Metal roof installation requires removing the old roof, installing underlayment and flashing, then fastening metal panels in a specific sequence
A metal roof installation typically takes two to five days depending on roof size and complexity. The process involves stripping the old roofing material, preparing the deck, installing a moisture barrier, running flashing around edges and penetrations, and fastening metal panels or shingles in overlapping rows. Most homeowners hire a contractor for this work because the height, weight, and precision required make it a specialized task. If you are considering doing this yourself, you need fall protection equipment, roofing experience, and knowledge of local building codes.
Metal roofing comes in two main styles: standing seam panels (which lock together at the edges) and metal shingles (which look like asphalt shingles but are made of steel or aluminum). The installation method differs between the two, and the contractor you hire will determine which approach fits your roof design and budget.
Key Takeaways
- Metal roof installation begins with complete removal of the old roofing material and inspection of the roof deck for damage or rot.
- Underlayment and flashing must be installed before any metal panels go down, and flashing placement around chimneys, vents, and edges is critical to prevent leaks.
- Metal panels are fastened with specialized fasteners that allow for expansion and contraction as temperature changes, not nailed like asphalt shingles.
- Most homeowners hire licensed roofing contractors because the work involves heights, specialized tools, and building code compliance that require training.
Removing the old roof and inspecting the deck
The first step is stripping away all existing roofing material down to the roof deck—the wooden or concrete structure underneath. This includes shingles, underlayment, and any nails or fasteners left behind. A roofing crew typically uses a shovel and pry bar to tear off the old material, which is then hauled away or recycled. This phase usually takes one full day on a standard residential roof.
Once the deck is bare, the contractor inspects it for soft spots, rot, or structural damage. Any wood that is spongy or discolored must be replaced before the new roof goes on. If the deck is sagging or uneven, it may need to be reinforced or leveled. This inspection step determines whether the project stays on schedule or requires additional framing work that adds time and cost.
Installing underlayment and ice-and-water shield
Underlayment is a synthetic or felt barrier that sits directly on the roof deck and protects it from moisture. For metal roofs, most contractors use a breathable synthetic underlayment rather than traditional felt, because metal roofs expand and contract with temperature changes and need room for air circulation underneath.
In cold climates, an ice-and-water shield—a sticky membrane—is installed along the eaves, valleys, and any areas prone to ice dams. This shield adheres directly to the deck and provides extra protection where water is most likely to back up. The underlayment is rolled out in overlapping rows from the eave to the ridge, with each row overlapping the one below by at least 4 to 6 inches. Fasteners or adhesive hold it in place temporarily until the metal panels are installed.
Running flashing around edges, penetrations, and valleys
Flashing is metal trim that directs water away from areas where the roof meets walls, chimneys, vents, or skylights. Without proper flashing, water will seep into these joints and cause leaks inside the home. Metal roof flashing is usually made of the same material as the panels—steel or aluminum—so it weathers at the same rate and maintains a uniform appearance.
Common flashing locations include the eave edge (drip edge), the gable ends, valleys where two roof planes meet, and around any roof penetrations like plumbing vents or furnace exhausts. Each piece of flashing is cut to fit the specific location and fastened to the deck before the metal panels are installed. The panels then overlap the flashing, creating a water-shedding seal. Flashing installation requires precision and knowledge of how water flows across a roof, which is why this step is often where leaks originate if done incorrectly.
Fastening metal panels or shingles in sequence
Metal panels are fastened with specialized fasteners—usually screws with rubber washers—that allow the metal to expand and contract without splitting or cracking. Unlike asphalt shingles, metal roofing is not nailed; nails would create fixed points that the expanding metal would pull away from, creating gaps and leaks.
For standing seam panels, the first panel is aligned at one edge of the roof and fastened along the top and bottom. The second panel is positioned so its edge locks into the first panel's seam, and the process repeats across the roof width. Once one row is complete, the next row is started at the eave and worked upward toward the ridge. For metal shingles, the process is similar to asphalt shingles—overlapping rows working upward—but each shingle is fastened with two to four screws rather than nails.
The fastening pattern and spacing are specified by the panel manufacturer and must be followed exactly. Fasteners that are too tight can prevent expansion; fasteners that are too loose allow the panels to shift. A contractor who has installed the specific panel type before will know the correct technique and fastener torque.
Installing ridge cap, trim, and final sealing
Once all panels are in place, the ridge cap—a specialized trim piece that covers the peak where two roof planes meet—is installed. The ridge cap is fastened with the same type of screws as the panels and is sealed with a compatible sealant to prevent water from entering at the ridge.
Gable trim, eave trim, and any other edge details are then installed and sealed. Some metal roofing systems use sealant tape or liquid sealant at panel seams or fastener locations; others rely on the mechanical overlap and fastener design to shed water. The contractor will follow the manufacturer's specifications for which sealing method is required.
Timeline and what affects installation speed
A straightforward metal roof installation on a single-story home typically takes two to three days. A larger or more complex roof—with multiple valleys, many penetrations, or steep pitch—may take four to five days. Weather delays the work; rain stops installation, and high winds can make working at height unsafe.
The condition of the existing roof also affects timeline. If the deck has rot that requires framing repair, or if the old roof is multiple layers thick and takes longer to remove, the project extends. Permit inspections—required in most jurisdictions—add one to two weeks to the overall timeline because the inspector must visit before underlayment is installed and again after the roof is complete.
When to hire a contractor versus DIY considerations
Metal roof installation is physically demanding and requires working at heights with fall protection equipment. It also demands knowledge of building codes, flashing details, and the specific panel system being installed. Most homeowners hire a licensed roofing contractor who carries liability insurance and can warrant the work.
If you have roofing experience, own fall protection equipment, and are comfortable reading technical specifications, you may be able to handle the installation yourself. However, mistakes in flashing or fastening can lead to leaks that are expensive to repair later. Many building departments require that roofing work be performed by a licensed contractor, so check your local code before planning a DIY approach. Even if you do the work yourself, you will likely need a permit and a final inspection.
Frequently Asked Questions
Can you install a metal roof over an existing asphalt roof?
In some cases yes, but most contractors recommend removing the old roof first. Installing over existing shingles can trap moisture and hide deck damage. Some jurisdictions also limit the number of roofing layers allowed by code. Removing the old roof costs more upfront but prevents problems later.
What fasteners should I use for a metal roof?
Use the fasteners specified by the panel manufacturer—usually stainless steel or galvanized screws with rubber washers rated for metal roofing. Do not use nails or standard wood screws. The rubber washer seals around the fastener hole and allows the metal to expand without cracking.
How do you prevent leaks where the roof meets a chimney?
Flashing is installed around the chimney before the metal panels go down. The flashing directs water down and away from the chimney joint. The metal panels overlap the flashing, creating a sealed transition. Proper flashing installation and sealant are critical; this is a common leak point if done incorrectly.
Do metal roofs need ventilation underneath?
Metal roofs benefit from air circulation under the panels to prevent moisture buildup. If your roof has an attic, soffit and ridge vents allow air to flow. If you are installing over a solid deck with no attic space, a breathable underlayment helps manage moisture. Check your local building code for ventilation requirements.
How long does a metal roof last?
A properly installed metal roof typically lasts 40 to 70 years depending on the material and climate. Steel roofs in coastal areas may corrode faster than aluminum roofs. Regular inspections and maintenance—clearing debris, checking fasteners—extend the roof's life.