One of the most common ways for rodents to enter an attic is through a gap between the shingles and the gutter. Gaps like this are extremely common in Washington State due to a quark in the residential building code. This gap, sometimes called a carpenter’s gap or construction gap, can be sealed off using a piece of metal flashing called a drip edge. This piece of metal is also known as gutter flashing or rake edge flashing.
How to check for drip edge flashing
If you’re stumped on how mice, rats, birds, or squirrels are getting into your attic, we highly recommend looking at the exterior of the roof line. If you have a hipped roof (shaped like a pyramid) you should check the entire perimeter. If you have a gabled roof you likely only need to check the two sides with gutters.
Slide your hand to the back of the gutter where it’s secured against the house. If you can fit your hand under the shingles it’s big enough for a rat to squeeze through. Remember, rats only need a gap the size of a quarter and mice only need a gap the size of a dime. Rodents usually leave signs on the areas they frequent the most. Look for chewing, greasy smears called rub marks, and of course droppings.
Drip edge wasn’t in Washington code until 2015
Washington State residential code only began requiring drip edge in 2015, meaning If your home was built in 2014 or earlier, there is a good chance you have a large gap running continuously around the perimeter of your roof. You can read the code yourself online.
Should you install drip edge flashing to seal the attic from rodents?
Yes, you should definitely install a drip edge (AKA gutter flashing) to seal out mice, rats, squirrels and birds. At a cost of $10 to $20 per foot installed, it’s fairly inexpensive and will save you money down the line compared to the cost of damage from an infestation.
In addition to blocking pests, drip edge flashing protects your house from wind and water dripping behind the shingles, hence the name “drip edge.” It’s a wise investment for any roof.