How to Install a Metal Roof on a Shed (Step by Step)

A screw driven on the rib of a corrugated panel is how a shed roof starts leaking in year two. The metal itself rarely fails. What fails is the neoprene washer that sat on a curved rib instead of a flat panel face, or the ridge left open because foam closures seemed like an optional step. Get fastener placement, underlayment, and ridge sealing right, and a metal roof will outlast the shed beneath it by years.

This guide covers installing an exposed-fastener metal roof on a shed from first course to ridge cap: what to gather, whether plywood is required, underlayment and closure sequence, panel lapping and fastening, and ridge cap installation.

TL;DR: Drive exposed-fastener screws in the flat of the panel, 1 to 2 inches from the rib, never on the rib itself. Over purlins at 24 inches on center or less, you can skip plywood, but always run underlayment over a solid deck. Lap panels one full rib with butyl tape in the sidelap. Cap the ridge with foam closures and fasten 12 inches on center.

What you need to roof a shed in metal

Gather these six components before you start. Skipping foam closures or using undersized screws creates the gaps that water eventually finds.

Do you need plywood under a metal roof on a shed?

No. Over purlins spaced 24 inches on center or tighter, corrugated and R-panel metal roofing is structurally sound without a solid deck. The GreenBuildingAdvisor discussion on whether metal roof sheathing is necessary confirms that purlins at 24 inches or less make solid decking unnecessary for outbuildings. A plywood deck adds cost and labor without improving the roof’s performance.

Where plywood does change the equation is condensation control. A solid deck without underlayment traps moisture between the sheathing and the underside of the metal. Over open purlins, that same moisture vents freely. Choose your deck approach based on how your shed is framed, not on assumptions about what metal roofing needs.

What to put down first: underlayment and closures

Over a solid deck, synthetic underlayment or 30-pound felt goes down before any panels. Start at the eave, work toward the ridge, and overlap each course 4 to 6 inches. Synthetic is the better choice under metal: standard felt can soften and bond to the underside of hot steel panels in summer.

Over open purlins, install a condensation-control barrier or vented closure strips at the eave instead. Either way, set your inside foam closures at the eave before the first panel goes on. Those closures fill the corrugation gaps at the bottom edge and block wind-driven moisture from working up under the panels.

If you are still framing, the purlin spacing you set now determines whether you need a solid deck at all, so lock it in as part of building the shed rather than after the walls are up.

Installing the panels: eave, overlap, and sidelap

Start at the rake on the downwind side so the sidelap faces away from the prevailing wind. Set the first panel with a 1-inch overhang past the eave trim. Lap each subsequent panel one full rib over the previous one, and run a bead of butyl tape in the sidelap before pressing the panels together. Butyl tape bonds the faces and seals the overlap without relying on fasteners alone.

Keep panels plumb as you work across the roof. A panel set slightly off-square compounds across every subsequent course; by the far rake you can be an inch or more out of alignment.

Where do the screws go? In the flat, not the rib

Screws go in the flat of the panel, 1 to 2 inches from the nearest rib, driven into a purlin or solid decking below. Spacing runs 12 to 24 inches on center depending on your wind zone and the panel profile you are using.

The reason placement matters is mechanical. A screw driven on the rib lands on a curved surface, and the neoprene washer cannot compress flat against the panel. The hole is never fully sealed, and water enters the fastener penetration on the first hard rain. This is the leading fastener-related cause of metal roof leaks on sheds.

Torque matters too: drive until the washer compresses to roughly the diameter of the screw head, then stop. Over-driving crushes the gasket; under-driving leaves it unseated. Two exceptions to the flat rule: round-wave corrugated panels, where some makers call for fastening on the crown instead, and standing-seam systems, which use hidden clips entirely. On any panel, the manufacturer guide governs both the fastening pattern and the warranty.

For the complete fastener schedule including spacing tables by panel type and building width, see the Metal Sales exposed-fastener installation guide.

How to install the ridge cap

Set outside foam closures on top of the last panel course, roughly 4 inches down from the peak. The outside closure fills the corrugation void so the ridge cap sits flat on both sides of the peak. Run a bead of butyl tape across the top of the foam before setting the cap.

Center the ridge cap over the peak with equal overhang on both sides. Where cap sections meet end to end, lap them 6 inches and tape the joint with butyl tape. Fasten through the high rib of the cap at 12 inches on center, driving each screw through the foam closure and into the purlin or decking below.

FAQ

What do you put under metal roofing on a shed?

Over a solid deck, run synthetic underlayment or 30-pound felt before the panels go on. Over open purlins, install a condensation-control barrier or vented closure strips at the eave. Foam closures at the eave and ridge are required in both cases to fill the corrugation gaps.

Do I need plywood under a metal roof for a shed?

Not if your purlins are spaced 24 inches on center or tighter. Corrugated and R-panel metal roofing spans that distance without solid decking. If your purlin spacing exceeds 24 inches, add a solid deck or reduce the spacing before installing panels.

Where do you put the screws on a metal roof?

In the flat of the panel, 1 to 2 inches from the nearest rib, into a purlin or solid decking below. Never on the rib. Spacing is 12 to 24 inches on center depending on your wind zone and panel profile.

What should you put down before putting on a metal roof?

Over a solid deck: underlayment first, then inside foam closures at the eave, then panels. Over open purlins: condensation barrier or vented closures at the eave first. Butyl tape goes in every sidelap and under the ridge closures before the cap is set.

A watertight shed roof starts with the details

The panels are the least likely component to fail. What leaks are the screw holes driven on the rib, the sidelaps left without tape, and the ridge gaps that closures were supposed to fill. Underlayment, screw placement, and ridge sealing are the three variables that separate a 20-year metal roof from one that weeps around a washer in year two. Metal also traps and radiates heat more aggressively than asphalt shingles, so plan ventilation alongside your roofing if your shed stores temperature-sensitive equipment.

Ready to start with the right structure? Browse our wood storage shed collection for kits designed with purlin spacing that makes exposed-fastener metal roofing a straightforward install from day one.