It usually means the roof deck under the shingles has been wet long enough to weaken or rot, most often from a leak or attic condensation.
Get My Free Estimate →A soft or spongy spot on a roof usually means the roof deck under the shingles has been wet long enough to weaken or rot. The water most often comes from a leak at flashing, vents or other openings, or from condensation in the attic.
Have it checked from the attic, replace the damaged decking promptly, and fix whatever let the moisture in. A soft area tends to grow the longer it stays wet.
Buckshot replaces damaged roof decking and fixes the leak or ventilation problem behind it. This guide explains what a soft spot means, what to check and how the repair works.
What a soft spot on a roof is
The roof deck is the layer of plywood, OSB or boards that the shingles are nailed to. When that wood stays wet, it loses strength and can start to rot.
A soft spot is an area where the deck gives underfoot or sags slightly. Roofers usually find them while walking a roof, and from the ground they can show up as a dip in the roof surface.
Do not walk on the roof to look for one. A weakened deck may not hold your weight.
What causes soft spots on a roof
Moisture is the most common cause of roof deck rot. It reaches the wood from outside through a leak, or from inside as condensation.
Leaks at flashing, vents and other openings
Water usually gets into a roof at seams, edges, flashing and anything that passes through it, such as vent pipes and chimneys. A small, slow leak can soak the deck for months before anyone notices it inside.
Condensation in the attic
Warm, moist air from the house can condense on the cold underside of the roof deck in winter. Repeated wetting from below weakens the wood the same way a leak from above does.
Our guide to frost in the attic explains how that moisture builds up, and good attic ventilation helps the deck dry out.
Storm damage
Hail, wind or a falling branch can crack shingles or loosen flashing. That opens a path for water that may not cause a visible leak right away.
Old repairs that trapped moisture
A patch laid over damaged wood, or roof cement smeared over a problem area, can hold water against the deck. The wood underneath keeps rotting out of sight.
What to check from inside the house
The attic is the safest place to look. On a dry day, use a flashlight to check the underside of the roof deck around the soft area.
- Dark staining or water marks on the wood
- Wood that looks crumbling, flaking or soft
- A musty smell
- Mold or mildew on the deck or rafters
Do not expect a ceiling stain every time. Water often runs along the deck or rafters before it drips, so the soft spot and the stain can be far apart, as our guide to water stains on the ceiling explains.
Why soft spots should be fixed soon
A soft spot rarely stays the same size. As long as the wood keeps getting wet, the rot spreads into the surrounding decking.
Rot can also reach the rafters that hold up the roof. If a whole section of the roof line has started to dip, read our article on why a roof sags.
A weak deck is also a safety risk. Anyone stepping on that area during a repair or inspection could break through.
Found a soft or sagging spot on your roof? Our on-site inspection is free, so you can find out how far the damage goes before it spreads.
Free on-site inspection · Family-owned since 1979How a soft spot on a roof is repaired
A lasting repair replaces the damaged wood and stops the moisture that caused it. Covering a soft spot with new shingles alone leaves the rot in place.
- Find the source. The leak, flashing failure or condensation problem is identified first.
- Open the area. Shingles and underlayment are removed over the soft spot and around it.
- Cut out the rot. Damaged decking is cut back to sound wood.
- Check the framing. Rafters under the area are checked and repaired if needed.
- Replace and rebuild. New decking goes in, followed by underlayment, flashing and shingles.
- Fix the cause. Flashing, vent boots or attic ventilation are corrected so the deck stays dry.
Our roof repair team handles the leak and the reroofing, and our decking crews replace the damaged wood. Our guide to roof decking and when to replace it explains the materials.
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Repair or replace the roof
A single soft spot on a sound roof is a repair. Several soft areas, or soft spots on an older roof, usually point toward a replacement.
During a roof replacement, the whole deck is exposed. Damaged sheets can be replaced everywhere at once, rather than one patch at a time.
How to prevent soft spots
Most soft spots start as small leaks or moisture problems that were not caught early. These habits help keep the deck dry.
- Have the roof checked after major storms
- Fix small leaks and damaged flashing as soon as you find them
- Keep vent boots and chimney flashing in good repair
- Keep attic ventilation balanced so moisture can escape
- Keep gutters clear so water does not back up at the roof edge
Get a soft spot checked
Buckshot Exteriors is family-owned, has served homeowners since 1979, and has offices in Madison, Wisconsin and Centerville, Iowa. We replace damaged roof decking and repair the leak behind it as part of our residential roofing work, and our on-site inspection is free.
Call (608) 909-9109 to schedule your free inspection, or send us a message and we will set a time. If you would rather check first, the attic checklist above is a good start.
Get a straight answer on your Madison roof
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