The average American house will have 5 or 6-inch gutters that work great to funnel any rainwater flowing off your roof and guide it to the downspouts. However, there are some homes with much larger slopes, fewer slopes, different roofing materials, and other factors that can affect what size gutter you may need. Some homes have slopes so high that the fast rushing water may overflow your average 5-inch gutter. That’s why we’re here to help you determine what size gutter you actually need.
The Benefits of Gutters and Downspouts.
The main job of your gutters is to divert rainwater away from your home. Several problems can occur without them due to water simply flowing down off the roof, especially during heavy rainstorms. Without gutters, that water will pool around the foundation of your home, potentially causing drastic and costly damages. Here are how gutters and downspouts are essential to protect your home.
Prevent Erosion Around Your Property
Heavy rainfall can actually erode the ground around your home. That water, the longer it sits and the harder it pounds down onto the dirt, the more erosion you’ll see. Diverting the water away from your home can prolong any erosion aside from that which occurs naturally.
Prevent Basement Flooding
During a torrential rainstorm, without gutters, that immense amount of water flowing off your roof will hit the ground near your home’s foundation and likely seep through and into your basement. This is not good! A flooded basement can cause extensive damage that requires costly repairs. Installing a proper gutter system is a whole lot cheaper!
Protect the Yard and Landscaping
Many people have bushes and flower beds planted up against the sides of their homes. If you care about these looking nice and staying that way, you’re going to want gutters to steer that water away from those areas. Even if they don’t get damaged, they will certainly get overwatered.
Protect Your Home’s Foundation
Your home’s foundation can crack and damage if water begins seeping down the sides of your home. Even the smallest crack can quickly grow as it’s pummeled with water. Keeping the integrity of your home’s foundation is imperative to having a long-lasting home.
Uphold the Integrity of Exterior Paint
If water is constantly running down the sides of your home, it can cause staining and lessen the quality of your home’s exterior paint. So installing gutters saves you the pain of ever having to repaint your home’s exterior, which is both expensive and labor-intensive.
Stop Mold and Mildew Growth
All of the above water infiltrations can cause mold and mildew growth in your basement, around your home’s exterior, under your siding—anywhere that water can get in and sit.
Proper Snow and Ice Melt
When the snow on your roof melts, it can easily flow down your gutters and safely away from your home. Without them, your home wouldn’t be able to handle such a mass amount of snow and ice shedding off the sides of your roof. It can also create a hazardous environment for anyone walking on the ground around your home. Falling snow and ice can be lethal.
Last but not least, your gutters are going to capture any debris that lands on your roof, then get washed away from your home. Imagine having to clean up all of the wet leaves and sticks around every edge of your home. Instead, they’ll all go to one place away from the corner of your home, and you can pick them up or allow them to decompose in one spot.
What Size Gutters Do I Need?
Most people can get away with using standard 5 or 6-inch gutters that your contractor recommends. Standard sized homes in mild climates should be ok, and those size gutters can handle typical rainfall. However, the size of the gutters you may need is also affected by the type of roof you have, how much rainwater your area gets, and your roof’s slope. Luckily some calculations can help determine the best possible gutter size for your home.
For example, your average gable roof, with two sides, would only need two measurements—the square footage and pitch of two sides. But more complex styles like hip roofs with four sides would need 4 calculations to determine how much that roof will put pressure on your gutters. Those area calculations, plus the slope and how much rain you expect to receive, all play a factor in determining what size gutters and how many downspouts you’ll actually need. The length and width of each side, added together, will give you your total drainage area.
How to Size Gutters for Your Home.
To know exactly what size gutters you need, you’ll have to do a few calculations first.
1 – Determine your roof’s pitch and your pitch factor.
The steeper your roof, the more it will capture windblown rain. To measure your roof’s pitch factor, you will need a tape measure and a level of at least 2-feet in length. Take the level and set it on the roof’s edge. At the 12-inch point, use your tape measure to measure the distance between the start of the roof and that midpoint. You’re finding the short side of the triangle, in a sense. Here are the roof pitch factors determined by your measurements:
- 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
- 0 to 3 in 12 = 1
These numbers are helpful because a very steep roof pitch will mean rainwater will flow much faster and overload your gutters. A flat or minimal slope will run much slower, and a smaller gutter may handle that.
2 – Your Area’s Maximum Rainfall Intensity
The U.S. Weather Bureau will collect rainfall intensity for certain regions, which comes in handy to determine your gutter size. Maximum rainfall intensity is the most rain that can fall in a 5-minute period, inches per hour. The higher your region’s maximum rainfall intensity is, the bigger the gutter you may need to handle that amount of water. You can find that information here.
3 – Sizing Your Gutters
It would help if you had your drainage area, which you calculated using the length and width of each side of your roof, your roof pitch, and your rainfall intensity to find out what size gutters to get. Note: If you have smaller drainage areas on one part of your roof, always use the biggest calculation you’ve gotten.
Here is an example equation for your adjusted square footage:
- Drainage area: 3,200 Sq. Ft.
- Roof Pitch: 1.2
- Rainfall Intensity: 1.04
3,200 x 1.2 x 1.04 = 3,993.6 square feet of drainage area.
Now that you know your adjusted drainage area, you can figure out which size gutter is best for your roof. There are two standard types of gutters. K-type and Half-round. The K-type is a squared gutter, and the Half-round is, you guessed it, half-round gutters. Here are the recommended sizes based on those two types.
- 5-inch 2,500 square feet
- 6-inch 3,840 square feet – Here is your recommended size.
- 5-inch 5,520 square feet
- 6-inch 7,960 square feet
These are all just average suggestions for your home. There are situations where you may need to get custom sizes or extra downspouts if you live in a climate susceptible to high amounts of rain. You can get custom 7 and 8-inch size gutters if the maximum rainfall intensity plus your roof’s slope and square footage bring you far beyond the suggested 5 or 6 inches. They will be more expensive to get, but in the long run, it’s saving you from all of those other damages that excessive rainwater around your home can cause.
Other options include increasing the gutter pitch, which may look a little weird but can help manage more water. And lastly, adding more downspouts, especially if your home is much larger. You can place downspouts every 40-50 feet.
In addition to sizing the proper gutters for your home, you can also install gutter guards, which help keep them free of debris and flowing properly without the need to get up on a ladder and clean out the clogs. What a pain! If you are considering installing some new gutters or gutter guards, we recommend giving Northface Construction a call. We can do both! We love to help homeowners improve their home’s efficiency and effectiveness, and a good gutter system can do just that. Contact us here to get started!