There are two reasons for water getting behind the gutter.
Rain gutter drip edge installation.
The roof leg should extend a minimum of 2 back onto the roof sheathing.
Use a measuring tape to determine the length of the gutter.
For drip edge installation align it for directing water flow into gutter alongside the roof edges.
Ideally it is recommended to nail about every 12 inches.
Home centers sell rolls of 6 in.
One of the reasons is that your shingles may be too short.
If your gutter has been previously installed rather than taking it down and redoing it you can easily place a small strip of metal flashing under the drip edge and over the back of the gutter as shown by the illustration at the bottom of this page so the water will shed into the gutter.
Don t exceed it more than 16 inches.
If there s a drip edge installed where the fascia meets your shingles and the gutter is hung below the drip edge get some roll flashing and tuck it up under the drip edge and over the top of the gutter.
Rain gutter installation can be a tricky job and a lot of.
While the vertical leg should be placed 1 4 1 2 away from the fascia.
Drip strip is designed to fill the gap between the bottom of the drip edge and the top of the gutter to insure the water will flow into the gutter preventing any damage to your fascia or other parts of your home or landscaping.
If the gutter run measures longer than 40 feet 12 2 m it should be positioned to pitch down from the middle aimed toward a downspout at each end.
Use tin snips to cut the gutter apron flashing roll in two 3 in.
To install a drip edge on a newly constructed roof or on a re roofing job attach the drip edge along the roof s eaves first.