You can install metal roofing directly over existing shingles, but it requires proper preparation and comes with trade-offs
Metal roofing can go over asphalt shingles without tearing them off first. This approach saves labor costs and disposal fees, and it leaves an extra insulation layer underneath. However, the shingles must be in reasonably good condition, the roof deck has to be sound, and you'll be adding weight that your framing needs to support. Most metal roof installations over shingles use exposed fasteners or standing seam systems, and the shingles create an uneven surface that affects how the metal panels sit and how water drains.
The decision to overlay or tear off depends on the condition of your existing roof, your budget, local building codes, and whether you plan to stay in the house long enough to justify the work. A roofer can inspect your current shingles and framing in an hour and tell you whether overlay is realistic for your roof.
Key Takeaways
- Metal roofing can be installed over shingles if the shingles are not curled, cracked, or missing, and if your roof deck is solid and not sagging.
- You must add furring strips or battens to create a level surface and proper drainage space between the metal and the shingles.
- Overlaying adds weight to your roof structure; a roofer or structural engineer should confirm your framing can handle it.
- Building permits and inspections are required in most jurisdictions, and some codes prohibit overlays or limit them to one layer.
- Tearing off the old shingles costs more upfront but gives you a chance to inspect and repair the deck and may extend the metal roof's lifespan.
When overlaying shingles is practical
Overlay works best when your shingles are relatively flat and intact. If shingles are curling at the edges, cracked, blistering, or missing in patches, the metal panels won't sit flush against them. Gaps and movement underneath the metal create places for water to pool and for the metal to flex unevenly, both of which shorten the roof's life.
Run your hand across the roof from a ladder or have a roofer walk it. If the surface feels reasonably smooth and you don't see daylight through holes, overlay is worth considering. If the shingles are more than 20 years old or show widespread damage, removal is usually the safer choice, even though it costs more.
Your roof deck also matters. Press on the deck with a screwdriver or awl in several spots, especially near the edges and around penetrations like vents and chimneys. If the wood is soft or the tool sinks in, the deck is rotting and must be replaced before any new roof goes on. A sagging roof or one with visible dips also signals deck problems that overlay won't fix.
Adding furring strips to create a level surface
Metal panels need a level, solid base. Shingles are bumpy and create valleys where water can sit. The solution is furring strips — thin horizontal boards, usually 1×2 or 1×3 lumber, fastened perpendicular to the roof slope over the shingles.
Furring strips serve three purposes: they level the surface so metal panels sit flat, they create an air gap that lets moisture escape from under the metal, and they give the metal fasteners something solid to bite into. Without them, fasteners driven through metal into shingles alone won't hold securely, and water trapped between the metal and shingles will rot the deck.
Strips are typically spaced 16 or 24 inches apart, depending on the metal panel profile and local code. They run horizontally across the roof slope and are fastened through the shingles into the deck below with corrosion-resistant fasteners — usually stainless steel or hot-dipped galvanized screws rated for roofing. A roofer will snap chalk lines to keep strips straight and may support proper spacing.
Weight and structural capacity
Metal roofing is lighter than asphalt shingles — typically 0.5 to 1.5 pounds per square foot compared to 2 to 3 pounds for shingles. However, when you overlay, you're adding the metal on top of the existing shingles, so the total load increases. Your roof framing has to support that combined weight.
Most residential roof framing built to current code can handle the overlay, but older homes or those with unusual designs may not. A structural engineer or experienced roofer can calculate the load and compare it to your framing's capacity. If the framing is undersized, you have two choices: reinforce the framing (expensive) or tear off the shingles to reduce the total load (more common).
Get this assessment in writing before you commit to the project. It's a small cost that prevents a costly mistake.
Fastening and drainage with metal panels
Metal roofing over shingles uses one of two fastening methods: exposed fasteners or standing seam systems.
Exposed fastener panels have screws that go through the panel face into the furring strips. These screws are visible from the ground and must be sealed with rubber washers to prevent leaks. They're cheaper than standing seam but require more maintenance — washers can degrade over time and need inspection every few years.
Standing seam panels have a raised seam that runs vertically up the roof. The panels lock together at the seams, and fasteners are hidden inside the seams. Standing seam is more expensive but lasts longer and requires less maintenance. Water sheds off the seams more reliably, which matters when you have an uneven surface underneath.
Regardless of the panel type, the furring strips create channels that allow water and air to move. This ventilation is critical — it prevents moisture from accumulating under the metal and damaging the shingles and deck below. Make sure gutters and downspouts are sized to handle the water volume, and may support the roof has proper slope for drainage. A flat or low-slope roof is a poor candidate for overlay.
Building codes and permit requirements
Most jurisdictions require a permit for metal roof installation, including overlays. The permit process involves submitting plans, having the work inspected during installation, and getting a final sign-off. Some areas limit the number of roof layers — you may not be allowed to overlay if there's already one layer of roofing over the original shingles.
Check with your local building department before you hire a roofer. They'll tell you whether overlay is allowed, what documentation you need, and what inspections are required. Some jurisdictions also have wind or snow load requirements that affect which metal panel profiles and fastening methods are acceptable in your area.
A reputable roofer will handle the permit process as part of the job. If a contractor says permits aren't necessary or tries to avoid them, that's a red flag.
Overlay versus tear-off: the trade-offs
| Aspect | Overlay | Tear-Off |
|---|---|---|
| Upfront cost | Lower — no removal labor or disposal | Higher — removal, disposal, and deck repair if needed |
| Timeline | Faster — no tear-off phase | Longer — removal adds 1–2 days |
| Deck inspection | Limited — hidden under shingles | Full — you see and can repair damage |
| Roof lifespan | Potentially shorter — moisture trapped under metal can shorten life | Potentially longer — clean deck and proper ventilation |
| Future re-roofing | More difficult — two layers to remove | Easier — only metal roof to remove next time |
| Resale appeal | Lower — buyers may worry about hidden damage | Higher — clean installation, full deck warranty |
Overlay makes sense if your shingles are in good shape, your deck is solid, your framing can handle the weight, and you're looking to save money now. Tear-off makes sense if the shingles are old or damaged, you want to inspect and repair the deck, you plan to stay in the house for 20+ years, or you're concerned about resale value.
The choice also depends on your roof's history. If you've already had one overlay or repair, a tear-off is usually better — you avoid stacking problems and give yourself a fresh start with a clean deck underneath.
Frequently Asked Questions
Can I install metal roofing over two layers of shingles?
Most building codes prohibit it. If your roof already has two layers, you must tear off at least one layer before adding metal. Check your local code, but the rule exists because the weight and moisture risk become too high.
What happens to the old shingles under the metal?
They stay in place and gradually deteriorate. The air gap created by furring strips slows decay, but moisture and temperature swings will eventually break them down. This is why tear-off is often preferred for long-term durability — you avoid trapping a deteriorating layer underneath.
Do I need to remove gutters before installing metal roofing over shingles?
Usually, yes. The roofer needs access to the fascia and edge of the roof to install metal panels and flashing properly. Gutters are typically removed at the start and reinstalled after the metal roof is done. Your roofer will include this in the scope of work.
Will the metal roof be noisier if it's installed over shingles?
No. The shingles and air gap actually provide some sound dampening. Metal roofs over shingles are typically quieter than metal roofs over bare deck.
How much does it cost to overlay shingles with metal roofing?
Costs vary by region, metal type, and roof size, but overlay is generally 20–30% cheaper than tear-off and replacement. Get quotes from at least two local roofers — they can give you actual numbers for your roof.