Video · Leaks & repairs
Two Ways to Track Down a Flat Roof Leak
- Mod bit
- Rolled
What this video shows
A roofing educator shows two practical ways to locate leaks in modified bitumen and rolled roofing. Finding the real entry point matters because water on a flat roof can travel a long way from where it drips inside.
Key points
- Measure from the ceiling stain to fixed reference points like walls and vents so you can transfer the spot to the roof.
- Check details first: seams, flashings, penetrations and drains cause most leaks, not the open field.
- Water testing works best in small sections, starting low and moving up, with someone inside watching.
- Sweep or blow the roof clean so you can actually see splits, open laps and blisters.
- A moisture meter can confirm wet wood, but on membranes pros use specialized scanners or infrared.
Products in this video
The products used or shown, or the closest match we could verify. Typical price ranges, not live prices.
Pin-type moisture meter · $25–$45
General ToolsGeneral Tools MMD4E Digital Moisture Meter
- Mod bit
- Built-up
- Rolled
- TPO
- PVC
- EPDM
- Spray foam
- Metal
- Silicone-coated
- Acrylic-coated
A pin meter for checking whether decking, framing and fascia got wet from a leak, and whether a repair area has dried enough to work on.
Read the fine print: It reads only what the pins touch. It can't see wet insulation under a membrane (pros use core cuts, impedance scanners or infrared for that), and pushing pins through a membrane makes new holes.
Best for: Checking wood decking, framing and fascia for leak damage
Check price on Amazon for General Tools MMD4E Digital Moisture Meter (opens in new tab)Affiliate link — we may earn a commission at no extra cost to you. Coverage and specs are the manufacturer's stated figures. Disclosure
Stiff push broom · $25–$45
LibmanLibman 825 Rough-Surface Heavy-Duty Push Broom, 24 in.
- Size
- 24 in.
- Mod bit
- Built-up
- Rolled
- TPO
- PVC
- EPDM
- Spray foam
- Metal
- Silicone-coated
- Acrylic-coated
Stiff bristles clear loose granules, grit and leaves off a flat roof before you wash, inspect or coat.
Read the fine print: Go easy on old mod bit. Scrubbing hard strips granules you want to keep.
Best for: Sweeping debris and loose granules before inspecting or coating
Check price on Amazon for Libman 825 Rough-Surface Heavy-Duty Push Broom, 24 in. (opens in new tab)Affiliate link — we may earn a commission at no extra cost to you. Coverage and specs are the manufacturer's stated figures. Disclosure
Cordless leaf blower · $120–$180
DEWALTDEWALT 20V MAX XR Cordless Leaf Blower (DCBL722B, tool only)
- Mod bit
- Built-up
- Rolled
- TPO
- PVC
- EPDM
- Spray foam
- Metal
- Silicone-coated
- Acrylic-coated
Cordless, so there's no cord dragging across the roof. Use it to clear drains and scuppers, and to blow off dust right before primer or coating.
Read the fine print: Tool only: the battery and charger are sold separately. Watch your footing, and don't walk backward while you blow.
Best for: Clearing leaves from drains and the final dust-off before coating
Check price on Amazon for DEWALT 20V MAX XR Cordless Leaf Blower (DCBL722B, tool only) (opens in new tab)Affiliate link — we may earn a commission at no extra cost to you. Coverage and specs are the manufacturer's stated figures. Disclosure
Wet-or-dry roof cement (caulk tube) · $7–$15
HenryHenry 208R Wet Patch Roof Cement, 11 oz cartridge
- Chemistry
- Asphalt
- Size
- 11 oz cartridge
- Mod bit
- Built-up
- Rolled
- Metal
The same wet-patch cement in a caulk tube, for nail holes, small splits and flashing edges where a trowel is overkill.
Read the fine print: Same asphalt limits as the can: let it cure before any coating, and don't use it on EPDM or PVC. A bead over a split is a stopgap, not a seam repair.
Best for: Pinholes, fastener heads and flashing edges
Check price on Amazon for Henry 208R Wet Patch Roof Cement, 11 oz cartridge (opens in new tab)Affiliate link — we may earn a commission at no extra cost to you. Coverage and specs are the manufacturer's stated figures. Disclosure
Read the full guide
Leaks & repairs How to find a leak in a flat roof On a flat roof the drip inside is often nowhere near the hole, because water runs along the deck and through insulation before it shows. Start at the stain, then check the usual suspects on the roof above and upslope: wall and curb flashings, pipe boots, edge metal, seams, drains and low spots where water ponds. If a dry inspection doesn't find it, hose-test one small area at a time, working from the drain up, giving each section at least 10 minutes with a helper watching inside.Video by Practical Roofing Concepts, embedded from YouTube. The summary, key points and cautions on this page are our own; Practical Roofing Concepts doesn't endorse TheFlatRoofPro.com or the products listed. Roofing work for hire generally requires a licensed roofing contractor.