushed from below.

Deck posts

Focus on bases

What to look for: The bottom 6–12 inches of each post, particularly where the post contacts or is near concrete. Posts in post-base hardware often trap moisture at the base despite the hardware.

How to test: Probe the bottom 6 inches of each post on all four sides. Apply lateral force to test for wobble. Inspect any hardware connections for rust and deteriorating wood at fastener holes.

Address Soon:Soft bottom section less than 6 inches. Post base can sometimes be sistered or the base section replaced.Address Now:Any post with more than 6 inches of soft wood, or any post that shows lateral movement. Deck posts are load-bearing — failure is a structural safety concern.

Ledger board

Highest priority structural check

What to look for: The ledger is where the deck frame bolts to the house. Look for water staining, discoloration along the top where the first joist meets the ledger, and any signs of moisture intrusion behind the ledger flashing.

How to test: Probe the ledger face along its full length. Check joist ends where they connect to the ledger hanger — joist ends are end grain and absorb moisture aggressively. Look for deteriorating joist hanger hardware (rust, distortion).

Address Now:Any softness in the ledger or adjacent joist ends. Ledger failure can cause complete deck collapse. Do not defer a ledger inspection finding.

2. Windows

Window rot is almost always found at the sill first. Check all windows, but prioritize north-facing and west-facing exposures, and any windows under areas where gutters have overflowed.

Window sills

What to look for: Paint failure (peeling, blistering, or bubbling), discoloration at the outer edge and end corners, gaps in the caulk where the sill meets the frame or brick mold, and any areas where the sill has pulled away from the adjacent trim.

How to test: Probe the corners and outer edge of every sill. These areas are most exposed to water accumulation. A screwdriver that sinks past 1/4 inch indicates active rot. Check under the sill overhang as well.

Watch:Paint failure without soft wood. Re-prime and paint this season. Re-caulk any gaps.Address Soon:Soft spot at sill corner or edge, less than 2 inches. Epoxy consolidation and filler repair is effective at this stage.Address Now:Soft sill that spans more than half the width, or any sill where the screwdriver penetrates the full depth of the wood.

Window frames and exterior casing

What to look for: Paint failure on the exterior casing (the flat trim surrounding the window), gaps at caulk joints between casing and siding, and discoloration at the base of the side casings where they meet the sill.

How to test: Probe the lower section of each side casing and the drip cap area above the window. Water enters at the top and migrates down, so damage often appears lower than the entry point.

Watch:Hairline caulk gaps. Re-caulk before summer rain season.Address Soon:Soft base section of side casing. Repair this season before summer humidity extends the damage.

Drip caps

What to look for: The drip cap sits atop the window head casing and directs water away from the frame. Damaged or missing drip cap flashing allows water to enter behind the top casing.

How to test: Visually inspect the top of each window exterior for the metal drip cap. If the drip cap is missing, bent, or has gaps at the siding, probe the head casing and top section of side casings.

Address Soon:Missing or damaged drip cap. Install before the summer storm season begins.

3. Doors

Exterior door frames — particularly the base of the jamb on the hinge side — are one of the most commonly rotted areas on St. Louis homes. Check every exterior door.

Door thresholds and sills

What to look for: Wood thresholds that have soft edges or visible decay. Discoloration at the bottom of the door opening where the threshold meets the subfloor or sill plate.

How to test: Probe the threshold edge and the wood at the base of the door opening on the exterior side. Check under the threshold where accessible.

Address Soon:Soft threshold that is still structurally sound. Replace the threshold and check the underlying sill plate.Address Now:Soft wood extending below the threshold into the sill plate or subfloor. This indicates rot has entered the structure.

Door jamb bases

What to look for: Paint failure, discoloration, and soft wood at the bottom 12 inches of both side jambs. The hinge jamb typically gets more exposure on storm-side elevations. Check the exterior casing at the same height.

How to test: Probe both side jamb bases and the exterior casing from the outside. Check the kick plate area — the metal kick plate on many storm doors hides rot underneath.

Watch:Paint failure without soft wood. Re-prime and paint; re-caulk the casing-to-siding joint.Address Soon:Soft base section less than 8 inches high. Epoxy repair is effective for isolated jamb rot.

4. Siding

Focus on the bottom courses and corners. Siding rot almost always starts at ground level and works up, or at corner intersections where water is channeled.

Bottom courses of siding

What to look for: The bottom 1–3 courses of siding on all elevations. Wood siding in contact with or close to the soil line, splash-back staining, and paint failure at the lower edge of each board.

How to test: Probe the lower edge and end grain of each board in the bottom two courses. Check the sheathing behind the siding by probing at any gaps.

Watch:Minor paint failure at board edges. Address before summer rain season.Address Soon:Soft lower edge on 1–3 boards. Remove boards and check sheathing before replacing.Address Now:Soft sheathing behind siding, or rot that spans more than 4 feet of a course. Sheathing rot can involve framing behind it.

Corners and around penetrations

What to look for: Corner boards where two siding runs meet, and areas where plumbing, electrical, or HVAC penetrates the siding. These are caulk-dependent joints that fail under freeze-thaw stress.

How to test: Visually inspect caulk at all penetrations. Probe corner boards at multiple heights, especially at the base. Look for any gaps between the corner board and adjacent siding.

Watch:Gaps at penetration caulk. Re-caulk before summer.Address Soon:Soft section of corner board. Corner boards run the full height of the wall — check the extent carefully.

5. Roof Line: Fascia, Soffits, and Rake Boards

Roof-line rot is often invisible from the ground. Binoculars help. Look for paint failure and discoloration as initial indicators, then get a closer look with a ladder where needed.

Fascia boards

What to look for: Fascia boards run horizontally along the roof edge and hold the gutters. Check the fascia face for paint failure and the top of the fascia where the roof sheathing overhangs — water can enter here and rot from the back side. Also check behind and around gutter mounting hardware.

How to test: From a ladder, probe the fascia face and top edge. Probe around each gutter spike or screw location — hardware holes that allow water in are common rot initiation points.

Address Soon:Soft section of fascia. Fascia replacement is relatively straightforward and significantly less expensive than letting rot migrate to the roof sheathing.

Soffits

What to look for: Soffits are the underside of the roof overhang. Check for paint failure, water staining (indicating a leak above), and any soft areas. Blocked soffit vents cause the interior of the soffit cavity to stay humid.

How to test: Check soffit vents visually — they should be open and show daylight or mesh. Probe any discolored areas of the soffit panel. Tap the soffit with a knuckle or screwdriver handle; hollow sound may indicate rot in the framing above the panel.

Watch:Blocked or painted-over soffit vents. Clear them before summer.Address Soon:Water staining on soffit panel without current active leak. Investigate moisture source and repair soffit framing.

6. Foundation Area: Sill Plates, Rim Joists, and Band Boards

This inspection requires crawl space access or basement access. Foundation-area rot is the most serious category — it is load-bearing and often goes undetected for years.

Sill plates

What to look for: The sill plate is the horizontal lumber that rests on top of the foundation wall and supports the house frame. It is directly exposed to any moisture that rises from the foundation or enters at the foundation-to-siding junction. Look for discoloration, fungal growth, and crumbling wood.

How to test: From inside the basement or crawl space, probe the sill plate on all accessible sides along its full length. Pay particular attention to areas under bathrooms, near downspout discharge points, and at exterior corners.

Address Now:Any soft section of sill plate. Sill plates are continuous load-bearing members — rot here affects the entire wall above it. Get a specialist assessment before the next rain season.

Rim joists and band boards

What to look for: The rim joist (or band board) runs along the outside edge of the floor framing, sitting on the sill plate. In older St. Louis homes, this area is often uninsulated and exposed to exterior moisture. Look for discoloration, frost damage (ice crystals visible in winter, staining after thaw), and soft wood.

How to test: Probe the inside face of the rim joist along its full length from the basement or crawl space. Also probe from outside if the rim joist is visible above the foundation wall.

Address Soon:Isolated soft section of rim joist without sill plate involvement. Repair is typically straightforward — sister a new joist alongside and address the moisture source.Address Now:Extensive rim joist rot or any rot that involves the sill plate. Structural assessment required.

What to Do With Your Findings

Categorize your findings into three groups after completing the inspection:

Maintenance items (Watch level): Schedule caulking, re-painting, and cleaning for April-May before summer moisture season begins. These are homeowner tasks that cost a few hundred dollars and prevent the next category.
Repair items (Address Soon): Get specialist estimates in April-May. Many repair-level issues can be completed in May-June before summer humidity accelerates any ongoing rot. Getting estimates early gives you options — waiting until fall means competing with full seasonal schedules.
Urgent items (Address Now): Contact a specialist this week. Structural rot issues do not improve with waiting, and safety concerns on decks and at foundational members should not be deferred. Our specialist network provides free estimates and can typically assess within a few days.

For background on what to expect from repairs, see our Wood Rot Repair Cost Guide and our guide on identifying different types of wood rot.

2026 Spring Wood Rot Inspection Checklist for St. Louis Homeowners