Most houses use rectangular 2x3 or 3x4 inch downspouts; round ones come in 3 and 4 inches. This Old House's rule of thumb is 1 square inch of downspout for every 100 square feet of roof. By that rule a 2x3 drains about 600 square feet and a 3x4 about 1,200. Add up the roof that drains to each downspout, then pick the size or add a downspout.
Size the downspout by the roof that drains into it.
Backed by Wood & Wood Seamless Gutters, more than 30 years in the gutter business.
The standard sizes
This Old House lists what each common size can handle, in square feet of roof draining to it.
- 2x3 inch rectangular: about 600 square feet.
- 3x4 inch rectangular: up to 1,200 square feet.
- 3-inch round: about 706 square feet.
- 4-inch round: up to 1,255 square feet.
Rectangular or round
Rectangular downspouts are the usual match for K-style gutters. Round ones go with half-round gutters and can also hang on K-style. The shape matters less than the area inside it.
Bigger downspout or more downspouts
When one downspout carries too much roof, you have two fixes: a larger size or another drop. This Old House also says a gutter run of 60 feet or longer should have at least two outlets.
A downspout that overflows at the top in a hard rain, while the gutter is clean, can mean it is too small or carrying too much roof. How many downspouts do I need? covers spacing.
What it costs
We price downspouts per foot: $14 for the smaller size and $16 for 6-inch work, elbows included. We set the size from your roof, so you do not have to pick it.
Call to install: every step
Three ways to start
- Call (617) 401-9301. It is answered any hour, and a missed call gets called back.
- Send the short form on the home page with your street address, and your number lands in your inbox.
- Text or chat through the chat window on this site.
Understand what you actually need
About fifteen minutes on the phone: the length of the roofline, the number of stories and the trees around the house. The roofline is measured remotely, so nobody comes to the house to sell. You get your price the same day, from the published per-foot rates.
- Gutters still in good shape: Gutter Clean Pro goes over the gutters you already have, from $18/ft.
- Gutters that need replacing: new gutters with the guard built in. T-Rex (continuous hanger) from $25/ft, or DoublePro (two filtration layers) from $30/ft.
- Fascia that cannot be drilled: Hover Pro, quoted for your house.
- Complex rooflines, third stories and copper are quoted separately, and we say so on the call, never after arrival.
Your plan, in writing
You get a written quote and your StormRail plan: photos of your house, the system, the gutter size and your color choices. The certified installer works from that same plan, so you and the installer are never on different pages.
A deposit capped at one third
Massachusetts law caps a home-improvement deposit at one third of the contract. We hold to that in every state we work in. Your quote names the exact figure before you pay anything.
Material ordered and confirmed
Your Alu-Rex system is ordered through the Alu-Rex distributor and confirmed before an install date is set, so the date you get is one the material can meet.
Scheduled with a certified installer in your county
A certified Alu-Rex installer working in your area takes the job, and you get the date without chasing anyone. In season we're typically booking four to six weeks out. We'd rather tell you that now than promise you Tuesday and send whoever happened to be free. Emergency work — a collapsed run, active water in the basement — gets triaged ahead of the queue.
Installed
The installer fits the system on the plan you already approved. Any balance is due as your quote states.
After the install
We check in after the job is done. Each system carries its own written Alu-Rex warranty:
- Gutter Clean Pro: manufacturing lifetime limited, clog performance lifetime limited, including coniferous areas
- T-Rex: manufacturing lifetime limited, clog performance 25-year prorated limited
- DoublePro: manufacturing lifetime limited, clog performance lifetime limited, including coniferous areas
Questions homeowners ask
Are downspouts a standard size?
Yes. 2x3 and 3x4 inch rectangles and 3- and 4-inch rounds are the common sizes.
Is a 3x4 downspout worth it?
Where one downspout drains more roof than a 2x3 can handle, yes. It carries about twice the area.
How do I get a price?
Call (617) 401-9301 and tell us where your downspouts overflow now. We size and price them on the same call.
Compare the systems before you call: all gutter guards, Gutter Clean Pro, T-Rex, DoublePro, and the full price list.
Sources
- This Old House: How to size gutters and downspouts www.thisoldhouse.com/gutters/21014888/how-to-size-gutters-and-downspouts
Get a number for your roofline
One call is enough to start: the address, how many stories, and what grows over the roof. The published per-foot rate is the starting point, and the full scope and total are confirmed in writing before you pay anything.
Call (617) 401-9301