Metal roofing over asphalt shingles is a roof-recover option when the existing roof has one sound layer of shingles, the roof deck and framing are structurally adequate, local code allows a recover, and the metal roofing manufacturer approves the installation method.

Reviewed:

For many residential exposed-fastener metal panels, an approved method is to install new underlayment over the shingles, add horizontal 1x4 or 2x4 furring strips fastened to the rafters or trusses, and attach the panels to the furring. Do not install metal over wet, rotten, badly curled, leaking, or heavily uneven shingles.

Metal Roofing Over Shingles: At a Glance

Question Practical answer
Can metal roofing go over shingles? Often, if there is one existing shingle layer and the roof is sound.
What is the usual installation method? Approved underlayment, horizontal furring strips, and metal panels fastened to the furring.
Can panels go directly over shingles? Sometimes, but only when the specific manufacturer approves the method.
When is tear-off necessary? When the shingles or decking are deteriorated, water-soaked, structurally inadequate, or when local code requires removal.
Can any metal roof be installed this way? No. Exposed-fastener panels, metal shingles, and standing-seam systems have different substrate and attachment requirements.
Is this suitable for every DIY project? No. Steep roofs, complex flashing, standing-seam systems, and damaged decking often require a qualified roofing contractor.

1. Check the Roof, Panel System, and Local Code First

Installing metal roofing over shingles is a roof recover, not a way to hide an existing roof problem. The roof must support the new roofing system and the loads created during installation.

Before ordering materials:

  1. Identify the exact metal roofing product.
  2. Download its current installation manual.
  3. Confirm the minimum roof slope.
  4. Check whether the product permits installation over shingles.
  5. Confirm the required substrate, underlayment, purlin spacing, fasteners, laps, sealants, and trim.
  6. Check local reroofing and permit requirements.

The International Residential Code model provisions cited here allow a roof recover when the new roof covering follows the manufacturer's approved instructions. They do not allow a recover over a water-soaked or deteriorated roof, or over two or more existing roof-covering applications. Local jurisdictions may adopt different or amended requirements.

Wind resistance depends on the product and the building location. Panel profile, gauge, clip or screw spacing, fastener pull-out resistance, building height, and local wind design loads all affect the attachment design.

2. Inspect the Shingles and Roof Deck

Metal roofing should not cover an active leak or structural damage.

Inspect the roof and attic for:

  • Soft or spongy areas
  • Sagging roof planes
  • Water stains
  • Missing, loose, or badly curled shingles
  • Blistered or severely uneven shingle surfaces
  • Rotten roof decking
  • Damaged rafters or trusses
  • Failed chimney, skylight, wall, valley, or plumbing flashing
  • More than one existing shingle layer

Sound shingles can often remain below a metal retrofit roof. Deteriorated shingles may need to be removed so the roof deck can be inspected and repaired.

Repair damaged decking and framing before installing underlayment or furring. The shingles are not an adequate structural attachment point for the new roof.

3. Choose the Installation Method

Method A: Metal Panels Over Furring Strips

This is a common approach for residential metal-panel reroofing.

The typical sequence is:

  1. Leave the sound shingles in place.
  2. Install the approved underlayment or moisture protection.
  3. Install horizontal furring strips over the roof.
  4. Fasten the furring into rafters or trusses.
  5. Attach the metal panels to the furring strips.

Fabral recommends 1x4 or 2x4 furring strips at 24 inches on center for certain residential reroofing applications. Union Corrugating recommends 1x4 lathing at 2-foot centers for some of its products. These dimensions are examples, not universal requirements. The selected panel's load tables and installation manual determine the final spacing and fastener design.

Furring creates a consistent attachment surface and reduces the chance that the uneven shingle pattern will show through the metal panels. It also raises the roof surface. Eave trim, rake trim, valleys, pipe boots, skylights, chimneys, and wall flashings must all account for that added height.

Method B: Direct Installation Over Shingles

Some metal roofing products can be installed directly over shingles with an approved underlayment. The method can be faster, but it is not acceptable for every panel.

Use direct installation only when:

  • The manufacturer specifically permits it.
  • The shingles are stable, dry, and sufficiently flat.
  • The fasteners achieve the required penetration and pull-out resistance.
  • The underlayment and flashing details are approved for the system.
  • Local code permits the roof recover.

Direct installation can allow the shingle pattern to show through the metal, especially when the existing shingles are uneven or dimensional. It can also make deck inspection and flashing replacement more difficult.

Method C: Tear Off the Shingles

Tear-off is usually the better choice when the existing roof has damage, multiple layers, severe unevenness, hidden leaks, or questionable structural conditions.

Removing the shingles exposes the roof deck. That makes it possible to repair damaged sheathing and flashing before installing the new metal roof.

4. Install the Underlayment

Shingles should not be the only moisture-control layer below a new metal roof.

Install the underlayment specified by the metal roofing manufacturer and local code. Depending on the system, it may be synthetic underlayment, roofing felt, a self-adhered membrane, or another approved moisture barrier.

Pay close attention to:

  • Eaves
  • Valleys
  • Roof-to-wall transitions
  • Chimneys
  • Skylights
  • Dormers
  • Plumbing penetrations
  • Areas where snow or wind-driven rain can accumulate

Install laps so water flows over the lower course and onto the course below. Do not leave underlayment exposed as the finished roof.

Fabral's installation guidance also calls for extra protection or self-adhered membrane in areas such as valleys, chimneys, skylights, and transitions.

5. Install the Furring Strips or Approved Substrate

If the metal roof is being installed over furring:

  1. Snap layout lines across the roof.
  2. Locate the rafters or trusses.
  3. Place the furring strips parallel to the eave and ridge.
  4. Keep the spacing within the panel manufacturer's requirements.
  5. Use structural fasteners long enough to pass through the furring and shingles and achieve the required penetration into the framing.
  6. Confirm that each furring strip is straight and firmly attached.

Do not secure the furring only to the shingles. The furring must transfer wind and other roof loads to the roof structure through an approved fastening pattern.

If the roof has irregular framing, unusual spans, high wind exposure, or a complex shape, have the attachment reviewed by the manufacturer, a roofing professional, or a structural designer.

6. Replace or Modify the Flashing

A metal panel can be installed correctly and still leak if the flashing is poorly designed.

Install or adapt:

  • Eave trim and drip edge
  • Rake or gable trim
  • Valley flashing
  • Ridge cap
  • Sidewall and endwall flashing
  • Chimney flashing
  • Skylight flashing
  • Pipe boots
  • Roof-to-wall transitions
  • Snow or ice protection where required

When furring strips are used, the new roof sits higher than the original shingles. Existing flashing may be too short or incorrectly positioned. Replace deteriorated flashing instead of covering it with metal panels.

7. Install the Metal Panels

Follow the installation sequence in the panel manual. The general process is:

  1. Start at the eave and on the side specified by the manufacturer.
  2. Align the first panel carefully because it controls the alignment of the rest of the roof.
  3. Maintain the specified eave overhang.
  4. Install fasteners in the approved locations.
  5. Keep side laps and end laps facing away from prevailing wind-driven rain when the manual requires it.
  6. Use the specified lap sealant and closure strips.
  7. Continue toward the ridge while checking panel alignment.
  8. Install rake trim, ridge closures, and ridge cap.
  9. Remove metal filings and cuttings from the roof surface at the end of each workday.

Fastener quantity and placement vary by product. Use the screws, washers, clips, sealants, and spacing specified for the selected panel. Wind uplift requirements may call for a different pattern near eaves, corners, ridges, and gable ends.

8. Preserve Roof Ventilation

Do not block existing soffit intake vents or ridge exhaust vents with underlayment, furring, insulation, or closures.

If the project uses a vented ridge cap, install the manufacturer's compatible vent and closure system. A metal roof retrofit may require different ventilation details because the new roof changes the height and airflow path at the ridge and eaves.

Common Mistakes to Avoid

  • Installing over two or more existing shingle layers
  • Covering rotten decking or active leaks
  • Fastening only into shingles
  • Using generic screw spacing instead of the panel manual
  • Reusing short or damaged flashing
  • Skipping underlayment
  • Blocking soffit or ridge ventilation
  • Installing incompatible metals that can cause corrosion
  • Walking on unsecured panels or underlayment
  • Leaving metal shavings on the roof
  • Installing standing-seam panels without following the clip and substrate requirements
  • Assuming a low-slope roof can use any metal panel

Safety Requirements

Roof installation creates a serious fall hazard. OSHA requires employees performing residential construction work at least 6 feet above a lower level to use compliant fall protection, such as guardrails, safety nets, or a personal fall-arrest system, subject to the applicable rules and exceptions.

Metal roofing has sharp edges and becomes more dangerous in wind, rain, frost, snow, or dust. Use appropriate gloves and eye protection, secure panels before walking on them, and do not work on a wet or slippery roof.

When to Hire a Roofing Contractor

Hire a qualified metal-roofing contractor when the roof has:

  • A steep slope or difficult access
  • Valleys, dormers, skylights, or multiple chimneys
  • Structural or decking damage
  • More than one existing shingle layer
  • A standing-seam metal system
  • High-wind or hurricane exposure
  • Unusual framing or long panel spans
  • Complicated roof-to-wall transitions
  • Limited attic access for inspecting the roof structure

Bottom Line

If the roof inspection finds damaged shingles, decking, flashing, or framing, remove the existing roof and repair those problems first. If the roof has one sound shingle layer and both local code and the product manual allow a recover, use the approved underlayment, substrate, fasteners, flashing, and ventilation details for that metal roofing system.