Flat Roofs leak because of caulking that is used to seal the flashing. Flashing is the number one cause of all flat roof leaks.
How to repair a leaky flat roof in 8 easy steps
The first place to look for a leak on a roof is the flashing. Any object like a chimney, skylight, vent pipe has flashing that could cause a leak.
Using caulking for leak repairs is a bad idea. Caulking has its place but not for sealing flashing on chimneys, skylights, roof vents, and drains. Instead, use Turbo Poly Seal. Watch this video https://www.youtube.com/watch?v=8mfBeFNOWbM&t=74s
Too much trust is put into caulking. Caulking always fails where it’s used on flashing. Where copper flashing meets a brick wall or on a chimney, people will use caulking to make the seal. This never works.
Here is the link to see how I used Turbo Poly Seal instead of caulking to repair flashing against a brick wall https://www.youtube.com/watch?v=8mfBeFNOWbM&t=74s
Steps on how to use Turbo Poly Seal:
1. After locating the problem area like flashing, metal edging or vent, remove any old tar or caulking
2. Remove any paint if any
3. Apply masking tape leaving a two-inch space on either side of the transition
4. Use sandpaper to roughen up any smooth surface
5. Use a disposable brush and apply one coat of Turbo Poly Seal covering roughly 2 inches on either side of the transition
6. Embed the Polyester fleece in the freshly painted coat of Turbo Poly Seal
7. Apply a final coat of sealant over the fleece making sure it is completely covered
8. Remove the masking tape