Metal roof installation requires removing the old roof, installing underlayment and flashing, then fastening metal panels in a specific sequence
A metal roof installation is a multi-day job that involves tearing off existing roofing, preparing the deck, installing a moisture barrier, and fastening metal panels with specialized fasteners. Most residential metal roofs use standing seam panels (where two panels lock together vertically) or metal shingles that look like asphalt but are made of steel or aluminum. The process takes 2 to 5 days depending on roof size and complexity, and requires working at height with proper safety equipment.
This is not a beginner DIY project. Metal roofing requires knowledge of flashing details, proper fastener spacing, and how to handle the material without damaging the finish. Most homeowners hire a contractor licensed in roofing. If you are considering doing this yourself, you should have roofing experience, fall protection training, and access to a safety harness system.
Key Takeaways
- Metal roof installation begins with removing the old roof down to the deck, then inspecting and repairing the wood structure underneath.
- Underlayment (a moisture barrier) and metal flashing around penetrations like chimneys and vents must be installed before any panels go down.
- Metal panels are fastened with rubber-washer screws driven through the ribs or flanges into the deck, with spacing and pattern determined by the panel type and local wind codes.
- Sealing, ridge caps, and trim pieces are installed last, and the entire roof must be inspected for fastener tightness and proper water shedding before the job is complete.
Removing the old roof and preparing the deck
The first step is to strip the existing roofing material down to the wood deck. This means removing shingles, underlayment, flashing, and any nails or fasteners. A roofing crew typically uses a shovel or roofing fork to pry material loose and throw it into a dumpster. This phase creates significant debris and dust, so the work area below should be cleared and tarped if needed.
Once the deck is bare, inspect it for rot, soft spots, or structural damage. Any wood that is soft, discolored, or spongy when probed must be replaced. This is the only time you can see the deck clearly, so this step is critical. If the deck has uneven spots, high spots can be shaved down and low spots can be shimmed with tapered wood. The deck must be relatively flat and solid because metal panels will telegraph (show) any bumps underneath.
Check that all roof penetrations—vents, chimneys, skylights—are in good condition. If a vent pipe is rusted or a flashing is damaged, now is the time to replace it. The deck should be swept clean of debris before the next step begins.
Installing underlayment and starter strips
Underlayment is a synthetic or felt moisture barrier that sits between the deck and the metal panels. It prevents condensation from forming on the underside of the roof and provides a secondary water barrier if wind-driven rain gets under the panels. Most metal roof installations use a synthetic underlayment (often called a "breathable" or "non-bituthene" type) rolled out horizontally from the eaves upward, with each row overlapping the one below by 4 to 6 inches.
Underlayment is stapled or nailed to the deck every 12 to 18 inches along the overlap. Seams should be sealed with tape if the product requires it—check the manufacturer's instructions. Some installers use a self-adhering underlayment instead, which sticks directly to the deck and requires no fasteners in the overlap area.
A starter strip (a metal trim piece) is then installed along the eave edge. This strip provides a finished edge and a surface for the first row of panels to rest against. It is fastened with fasteners spaced 12 to 16 inches apart, depending on wind load requirements in your area.
Installing flashing around penetrations
Flashing is metal trim that directs water away from roof penetrations like vents, chimneys, and skylights. Each penetration requires a flashing kit designed for metal roofing. These kits typically include a base flashing (the part that sits on the deck) and a cap flashing (the part that overlaps the metal panels).
Base flashing is installed first, sitting on top of the underlayment and fastened to the deck. The underlayment is then brought up and over the top edge of the base flashing to create a water-shedding overlap. Once panels are installed, the cap flashing is slipped under the upper panels and over the lower panels, creating a shingle-like overlap that directs water down and away.
Flashing installation is one of the most common sources of leaks in metal roofs. Each penetration must be sealed with a compatible sealant (usually silicone or polyurethane, not asphalt-based caulk), and fasteners must be sealed with rubber washers to prevent water entry. If you are hiring a contractor, ask specifically how they handle flashing details and whether they use sealant on all fasteners.
Fastening the metal panels in sequence
Metal panels are installed from the eave upward, working across the roof. The first row is aligned with the starter strip and fastened with rubber-washer screws. These screws are driven through the ribs or flanges of the panel into the deck below. Fastener spacing is typically 12 to 24 inches along the ribs, depending on the panel profile and local wind codes. In high-wind areas, fastening may be closer together or use additional fasteners.
Each screw must be driven perpendicular to the deck (straight down, not at an angle) and tightened until the rubber washer is compressed but not crushed. Over-tightening can compress the washer too much and allow water to seep in; under-tightening leaves a gap. This is a detail that separates a good installation from a poor one.
The second row of panels is installed by locking or overlapping the first row, depending on the panel type. Standing seam panels lock together along their vertical edges; metal shingles overlap like asphalt shingles. Each row is fastened in the same pattern as the first. The process continues upward until the ridge is reached.
Installing ridge caps and trim
The ridge cap is a metal piece that covers the peak of the roof where the two roof planes meet. It is installed over the top row of panels and fastened with fasteners spaced 12 inches apart. Ridge caps must be sealed with sealant along their base to prevent wind-driven rain from entering.
Gable trim (also called rake trim) is installed along the sloped edges of the roof where it meets the gable wall. This trim is fastened to the edge of the deck and sealed with sealant. Hip and valley trim are installed in the same way if the roof has hips or valleys.
All trim pieces should be sealed with a compatible sealant at the base and at all fastener locations. The sealant should be applied in a continuous bead, not in dots. Once all trim is installed and sealed, the roof is inspected for any fasteners that may have backed out during installation, and a final walk-through is done to confirm all panels are properly seated and all seams are sealed.
Inspection and final checks
Before the job is considered complete, the entire roof should be inspected from the ground and from above. Walk the roof carefully (with fall protection) and check that all fasteners are tight, all seams are sealed, and all trim is properly installed. Look for any gaps between panels, any fasteners that are missing or backed out, and any areas where water could enter.
A pressure test is sometimes performed to check for leaks, though this is not standard practice on all jobs. If the roof is going to be walked on regularly (for maintenance or cleaning), make sure the contractor has installed walk pads or marked safe areas, because walking on metal panels can damage the finish and create stress points.
The contractor should provide you with a warranty document that specifies what is covered and for how long. Most metal roof warranties cover material defects and workmanship for 10 to 20 years, though some cover longer. Keep this document and any maintenance records, as they may be needed if a warranty claim arises.
Frequently Asked Questions
Can you install a metal roof over an existing asphalt roof?
Most metal roof manufacturers recommend removing the old roof down to the deck. Installing over asphalt shingles can trap moisture, hide deck damage, and create an uneven surface that causes panels to flex and fasteners to back out. Some contractors do install over existing roofing in specific cases, but this voids many warranties and is not considered best practice.
What fasteners should be used for metal roofing?
Use fasteners specifically designed for metal roofing: typically stainless steel or galvanized screws with rubber washers rated for the panel type and climate. The screw length depends on the panel profile and deck thickness. Using the wrong fastener type or size is a common cause of leaks and panel damage. Always follow the panel manufacturer's fastener specifications.
How do you prevent leaks around vents and chimneys?
Proper flashing installation and sealing are the keys. The base flashing must sit on the deck with underlayment brought over its top edge. The cap flashing must overlap the panels above it. All seams and fasteners must be sealed with a compatible sealant. If leaks occur after installation, the flashing detail is usually the source.
How long does a metal roof installation take?
A typical residential metal roof takes 2 to 5 days to install, depending on roof size, complexity, weather, and crew size. A straightforward gable roof on a small house might take 2 days; a large roof with multiple penetrations, valleys, or hips can take a week or more. Weather delays are common, as roofing cannot be done in heavy rain or high winds.
Do metal roofs need maintenance after installation?
Metal roofs require minimal maintenance compared to asphalt shingles. Inspect the roof annually for any fasteners that may have backed out, check that trim seals are intact, and clear debris from valleys or gutters. If you walk on the roof, use walk pads to avoid damaging the finish. Most metal roofs do not need cleaning unless algae or moss growth occurs in humid climates.