How to Find a Roof Leak: Loft Checks, Outside Signs and Safety

A brown patch on the ceiling is rarely a sign that the hole is right above it. Water travels, and by the time it shows up in a room it may have run along a rafter, across insulation or down a wall for some distance. That's why finding a roof leak is mostly detective work, and the first clues are usually inside the house, not on the roof.

I've pulled together the method below from a home-insurance guide and a well-known home-improvement guide, plus the Health and Safety Executive's page on ladders. Note that the second of those is written for American homes, so I've kept to the parts that apply to any pitched roof. The big theme is staying safe: you can do nearly all of the searching from the ground and the loft.

Why a roof leak and its stain rarely line up

The home-improvement guide makes this point clearly: water can run sideways along sheathing or through insulation before it drips into a room, so the leak may sit several feet from the stain. The insurer guide adds that damp or mould close to the mark tells you the source is nearby, but not exactly where.

So the job is to start at the stain and work upwards and outwards, treating it as a trail to follow rather than a target.

Signs of a roof leak to look for first

• Drips during rain. Note where and when they start, and whether they stop when the rain does.
• Moisture or mould on ceilings or walls near the mark.
• Daylight in the loft. With the lights off, light coming through the roof means there's a gap.
• Missing tiles. The insurer guide says to look especially for several clustered around the leak, rather than one or two.
• Cracks in the seams or surface if you have a flat roof.
• A sagging roof. If it looks curved or wavy instead of straight, treat it as a possible structural problem and call a professional.

How to check the loft for a roof leak

The loft is where most of the evidence is. Take a torch and, if you can, do this on a rainy day, because the home-improvement guide and the insurer guide both point to the underside of the roof as the place to look.

1. Check the floor first. If there are no floorboards, the home-improvement guide says to step only on the joists so you don't go through the ceiling below.
2. Start directly above the stain and look at the underside of the roof for darker patches, damp or mould. Mould tends to stay put even after a dry spell, which makes it a good marker.
3. Look at the insulation. It shows water damage faster than wood does, and the guide suggests moving it aside around the damaged area and following the wet path back to where the water gets in.
4. Look for anything that pierces the roof, such as a stray nail, and then at vent seals, which the guide says can weaken over time.
5. Look at the roofing felt or underlay if you can see it. A hole there can be a source of a leak.
6. Wear gloves and safety glasses when handling insulation. The guide also recommends a respirator.

Checking the outside of the house from the ground

Next, step back and look at the roof from the garden or pavement. Binoculars help here. You're searching for slipped, cracked or missing tiles, a patch that looks different from the rest, and damaged flashing around the chimney, vents and other openings. If flashing is new to you, I've explained what roof flashing is and what it does in plain English.

The insurer guide lists the usual causes of leaks as storms with heavy rain, hail or high winds, cracked or broken tiles left unrepaired, damaged flashing, damaged underlay or felt, and blocked gutters, moss, weeds or branches affecting the roof. Gutters deserve their own look, because an overflowing gutter can send water where it shouldn't go. Our guide on how to clean gutters covers the safe way to clear them.

The hose test, and why I'd leave the roof end to a roofer

If the loft and the outside both leave you stuck, one method in the home-improvement guide is to simulate rain on a dry day. Two people are needed: one wets the roof with a hose in small sections, starting low and working up, and the other sits in the loft with a torch watching the underside for water.

The catch is that the person with the hose is on the roof. I wouldn't suggest that for a home owner. The HSE says ladders can be a sensible option for low-risk, short jobs, which it defines as no more than 30 minutes at a time. Standing on a wet pitched roof with a hose doesn't fit that description. If you want a hose test, ask a roofer to do it.

Limiting the damage while you wait for a repair

The insurer guide lists the sensible steps to take once you've spotted a leak:

1. Put a bucket or container under the drip so water doesn't spread.
2. Move belongings out of the way and make a note of anything damaged.
3. Take photos and videos of the damage and the weather conditions.
4. Call your insurer. For minor damage the guide says to get approval before repairs, and if the damage is severe a roofer can make repairs, but keep the receipts.
5. In an emergency, act straight away. The guide says insurers generally accept that urgent action was needed.

The guide also notes that damage on a roof over 10 years old may be treated as wear and tear, depending on your policy, so read yours.

When to call a roofer instead

• You can't find where the water's coming in.
• The leak comes back after a repair.
• There's ceiling damage, mould, or any sign the roof is sagging.
• The only way to see the problem is to climb onto the roof.
• The roof is steep, high, wet or icy.

The insurer guide and the home-improvement guide both say to bring in a professional roofer when the source isn't obvious or the damage is severe. I'd add one rule of my own: if you wouldn't be happy standing on the roof, don't.

Sharing what you know about roofing

A good leak diagnosis comes down to patience and knowing how water behaves on a roof, and that's knowledge other homeowners would value. If you work in the trade and write about it, there may be a place for your words.

Roofing contractors can see roofing blogs that accept articles from experts on this page.

Frequently asked questions

Where does a roof leak usually start?

It can start somewhere other than where the stain shows. The guides say water can run along rafters, insulation or walls before it appears. Common causes include broken tiles, damaged flashing, damaged underlay and blocked gutters.

Can I find a roof leak from inside the house?

Often, yes. Go into the loft with a torch, ideally in the rain, and look at the underside of the roof above the stain for damp, mould, wet insulation or daylight coming through.

Is it safe to look for a roof leak from the roof itself?

I wouldn't advise it. The HSE says ladders suit low-risk, short jobs of no more than 30 minutes. Use binoculars from the ground and ask a roofer to inspect anything that needs a closer look.

What should I do straight after I notice a leak?

Catch the water in a container, move belongings, photograph the damage and call your insurer. For minor damage, insurers may want approval before repairs, so check your policy first.

How do I know when the leak needs a roofer?

Call one if you can't find the source, the leak returns, the ceiling is damaged, there's mould, or the roof looks sagging.