Why outbuildings need gutters too
- Doorways: roof water pours onto the spot in front of garage doors and shed doors, creating puddles, ice in winter and erosion.
- Siding and sills: splashback rots wood siding, trim and sill plates, especially on sheds sitting close to the ground.
- Slabs and foundations: water at the edge of a garage slab undermines it and, in clay soils, can make it heave.
- Neighbors and the house: outbuildings near property lines or the house can dump water where it causes problems.
- Contents: water seeping under doors damages stored tools, equipment and vehicles.
Sizing for outbuilding roofs
Garages and sheds often have simple gable roofs, which makes gutters easy. But pole barns and workshops can have large, steep metal roofs that shed water fast. A 30-by-40-foot pole barn roof is 1,200 square feet or more; with metal roofing, water arrives at the gutter quickly and in volume. 6-inch gutters with 3x4-inch downspouts are common on larger outbuildings. See 5-inch vs. 6-inch gutters and downspout size and placement.
Attachment without a fascia board
Many sheds and pole barns have no fascia board, or only thin trim. Options include:
- Adding a fascia board to the rafter or truss tails before gutters go up.
- Roof straps that fasten under the roofing and hold the gutter from above.
- Wrap-around hangers designed for metal buildings.
- Half-round gutters on brackets, which hang without needing a flat fascia. See half-round vs. K-style.
On metal roofs, the gutter must sit where water from the panel edges falls into it; metal roofs often overhang more, and snow sliding off them can tear gutters loose. See gutters for metal roofs.
Where the water goes
Downspouts should discharge away from doorways, driveways and foundations, and not toward the house or a neighbor. For detached garages, a downspout at the back corner with an extension onto the lawn is often enough. For barns and workshops, water can be routed to a swale, a rain garden or a buried line to a daylight outlet. See underground downspout drainage.
Rainwater collection
Outbuildings are ideal for rainwater harvesting: a shed or garage near the garden can feed barrels or a tank without affecting the house. Metal roofs are a clean collection surface. See rainwater harvesting from your gutters.
Materials
Seamless aluminum works for most outbuildings. Galvanized or painted steel suits barns and farm buildings, especially where equipment might bump downspouts. Vinyl is cheap for small sheds but weak in cold, sun and snow. Match gutter color to the building trim or roof. See gutter materials compared and how to choose gutter color.
Snow and ice over doors
On garages and barns, snow and ice sliding off the roof over a door is a hazard to people and vehicles. Gutters alone do not stop it. Snow guards above doors, or placing doors on gable ends where snow does not slide, help. Where gutters run above doors in snow country, use strong hangers at close spacing. See snow load and gutters.
Wood-sided sheds and old barns
Older barns and sheds with wood siding, board-and-batten or log walls suffer most from roof splash. The bottom few feet of siding and the sill beam take the most water and rot first. Gutters, combined with a gravel strip along the base of the wall, keep splash off the wood and add years to the building.
Guards on outbuildings
Sheds and garages under trees clog just like houses, and they are often checked less. Guards save trips up the ladder. On barns with bird problems, guards also keep nests out of gutters. See are gutter guards worth it?
Carports, lean-tos and porches
Carports and lean-to roofs attached to garages or barns are often low-slope and drain right where people walk or park. A gutter along the low edge, with a downspout routed away from the driveway, keeps the area dry and prevents ice in winter. On low-slope roofs, make sure the roof edge directs water into the gutter. See gutters for flat and low-slope roofs.
Workshops and ADUs
Backyard workshops, studios and accessory dwelling units (ADUs) are usually treated like houses: they have finished interiors, often a foundation, and sometimes plumbing and electrical. They deserve the same gutter and drainage care as the main house, including downspouts that discharge away from the foundation and do not flow toward the main house. Some cities have stormwater rules for new ADUs; ask your building department. See downspouts and your foundation.
Sheds on skids and gravel pads
Many sheds sit on skids or a gravel pad rather than a foundation. Roof water dripping along the edges washes gravel away and keeps the skids wet, which rots them. Even a small gutter on the drip side with one downspout carried a few feet away can double the life of a shed floor.
Do it with the house
If you are replacing the house gutters, adding the garage and shed at the same time costs less than a separate visit and gives a matching look. Ask the installer to include outbuildings in the estimate. See what happens on gutter installation day.
Permits and property lines
Gutters themselves rarely need permits, but where an outbuilding sits close to a property line, many towns and HOAs have rules about water flowing onto neighboring lots. Route downspouts so water stays on your side and drains away from both properties. If you are building a new garage, shed or ADU, ask the building department whether a stormwater plan or drainage detail is required.
Barns and animals
On farms, roof water from barns falling into barnyards and paddocks turns them into mud and increases runoff of manure into streams. Many conservation districts help farmers install gutters and downspouts on barns to keep clean roof water separate from manure areas. Ask your county conservation district whether cost-sharing is available for barn gutters and roof runoff structures.
Quick checklist
- Where does water fall now, and what does it damage?
- Is there a solid fascia or will one need to be added?
- Is the roof metal, and does snow slide off it?
- Where can the downspouts discharge safely?
- Would a rain barrel be useful here?
Cost
HomeGuide puts seamless aluminum gutters at about $6 to $12 per linear foot installed nationally. A detached two-car garage might need 40 to 50 feet of gutter and two downspouts; a small shed much less. Adding a fascia board, roof straps or underground drainage adds cost. See our cost guide.