How to Find a Roof Leak (Before It Costs You a Ceiling)

First, tonight: limit the damage

1. Move anything valuable out from under it.
2. Put a bucket down. Lay a towel in the bucket to stop the drip noise driving you mad.
3. If the ceiling is bulging, pierce it in the center with a screwdriver, into the bucket. That sounds wrong and it is right: draining it at one controlled point beats letting the water spread until the whole sheet of drywall comes down.
4. Photograph everything before you clean up, for your insurer.

Why the stain is not under the hole

Water enters the roof, hits the sheathing, and runs downhill along the underside of the deck or along a rafter until it finds something to drip off. That can be ten or fifteen feet from where it got in. Chasing the stain is how you end up with a patched roof that still leaks.

Finding it from the attic, which is where you should start

Go up with a flashlight on a bright day, and turn the attic light off.

• Look for daylight through the deck. Obvious, and it does happen.
• Look for water staining on the underside of the sheathing, then follow the stain uphill. Water runs down; the entry point is always above the highest wet mark.
• Check every penetration from below: vent pipes, bath fans, chimney, anything that comes through the deck.
• Feel the insulation for damp patches.
• Look for rusted nail shanks, which means condensation rather than a leak.

Mark the highest wet point with a marker or a piece of tape. That is roughly what is above it on the roof.

The garden hose test

Two people, on a dry day, with the roof dry to start.

1. One person in the attic with a flashlight, watching the suspect area.
2. One person on a ladder with a hose, starting low on the roof, at the eave directly below the suspect area.
3. Run water on one small area for several minutes. Not a spray across the whole roof.
4. No leak? Move up two or three feet and repeat.
5. Work upward until the person inside says water is coming in. That spot, or just above it, is your entry point.

The discipline is isolating one small area at a time. Hosing the whole roof tells you it leaks, which you already knew.

The five places leaks actually come from

1. Pipe boots, by a mile the most common

The rubber collar around a plumbing vent pipe dries out, cracks and splits, usually between years ten and twenty. It is also the cheapest thing on this list to fix.

2. Step flashing where a wall meets the roof

Individual metal pieces woven into each shingle course. When someone caulks over the joint instead of replacing the flashing, it fails again within a year or two.

3. Valleys

Two roof planes dumping into one channel means a lot of water at high speed. Debris packs in, the water backs up sideways under the shingles.

4. Chimney and skylight flashing

The counter-flashing should be let into the mortar joint. Caulk alone is a two-year fix at best.

5. Ice dams at the eave

If it only leaks in winter, during a thaw, this is almost certainly it. That is an attic insulation and ventilation problem, not a shingle problem. See ice dam removal and prevention.

Things that look like a roof leak and are not

• Condensation. Frost on the nails in winter, damp across a wide area rather than one spot, worse in cold weather. That is a ventilation problem.
• A plumbing leak in a wall or an upstairs bathroom.
• An HVAC condensate line backed up in the attic, which drips all summer and never in winter. The tell is that it leaks when it has not rained.

Test: does it only ever happen during or after rain? If no, look at plumbing and HVAC first.

When to stop and call someone

If the roof is steep, wet, icy, or you would be on a ladder above one story, stop. A repair costs a few hundred dollars. A fall costs considerably more. We inspect free anywhere in Ward County and send you the photos either way.

Questions we get asked