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How To Find Leaks In Your Roof?

Identifying the source of a ceiling leak is similar to putting together a puzzle. You might think it’s simple enough, but finding where water is coming into the home may be an exercise in trial and error. 

A thorough inspection and eliminating the most obvious causes is a good starting point when you want to identify the source of the leak in your ceiling.

Roof leaks can be caused by missing shingles, gaps in the metal flashing around chimneys and vent pipes, or small holes in the roofing. 

The source of a leak often isn’t obvious on the roof itself, and it can be hard to pinpoint since the water may run down the roof decking and rafters before dripping onto the ceiling below.

What is Leak Detection?

As indicated above, finding a leak in a roof may be the hardest part of fixing a leaky roof. Finding the actual spot where the roof leaks is difficult because water can enter the roof in one place and flow to another position before it starts soaking into the ceilings or walls.

Clear signs you have a roof leak

Unless you’re someone who periodically goes into the ceiling space, chances are you won’t become immediately aware of a roof leak until it causes some form of damage to other parts of your home. 

The most common sign that you have a leak in your roof is when you spot water damage on your ceiling or the walls in your home.

Water damage often shows as either a slight discolouration (typically a yellow, brown, or black colour) or warping of the material on your ceiling or walls (e.g. warped wallpaper). 

Often it can be a combination of both. When the damage shows as more severely warped or discoloured, this typically means it’s water damage that has built up over a longer period of time.

Sustained water damage can present several risks as time goes on, both in a structural and health-related manner.

In terms of structure, the more water damaged your ceiling and/or walls become, the more they are weakened. Eventually, the most severe water damaged ceilings and walls can start to rot away or even collapse.

On the health side of things, water damage can become a breeding ground for mould, which can create a range of health issues. These include respiratory problems, itchy eyes, chronic coughing, rashes, headaches and/or migraines, sinus issues, frequent sneezing, and constant tiredness.

So whether you look at it from a structural or health-related angle, the water damage that can occur from a roof leak needs to be resolved ASAP.

How to Locate the Source of a Roof Leak

Finding where the leak is coming from isn’t as simple as just finding a wet patch on the ceiling. Often the location of the actual leak is not always where the water ends up staining your plasterboard and ruining your paintwork. 

Water can enter your roof at one end of the house and trickle down through insulation before soaking into a weak spot in your ceiling.

Take a walk outside and visually inspect your roof. Start with the parts of the roof that are higher than the location of any stains inside, or any obvious signs of roof penetrations. 

If you can spot any damaged spots on your roof, tiles, corrugated iron sheets, or shingles, this could be the location of the leak. 

You might also see water spots under your roofline on exterior walls. This could be a sign that your flashing is damaged and needs to be repaired or replaced.

Once you’ve had a look outside, have a closer inspection on the inside of your house and roof. Inspect your ceiling and look for peeling paint, moisture marks, and brown, grey, or yellow stains. 

These are all tell-tale signs of a leaking roof. To be extra thorough, grab a flashlight and take a look inside your roof space or attic. Mould, water stains, and damp rafters or beams are obvious signs of a roof leak, and you might even be able to follow the flow of water to the source.

  • Begin by locating the leak on the inside of the home. Confirm that the source of the water on the inside of the home is a result of a roof leak and not due to a problem associated with other components of the home. Other sources of potential leaks in the home include plumbing, roof scuppers, roof drains, HVAC, and condensation.
  • Once you have determined that a roof related issue causes the leak, measure the location of the leak in the living space from two fixed points. These fixed points can be perpendicular to exterior walls, a fireplace chimney, or other components that extend through the finished ceiling to the attic space or roof surface.
  • Go into your attic and locate the source of the leak on the underside of the roof deck using the measurements taken from your home’s living space. Review the active leak and note the surface where the leak is dripping from. The location of the actual entry point of the water into the attic space may be slightly different than where the leak is showing on the interior of the home so you may need to expand your search area once you are in the attic.
  • Measure the location of where the water is entering the attic space from two fixed points. Look for fixed points such as vent pipes for bathrooms, chimneys, or vents. If these roof penetrations are not available, base your measurements on two perpendicular exterior walls.
  • Safely gain access to your roof and apply the measurements taken from the attic space to the roof surface. You would need to adjust your measurements to take into account the depth of the exterior bearing walls and soffit overhangs if your measurements were based on the location of exterior walls.
  • Locate the approximate location where the water is entering your attic space. Begin to work outward in concentric circles from the location where you determined the leak is occurring. As you review the roof remember that any opening in the roof system is an opportunity for water to enter your home. If the roofing materials show any openings where water can penetrate your home’s building envelope, this will result in a roof leak.

Finding the source of some leaks is easy. Others will require detective work and possibly a garden hose and an inside spotter. 

If you don’t feel comfortable on a roof, call any local service to do a free roof damage analysis for you. Sometimes this can be as hard as finding the smallest leak! Here are some tips that may help you find a pesky roof leak

The Field of Shingles

If your roof is older, the leak may be within the roof field. This means the expanse of shingles, slate, or shakes. If your roof is asphalt, then you can walk around with ease. Other materials such as slate, concrete tile, or clay tile may not be so forgiving. 

You can crack roofing if you walk on it, so be careful. With regular shingles, look at the tops of the vertical knockouts. Look for missing coloured granules. Look for cracks. Possibly a nail has backed itself out of the roof sheathing. Simply take your time and hunt.


A valley is a line where two roof planes intersect. There are different types such as metal flashing or rolled roofing. 

Other places simply lace the shingles together. Valleys can cause big problems if you do not trim the shingles correctly. When you trim a shingle for a valley, you end up with a chisel point on the end of the shingle. 

If a second cut is not made to make this point like an arrow point, then water can travel along the top of the shingle and find its way inside your house. The shingle wrapper tells you how to make this simple second cut.

Head Wall Flashings

Some roofs stop at a vertical wall. A metal flashing must be in place to direct water streaming down the wall away from the stopping point of the shingles. This flashing may be behind wood siding or in front of a brick wall. 

The flashing should extend over the shingles at least three inches. If the wall is brick or another masonry, the flashing must bend and extend one inch into a mortar joint. 

Tar, caulk, or roofing cement should never be used in conjunction with these materials. If you see them, it is a sign that someone tried to patch a leak!

Wall Step Flashing

Some roof leaks happen at step flashings. You find these flashings where a roof climbs alongside a vertical wall. As each row of shingles is laid, a step flashing is installed over the shingle next to the wall. 

Part of the flashing turns up on the wall, and the other portion gets covered by the next row of shingles. Look for rust or holes in these flashings. In reality, if all is well, you will be able to see only the smallest portion of these flashings.


These are the source of many a leak. Chimneys contain four different types of flashing. All must be in good shape, or you will have a leak. In addition, the counterflashing that goes into the brick mortar joint must not be damaged. 

A hairline crack above the flashing can allow vast amounts of water to run behind the flashings. Look for soldered corners of flashing that might have broken or have holes. Do not use caulk to repair these flashings!

Plumbing Vent Flashings

May newer vent flashings incorporate a rubber seal with an aluminium flashing. The rubber can fail in as little as 10 to 15 years. Look for cracked rubber around the plumbing pipe. The flashing should dive up and under the shingles that extend up the roof from the middle of the plumbing vent. The bottom half of the flashing should be exposed and actually cover the shingles.

Furnace or B-Vent Flashing

These flashings are identical to plumbing vent flashings. However, they sometimes have a metal storm collar. These simply fit tightly around the vertical pipe that exits the roof. If they become loose, the storm collars can cause leaks.

Ice Dam Leaks

Ice dam leaks especially plague people in very cold climates. These leaks can happen even if your roof is not damaged. Ice dams block the natural flow of water down a roof. The water begins to back up under flashings, shingles, tar paper, etc. 

Once the water begins to flow into the house, it can drip for days. The only means of prevention is to install membranes under the roofing. The membranes won’t stop the ice but will stop water leaks if installed properly.

Wind Blown Rain Leaks

Wind-driven rain can also be a major problem. Once again, you could actually have a good roof and wind will drive water up and under your roofing materials. The only lines of defence are tar paper and the ice dam membranes. 

If you have metal valleys, you may want to hem the edges. This means that the hidden edges of the valley actually have a 180-degree bend. 

This creates a channel that directs windblown rain back to the bottom of the valley. It’s a good idea to cement under shingles on the edges of roofs that face the wind.  Don’t underestimate the power of a 70 mph sustained wind-driven rain.

Non-Roof Leaks!

Sometimes you think you have a roof leak when in fact the roof is fine. Attic condensation is a prime example. High humidity can cause condensation and “rain” to fall in your attic. It can also make the underside of the roof sheathing look wet. You think you have a leak instead. 

Chimney crowns can develop cracks. The inside surface of the chimney gets discoloured or the plaster bubbles. You think a roof leak is a cause. Siding can be missing above a roof. This can cause water to enter behind head flashings. Have a snoop around for the leaks!

Leak Sources Other Than Your Roof

If you experience a leak in your home, you can choose to make the repair yourself or hire a professional roofing contractor to complete the repair. 

If you place a service call with a professional roofing contractor and he determines that the cause of the leak is something else unrelated to the roof on the home, he may still charge you a diagnostic fee. 

In order to avoid this charge, it is recommended that the homeowner attempt to rule out other causes of leaks. These may include:

  • Air conditioning leaks
  • Condensation
  • Pest infestation

How to Test for Water Leaks on Your Roof

There are many ways to test for water leaks on your roof, depending on the type of roof that you have, the resources that you have access to, and the amount of experience you have doing home repairs.

The Garden Hose Method for Finding Roof Leaks

One way to test for leaks is to run your garden hose over the roof and see if or where drips come in on the inside.

Get someone to help you by going outside and running the hose over the roof while you are inside around the area(s) you suspect the roof leak is coming from.

Start with the areas just above the potential leak, and isolate small areas one at a time so you can pinpoint the leak.

For instance, soak one side of the chimney or skylight first, then do the other sides and the top so you can get the most accurate idea of where the leaks are happening.

Spend at least a few minutes on each side and note that the entire process may take at least an hour, so you should be ready to settle until you see a drip.

When you or your assistant see a drip or leak inside, then find a way to mark the spot and bring the hose upstream from the leak and see if it continues, and don’t be afraid to change directions if you can’t source it immediately.

You (or your helper) should stay inside the house near where you suspect the leaks may be occurring and look for drips or moisture to appear, and inform the person wielding the hose to move the stream in various directions upwards of the leak until you find a source.

If you or your assistant(s) can access the roof, don’t be shy about removing shingles in the area that you’ve deemed to be problematic in order to pinpoint the source of the leak and discover the exact spots you need to fix.

You’ll likely see water-stained or even rotten wood or at least discoloured felt paper located directly around the rook leak.

This is perhaps one of the easiest methods for finding a leak, but the exact methods you use can be determined by the type of roof and access to the roof that you have along with your home repair skills and access to qualified helpers.

One thing to remember is that that once you find the leak and are getting ready and gathering supplies to repair it, make sure you mark where it is located and use a measuring tape to determine the amount of area you need to cover (this is particularly helpful if you are using the plastic sheeting method described in one of the sections below).

You can use those measurements to determine the area that you need to cover on the outside of your roof with the plastic sheeting, or the inside with plywood or shingles.

Why do I need this?

Unattended roof leaks can lead to a number of undesirable outcomes including but not limited to flooding, staining, ceiling, and wall collapse, and damaged household goods.

Remember that once a roof leak is found, it needs to be fixed. This may be something as simple as a tile or metal sheet replacement, or part of a more substantial issue with your roof.

Leaks only get worse. Act quickly once you’ve pinpointed the location of yours. Fortunately, in many instances, it takes only a modest roof repair to fix the leak. For example, replacing a shingle. If you don’t feel comfortable on the roof, however, or if the leak seems extensive, do not hesitate to contact a professional.


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