Don’t just go with your gut(ter) feeling
Whether you’re adding gutters to a new home or replacing worn-out ones, measuring is a crucial first step toward determining the cost and scope of gutter installation. If you hire a local gutter repair contractor or installation pro, they will take the measurements as part of the job. If you’re considering installing your own gutters, however, or simply want to get some reliable estimates without inviting multiple companies over for a home visit, you can also measure your home’s gutters as a DIY project. Read on and we’ll tell you how.
The first step is to determine the square footage of your roof. If you don’t have the measurements handy, you’ll need to use a study extension ladder, held in place securely by an assistant on the ground. Ladder safety is critical, and goes a long way to prevent broken bones or other, more serious injuries.
Use your tape measure to calculate the length and width of each part of your roof. Multiply the length of each section by its width to calculate the area. Once you have the area for each section, add up the results for your total square footage. If you have a classic symmetrical gable-end roof, you can simply double the area after measuring one side rather than measure them both separately.
The next thing you need to know is the pitch (also known as the angle or slant) of the roof. The roof’s slant is traditionally measured by the number of inches it rises vertically for every 12 horizontal inches of roof.
To calculate it, place one end of the level against the roof so that the other sticks out horizontally. Once it has been leveled, measure the distance from the end of the 12-inch level to the roof. The result will allow you to determine the roof pitch multiplier (or the roof pitch factor):
0–3 inches: 1 pitch multiplier
4–5 inches: 1.05 pitch multiplier
6–8 inches: 1.1 pitch multiplier
9–11 inches: 1.2 pitch multiplier
12+ inches: 1.3 pitch multiplier
The other factor to consider when determining the right size of gutter for your home is the volume of rain that will fall on the roof. The US National Weather Service records data on maximum rainfall intensity: the maximum volume of precipitation that can be expected to occur during a five-minute span in a particular area. Find the number for your area and write it down.
Use the measurements you have recorded to determine your roof’s adjusted square footage and the size of gutter that’s right for your home. To get the adjusted square footage, multiply the recorded square footage by the pitch multiplier and the inches-per-hour rainfall intensity.
Let’s say, for example, that you measured 1,000 square feet of roof and found a pitch multiplier of 1.1. The maximum rainfall intensity in your area is 4.76 inches per hour. Multiply them together for an adjusted 5,236 square feet.
Up to 2,500 adjusted square feet: 5 inch half-round gutters
Up to 3,840 adjusted square feet: 6 inch half-round gutters
Up to 5,520 adjusted square feet: 5 inch K-style gutters
Up to 7,960 adjusted square feet: 6 inch K-style gutters
Walk around the perimeter of your house with an eye on the gutters and count the number of corner pieces and end caps, distinguishing between left and right sizes. Add to your total three elbow pieces for each downspout.
On your walk, you should also note the number of downspouts. The general wisdom is that you should have one downspout for every 25 to 35 linear feet of gutter. Never run more than 40 linear feet of gutter between downspouts. If you live in an area with a high maximum rainfall intensity, adding more downspouts can lighten the load on the gutters.
A confident and experienced DIYer can learn to safely install gutters themselves. It’s a difficult and potentially dangerous process, however. In many cases, hiring a local gutter installation professional will be the best way to go. The typical cost for gutter replacement is $4 to $30 per linear foot, and the installers will handle the measurement as well as every other part of the process.
Most gutters fall between four to six inches in size. The standard size for seamless gutters is five inches, while other styles are typically either four or six inches wide. In some cases, homes feature seven inch gutters, but this is far more common on larger commercial structures than residences.
For your gutters to function properly, you need downspouts (or a comparable alternative, like a rain chain) to carry water away from the roof and the foundation below. Without them, water would just pool in the gutters, leading to overflow and corrosion.
Nearly every home requires some system to direct water away from the foundation and the surrounding soil, but gutters are not the only option. Installing drip edges alone will probably not be enough, but you can pair them with a drip path made up of concrete, plastic, or metal objects that steer the flow of water. Or you could opt for French drains, which collect and redirect water runoff at ground rather than roof level.
