Granule Loss, Caulk at the Chimney, and an Attic That Smells Musty in July
A 1998 two-story colonial with a 1,400-square-foot attic footprint. The roof has a single layer of architectural shingles. The south slope shows heavy granule loss in both valleys and along the lower third, with about 3/8-inch curl at the rake. The brick chimney has shingles run directly against the masonry, and the joint is sealed with a bead of caulk; no step flashing or counterflashing is visible. The attic has six soffit vents rated 65 square inches net free area each and a 12-foot ridge vent rated 18 square inches per linear foot. The buyer reports the attic "smells musty in July," and there is dark staining on the sheathing near the ridge.
1. Compute the required and provided attic ventilation and judge whether it explains the symptoms.
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Required net free area: 1,400 ÷ 150 = 9.33 sq ft = about 1,344 sq in, balanced roughly 50/50 - about 672 sq in intake and 672 sq in exhaust. (If the 1/300 exception applies because a vapor retarder is present and the venting is balanced, the total drops to 672 sq in, 336 each. That is a floor, not a target.)
Provided:
- Intake: 6 × 65 = 390 sq in (about 2.7 sq ft)
- Exhaust: 12 ft × 18 = 216 sq in (1.5 sq ft)
Both are below even the 1/300 allowance, and the balance is wrong.
Judgement: the musty smell and the dark staining near the ridge fit condensation from a poorly flushed attic - warm moist air rising and not being carried out - rather than a roof leak. But the staining has to be checked: probe for soft sheathing, look for a mold-like pattern or a leak at the ridge, and check whether insulation is blocking the soffit openings.
Recommend: clear or baffle the soffits, add intake area, balance exhaust to it, and have the sheathing evaluated. Ventilation numbers give you the diagnosis; the staining confirms it needs a look.
2. Evaluate the chimney flashing detail and explain the risk.
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What is there: shingles butted to brick with a surface bead of caulk. That is a maintenance seal, not flashing, and it is a one-season repair at best.
What should be there: step flashing woven in with each shingle course and lapped up behind the brick, counterflashing set into a reglet cut into the masonry so water running down the chimney is thrown out over the roof, and a cricket on the uphill side where the chimney is more than 30 inches wide.
The risk: when the caulk fails - and it will - water gets behind the shingles at the masonry, soaks the deck and the framing around the chimney, and often shows up as a ceiling stain well away from the chimney, which makes it hard to trace. Rot behind the brick and at the deck edge is common in this exact detail.
Report: no visible step or counterflashing, caulk-only joint at the masonry, and the fact that the hidden flashing cannot be verified without lifting shingles. Recommend evaluation and correction by a roofing contractor, as a separate line from the shingle condition.
3. How do you report the shingle condition without overpromising on remaining life?
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Do not put a number of years on it. A remaining-life figure is a prediction, and the buyer will treat it as a warranty on a roof you only saw from the outside.
Report the objective evidence:
- Heavy granule loss concentrated in the valleys and the lower third of the south slope.
- 3/8-inch curl at the rake.
- Any exposed mat, plus granule accumulation in the gutters and at the downspouts (that is where lost granules end up and it corroborates what you saw).
Then characterize, don't quantify: the south slope is at or near the end of its service life; localized failure and leaks should be expected; recommend a roofing contractor evaluate and quote replacement, plus a moisture check of the decking while it is open.
Why: "five years left" is a warranty you cannot support - you have not seen the underlayment, the fasteners, or the deck. "At or near end of service life" communicates urgency without transferring a guarantee you have no way to honor.