What You Need Before You Start
Metal roof installation requires specific tools, materials, and safety equipment before you cut into your existing roof. You will need a roofing nailer or screw gun, metal snips or a circular saw with a metal-cutting blade, a tape measure, roofing underlayment, metal panels or shingles, fasteners rated for metal roofing, flashing kits, and ridge caps. Most metal roofs use either standing seam panels (which interlock along vertical ribs) or metal shingles that look like traditional asphalt but are made of steel or aluminum.
Safety equipment is not optional: a fall-arrest harness, roof brackets, a hard hat, work gloves, and eye protection are required. Metal roofing is slippery when wet or dusty, and the edges are sharp. You will also need a helper — metal panels are long and awkward to position alone, and you should never work on a roof by yourself. If your roof pitch is steeper than 6:12 (meaning it rises 6 inches for every 12 inches of horizontal run), or if your roof is higher than one story, hire a contractor instead.
Key Takeaways
- Metal roofs attach with fasteners that penetrate the panel and seal with a rubber washer, so fastener placement and tightness directly affect whether your roof leaks.
- Underlayment goes down before any metal panels, and it must be rated for metal roofing — standard asphalt underlayment can trap moisture under metal and cause rust.
- Panels run from the eave to the ridge and overlap in a specific direction; installing them backward or upside down will cause water to run under the seams instead of off the roof.
- Flashing around chimneys, vents, and valleys requires custom cutting and sealing, and mistakes here are the most common source of leaks in metal roofs.
- Metal roofs expand and contract with temperature changes, so fasteners must be loose enough to allow movement or the panels will buckle and fasteners will back out.
Remove the Old Roof or Prepare the Existing Deck
You have two options: tear off the old roof down to the wood deck, or install the metal roof over the existing shingles. Tearing off takes longer but gives you a chance to inspect the deck for rot or damage and to replace any soft spots. Installing over existing shingles is faster but adds weight and can trap moisture if the old roof is damaged underneath.
If you tear off, remove all shingles, nails, and debris. Inspect the wood deck for soft spots, rot, or missing sections. Replace any damaged plywood or boards before you proceed. If you install over existing shingles, make sure they are firmly attached and not curling or lifting. Sweep the roof clean of debris and fill any large gaps or holes with roofing cement.
Either way, the deck must be solid and relatively flat. Metal panels will follow the contours of the deck underneath, so high spots or dips will show through and can cause fasteners to miss the ribs or panels to sit unevenly.
Install Underlayment and Drip Edge
Underlayment is a moisture barrier that sits between the deck and the metal panels. Use underlayment rated specifically for metal roofing — it is usually synthetic (not asphalt-saturated felt) and allows moisture to escape while blocking water from below. Roll it out horizontally starting at the eave, overlapping each row by 4 to 6 inches as you move up toward the ridge. Staple it every 12 inches along the overlap and every 24 inches across the field.
Install drip edge along the eaves and gables before the underlayment at the eave, so water runs off the edge and not behind the fascia. Nail it every 12 inches with roofing nails. At the gables (the sloped sides), install drip edge after the underlayment so it sits on top and directs water onto the panels.
Lay Out and Cut the First Course of Panels
Measure the width of your roof and plan how the panels will fit. Most metal panels are 24 to 36 inches wide, and they overlap by 1 to 1.5 inches on the side. Calculate how many panels you need and whether you will have to cut the last panel to fit. Panels should run perpendicular to the eave — meaning they go up and down the slope, not across it — and they should start at one gable and run to the other.
Snap a chalk line along the eave 1.5 inches up from the drip edge to mark where the first panel's bottom edge will sit. This offset ensures the panel overhangs the drip edge slightly. Cut the first panel to length if needed using metal snips or a circular saw with a metal blade. Metal shavings are sharp and will stick to your skin and clothes, so wear long sleeves and gloves.
Position the first panel so its bottom edge aligns with the chalk line and its side edge is flush with the gable drip edge. Have your helper hold it in place while you fasten it.
Fasten Panels and Maintain Proper Spacing
Metal panels attach with fasteners — either nails or screws — that go through the panel and into the deck. Each fastener has a rubber washer that seals around the hole. Fasteners go into the ribs (the raised parts) of the panel, not the flat areas, because the ribs are where the panel is supported underneath. Consult your panel manufacturer's instructions for the exact fastener pattern — typically you will use one fastener per rib at the eave, then one fastener per rib every other row as you move up the roof.
Do not overtighten fasteners. The rubber washer should be compressed but not squeezed flat. Overtightening pulls the washer out of shape and creates a gap where water can seep in. Undertightening leaves the washer loose and water can run under it. The fastener should be snug enough that you cannot turn it by hand but not so tight that you have to strain with the gun.
Overlap the side seams by 1 to 1.5 inches and fasten through both layers at the overlap. Stagger the fasteners so they do not line up vertically — this prevents water from running down a line of holes.
Install Flashing Around Penetrations and Valleys
Flashing is custom metal that directs water around chimneys, vents, skylights, and valleys (the low spots where two roof slopes meet). Flashing is the most leak-prone part of a metal roof installation because it requires precise cutting and sealing.
For a vent pipe, slide the flashing boot over the pipe before you install the panel that will sit under it. Fasten the flashing to the deck with fasteners in the flanges (the flat parts that extend beyond the boot). Then install the panel above the vent so it overlaps the top of the flashing. Seal the overlap with roofing sealant rated for metal roofing.
For a chimney or skylight, install flashing on all four sides: a base flashing that sits under the panels below the obstruction, side flashings that run up the sides, and a cap flashing that sits on top of the panels above the obstruction. Each piece must overlap the one below it so water runs down and off. Seal all seams with metal-roofing sealant and fasten according to the flashing manufacturer's instructions.
Valleys require a valley flashing that runs the length of the valley. Cut panels to fit on either side of the valley and overlap the valley flashing. Seal the overlap with sealant.
Install Ridge Cap and Final Details
The ridge cap covers the peak where the two roof slopes meet. It is usually a U-shaped or angled piece that sits over the top panels and fastens to both sides. Install it after all the panels are in place. Fasten it with fasteners spaced every 12 inches, using the same snug-but-not-tight rule as the panels.
Install gable trim along the edges where the panels meet the gable drip edge. This trim covers the cut ends of the panels and directs water away from the gable. Fasten it every 12 inches.
Walk the roof and check all fasteners one more time. Look for any gaps between panels or flashing and panels. Seal any gaps with metal-roofing sealant. Do not use standard roofing cement or caulk — it breaks down under UV light and temperature swings. Metal-roofing sealant is formulated to flex and adhere to metal.
Frequently Asked Questions
Can I install a metal roof over asphalt shingles?
Yes, if the shingles are in good condition and firmly attached. You save the cost and labor of tear-off, but you add weight to the structure and cannot inspect the deck underneath. If the old roof has soft spots or leaks, those problems will remain hidden under the metal roof.
What fasteners should I use?
Use fasteners recommended by your panel manufacturer — usually stainless steel or coated steel screws with rubber washers for metal panels. The washer material matters: it must be compatible with the panel material (steel, aluminum, or copper) to prevent corrosion. Mismatched fasteners can rust and stain the roof.
How much should I tighten the fasteners?
Tighten until the rubber washer is compressed but not flattened. You should not be able to turn the fastener by hand, but you should not have to strain the gun. Overtightening squeezes the washer out of shape and creates leaks; undertightening leaves gaps. Most manufacturers recommend a torque of 8 to 12 inch-pounds if you are using a torque-limiting screw gun.
What do I do if panels buckle or fasteners back out?
Buckling usually means fasteners are too tight or panels were installed without room for expansion. Metal expands and contracts with temperature, and fasteners must be loose enough to allow movement. If panels buckle, loosen the fasteners slightly and see if the buckle flattens. If fasteners back out, it usually means they were not tight enough initially or the washer degraded. Replace them with new fasteners and tighten to the correct tension.
Do I need to seal the seams between panels?
Standing seam panels interlock and do not require sealing. Metal shingles overlap like asphalt shingles and do not require sealing either. However, all seams around flashing, valleys, and penetrations must be sealed with metal-roofing sealant to prevent water from running under the overlap.