The drawing below illustrates the amount of rain a different pitch roof will collect. Assuming the rain comes straight down they are all the same, even though the roof area of a 12/12 pitch roof is more than that of a 4/12 roof the building area (foot print) is the same.
Calculate The Best Size For Your House
Gutters are essential to the longevity of your home. Without gutters and downspouts leading rainwater away from the house, foundations become feedlots for mold that can sicken your family and rot your house. Once you’ve settled on a material, and a profile, you’ll need to pick a size. This procedure for sizing your gutter system is based on roof size, your area’s likely rainfall intensity, gutter volume and downspout size and frequency.
The difference will be the rate the roof will shed water, the roof material (metal, wood, asphalt) also regulates run off. Larger downspouts or more downspouts may want to be used for say a 12/12 metal roof. A standard rule for downspouts is that a 2 x 3 will drain 600 sq. ft. area, 3×4 1200 sq. ft. area.
One foot of 5″ K-Style gutter holds 1.2 gallons of water.
One foot of 6″ K-Style gutter holds 2.0 gallons of water.
The increase in a 50 ft. length of material due to an increase in temperature of 100 degrees Fahrenheit.
Increase (in inches) Galvanized steel (13/32″), Copper (5/8″), Stainless Steel (5/8″), Aluminum (25/32″) & Vinyl (1.92″ see note below.) Wood (1/2″) Wood expansion is influenced more by moisture rather than heat.
NOTE: Based on .000032″ of expansion for one inch of material for every one degree F. increase. The expansion figure used for vinyl is a approximate figure. Test results range from .000031″ to .000037″.
On a 1 foot square flat surface area one inch of rain will produce .62 gal. of water. Using this value, you can calculate the amount of water that will come down your downspout on a given rain.
This link will give you the yearly rain fall in your area. //countrystudies.us/united-states/weather/ (Courtesy of countrystudies.us)
Minneapolis MN Homeowners
Minneapolis Weather – Minnesota – Average Temperatures and Rainfall Minneapolis MN
|Avg. Precip.||1.0 in||0.9 in||1.9 in||2.4 in||3.4 in||4.1 in||3.5 in||3.6 in||2.7 in||2.3 in||1.6 in||1.1 in|
Degrees in Fahrenheit
Using the drawing illustration below, if line A is 15 feet and line B is 50 feet you would have 750 sq. ft. of roof area and it will produce 465 gallon of water for every 1 inch of rain fall. If you use this figure to include the entire 30′ x 50′ building it is surprising at the amount of rain water that a building or home will produce with a 1″ rain. (930 gal)
Star Symbol = Down Spout location
Circle Symbol = High point of gutter
To calculate your water collecting roof area multiply line A by line B. There should be at least one 2″ x 3″downspout for every 40′ of gutter or 600 sq ft. of roof area, the gutter should be secured every 2′. The back of the gutter should always be under the metal roof drip-edge on less then 6/12 pitch roofs. This will prevent water sucking back and running behind the gutter and rotting out the face board.
Make Your Minnesota Home Leaf Free
Gutters can have a huge impact on the physical condition of your home. If your rain gutters and downspouts are working properly they will prevent roof and fascia board damage as well as prevent basement flooding by re-routing water a safe distance away from your foundation. But left to their own, rain gutters can clog, grow weeds and fungus, and overflow causing all sorts of problems for homeowners.