What it usually means, the likely causes in order, what to safely try first, what a pro charges in Canada, and when to stop and call one.
This guide covers the common cases. Describe your exact problem and get a personalized diagnosis — free to start, with a DIY vs. call-a-pro verdict and a real cost estimate.
A soft spot in the siding, or a suspicion of rot behind it, deserves respect out of proportion to how small it looks from outside. The suspected cause is long-term moisture intrusion damaging the sheathing underneath, and sheathing is not decoration: it braces the wall and holds the siding. Rot spreads quietly while the surface may show only a subtle bulge, a crack in the paint, or a panel that flexes when pressed. By the time damage is obvious from the street, the affected area inside the wall is usually larger. This guide is about confirming the suspicion safely and scoping it honestly, not about reassuring yourself out of it.
Treat suspected rot as a priority, not a panic. It worsens if delayed, because the moisture source keeps feeding it and soft sheathing holds fasteners and structure less well with time. Move faster if the soft area is growing, sits below a known leak or failing gutter, is at the base of a wall near grade, or involves trim around a door or window that is also soft, since those locations often connect to framing, not just sheathing.
Water entering at a window corner, a deck ledger, a vent, or a failed flashing detail can run down inside the wall and soak the same patch of sheathing for years. The entry point is often above or beside the soft spot, not directly behind it, which is why tracing the water path matters more than staring at the damage.
Overflowing gutters, a missing kick-out flashing where a roof meets a wall, or a downspout discharging against the siding can drench one section of wall every rain. Rot concentrated under a roof-to-wall junction or below a gutter end is a strong match for this cause.
Joints around windows, doors, and corner boards depend on sealant and proper flashing. As sealant ages and cracks, wind-driven rain is pushed behind trim, where it dries slowly and rots the sheathing and trim from the back side while the front still looks freshly painted.
Soil, mulch, or pavement built up against the siding, and rain splashing off a hard surface at the base, keep the lowest course wet. Rot that is worst in the bottom portion of the wall, improving as you press higher, usually reflects this slow, wet foundation-line environment.
| Job size | Typical estimate (CAD) |
|---|---|
| Simple fix — the straightforward version of this repair | $300–$800 |
| Major job — complex, hidden, or replacement-level work | $2,000–$8,000 |
Estimates only, calibrated to Greater Toronto Area trade rates and adjusted by region on this site — not a quote. Your exact price depends on the cause, parts, and access. A personalized diagnosis narrows this range using your specific symptom.
This one is professional territory once the suspicion is credible. A homeowner can document, find the likely water source, fix a gutter overflow, and clear grade contact, and those steps genuinely limit further damage. Opening the wall, replacing rotted sheathing or framing, and rebuilding the flashing and siding layers in the correct order is contractor work, and it should include fixing the entry point, not just the rot. Ask any quote to state what happens if the opened area is larger than expected, because with rot it often is.
Usually further than the surface suggests. The area you can feel is where damage is advanced; surrounding sheathing may be damp, stained, or partly degraded without feeling soft yet. That uncertainty is normal and is why reputable contractors quote the visible scope with a stated approach for what opening the wall reveals, instead of pretending the hidden extent is already known.
That hides the problem without fixing it, and it can make things worse by trapping moisture behind new material while the sheathing continues to weaken underneath. New siding also needs sound sheathing to fasten to. The correct sequence is to open, remove damaged material back to sound wood, fix the water entry, then rebuild the layers and side over them.
Rot needs moisture, so a source genuinely fixed and a wall that dried out can leave old, dry damage that is no longer spreading, though the weakened sheathing still lacks strength. A contractor can probe whether the wood is damp and actively degrading or dry and historical. Either way, soft sheathing that no longer holds fasteners usually needs replacement, but the urgency differs.
Often not, because gradual water intrusion and maintenance-related deterioration are commonly excluded, while sudden events sometimes are covered. Policies vary, so this is a question for your insurer with photos and a timeline, not an assumption to build a plan on. Regardless of coverage, stopping the water source promptly is both the practical and the documentation-friendly first move.
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