I cannot stress enough how important managing your roof and exterior landscaping drainage can be.  Here’s something to think about.
More than 600 gallons of water will shed off of the average size home from 1 inch of rainfall.  If you have 4 gutters that is more than 150 gallons of water pouring out of 1 downspout.  That amount of water can do a significant amount of damage.
If you’d like to do the calculation for your house here are the steps:
1.    Figure out the footprint  of your roof. Length x Width
My house is approximately 40 ft wide by 20 ft deep = 800 sq ft
2.    Convert to inches (multiply each dimension by 12 or the area by 144)
480 in x 240 in = 115,200 sq in or
800sq ft x 144sq in = 115,200 sq in
3.    Multiply by the area by the inches of rainfall
1 in x 115,200 sq in = 115,200 cubic inches of water
4.    Divide by the number of cubic inches in a gallon
1 Gallon = 231 cubic inches
115,200 cubic inches/231 cubic inches = 498.7 gallons of water
Almost 500 Gallons of water shedding off of my roof in a 1 in rainstorm, what about your house!
Tips for managing roof drainage.

Extend all downspouts far enough away from your house to be sure no water runs back towards the foundation.  You can get flexible gutter extensions at your local hardware store.


Inspect and clean your gutters regularly.  Water should flow freely towards the downspouts.

Inspect and clean any underground drainage to be sure water is flowing away from your house and is not backing up due to a clog.

Make sure your gutters are sloped towards your downspouts so that water doesn’t pool in the gutters.

Make modifications to your landscaping to be sure water is not flowing back towards your foundation.  Remove vegetation, check for things that cause dams like edging, sidewalks, patios or fencing.