Wood Rot Repair: Signs, Costs, and When to Call a Pro
Dry rot vs. wet rot, the six signs to look for, what repair vs. replacement actually costs, and how St. Louis homeowners save 60–80% by repairing early.
Wood rot repair is one of the highest-leverage investments a homeowner can make. Left untreated, a $300 window sill repair becomes a $2,500 full window frame replacement. A $500 sill plate treatment becomes a $12,000 floor system repair. The cost difference between catching wood rot early and discovering it late is measured in thousands of dollars — sometimes tens of thousands.
This guide covers everything you need to know about wood rot: the two types (dry rot and wet rot), how to identify it before it becomes structural, what repair and replacement actually costs at each severity level, the limits of DIY approaches, and how to prevent recurrence. For St. Louis homeowners, we've included a recommendation for the area's most trusted wood rot specialist.
The core principle: early-stage wood rot is repairable at a fraction of replacement cost. Late-stage structural rot is expensive regardless of approach. The difference is detection timing.
Dry Rot vs. Wet Rot: What's the Difference?
Both types of wood rot are caused by fungi and both require moisture to initiate. The difference is in how they spread, what they look like, and how dangerous they are to your structure.
Dry Rot
Despite the name, dry rot requires moisture to start — typically 20% or higher wood moisture content. The fungus responsible (Serpula lacrymans) is uniquely dangerous because it can transport water through its mycelium network and spread into dry wood and through masonry, concrete, and plaster beyond the original moisture source. Dry rot can travel through an entire floor system starting from a single wet spot.
Wet Rot
Wet rot is caused by several fungal species and requires higher sustained moisture levels than dry rot. It is more localized — it doesn't spread through masonry or beyond the moisture zone — but it causes deep structural degradation in constantly wet environments: crawl space sill plates, subfloor joists near plumbing leaks, and exterior framing in chronic contact with moisture. Wet rot that reaches structural members is a serious problem despite its limited spread.
6 Signs of Wood Rot to Look For
Most wood rot is detectable well before it becomes structural — if you know what to look for. These six indicators cover the progression from early surface warning to advanced damage.
Discoloration and Paint Failure
Paint peeling in isolated sections — particularly around window frames, door frames, and fascia boards — is often the first visible indicator. Moisture trapped beneath paint compromises adhesion from the inside out. The wood underneath may be soft or show a darkened, water-stained appearance. Don't assume peeling paint is just a painting problem.
Soft or Spongy Wood When Pressed
Press firmly on suspect areas with your thumb or knuckle. Sound wood resists pressure. Wood affected by rot feels soft, spongy, or compresses under moderate pressure. This is the single most reliable field test. Apply it to window sills, door frames, porch posts, deck boards, and any wood in contact with soil or near a chronic moisture source.
Probe Test — Screwdriver Penetration
A screwdriver or awl is the professional's basic diagnostic tool. Press the point into suspect wood without hammering. Healthy wood resists penetration. Wood with internal rot allows the probe to sink 1/4 inch or more with hand pressure alone. This test is especially useful for assessing sill plates and rim joists that aren't easily visible — probe through a small access point or from the basement or crawl space.
Cube-Pattern Cracking (Dry Rot Indicator)
Dry rot produces a distinctive failure pattern: the wood develops a grid of cracks that create cube-shaped fragments. This cracking pattern differs from moisture-driven shrinkage or weathering. If you see cube-cracking on wood in a crawl space, basement framing, or any enclosed structure, treat it as a dry rot indicator and have it evaluated — dry rot can spread beyond the moisture source through masonry and other building materials.
Musty or Fungal Odor in Enclosed Spaces
Crawl spaces, basements, and enclosed wall cavities affected by wet rot or dry rot produce a distinctive musty, earthy, or sometimes sweet fungal odor. If opening a crawl space access or a cabinet door against an exterior wall produces a sudden musty smell, wood rot in that enclosed space is a serious possibility. The odor source is fungal growth — not just dust or age.
Visible Fungal Growth or White/Brown Mycelium
Advanced dry rot produces visible mycelium — thin white, gray, or rust-colored strand-like threads that spread across wood surfaces and into adjacent materials. This is the fungal root system. If visible mycelium is present, the rot has been active for a significant period. Immediate professional assessment is warranted — and the source of moisture driving the growth must be identified and corrected before repair.
Wood Rot Repair Costs: Minor, Moderate, and Major
Professional wood rot repair typically saves 60–80% compared to full replacement. Here's what each severity level costs and what the repair approach involves.
Epoxy consolidant is applied to stabilize remaining sound wood fiber. After curing, epoxy filler restores the original profile. The surface is primed and painted. The repaired section performs identically to the original wood and accepts paint normally. Minor repairs are completed in a single visit.
A full window sill replacement with new casing and painting often runs $600–$1,200. Repair at $200–$500 is a 50–70% savings.
Moderate repairs combine epoxy consolidation with partial wood replacement — removing only the structurally compromised sections and splicing in new pressure-treated or composite material where the damage is too deep for consolidant alone. The repair is blended for a seamless finish.
Full window frame replacement with trim and paint typically runs $1,500–$3,000 per window. Repair in this tier saves 50–65% in most cases.
Structural repairs require temporary support of the load while compromised members are treated, sistered, or replaced. A full engineering assessment may be required on older homes. The moisture source driving the rot must be corrected — vapor barrier, grading, drainage, or plumbing — before structural wood is repaired. Without moisture correction, rot recurs.
Partial joist replacement and sistering averages $1,500–$3,500 versus full floor system replacement at $8,000–$25,000+. Repair, when structurally viable, is the rational choice.
DIY Wood Rot Repair: When It Works and When It Doesn't
Epoxy wood repair products have made cosmetic wood rot repair genuinely accessible to competent DIYers. But there are clear limits.
DIY is appropriate when:
- ✓Rot is confined to cosmetic trim (window sills, door casing, fascia)
- ✓The probe test shows penetration of less than 1/4 inch
- ✓No structural members are involved
- ✓The moisture source has been identified and corrected
- ✓You have experience with epoxy consolidant and filler products
Call a professional when:
- !Floor joists, sill plates, or rim joists are affected
- !Load-bearing posts or beams show soft spots
- !Visible mycelium indicates dry rot spread
- !Probe penetration exceeds 1/4 inch in any structural member
- !Rot is in a crawl space or enclosed wall cavity
The single most important rule in DIY wood rot repair: correct the moisture source before applying any repair product. Epoxy filler applied over active wet rot will fail within months. The moisture driving the rot — poor drainage, a plumbing leak, failed caulking, inadequate crawl space ventilation — must be resolved first. If you can't identify the moisture source, call a professional before attempting repair.
Wood Rot Experts
St. Louis Metro — Kirkwood · Webster Groves · Clayton · Creve Coeur · Chesterfield and surrounding areas
Wood Rot Experts is the St. Louis metro's dedicated wood rot repair specialist, serving homeowners in Kirkwood, Webster Groves, Clayton, Chesterfield, Creve Coeur, and the surrounding area. Their approach combines epoxy consolidation, precision partial replacement, and moisture source correction — addressing the root cause alongside the visible damage. Their clients typically save 60–80% compared to full replacement of affected sections.
- ✓Saves 60–80% over full wood replacement in most cases
- ✓Corrects moisture source alongside structural repairs
- ✓Serves Kirkwood, Webster Groves, Clayton, and St. Louis metro
- ✓Handles both dry rot and wet rot — including crawl space and sill plate repairs
- ✓Free assessment to determine repair vs. replacement viability
Wood Rot Prevention: 5 High-Impact Steps
Every wood rot problem has a moisture source. These five steps address the most common sources in St. Louis-area homes and substantially reduce recurrence risk.
Maintain Positive Drainage Away from the Foundation
Soil grading should slope away from the foundation at a minimum 6-inch drop over 10 feet. Flat or negative-grade landscaping channels water toward the sill plate — the most common cause of structural wood rot in St. Louis homes. Regrading is a $300–$1,000 project that prevents thousands in structural repairs.
Keep Wood-to-Soil Clearance at 6 Inches or More
Any wood-to-soil contact is a rot initiation point. Siding, trim, deck posts, and stair stringers that touch soil retain moisture and invite fungal colonization. Maintain at least 6 inches of clearance between all wood framing/siding and the ground surface.
Inspect and Maintain Caulking at All Wood Joints
Window frames, door frames, and any joint between wood and a dissimilar material (brick, concrete, metal) should be caulked with a flexible exterior-grade sealant. Caulk degrades and shrinks over 5–10 years — failed caulk is an open channel for water into end-grain wood, which absorbs moisture rapidly and rots first.
Keep Gutters Clear and Downspouts Extended
Clogged gutters overflow against fascia boards and the soffits above them. Downspouts that terminate at the foundation deposit roof water directly against the sill plate. Gutters should be cleaned twice annually in the St. Louis area. Downspout extensions should discharge at least 6 feet from the foundation.
Ventilate Crawl Spaces and Inspect Annually
Crawl space moisture causes the majority of structural wood rot in St. Louis homes. Crawl spaces should have continuous vapor barrier covering the soil, vents for cross-ventilation (or a sealed conditioned space with a dehumidifier), and annual professional inspection. Most homeowners never inspect their crawl space — by the time rot is detected from above-floor symptoms, the damage below is extensive.
Frequently Asked Questions
How much does wood rot repair cost?
Wood rot repair costs range from $200–$500 for minor surface damage, $500–$1,500 for moderate damage (a full window frame or porch post), and $1,500–$5,000+ for major structural damage (floor joists, sill plates). Professional repair typically saves 60–80% compared to full replacement.
What is the difference between dry rot and wet rot?
Dry rot is caused by a specific fungus that can spread beyond the moisture source and produces cube-patterned cracking. Wet rot is localized to areas of persistent moisture and causes deep damage in constantly wet environments. Both require professional assessment when structural members are affected.
Can I repair wood rot myself?
Minor surface wood rot on door frames or window sills can be addressed DIY with epoxy consolidant and filler. Any rot affecting structural members — floor joists, sill plates, load-bearing posts — requires professional assessment. Improper structural repairs can fail silently under load.
How do I know if my wood rot is structural?
Probe the wood with a screwdriver — structural concern begins when the probe sinks more than 1/4 inch without resistance. Soft wood in floor joists, sill plates, rim joists, or load-bearing posts requires professional evaluation before any repair.
Suspected Wood Rot in Your St. Louis Home?
Wood Rot Experts serves Kirkwood, Webster Groves, Clayton, Chesterfield, and the wider St. Louis metro. Free assessment — no obligation. Act now and save 60–80% over full replacement.