Downspout Sizes must not exceed the bottom width of the gutter. To limit the effects of thermal expansion in gutters, 50 ft. (15 m) is a practical maximum gutter length to be served by a downspout.
As a general rule, contractors recommend having a downspout per every 20 feet of gutter, but depending on the gutter's capacity, it's not rare to see that distance go as far as 30-50 feet. Large gutters will offer a wider structure to channel more water at a time.
In general, it is recommended that the maximum length of a gutter with a single downspout should not exceed 30 to 40 feet (9 to 12 meters) to ensure proper water drainage. However, this is a general guideline, and it's always best to consult with a professional gutter installer or engineer for your specific situation.
gutter capacity and length. To limit the effects of thermal expansion in gutters 50 ft(15.3 m) is a practical maximum length of gutter to be served by a downspout.
A maximum 12 m gutter length served by each downpipe is to ensure effective fall and adequate capacity to discharge all water anticipated during a storm having an average recurrence interval of 20 years.
If at all possible, the downspout should end in an elbow and extension that directs the water 5 to 6 feet away from your foundation. However, make sure that it does not extend onto your neighbor's property. The extension should be at a 30 degree or more angle in relation to the ground.
Size of the Gutter Drainage Area: As a rule of thumb, one downspout should be placed every 25-35 linear feet of guttering. Depending on the local climate and rainfall intensity, some homeowners may need more downspouts. Many homeowners add extra downspouts to boost the drainage capacity of their gutters.
For lifetime, worry-free gutters, we use the thickest aluminum, and the best-hidden hangers on the market to stand up to tough winters and strong storms. All of our seamless gutter systems run anywhere from a few inches to 100 feet.
To keep it easy, we recommend that you install one downspout every 20-40 feet of gutter. This will ensure that you are taking the proper precautions to defend against potential water damage to your house. The average home has 2-3 downspouts.
Seamless aluminium guttering is available in a continuous length of up to 40 meters long depending on site conditions.
Larger downspouts are also less likely to clog. Leaves, twigs, and other debris that might get caught in a smaller downspout can easily pass through a larger one. This not only reduces the frequency of clogs but also diminishes the need for regular cleaning.
The general rule of thumb is for metal roofing to overhang the gutters by no more than 50mm (approximately 2 inches). Any further will change the look of your home, curb appeal and how the excess water flows from the roof to the gutters during a storm.
How many downspout installations should your gutters have? If we have to sum it up in a single rule, gutters need a downspout around every 30 to 40 feet. For most homes, this means installing spouts at either end of a gutter section.
Residential Downspout Sizes
Typically, residential downspouts come in two sizes: 2x3 inches and 3x4 inches. The former is often used for smaller roofs, while the latter is preferred for larger homes. A 2x3 inch downspout can handle roughly 600 square feet of roof area for every inch of rainfall within an hour.
A common guideline is that you need one downspout per 40' span of gutter for proper drainage, but this is usually not enough for a 2”x3” downspout. A homeowner should also consider the size of the roof which will factor into how much water is going into the gutter.
The general rule of thumb is one downspout for every 20-30 feet of gutter. This may vary depending on several factors such as the pitch of your roof, the volume of rainfall in your area, and the capacity of your gutters.
Note that gutters require expansion joints at 40′ centers. In this example your maximum spacing of downspouts should be 40′.
As mentioned above, the water should be diverted at least 4 to 6 feet away from the house. If a home has basement walls, it should be at least 6 feet away. The furthest away from the foundation the better.
A standard size downspout is 2×3. That means that is is 2 inches deep by 3 inches wide. An oversized downspout is 3×4 so it is 3 inches deep by 4 inches wide. This gives it twice the volume or carrying capacity.
Downspouts must also be sized to handle this level of rainfall. Rectangular 2 x 3-inch downspouts have a capacity of 600 square feet, while 3 x 4-inch downspouts can handle 1,200 square feet. Choosing the 3 x 4-inch rectangular downspouts, we'd need at least seven to handle the expected water flow.
One of the most important benefits of installing buried downspouts is protecting your home's foundation from water damage. Improper drainage can result in pooling water that seeps into the ground near the foundation, causing cracks, shifting, and other structural issues over time.
Redirecting roof runoff is as simple as adding a downspout extension. These are plastic (PVC) or metal extensions that attach to the bottom of your existing downspout. The extension should carry your roof runoff at least three to five feet away from your home to prevent any water damage to your home or foundation.