Exterior Rot Repair: Why It Keeps Coming Back and How to End It

Rot is the most repeated repair in Massachusetts — and the most repeated re-repair, because most rot fixes treat the symptom and reinstall the cause. Wood doesn’t rot from age; it rots from staying wet, and every punky window sill, soft corner board and crumbling post base has a water source feeding it. Here’s how we approach rot so the repair is the last one: find the water, fix the detail, and choose materials by location.

Where Houses Rot — and Why There

The hit list is predictable because the physics are: window sills and door thresholds (horizontal surfaces holding water against end grain), corner boards and trim bottoms (wicking splash-back from the ground or roof), post bases and stair stringers (end grain on concrete, drinking from below), fascia behind failed gutters, and anywhere flashing quit — deck ledgers, door hoods, roof-wall joints. Every one of those is a water-delivery detail first and a wood problem second. Paint failure is the early warning; soft under a screwdriver is the confirmation — the same probe test from the fall checklist and spring checkup.

The Repair Ladder

1. Epoxy consolidation — $200 to $800. For small, contained rot in pieces worth saving (historic sills, ornate trim): the soft wood gets consolidated and rebuilt with structural epoxy. Legitimate for the right piece, a band-aid when it’s used to avoid finding the leak.
2. Cut out and replace — $500 to $3,000 per area. The standard fix: rot cut back to sound wood, new material in, and the flashing or gap that caused it corrected. That last clause is the whole difference between a repair and a subscription.
3. Structural repair — $2,000 to $10,000+. When the probe goes through trim into framing — sill beams, rim joists, porch framing — it’s carpentry of the kind in our porch guide and floor framing guide. Caught early it’s a section; ignored, it’s a season.

Wood, PVC or Composite: Choose by Location, Not Ideology

Cellular PVC trim (Azek and kin) and composites don’t rot — full stop — which makes them the default for the chronic offenders: anything within splash distance of the ground, water-table trim, post wraps, north-side shade zones. The honest trade-offs: PVC costs more up front, moves with temperature (installation detail matters), and holds nothing structural — it’s a skin, not a bone. Real wood — properly primed on all six sides, flashed, and kept clear of the ground — still earns its place on historic facades and anywhere profile-matching matters, per the same preservation logic we apply inside. The decking version of this decision has its own numbers in composite vs. wood decking.

Frequently Asked Questions

Why does the same spot keep rotting after every repair?

Because the water source was never on the work order. A sill that rots every five years has a gutter, flashing or caulk failure above it; replacing the wood resets the timer without stopping the clock. Ask whoever bids the repair one question: “What’s getting the water there, and what in this price fixes that?”

Is it rot or termites/carpenter ants?

Sometimes both — insects love wood that water softened first. Galleries and sawdust point to ants (which nest in wet wood but don’t eat it: still a moisture problem); mud tubes point to termites and a pest professional. Either way the carpentry fix is the same: dry it, replace it, close the water path.

Can rot repairs wait until the painting project?

Pairing them is smart — paint protects the repair and the repair makes the paint last. What shouldn’t wait is the probe test: rot grows on its own schedule, and the difference between fall and spring on an active leak can be the difference between trim and framing.

Make This the Last Time You Fix That Spot

Send photos of the soft spot and we’ll diagnose the water source with the repair — free written estimate, with the wood-vs-PVC call made honestly for each location. Repair work is in the project gallery.