Box 6" Gutter — Sizing & Cost Guide
The box 6-inch gutter provides strong water-handling capacity of 7,600 square feet at 1 inch per hour in a modern rectangular profile. It is a popular choice for commercial buildings, flat-roofed structures, and contemporary homes. The square profile allows it to blend seamlessly with parapet walls and flat fascia treatments. Box gutters at this size are frequently used in conjunction with internal drainage systems on commercial buildings.
Box 6" Specifications
Available Materials
Maximum Roof Area by Rainfall Intensity
The table below shows the maximum effective roof area (in square feet) that the Box 6" gutter can drain at various rainfall intensities. The capacity of 7,600 square feet is rated at 1 inch per hour. At higher rainfall intensities, the maximum serviceable roof area decreases proportionally because more water enters the gutter per unit of roof area. Use your local rainfall intensity (available on the states page) to determine if this profile is adequate for your home.
| Rainfall Intensity | Max Effective Roof Area | Typical Home Size |
|---|---|---|
| 1 in/hr | 7,600 sq ft | Large home or commercial |
| 1.5 in/hr | 5,066 sq ft | Large home or commercial |
| 2 in/hr | 3,800 sq ft | Large home or commercial |
| 2.5 in/hr | 3,040 sq ft | Large home or commercial |
| 3 in/hr | 2,533 sq ft | Standard two-story home |
| 3.5 in/hr | 2,171 sq ft | Standard two-story home |
| 4 in/hr | 1,900 sq ft | Small to medium home |
| 4.5 in/hr | 1,688 sq ft | Small to medium home |
Cost Estimate for Box 6"
The cost of Box 6" gutters ranges from $14 to $24 per linear foot for materials. This price range reflects variations in material thickness, finish options, and regional availability. Professional installation typically adds $3 to $8 per linear foot depending on the height of the building, accessibility, and local labor rates. The table below shows estimated material costs for common gutter run lengths. Total installed cost including downspouts, hangers, end caps, and labor is typically 2 to 3 times the material cost.
| Gutter Run | Material Cost (Low) | Material Cost (High) |
|---|---|---|
| 80 ft | $1,120 | $1,920 |
| 100 ft | $1,400 | $2,400 |
| 120 ft | $1,680 | $2,880 |
| 150 ft | $2,100 | $3,600 |
| 200 ft | $2,800 | $4,800 |
| 250 ft | $3,500 | $6,000 |
| 300 ft | $4,200 | $7,200 |
box Profile Details
Box gutters feature a clean rectangular cross-section that complements contemporary and modern architectural styles. The straight lines and geometric form work well with flat-roofed buildings, commercial structures, and minimalist residential designs. Box gutters can be integrated into the roof structure behind parapet walls for a completely hidden drainage system. They are available in a range of materials including aluminum, galvanized steel, stainless steel, and copper.
When selecting the Box 6" gutter for your project, consider the total effective roof area draining to the gutter system, the local rainfall intensity for your area, and the number and placement of downspouts. A general rule is to keep the capacity utilization below 75 percent of the rated maximum to provide a safety margin for storms that exceed the design intensity. For homes in areas with frequent heavy rainfall or large roof areas, upgrading to the next larger size within the same style family is a worthwhile investment that adds minimal cost but significantly reduces the risk of overflow during extreme weather events.
Proper installation is critical to gutter performance regardless of the profile selected. Gutters should be sloped toward the downspouts at a rate of approximately 1/16 inch per foot to ensure water flows to the outlets rather than pooling in the gutter. Hanger or bracket spacing should not exceed 36 inches, and many professionals recommend 24-inch spacing for durability and to prevent sagging under water and ice loads. All joints, end caps, and corners should be sealed with high-quality gutter sealant, and downspout connections should be secured with rivets and sealed to prevent leaks at the transitions.
State Compatibility for a Typical 2,000 sq ft Home
For a typical 2,000 square foot home with a 4/12 roof pitch (effective area of approximately 2,100 sq ft), the Box 6" gutter is adequate in 46 states and insufficient in 5 states based on the 1-hour, 10-year storm rainfall intensity. States where this profile is adequate are shown in green; states requiring a larger gutter are shown in red. For borderline cases, adding more downspouts or upgrading to the next size provides an appropriate safety margin.
Downspouts and Outlets for Box 6"
Downspouts are sized to the roof they drain, not to the gutter profile. Fine Homebuilding's rule is 100 sq ft of roof per square inch of downspout at 1 in/hr (600 sq ft for a 2x3, 1,200 for a 3x4), divided by local intensity. The table runs that rule for the six reference roof sizes at a 4/12 pitch and the median state design intensity of 2.6 in/hr, alongside whether the Box 6" itself has the capacity for each roof. A 3x4 outlet is the natural fit for a 6-inch bottom; SMACNA's sizing notes do not allow a downspout wider than the gutter bottom.
| Roof | Eff. roof (4/12) | Box 6" adequate? | Capacity used | Peak runoff | 2x3 needed | 3x4 needed |
|---|---|---|---|---|---|---|
| Small Home (1,000 sq ft) | 1,050 sq ft | Yes | 36% | 28 gal/min | 5 | 3 |
| Medium Home (1,500 sq ft) | 1,575 sq ft | Yes | 54% | 43 gal/min | 7 | 4 |
| Standard Home (2,000 sq ft) | 2,100 sq ft | Yes | 72% | 57 gal/min | 10 | 5 |
| Large Home (3,000 sq ft) | 3,150 sq ft | No | 108% | 85 gal/min | 14 | 7 |
| Very Large Home (4,000 sq ft) | 4,200 sq ft | No | 144% | 113 gal/min | 19 | 10 |
| Estate Home (5,000 sq ft) | 5,250 sq ft | No | 180% | 142 gal/min | 23 | 12 |
Run Length Details for Box 6"
Three numbers follow from the length of each continuous run. Hanger count assumes one every 24 inches plus one at the end (36 inches is the usual maximum). Drop is the total fall from the high end to the outlet at 1/16 inch per foot, with Fine Homebuilding's steeper 1/8 inch per foot shown beside it. Movement is how much the run lengthens between a winter night and a sun-heated summer afternoon, a 100 °F swing, for each material this profile comes in; sealed joints and end caps have to absorb it, and long runs get an expansion joint or a second outlet.
| Run | Hangers @ 24" | Drop @ 1/16"/ft | Drop @ 1/8"/ft | Movement, aluminum | Movement, galvanized steel | Movement, stainless steel | Movement, copper |
|---|---|---|---|---|---|---|---|
| 20 ft | 11 | 1.3" | 2.5" | 5/16" | 3/16" | 1/4" | 1/4" |
| 30 ft | 16 | 1.9" | 3.8" | 7/16" | 1/4" | 3/8" | 5/16" |
| 40 ft | 21 | 2.5" | 5.0" | 5/8" | 5/16" | 7/16" | 7/16" |
| 50 ft | 26 | 3.1" | 6.3" | 3/4" | 3/8" | 9/16" | 9/16" |
| 60 ft | 31 | 3.8" | 7.5" | 15/16" | 1/2" | 11/16" | 11/16" |
Other Gutter Profiles
Compare the Box 6" with other gutter profiles to find the best match for your project. Each profile offers different trade-offs in capacity, appearance, cost, and material availability.
How This Guide Works
- Capacity is the effective roof area the profile drains at 1 in/hr (5" K-style 5,520 sq ft and 6" K-style 7,960 sq ft are the published figures; half-round, box and fascia values follow manufacturer data). Divide by your intensity and pitch factor for the footprint it serves.
- The median state design intensity used in the tables is 2.6 in/hr, a statewide 1-hour, 10-year value. SMACNA and Fine Homebuilding size to the 5-minute, 10-year burst, which is higher, so a contractor's design tends to be one size larger.
- Downspout counts: 100 sq ft of roof per square inch of downspout at 1 in/hr, scaled to intensity. Hangers at 24 inches; slope 1/16 inch per foot. Thermal movement uses Engineering ToolBox expansion coefficients (aluminum 23, galvanized steel 11.7, stainless steel 17.3, copper 16.4 x 10-6 per °C).
- Prices are national material estimates per linear foot; installation, downspouts, hangers and sealant are extra.
- Sources: Fine Homebuilding #125, Sizing Gutter Systems (capacity and downspout rules); This Old House, How To Size Gutters and Downspouts (pitch-factor table, downspout spacing); the SMACNA Downspout & Gutter Sizing Calculator, built on the Architectural Sheet Metal Manual; NOAA's Precipitation Frequency Data Server (Atlas 14) for point rainfall intensities.
Frequently Asked Questions
How many downspouts does a Box 6" gutter need?
Size the downspouts to the roof, not the gutter: Fine Homebuilding's rule is 100 sq ft of roof per square inch of downspout at 1 in/hr, so a 2x3 drains 600 sq ft and a 3x4 drains 1,200 sq ft, divided by your local intensity. For a standard 2,000 sq ft home at a 4/12 pitch and the median state intensity of 2.6 in/hr, that is 10 two-by-three or 5 three-by-four downspouts. A 3x4 outlet fits the 6-inch bottom of this profile; SMACNA's rule is that a downspout cannot be wider than the gutter bottom.
How far apart should hangers be on Box 6" gutters?
Every 24 inches is the durable choice, with 36 inches the usual maximum. A 40-foot run of Box 6" needs 21 hangers at 24-inch spacing, and should drop 2.5" from the high end to the outlet at 1/16 inch per foot (5.0" at Fine Homebuilding's 1/8 inch per foot). Heavier materials such as copper and steel, and any climate with ice loads, argue for the tighter spacing.
Does a aluminum Box 6" gutter expand in the heat?
Yes. Aluminum expands about 23 millionths of its length per degree Celsius, so a 40-foot run moves roughly 5/8" between a winter night and a sun-heated summer afternoon (a 100 °F swing). Sealed joints and end caps have to absorb that movement; on long continuous runs installers add an expansion joint or split the run with two outlets rather than relying on sealant alone.
What size roof can a Box 6" gutter handle?
Rated capacity is 7,600 sq ft of effective roof at 1 in/hr. At the median state design intensity of 2.6 in/hr on a 4/12 roof that works out to a horizontal footprint of about 2,783 sq ft; at 4 in/hr it falls to 1,809 sq ft. Check your own state's intensity on the state pages, then keep capacity use under about 75% for storms that beat the design value.
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