Can you put a metal roof over shingles?
Yes, physically, and many contractors do. Code generally allows two total layers, so one over a single shingle layer, with a slip sheet or purlins between. We tear off instead: an overlay hides the deck, traps heat and complicates future work. Our metal rate is $1,563 to $2,575 per square.
Metal over asphalt shingles: what actually happens
The mechanics are straightforward. A metal panel roof can be installed over one existing layer of asphalt shingles, either directly over a slip sheet or high-temperature underlayment, or on a batten and purlin system that lifts the panel off the shingle and creates an air gap. Most residential building codes allow a maximum of two total roof coverings, so an overlay is permissible where there is only one layer already and the deck is sound.
| Approach | What it gains | What it costs you |
|---|---|---|
| Direct over shingles with underlayment | Cheapest and fastest. No tear-off, no disposal. | The panel telegraphs the texture of the shingle underneath, the deck is never inspected, and the assembly runs hot. |
| Battens or purlins over shingles | A flat plane to fasten to and an air gap that helps the assembly run cooler. | More material and labour, a higher roof line at the edges, and the same blind spot about the deck. |
| Full tear-off to deck | The deck is seen and repaired, the underlayment sits on a flat surface, and the assembly is what the manufacturer designed. | The tear-off and disposal cost, which on a single layer is a real but modest share of the job. |
What we do, and why: we tear off. A metal roof is a forty to seventy year decision, and installing it over a surface nobody has looked under means committing to a deck for the next half century on the basis of a guess. If there is soft sheathing under those shingles it does not improve, and getting to it later means removing a metal roof, which is the expensive way to find out. The saving from an overlay is real; it is just small next to the cost of being wrong.
Can you put a metal roof over an existing metal roof?
Yes, and on agricultural and commercial buildings it is routine — a new exposed-fastener panel over an old one on purlins is a standard recover. On a house it is less common and needs three questions answered. Is the existing panel flat enough to fasten through or does it need battens. Is there condensation trapped between the two layers, which is the usual failure. And is the existing fastening still sound, since the new roof loads through it.
A standing-seam roof over an old exposed-fastener panel is normally done on a purlin system, which lifts the new panel clear and gives the clips something to fix into. What is not sensible is fastening a new panel directly through an old one into unknown substrate, because the fastener has to reach solid wood or steel and nobody can confirm it does from above.
What metal costs against asphalt
Standing-seam metal on our published book runs $1,563 to $2,575 per square complete, against $788 to $1,300 per square for architectural asphalt. On a typical 24-square Maryland house that is $37,500 to $62,000 for metal against $19,000 to $31,000 for asphalt. Roughly double the money, for roughly double the service life, which is close to a wash on cost per year and a clear win if you are staying in the house.
Where metal is the wrong call: if you are selling within five years, because the premium does not come back in the sale price; and on a heavily cut-up roofline with many dormers and valleys, because the custom trim bending on a complex roof costs more than the extra life is worth. Where it is clearly right: long clean runs, low-slope sections a shingle cannot serve, and houses people intend to keep.
It is a legitimate method and it is not the same roof. The deck is never inspected, the assembly runs hotter, and any future work on the roof means dealing with two coverings. The saving is real and should be stated as a trade rather than as a free lunch.
Ask instead: What is the condition of the deck under those shingles, and how would you know?Manufacturer coverage on a panel system generally assumes a specified substrate and installation. An overlay can change what is covered, and the place to find that out is the written warranty document before signing, not a claim in year twelve.
Ask instead: Send me the manufacturer warranty document that applies to an overlay installation.Metal over existing roof questions
Can you put a metal roof over shingles?
Physically yes, and residential codes generally permit a maximum of two total roof coverings, so a metal panel over one existing layer of asphalt is usually allowed where the deck is sound. It is done either directly over a slip sheet or high-temperature underlayment, or on battens and purlins that lift the panel and create an air gap. What you lose is any knowledge of the deck condition, since nobody looks at it, and a metal roof is a forty to seventy year commitment to whatever is under there.
Can you put a metal roof over an existing metal roof?
Yes, and on agricultural and commercial buildings it is a routine recover. On a house it needs three things confirmed first: whether the existing panel is flat and sound enough to build off or whether purlins are needed, whether condensation is trapped between the layers, and whether the existing fastening is still holding, because the new roof loads through it. A standing-seam panel over an old exposed-fastener roof is normally done on purlins rather than fixed directly through it.
Is it cheaper to put metal over shingles?
Yes, by the cost of the tear-off and disposal, which on a single existing layer is a real but modest share of the job. Whether it is cheaper over the life of the roof is a different question: an overlay runs hotter, the deck is never seen or repaired, and any future work on that roof means dealing with two coverings at once. On a forty to seventy year product, we take the view that the tear-off is worth paying for.
What underlayment goes under a metal roof?
A high-temperature synthetic underlayment, because the underside of a metal panel gets far hotter than the underside of a shingle and standard felt or ordinary synthetic can soften and fail. Ice-and-water membrane still goes at the eaves and in the valleys, and it should also be a high-temperature grade. On an overlay the same rule applies with a slip sheet between the metal and the old shingle surface, so the panel is not sitting on abrasive granules that will wear it from below.
Does a metal roof over shingles make noise?
Less than people expect, and the variable is the assembly rather than the metal. A panel fixed over a solid deck with underlayment is only marginally louder in heavy rain than asphalt, and the shingle layer underneath an overlay actually damps it further. What is genuinely loud is a panel on open purlins over an unlined space, which is the agricultural building most people are remembering when they ask.
Will a metal roof over shingles cause condensation?
It can, and it is the main technical objection to a direct overlay. Warm moist air reaching the cold underside of a metal panel condenses, and if that happens in a sealed space between the panel and the old shingle it has nowhere to go. A ventilated batten system, correct high-temperature underlayment and adequate attic ventilation are what prevent it. A full tear-off with the panel installed on the designed assembly avoids the question entirely.
Where to go next
If metal is the direction, these cover the detail and the alternative.
Standing-seam metal roofing
24-gauge concealed-fastener metal, site-bent trim, and the roofs it is and is not right for.
See the service →DetailsMetal roof details that decide the life
Underlayment, ridge cap and vent, trim, pipe boots, screws and chimney flashing.
Read the guide →LifespanHow long does a roof last, by material
Asphalt, metal, flat and tile compared on service life and cost per year.
See the numbers →DeckingRoof decking and sheathing
How OSB, plywood and old plank sheathing fail, and why the per-sheet replacement rate belongs in your contract.
Read the standard →