Drips in February, Dry in October
A 40-by-60-foot insulated shop with a 4/12 gable standing-seam roof was completed last October. The panels are screwed to 2x4 purlins on trusses. R-19 vinyl-faced batts are draped between the bottom chords, and the vinyl facing is neither sealed nor taped anywhere. There is no underlayment, no ridge vent, and no eave vent. In February the owner calls: water drips from the ceiling near the ridge, rust streaks run down the underside of the panels, and the problem is worst on cold mornings after his wood stove has burned all evening. A heavy October rain produced no drips at all. Two other contractors have quoted $6,800 to "reseal the whole roof." He wants your price by Friday.
1. How do you tell whether this is a leak or condensation, and which is it?
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Build the diagnosis from the sequence of events rather than from the panels.
| Observation | Leak | Condensation |
|---|---|---|
| October downpour | Would drip | No drips |
| Timing | During/after rain | Cold mornings, after the stove runs |
| Pattern | Localized, tracks a path | Broad, worst near ridge and on the cold panel underside |
| Staining | Rust rings under specific laps | Uniform rust streaks along the panel underside and at fasteners |
Every row points the same way: condensation, not a leak. The mechanism is straightforward. The vinyl facing on the batts is a vapor retarder in name only - it is draped and untaped, so warm moist air from the shop and the wood stove bypasses it at every purlin, seam, and perimeter, rises into the unheated cavity, and hits a cold steel panel. The panels condense, the water runs back down the slope toward the ridge on the pans, and the purlins stay cold enough to condense on their own.
Confirm before you quote: a moisture meter on the deck, thermal imaging on a cold morning, and a look at the stove's combustion air and flue. Do not skip this - if you sell a fix based on a guess, you own the outcome.
2. What is the correct repair, and what do you tell him about the $6,800 reseal?
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Tell him the reseal is money set on fire. There is no seam to seal. Adding sealant to a roof that is not leaking changes nothing about where the moisture is coming from, and it will not survive the panel movement it is being asked to bridge.
The fix is to control the air and the thermal boundary:
- Air-seal the warm side. Tape and seal the vinyl facing at every seam, purlin, penetration, and perimeter, or replace it with a properly detailed air barrier. Air movement, not vapor diffusion, is carrying the water.
- Fix the thermal boundary. Right now the roof plane is uninsulated and cold. Either bring insulation to the roof - rigid board above the purlins with thermal blocks so the purlins do not become condensing surfaces - or move to a closed-cell spray-foam assembly applied to the underside of the panels between purlins, detailed so the purlins are covered.
- Deal with the stove. A wood stove in a tight shop is a moisture and pressure machine. Verify combustion air is drawn from outside and that the flue is not leaking products into the attic.
- Ventilate the cavity if any part of the assembly remains unconditioned.
None of this is a roof-covering repair, and the proposal should say so in plain language.
3. Write the commercial terms: how do you structure the proposal so an uncertain diagnosis does not become your warranty?
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Sell the diagnosis separately from the remedy, and write the limits into the document.
- Phase 1 - assessment, fixed fee. Moisture readings, thermal imaging on a cold morning, air-leakage inspection, and a written report with photos. This gets you paid for judgment and keeps you from bidding a remedy for a cause you have not confirmed.
- Phase 2 - scope by line item. Air sealing, insulation strategy, ventilation, and any panel or fastener work, each priced separately so the customer can phase it.
- Explicit exclusions. No roof-covering replacement, no gutter work, no correction of the stove or its flue, no interior finish repair.
- A cause statement, not a leak warranty. The proposal states that the work addresses condensation caused by warm-side air leakage and an uninsulated roof plane, and that the contractor does not warrant against moisture from interior processes, combustion appliances, or future penetrations.
- Verification. Offer a return visit after the first cold snap to confirm the drips have stopped, and make that visit part of the price.
A contractor who diagnoses correctly and writes a narrow scope keeps the customer; one who reseals a roof he knows is not leaking buys himself a callback every February.