A roof, several layers
When dealing with a roof leak, read the roof as a stack of layers. Water that gets past the top runs into the next layer, follows it downhill, and only gets through where it finds a gap.
Sloped. Water slips under a shingle and runs over the underlayment. A nail or a joint between two deck boards lets it through. It then follows a rafter, drips into the insulation, spreads over the vapour barrier, and appears at a drywall joint or around a ceiling light.
Flat. On a flat roof, the detour is even longer. Once in through an upturn or a membrane seam, water soaks the insulation underneath and reaches a low point. It can come out at the other end of the unit. The insulation sometimes holds the water for several days before letting it go.
The information that guides the search
We ask questions before taking out the ladder. Have these answers ready. They tell us where to start.
- The date the water first appeared.
- Whether it comes back with every rain or only when it is windy.
- The wind direction on those days.
- Whether it happened in winter, during a thaw.
- What has recently been added or redone up there: skylight, antenna, air conditioner, other work.
From the ceiling to the roof: the order of checks
- Read the stain. We note its shape and its distance from the exterior walls.
- Follow the wood. When the attic can be accessed, we look for dark streaks, rusty nails, and crushed or wet insulation. These marks form a trail leading up toward the water's entry point.
- Inspect the top, starting with the weak points. We look upslope from the stain, and first where a roof often gives way: flashings, chimney, vents, valleys, skylights, edges. The open surface comes last.
- Spray, if nothing shows. The roof is wetted one zone at a time, starting from the bottom, while someone watches inside. As soon as water appears, the zone just sprayed is the cause. The test is long, and the repair is no longer done blindly.
- Measure, on a flat roof. A thermal camera or a moisture meter helps locate wet insulation hidden under the membrane. If needed, we cut out a small square to examine the layers, then patch it.
Frequently asked questions
Can I do my own investigation?
You can do part of the investigation, without climbing. If the attic hatch can be reached without standing on anything, light up the inside with a flashlight and look from the opening, without going in. Photograph the water marks on the wood. Insulation that looks like vermiculite may contain asbestos and must not be touched. The roof itself is the roofer's territory.
Is the leak search billed?
Each contractor has its own way of billing a leak search. It is sometimes included in the price of the repair, sometimes counted separately, especially when the roof has to be sprayed. Ask when you book the appointment.
The water is back despite the work. What now?
Call the same contractor and say what the weather was when the water came back. Two separate entry points are possible, and so is a first repair made next to the real source. A written warranty is there for exactly this.