How to Find a Roof Leak — A BC Roofer's Method

Water is a liar. The stain on your ceiling is rarely under the actual hole, because water runs along rafters and sheathing before it drips. Here is the method we use to trace a leak back to where it really started, what to check first, and the moment to stop and call someone. From Paragon Roofing BC, family owned since 2010.

HS
Harman Singh — Senior Roofing Specialist
2026-06-21 | Updated 2026
Quick answer
Find a roof leak by working backwards from the drip. Water enters at a gap and travels along the sheathing before it drips, so the entry point is always uphill of the stain. Start in the attic on a dry day, follow any water trail to its highest point, and look near roof penetrations like vents, chimneys, skylights, and valleys, where most leaks begin.
Water travels
The drip is rarely under the hole
Penetrations
Where most leaks actually begin
Attic first
The dry day detective work

Start with this truth and the whole job gets easier. Water does not fall straight down through a roof. It finds a gap, runs along the underside of the sheathing, tracks down a rafter, pools on a ceiling joist, and only then drips into your living room, often a couple of metres from where it got in. So the brown ring on the ceiling is a clue, not an address. Finding the real entry point means thinking like water and working backwards. Patiently.

Start in the attic, on a dry day

The attic is where the truth lives. Grab a good flashlight and go up during daylight, ideally when it is not actively pouring, and look at the underside of the roof deck. You are hunting for the trail water leaves behind: dark staining on the wood, streaks running down a rafter, a rusted nail, a patch of damp insulation, a faint bloom of mould. Follow any stain uphill. Water runs down, so the highest point of the stain is closest to the entry. On a sunny day, kill the flashlight for a second and look for pinpricks of daylight coming through the deck. Those little stars are leaks waiting to happen.

Know where leaks actually start

Here is the part that surprises people. The wide open field of shingles is almost never the culprit. Leaks live at the interruptions, the spots where something pokes through the roof or two planes meet. Chimneys. Skylights. Plumbing stacks and vents. Valleys where two slopes funnel water together. The flashing where a roof meets a wall. Get the locations of these on your roof clear in your head, then map them against where the attic stain sits. The leak is almost always near one of them, uphill of the drip.

Common leak points, ranked by how often we find them

Leak point Why it fails What to look for
Flashing at walls and chimneys Sealant ages, metal lifts, mortar cracks Gaps, rust, loose or lifted metal
Plumbing stack boots Rubber collars dry out and split Cracked or perished rubber at the pipe
Skylights Seals and flashing degrade over time Stains at the skylight corners inside
Valleys Debris dams water, fasteners back out Moss buildup, loose valley metal
Missing or lifted shingles Wind damage and age Bare spots, granules in the gutter
Nail pops Fasteners work loose, expose a hole Raised bumps, rust streaks below

The water test, done carefully

If the attic trail is ambiguous, you can recreate the leak. One person runs a garden hose on the roof while a second watches inside the attic. Work in sections. Soak low first, near the drip, then move uphill bit by bit, pausing a few minutes at each spot. The moment water appears inside, you have found it. This takes patience and two people, and it only works safely from a ladder or a low slope you can stand on without risk. If the roof is steep, wet, or high, do not climb it. That is not where you save money.

When to stop and call us

The roof is steep, wet, or high
Step away from the ladder. A fall costs far more than a service call. We have the gear and the footing for it.
The stain keeps spreading
An active, growing leak is rotting your deck right now. Get it looked at before the next atmospheric river.
You found the spot but not the cause
Plenty of leaks have more than one entry, or hide behind flashing only a teardown reveals. We chase the root.
It is a flat or low slope roof
These hide leaks differently, often far from the entry under the membrane. They need a trained eye.

Tracing a leak is detective work, and a careful homeowner can often get close. But finding water and stopping it for good are two different jobs. We do leak detection and repair across Metro Vancouver, and on a wet coast that is most of our winter. If the trail goes cold, or you would rather not be on a ladder in November, call us. See our leak detection and repair and roof repair pages.

Frequently Asked Questions

Why is my ceiling stain not under the leak?

Because water runs sideways before it drips. It enters at a gap, travels along the underside of the sheathing or down a rafter, pools, and finally drips, often a metre or two from the true entry point. That is why you trace a leak by following the stain uphill in the attic rather than assuming the hole is directly above the drip.

Where do most roof leaks start?

At the interruptions, not the open field of shingles. Flashing at walls and chimneys, plumbing stack boots, skylights, and valleys are the usual suspects. These are the spots where something penetrates the roof or two planes meet, and they fail long before a healthy field of shingles does. Map those locations against your attic stain and you are usually close.

Can I find a roof leak myself?

Often, yes, with patience and a dry day. Start in the attic with a flashlight, follow any water trail uphill, and look for daylight through the deck. A two person hose test can confirm a suspect spot. What you should not do is climb a steep, wet, or high roof to investigate. Finding the clue is safe from the attic; chasing it across a slick roof is not.

How does the hose test work?

One person runs a hose on the roof while another watches in the attic. You soak low near the drip first, then move uphill in sections, pausing a few minutes at each. When water shows inside, that section is the source. It only works safely on a roof you can reach from a ladder or stand on without risk, so leave steep or high roofs to a pro.

My roof is flat. Is finding the leak different?

Yes, and harder. On a flat or low slope roof, water can travel a long way under the membrane before it finds a way down, so the interior drip can be far from the breach. These systems hide their leaks, which is why flat roof leak hunting usually needs a trained eye and the right approach rather than a quick visual check.

Should I just patch it myself once I find it?

You can buy time with a temporary fix, but a lasting repair means understanding why it failed, which often hides behind flashing or under shingles. Many leaks also have more than one entry. If the stain keeps spreading or you are not certain you found the root cause, get it properly diagnosed before the damage reaches your deck and framing.

Leak You Can't Pin Down? We'll Find It.

We trace roof leaks back to the real source across Metro Vancouver, then fix them for good. No guesswork, no climbing on a wet roof yourself. 20 year workmanship warranty on repairs.

Book Free Estimate Roof Repair Call us any time: 604‑358‑3436
HS
Harman Singh
Senior Roofing Specialist & Project Manager — Paragon Roofing BC
CertainTeed Master Roofer IKO Master Roofer BC Licensed Contractor

15+ years of Lower Mainland roofing experience. Harman leads project teams across Metro Vancouver and the Fraser Valley with a focus on institutional quality work for residential, strata, and commercial properties. Direct line: 604‑358‑3436.

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