Roof Gutter Drainage Calculator

This means the downspout end of the gutter should be set 3 4 of an inch lower than the other end.

Roof gutter drainage calculator.

Metal era recommends that you verify all data obtained. Take the roof s total square footage and divide by the total square footage handled by one drain. This calculator serves as an information source only. Now architects engineers designers and contractors can easily and accurately size downspouts and gutters according to the specifications in smacna s architectural sheet metal manual 7th edition 2012.

The result is the number of drains needed. The roof drain calculator below is based on the maximum amount of rainfall in inches per hour of the hypothetical worst storm in the past 100 years and which has a two percent chance of occurring in any given year. For example if you have 30 feet of guttering the calculation is 1 4 x 3 0 75 i e. Gutter calculator this calculator uses the equations that are laid out in the smacna handbook.

We recommend using this calculator as a basic tool to begin determining the requirements for your drainage system however all information should be verified by hand prior to ordering or installing your gutter system. Or 12 drains required. To use this calculator simply enter the information in the form on the left and your data will be output on the right side. The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website.

As a general rule gutter slope is set at 1 4 inch per 10 feet of guttering. 50 000 4 400 11 36. The roof pitch or slope factors for roof pitch are used to multiply or increase the rainfall rate if we are draining a sloped roof the roof drain or gutter or drain piping or downspout leader size diameter other size constraints e g. Calculator is based on chapter 1 of smacna s architectural sheet metal manual 7th edition asmm.

A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour. The number of roof drains shown should be verified with local code requirements. Size downspouts to fit the gutter. For example in the u k.

Calculator notes and assumptions. Box gutter with rain water head at end of box gutter. Rainfall wizard is based on table 1 2 rainfall data and drainage factors page 1 2 1 3 of the architectural sheet metal manual 7th edition. Simplified suitable for flattish roofs with little or no vertical faces or steep roofs draining to one side of box gutter only or any roof if you are in a hurry and make the necessary allowances for all catchments.