Roof Trim · Metal building trim guide
Metal Building Gutters and Downspouts for R-Panel and PBR Roofs
Gutters catch water at the low edge of a metal roof and downspouts carry it to the ground, away from your slab.
Also called: eave gutter, box gutter, sculptured gutter, rain gutter, downspout pipe
Metal building gutters and downspouts catch the water that sheets off a metal roof and carry it down and away from the building. A metal roof sheds water fast, and in a Houston downpour that water can wash out the dirt around a slab, splash mud up the walls, and soak whatever is parked under the eave.
This guide explains how gutters work on R-panel and PBR roofs, how to measure and count every piece, how many downspouts to plan, and how to hang it all so it does not leak or sag. It is written for contractors and owners of carports, barns, shops and sheds.
What Are Metal Building Gutters and Downspouts?
A gutter is an open trough bent from sheet metal that hangs along the low eave of the roof. Metal buildings usually use an eave gutter in a box or sculptured shape, though other styles are used too. A downspout is the square or rectangular pipe that drops from the gutter outlet to the ground.
Together they control water. They keep runoff off your doors and walk paths, protect the soil around the slab or posts, cut down on mud splash and rust at the base of the walls, and finish the eave line with a clean look.
Where Gutters Go on a Metal Building
Gutters run along the low eaves, the edges where water runs off. A gable building has two eaves, so it can have gutters on one or both sides. A single-slope lean-to or carport has one low eave.
On many metal buildings the gutter takes the place of the eave trim. On others it hangs along with the eave trim. Downspouts go at the ends of each gutter run and at points in between on long buildings. Put them where the water has somewhere to go, not at a doorway.
Metal Building Gutters and Downspouts: Sizes and Colors
Gutters and downspouts are typically 26 gauge steel in Galvalume or painted colors to match your trim. Metal building gutters come in a few sizes and shapes, so ask us what fits your eave and roof size. A bigger roof sheds more water and needs a bigger gutter or more downspouts.
Gutter pieces are often 10 ft long, though longer lengths may be available; ask us. Downspouts are commonly sold in 10 ft lengths with matching elbows, outlets and straps. Gutters must fit the depth of your eave framing, and custom gutters can be bent for odd eaves.
How to Measure Gutters and How Many Pieces to Order
Formula: gutter length = eave length per side x sides with gutter x 1.10, rounded UP to whole pieces. A common rule of thumb is about one downspout per 30 to 40 ft of gutter, with at least one at each end of long runs. Each downspout is about as long as the eave height.
Worked example: a 30 x 40 gable building with 12 ft walls and a 3:12 pitch, gutters on both 40 ft eaves. Gutter: 80 ft x 1.10 = 88 ft = 9 pieces of 10 ft gutter. Downspouts: one at each end of each eave = 4 downspouts. Each drops about 12 ft, so plan 2 pieces of 10 ft pipe each = 8 pieces.
Add the parts: 4 end caps (one each end of each run), 4 drop outlets, about 3 elbows per downspout (12 total), gutter straps about every 3 ft (14 to 15 per side, about 30), and 2 to 3 downspout straps per downspout. Houston gets heavy, fast rain, so many owners add downspouts rather than stretch the rule of thumb.
How to Install Gutters and Downspouts on a Metal Roof
Hang gutters after the roof panels are on. Details vary by gutter style and building, so follow the maker's sheet when you have one.
- Decide where each downspout will drop and mark the outlet spots on the gutter.
- Cut the outlet holes and set the drop outlets with sealant and rivets or stitch screws before you hang the gutter.
- Set the gutter so the front lip sits a bit lower than the back. That way, if it ever overflows, water spills out the front and not behind the gutter into the wall. Many metal building gutters hang level with enough outlets; others get a slight slope toward the outlets. Both are used.
- Fasten the back of the gutter to the eave member and add gutter straps about every 3 ft, screwed to the tops of the panel ribs with #14 lap screws.
- Lap joints about 2 to 4 inches with the upstream piece inside the downstream piece, so water flows over the lap, not into it. Seal with gutter sealant and fasten with rivets or stitch screws.
- Seal and fasten the end caps. Attach elbows and downspout pipe, upper piece inside the lower piece, and strap the downspout to the wall every few feet.
- Add a bottom elbow or splash block so water lands away from the slab.
Common Gutter Mistakes to Avoid
- Lapping gutter joints the wrong way so water runs into the seam.
- Too few downspouts for a big roof, so the gutter overflows in heavy rain.
- Setting the front of the gutter higher than the back, which sends overflow behind it.
- Leaving out straps, so the gutter sags under water and leaves.
- Dumping the downspout right at the slab edge or at a door.
- Forgetting end caps, outlets and elbows on the order.
What to Order With Metal Building Gutters and Downspouts
Get the whole gutter kit at once so the colors match and nothing is missing:
- Gutter pieces, end caps and drop outlets.
- Downspout pipe, elbows and downspout straps.
- Gutter straps or hangers.
- Gutter sealant, rivets and color-matched lap screws.
- Eave trim and inside closures if your building uses both.
Get Metal Building Gutters and Downspouts in Houston From Ironrod Steel
Ironrod Steel Co. rolls its own R-panel and PBR roofing and supplies matching trim, gutters, downspouts, closures and screws. Send us your building size, eave height and photos, and we will help you plan the gutter runs and count the parts. Pick up at 8122 Hillsboro St in Houston or ask about delivery across Houston and Southeast Texas. Call or text (281) 902-7619.
Gutter and Downspout FAQ
How many downspouts does a metal building need?
A common rule of thumb is one downspout for every 30 to 40 ft of gutter, with one at each end of long runs. Big roofs and heavy-rain areas like Houston often need more. When in doubt, add a downspout.
Should metal building gutters be sloped?
Practice varies. Many metal building gutters hang level and rely on enough outlets, while others get a slight slope toward the downspouts. Either way, keep the front lip lower than the back so any overflow spills out the front.
Do I need eave trim if I have gutters?
It depends on the building. On many metal buildings the gutter replaces the eave trim. On others both are used. Tell us how your eave is framed and we will help you decide.
How long should a downspout be?
About the same as your eave height, from the gutter to the ground, plus elbows at the top and bottom. A 12 ft eave usually takes two 10 ft pieces per downspout, cut to fit.
Which way do gutter pieces overlap?
The upstream piece goes inside the downstream piece, so water flows over the lap toward the outlet. Seal every lap and fasten it with rivets or stitch screws.