Short answer: Most roof leaks come from flashing (around chimneys, walls, skylights and valleys), cracked vent pipe boots, or missing and damaged shingles. Water runs along the roof deck and rafters before it drips, so This Old House advises following the water stains uphill in the attic to find the source. A garden hose test with a helper can confirm it. Steep, high or wet roofs are a job for a roofer.
Quick diagnosis
| What you notice | Most likely cause | What to check | Call a pro? |
|---|---|---|---|
| Stain near a chimney | Chimney flashing or crown | Look in the attic by the chimney | Yes |
| Stain under a plumbing vent | Cracked vent pipe boot | Look at the boot with binoculars | Often |
| Stain along a valley | Valley flashing or shingles | Check the attic under the valley | Yes |
| Leak only in winter, at eaves | Ice dams | Check for ice on the roof edge; attic heat loss | Often |
| Leak after wind storm | Missing or lifted shingles | Look from the ground | Yes |
| Drips only on cold mornings, no rain | Attic condensation | Check attic ventilation and insulation | Often |
Trace it from the inside
- In the attic, use a flashlight to look at rafters, roof sheathing and insulation for stains, wet spots or mold. Step only on framing.
- Follow the stains uphill to the highest wet point.
- Mark the spot, and consider pushing a nail up through it so you can find it from outside.
- Contain dripping water with a bucket and move belongings.
The hose test
With a helper in the attic, run a garden hose on the roof starting low and working up, a few minutes at each area (around the chimney, vent, valley). When the helper sees water, you have found the leak.
Safety
This Old House advises checking from the ground with binoculars first, using a sturdy ladder that extends at least 3 feet above the roof edge, and calling a professional for steep, multi-story or slippery roofs.
When to call a professional
- The leak is at a chimney, valley or skylight, or you cannot find it.
- The roof is steep, high or you are not comfortable on a ladder.
- There is rot, sagging sheathing, wet insulation or mold.
- Water is near light fixtures or wiring: turn off that circuit.
What it usually costs
HomeGuide (2026) lists minor roof leak repairs at about $150 to $1,000, moderate repairs with water damage at $1,000 to $3,000, and major repairs at $3,000 to $6,000+. Cracked vent boots run about $250 to $600, minor chimney repairs $150 to $700, valley flashing $300 to $1,500, and a roof inspection about $100 to $400.
Frequently asked questions
Why does my roof leak only in heavy rain?
Wind-driven or heavy rain can push water under flashing or shingles that hold up in light rain.
Can I fix a roof leak from the inside?
You can contain the water and find the source from the attic, but the actual repair is on the outside.
Related problems
Sources
This guide is general information, not a substitute for an inspection by a licensed professional. See our disclaimer.