Can a Metal Roof Go Over Existing Shingles in North Carolina?

You can put a metal roof over shingles in North Carolina in some cases, but not by default. The general rule for Interlock roofs is that a single layer of asphalt shingles may stay in place only if an inspection finds it suitable and the local code allows it. If the existing roof fails that test, it comes off.

The idea appeals for obvious reasons. Skipping tear-off avoids loading old shingles into a dumpster, shortens the job and lowers the price. Lightweight metal shingles add little load: Interlock aluminum panels weigh roughly 0.4 to 0.7 lb per square foot.

But the old roof becomes the base for the new one, and a new roof is only as good as what it sits on. In North Carolina's humid climate, a roof that has leaked even a little can hide soft decking, rotted edges and rusted nails that you cannot see from the ground. The decision should rest on what an inspection finds, not on the savings alone. This article explains the code rules, the trade-offs and how a careful contractor makes the call.

The building code allows a new roof over an existing one only under limited conditions. North Carolina uses its own residential code, based on the International Residential Code with state amendments, and the Office of State Fire Marshal has stated that reroofing jobs must comply with the North Carolina Residential Code.

The model International Residential Code (section R908.3.1.1) says the existing roof covering must be removed before a new one is installed in any of these cases:

• the existing roof or covering is water-soaked or deteriorated to the point that it is not an adequate base for more roofing;
• the existing covering is slate, clay, cement or asbestos-cement tile;
• the existing roof already has two or more applications of any type of roof covering.

The model code also permits some recovers, for example when the new covering is installed according to the manufacturer's approved instructions. City and county inspection departments apply the North Carolina version of these rules, and they decide how they apply to your house. Ask your local building inspections office, and see our guides to the NC Residential Code and reroofing and roof permits in NC.

The old roof must come off when the code requires it, when the manufacturer requires it, or when an inspection shows it is not a sound base. In practice that covers:

• Two or more existing layers. Many older North Carolina homes were reroofed once over the original shingles. A third layer is not an option under the model code.
• Soft, rotted or delaminated decking. Common around chimneys, valleys, skylights and eaves after years of small leaks.
• Curled, buckled or badly cupped shingles. An uneven base telegraphs through and makes a flat, tight metal installation difficult.
• Slate and tile. The model code requires removal, and they are too heavy and uneven to roof over anyway.
• Cedar shingles and shakes. The model code permits some metal coverings over wood shakes, but for Interlock roofs, cedar shingles and cedar shakes are always removed first.

If a contractor offers to roof over without going into the attic or looking closely at the edges, treat that as a warning. The inspection is the whole basis for the decision.

The advantages of roofing over a sound single layer are real, which is why the option exists. They are:

• Lower cost. Tear-off labor and dumpster fees drop out of the price.
• Shorter job. The house is not stripped down to bare deck, so the exposure to a sudden summer thunderstorm during installation is lower.
• Less mess. Fewer nails and less debris in the yard, flower beds and driveway.
• A little extra insulation and sound damping. The old layer adds a modest buffer, though not a substitute for proper attic insulation.

A lightweight aluminum roof makes the option more practical than a heavy one would, because the added load on the framing is small. On a simple roof with a sound deck, one layer of flat-lying shingles and no history of leaks, roofing over can be a reasonable choice and the inspection may support it.

Keep the savings in proportion. Tear-off is one part of a roofing estimate, alongside materials, underlayment, flashing, trim and installation labor, all of which stay in the price whether the old layer comes off or not. Ask the contractor to price both options so you can see the real difference on your house before deciding.

The main risk of leaving old shingles is that problems underneath stay hidden. Once the new roof goes on, nobody will see the deck again for decades. The common risks:

• Hidden deck damage. Soft spots and rot keep spreading under a new roof, and fasteners in weak wood hold poorly in high wind.
• Trapped moisture. If the old roof was damp or the attic poorly ventilated, moisture can stay in the assembly in a humid North Carolina summer.
• Flashing compromises. Wall, chimney and valley flashings have to be fitted over or around the old layer. Done carelessly, that is where leaks start.
• Ventilation changes. Ridge and soffit ventilation still have to work after the new roof is on.
• Insurance and inspections. Some insurers and buyers' inspectors ask how many layers are on the roof. See roof age and home insurance.

Tear-off avoids all of these. The crew replaces damaged sheathing, installs new underlayment over clean decking and builds new flashing from the deck up.

A careful contractor decides by inspecting the roof from above and below, not by looking at it from the driveway. The inspection should include counting the layers at the eaves and rakes, walking or closely examining the roof surface, checking flashings at walls, chimneys and skylights, and going into the attic to look at the underside of the deck.

In the attic, water stains, darkened or soft sheathing, rusted nail tips and mold all point to moisture problems that favor a tear-off. So do sagging areas between rafters. A dry, solid deck with one flat layer of shingles is the case where roofing over may be acceptable.

The contractor should also confirm what the local inspections office requires and whether a permit is needed for your job, and should state the decision in writing in the estimate. If two contractors disagree, ask each to explain what they saw. The one who went into the attic usually has the better answer. Our roof replacement page describes what a full replacement involves.

On an Interlock aluminum roof, the tear-off decision follows the same rules: cedar shingles, cedar shakes, concrete or clay tile and natural slate are always removed, and a single layer of asphalt may stay only if an inspection finds it suitable and the local code allows it. Rotted sheathing is replaced either way, and the estimate should say how damaged decking found during the job will be handled and priced. The roof must have a pitch of at least 3/12.

Panels are installed from the eaves up over underlayment, each one locking to its neighbors on all four sides with the fasteners hidden under the next course. Trim, ridge and flashing pieces are fitted at every edge, wall, chimney and valley.

Metal Roof NC, an authorized Interlock aluminum roofing dealer, gives a project-specific estimate before work begins, including whether the existing roof stays or comes off. See aluminum shingles, the roof replacement timeline and the service areas for more.