Gutters are meant to handle much of the rainfall on your roof but how do you know the right gutter size for your home? The good news is you don’t have to be an engineer to figure out the size your gutters should be to maximize rainwater outpour.
Most homes actually typically use one of two gutter sizes, either the 5-inch K-style or the 6-inch half round. K-style gutters are the most widely used residential gutter thanks to their affordability, ability to be made in most materials, and their shape. A K-style gutter comes with 2 x 3 inch or 3 x 4 inch downspouts maximizing the amount of water they can hold and the force they can sustain. Half-round gutters, as their name suggest, are completely round or have a straight back. Their wide diameter and smooth shape allows for water to drain faster and are somewhat self cleaning which is very appealing to homeowners.
Square Footage of Drainage Area
The total square footage of the drainage area, or the area from which water will run off, will help determine how to find the right gutter size for your home. For a standard, gable roof you only need to calculate the slope multiplying length by width to determine square footage. Calculating the total square footage for roofs with more than one facet will require a little more work since you will need to calculate each square footage and combining them to find the total square footage. Once you have determined the square footage, write these numbers down and save to refer to in the next steps.
Factor in Roof-Pitch
Now you will need to factor in the roof-pitch into the square footage of your drainage area to know the roof’s steep. Why does roof steepness help determine into the gutter size of your home? The steeper a roof, the more rainwater it will collect during windy conditions and the bigger it the gutter size will need to be. To calculate your roof’s pitch you will need a ladder, a level, a ruler, and maybe a person to assist. If you have an extremely steep roof please contact an EMA professional for safety purposes.
Once on top of your roof place the level at the center of the top ridge. Holding one end, level it against the roof and measure the distance between the roof and the middle point of the level underneath. The level should read 12-inch runs so if your level shows a 5 inch gap then your pitch is 5-in-12 pitch. Compare what you measure with the table below to find your roof-pitch factor.
| Roof Pitch | Roof-Pitch Factor |
|---|---|
| 12 in 12 or higher | 1.3 |
| 9 in 12 to 11 in 12 | 1.2 |
| 6 in 12 to 8 in 12 | 1.1 |
| 4 in 12 to 5 in 12 | 1.05 |
| Flat to 3 in 12 | 1 |
Rainfall Intensity
Next, you will need to find the rainfall intensity for your home’s location. This is provided by the Weather Bureau which calculates rainfall at it’s highest intensity in a 5-minute interval or inches per hour. The higher your rainfall intensity, the bigger a gutter size your home needs in order to not be overwhelmed during a heavy storm. If your location is not recorded, just find the nearest location to you.
Gutter Size
Now that you have the above calculations, you can find the adjusted square footage by multiply the original drainage square footage by the roof-pitch factor and then the rainfall intensity. Compare your numbers with the chart below to find the recommended gutter size for your home.
K-Style:
Five-inch 5,520 square feet
Six-inch 7,960 square feet
Half-round:
Five-inch 2,500 square feet
Six-inch 3,840 square feet
If different areas of your roof call for different gutter size, go with the bigger sized gutter.
Gutters are an important factor in your roof and overall well being of your home. If you need any assistance with finding the right gutter size for your home or have any questions or concerns please do not hesitate to contact our EMA Construction professionals.