Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.
Gutter drainage work estimate needed.
A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.
These estimates are for basic work performed in serviceable conditions by qualified trade professionals using mid grade materials.
Then use the chart below to see what size gutter you need.
Work not mentioned on this page and or work using master craftsman premium materials and project supervision will result in higher costs.
For example if you have 30 feet of guttering the calculation is 1 4 x 3 0 75 i e.
Seamless aluminum gutters costing around 10 linear foot are the cheapest and best performing option while copper gutters are the most expensive at 25 per foot and vinyl gutters are easiest to install for diy homeowners.
The runoff for each zone was in gallons per minute.
Doubling the number of downspouts halves the required capacity for each.
If a roof s various drainage areas call for different size gutters go for the biggest one k style.
Using the table below will help calculate the volume of water to be stored.
5 inch 5 520 square feet.
Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage.
To calculate the volume of water that needs to be stored multiply the amount of runoff from each drainage zone by 15.
6 inch 7 960 square feet.
Working out gutter slope as a general rule gutter slope is set at 1 4 inch per 10 feet of guttering.
Installing 200 linear feet of gutters costs as little as 600 if you do the work yourself to as much as 2 500 3000 when hiring a contractor depending on the material you install.
This means the downspout end of the gutter should be set 3 4 of an inch lower than the other end.