1 your roof sheets have a hole in them or your screws or nails or equivalent are not watertight anymore or 2 the more common reason is where roof sheets are cut too short or they don t overhang far enough into the gutter.
Water leaking behind gutter.
When the roof shingles do not extend past the metal drip edge the water will suck back on the metal drip edge this is called capillary action and run behind your gutters.
The first cause is when the roofing material is installed many roofers will not extend the roofing material past the roof edging or drip edge.
If the gutters are clogged it s possible that the water is overflowing the gutters and this is contributing to the leak.
A gutter apron is a bent piece of flashing that tucks up under the shingles and over the gutter.
Gutters are supposed to direct water away from your roof and into the ground.
Home centers sell a gutter apron in 10 ft.
Some of the water may leak behind the gutters down towards the soffit and the fascia.
The first thing you should do after it stops raining is to get up on a ladder to check that the gutters themselves aren t clogged.
If the gutter is clogged some of that water will back up on the roof soaking it.
Capillary action is a water activity in which water adheres to a surface and follow the surface around.
There are a few elements that come into play that cause water to run behind the gutter.
If water is dripping behind your gutter it s probably because it was installed without any flashing over the back of the gutter.
The gutter apron will prevent the dripping.
And it doesn t stop there.
Over time rain gutters often start to pull away from the roof allowing water to drip over the gutter sides or between the gutters and the walls.