How do roofers find where a roof is leaking?

The search starts at the stain inside and works uphill, because water travels before it drips. Where an attic can be entered, the underside of the deck is examined first for staining, rusted fasteners and daylight. Then every penetration, flashing and valley on the slope above the stain is inspected, and where several suspects remain, water is run on the roof from the lowest suspect upwards until the drip reappears.

Does a thermal camera find roof leaks?

It can show temperature differences that indicate wet insulation or a wet deck under the right conditions, and it shows nothing useful under the wrong ones. It does not show what is happening underneath a shingle, so it supports a diagnosis rather than making one.

How a Roof Leak Is Traced

Start inside, if there is any way in

The single most useful place to stand when looking for a roof leak is in the attic, under the slope, in daylight, with the lights off. Water leaves a track on timber and insulation that lasts for months: dark staining on the underside of the deck, a line of discolouration down the flank of a rafter, matted or discoloured insulation, rusted nail shanks, and on plank decking a stained seam that runs away from the wet area like a river on a map.

Daylight matters twice over. It shows the staining, and it shows daylight itself, coming through at any point where the roof is genuinely open. Pinpricks of light around a penetration are worth more than an hour of speculation on the roof surface.

Not every house allows this. Cathedral ceilings, insulated rafter assemblies, low slope additions and cramped attics over one part of a house are all common in this housing stock, and in those cases the search has to happen from above with the interior evidence as the only guide. That is harder and it is worth saying so rather than pretending otherwise.

Looking down from a roof at dark stripped plank decking on a Keys Roofing job, with an orange handled tear off bar, an aluminium D handle roofing shovel and two red flat shovels lying across the boards, an aluminium ladder hooked over the eave, a worker in a camouflage jacket and gloves crouched at the roof edge, and a brick paver patio, timber fence and lawn below. — **Plate six // getting to it** Nothing about a leak is diagnosed from a driveway. The work of finding one is the work of getting access to the slope above the stain and to every detail on it, which is also the reason a real inspection takes time and a sales call does not.

The search order

OneFix the stain's position in the building Which room, which wall, how far from the outside wall, how far along. Then translate that into a position on the roof, allowing for the fact that the entry is uphill and may be well off to one side.
TwoEverything that penetrates the roof above it Plumbing vents, flue stacks, box vents, ridge vents, satellite mounts, old aerial fixings, anything ever screwed to the roof and removed. Penetrations are where roofs leak.
ThreeEvery joint and change of plane above it Walls, chimneys, dormer cheeks, valleys, headwalls, skylights, the junction where a lower roof meets a taller wall.
FourThe field, and its fasteners Lifted, cracked, missing or tented shingles, popped fasteners, exposed nail heads, and anything that has been sealed before.
FiveThe edges Drip edge, rake, eave, gutter line and the condition of the first two courses, which are where backed up water shows first.
SixWater, deliberately, if needed Where the search has produced a shortlist rather than an answer, running water on the roof in a controlled way, starting low and working up one suspect at a time, with somebody watching inside. It is slow and it is the only method that proves a diagnosis rather than supporting one.

Rule of the trace

A previous repair is not an absence of evidence. It is somebody's written record of where they were wrong.

Why the water test is done from the bottom up

Because water applied to the top of a roof will run over every suspect below it at once, and when the drip appears inside you will have learned nothing except that the roof leaks somewhere. Starting at the lowest suspect and moving up one detail at a time means that when the drip appears, the last thing wetted is the answer. It requires patience and two people, and it is the difference between a diagnosis and a guess.

What a written leak report should contain

The interior evidence: Where the water is showing, photographed, with a note of what is above it structurally.
The attic evidence: If accessible: staining on the deck and framing, condition of the insulation, any daylight, photographed.
The entry, identified: A photograph of the actual failure on your actual roof, not a diagram and not a picture of a similar failure elsewhere.
Everything else found: Including faults that are not leaking yet, marked as such, so you can decide what to do about them rather than discovering them next year.
The scope: What will be removed, what will be fitted, how far the work extends either side of the fault, and what happens if opening it up reveals wet decking.
The honest uncertainty: Where the diagnosis is a shortlist rather than a certainty, that should be said, along with what would confirm it.

The limits of an infrared camera and a drone

Both are useful and neither is a diagnosis. A thermal camera shows temperature difference, which under the right conditions reveals wet insulation or a wet deck, and under the wrong conditions shows nothing at all or shows a warm duct. A drone gives a good overhead survey of a steep or fragile roof and can find missing shingles and obvious damage from a safe distance. Neither one tells you what is happening under a shingle, which is where leaks live. Treat a contractor who leads with the technology and does not want to open anything up with the same caution you would apply anywhere else.

What Keys does with what it finds

Photographs, measurements and a written scope, given to you. If the roof is repairable you get a repair scope. If it is not, you get told that and why, with the evidence. If the problem turns out not to be roofing, which happens with condensation, plumbing and masonry, you get told that too, and Keys does not take the job. Keys does roofing, gutters and downspouts across greater St. Louis and installs Atlas and Malarkey shingles.

The method