Can You Put a Metal Roof Over Shingles in Pennsylvania?

1 day ago

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In many cases, yes. Pennsylvania has enforced the 2021 International Residential Code through its Uniform Construction Code since January 1, 2026, and that code permits a new roof covering over an existing one when it "is installed in accordance with the roof covering manufacturer's approved instructions." The same code bars it over a roof that is water-soaked or deteriorated, over slate or tile, and where the roof "has two or more applications of any type of roof covering."

Standing-seam systems get their own line in the code. It says "complete and separate roofing systems, such as standing-seam metal roof systems," that carry roof loads straight to the structure "shall not require the removal of existing roof coverings." The code does not say whether that line overrides the two-layer limit, so a roof with two layers already on it is a question for your local code official. The Metal Construction Association adds a framing rule: purlins over old shingles must be fastened to the rafters, "not just the roof sheathing." Below are the code rules, panel pitch limits, purlins, underlayment and weight.

Does Pennsylvania Code Allow a Metal Roof Over Shingles?

Yes, with limits. Pennsylvania regulation 12-125 updated the Uniform Construction Code by "adopting nearly all the provisions of the 2021 International Code Council codes," effective January 1, 2026, and the 2021 IRC is the residential code in that set.

A recover, or roof-over, is a new roof covering installed on top of an existing one without tearing off down to the deck. Under the 2021 IRC, a recover is allowed when the new covering goes on per its maker's approved instructions, and in the two other cases covered below. A full replacement means removing the existing layers "down to the roof deck."

Call your local code office before ordering panels for a roof-over.

When Do the Old Shingles Have to Come Off?

The 2021 IRC lists three conditions that rule out a recover:

The existing roof or covering is water soaked or deteriorated so it "is not adequate as a base for additional roofing."
The existing covering is slate, clay, cement or asbestos-cement tile.
The roof already has two or more applications of any type of roof covering.

The Metal Construction Association's 2021 retrofit paper adds field checks. "Any areas that feel spongy or deflect when walked on may require removal of the roofing," and a questionable deck can be checked with "a fastener pull-out test, similar to ASTM D1761, seeking resistance of at least 80 pounds." If the existing roof shows signs of leaking, MCA points to "a full tear-off."

Flashing counts too. The code says existing flashings, edgings, outlets and vents "shall be replaced where rusted, damaged or deteriorated." Check pipe boots and vent flashing before you place the order.

What Does the Code Say About Standing-Seam Systems?

The 2021 IRC treats a complete, separate system differently. Standing-seam metal roof systems "designed to transmit the roof loads directly to the building's structural system" that "do not rely on existing roofs and roof coverings for support" do not require removing the old roofing.

That language describes how the system is built, not a blanket permission. The code does not state that it overrides the two-layer limit, and MCA's own advice is to "check the local building code to determine the allowable number of layers." If you are looking at standing seam over a two-layer roof, get the code office's answer in writing before you buy. For more on the panel style itself, see CGR's guide to standing seam metal roof panels and what to buy.

The code also allows metal panels and metal shingles over an existing wood shake roof when applied per its separate wood shake section.

What Roof Pitch Do Metal Panels Need?

The 2021 IRC sets minimum slopes by panel type:

Panel type	Minimum slope (2021 IRC)
Lapped, nonsoldered-seam panels without lap sealant	3:12
Lapped, nonsoldered-seam panels with applied lap sealant	1/2:12
Standing-seam systems	1/4:12

Exposed-fastener panels like WV Metal's Max-Life fall in the lapped category. WV Metal's 2015 Max-Life installation guide calls for "at least a 3/12 pitch with an 8" end lap when using more than one panel in a row," with side lap seams facing "away from the prevailing wind-driven rain." Its current spec sheet lists the Max-Life panel at 36 inches of coverage, ribs 9 inches on center, 29 gauge, in lengths up to 44 feet.

The code also says metal panels go on "solid or spaced sheathing," except panels designed for spaced supports. A shingle roof gives you solid sheathing underneath, so the question becomes how the panels attach through it.

Do You Need Purlins Over the Old Shingles?

MCA's retrofit paper covers purlin installs and is specific about fastening: purlins "must be mechanically fastened (e.g., screws or nails) to the roof structure (i.e., existing rafters) and not just the roof sheathing." Mark rafter lines before the first purlin goes down.

MCA says a purlin cavity lets "fresh air" move between the old roof and the new metal, which "reduces heat gain in the summer." MCA also warns that "installing some metal roofing materials over higher profile shingles may cause visual telegraphing," and that deflections "could impact uplift resistance."

For fasteners, the code points to the panel maker's instructions; without them, "galvanized fasteners shall be used for steel roofs," and stainless steel is also acceptable.

Which Underlayment Goes Under Metal Over Shingles?

The 2021 IRC requires underlayment under metal panels, so check the panel maker's instructions and the code office for the type. MCA notes that on a retrofit "an additional code compliant underlayment may be required."

Owens Corning ProArmor synthetic underlayment is one fit. Owens Corning says ProArmor is designed for use under metal and asphalt shingle roofing only, and its product data lists ASTM D226 Type II and ASTM D4869 Type IV. Each roll is 42 inches by 286 feet, covers 10 squares and weighs 23.5 pounds. It can be left exposed up to 90 days. Owens Corning's July 2021 instructions call for side laps of at least 3 inches and end laps of at least 4 inches on slopes of 4:12 and steeper (12 inch end laps from 2:12 to under 4:12), 6 inch laps over hips, ridges and valleys, two layers on lower slopes, and fasteners with caps at least 1 inch across. CGR's roof underlayment guide for Western PA compares the main types.

How Much Weight Does a Metal Roof Add?

Far less than a second layer of shingles. MCA puts metal roofs at "40 to 140 pounds per 'square'" (100 square feet), against other roofing materials that "can be as heavy as 250 pounds per square or more." ProVia's metal roofing myths article (updated July 2026) lists an average asphalt shingle roof at 240 to 270 pounds per square and its metal roof system at 108 pounds per square.

Even so, MCA cautions that "the added weight of the double layer of roofing may exceed the structural design of the deck and/or roof framing." An older roof with undersized rafters still needs a look.

ProVia's metal roofing brochure lists 26-gauge steel, a UL 2218 Class 4 impact rating, a Class A fire rating under ASTM E108 and a Kynar 500 finish. CGR's posts comparing metal roofing vs shingles for PA homes and what metal roofing panels cost cover the budget side.

FAQ

How many layers of shingles can a metal roof go over?

The 2021 IRC bars a recover where the roof "has two or more applications of any type of roof covering." Over a single layer in sound condition, follow the panel maker's approved instructions.

Do you need a permit to put a metal roof over shingles in PA?

Ask your local code office before you order. It can tell you what the job needs under the Uniform Construction Code.

Do you need furring strips or purlins?

It depends on the panel and the old roof. Where purlins are used, MCA says they must be fastened into the rafters, not just the sheathing.

Will the old shingles show through the metal?

They can. MCA warns that some metal over higher profile shingles "may cause visual telegraphing."

Is underlayment required for metal over shingles?

Yes. The IRC requires underlayment under metal panels, and MCA says a retrofit may need an additional code-compliant layer.

Can metal go over a wood shake roof?

The 2021 IRC permits metal panels and metal shingles over existing wood shake roofs when applied per its wood shake section.

Order Metal Roofing at CGR Wholesale

CGR Wholesale Roofing & Siding Supply Center "proudly stocks the full range of WV Metals roofing products," including the Max-Life, Max-Loc and R-Panel lines on its WV Metals page, and now offers ProVia metal roofing in shake, slate and barrel tile styles. Its Owens Corning page lists ProArmor synthetic roof underlayment and links its data sheet. Bring your roof measurements and pitch to the Rostraver showroom, open Monday through Friday 7:00 AM to 4:00 PM and Saturday 7:00 AM to 12:00 PM, or call to arrange delivery to the job site.