05 Nov

• Rinuom Danuom
• November 5, 2025
• Roof Installation

How to Install Metal Roofing Over Shingles: Complete Guide

Installing metal roofing over shingles eliminates costly tear-off labor, reduces waste, and can save homeowners $2,000–$5,000 compared to full replacement. This overlay method works when existing shingles are in good condition, local codes permit it, and proper preparation with underlayment and furring strips creates a ventilated, flat surface for metal panels. However, the approach isn’t suitable for every roof damaged shingles, structural issues, or poor ventilation can compromise the new metal roof’s performance.

This guide covers when overlay installation makes sense, required materials and tools, step-by-step installation process, ventilation strategies, code compliance, and common mistakes that lead to leaks or premature failure.​

Can You Install Metal Roofing Over Shingles?

According to the Metal Roofing Alliance, metal now accounts for nearly 15% of all residential roofing installations in the U.S., up from under 5% a decade ago — a trend driven by energy efficiency, longevity, and improved aesthetics.

Short Answer: Yes, in most cases, but only if specific conditions are met.​

When Overlay Works:

• Existing shingles are flat, intact, and have minimal damage
• Only one layer of shingles currently exists (most codes prohibit more than 2 total layers)
• Roof structure is sound (no sagging, rot, or water damage)
• Local building codes permit overlay installation
• Adequate ventilation can be maintained or improved

When You Must Tear Off:

• Shingles are curling, cracked, or severely degraded
• Multiple layers of shingles already present
• Roof deck shows soft spots, rot, or structural damage
• Poor ventilation cannot be corrected with overlay method
• Local codes prohibit overlay (check with building department)

Weight Considerations: Metal roofing weighs 1/3 to 1/2 as much as asphalt shingles, making it structurally safe to install over existing materials without additional support.​​

Benefits of Installing Metal Over Shingles

Cost Savings

Tear-Off Costs Avoided:

• Labor: $1.50–$3.00 per sq ft
• Disposal fees: $500–$2,000 (depending on roof size, local tipping fees)
• Dumpster rental: $300–$600

Total Savings: $2,000–$5,000 for typical 2,000 sq ft roof.​

Time Efficiency

Timeline Comparison:

• Full tear-off + install: 3–7 days
• Overlay installation: 1–3 days

Faster completion means less weather exposure risk and disruption.​

Environmental Benefits

Keeping old shingles out of landfills reduces construction waste. Asphalt shingles account for 11 million tons of landfill waste annually.​

Additional Insulation

The existing shingle layer adds an insulating barrier between metal and deck, improving thermal performance and reducing noise during rain.​

Drawbacks to Consider

Potential Issues:

• Hidden damage: Existing roof problems remain concealed until they worsen​
• Trapped moisture: Poor ventilation can trap moisture between layers, causing rot​
• Uneven surface: Lumps or ridges in old shingles telegraph through metal if not corrected
• Warranty concerns: Some metal roofing manufacturers void warranties for overlay installations (verify before purchasing)​
• Future repairs: Next roof replacement requires removing both layers, increasing cost

When Drawbacks Outweigh Benefits: If existing shingles have widespread damage, structural issues exist, or ventilation is poor, tear-off and fresh start are safer long-term investments.​

Step-by-Step Installation Process

Step 1: Roof Inspection

Critical Checks:

• Walk entire roof to identify soft spots, sagging, or damage
• Inspect shingles for curling, missing granules, cracks
• Check fascia, soffits, and edge details for rot
• Verify adequate attic ventilation (1 sq ft vent per 150 sq ft attic)
• Confirm local code permits overlay (call building department)

If Problems Found: Repair damaged areas or consider full tear-off.​

Step 2: Clean and Repair Surface

Preparation:

• Remove loose or damaged shingles
• Hammer down raised nails
• Replace missing shingles to create flat surface
• Clean debris, moss, and dirt from roof
• Trim overhanging tree branches

Pro Tip: Use roof jacks and safety harness. Metal roofs are slippery during installation.​

Step 3: Install Synthetic Underlayment

Purpose: Moisture barrier and smooth surface for metal panels.​

Material: High-temperature synthetic underlayment (not felt—traps heat)

Installation:

• Roll out horizontally from eaves to ridge
• Overlap seams 6 inches
• Staple or nail every 12–18 inches
• Ensure wrinkle-free application

Critical: Use breathable underlayment to prevent moisture trapping between layers.​

Step 4: Install Furring Strips (Purlins)

Purpose: Creates ventilation gap, flat surface, and attachment points for metal panels.​

Material: 1×4 or 2×4 treated lumber

Spacing: 24 inches on-center (perpendicular to metal panel direction)

Installation:

1. Snap chalk lines to mark furring strip locations
2. Run strips horizontally across roof (vertical for vertical-seam panels)
3. Secure through shingles into rafters with 3-inch deck screws
4. Verify strips are level and straight (use string lines)
5. Add blocking at panel seams and ridge

Ventilation: Leave 1–2 inch gaps at eaves and ridge to allow airflow beneath metal.​

Step 5: Install Drip Edge and Trim

Before Panels:

• Install drip edge at eaves (over underlayment, under metal)
• Install rake trim at gable ends
• Flash valleys with metal valley flashing (if applicable)
• Prepare vent pipe and chimney flashings

Step 6: Install Metal Panels

Panel Types:

• Exposed fastener panels: Screws penetrate through panels (most DIY-friendly)
• Standing seam: Hidden fasteners, clips attach to furring strips (professional install recommended)

Installation (Exposed Fastener):

1. Start at eave, align first panel with edge (1-inch overhang)
2. Square panel using rafter square
3. Fasten with metal roofing screws (with neoprene washers) into furring strips
4. Overlap next panel per manufacturer specs (typically 1–2 inches)
5. Maintain consistent overlap and screw pattern across roof
6. Work from bottom to top, eave to ridge

Fastener Placement:

• High ribs (standing seam clips)
• Flat sections (exposed fastener—every other rib, 12–18 inches apart)
• Always into furring strips, never just shingles

Pro Tip: Pre-drill screw holes in cold weather to prevent panel cracking.​

Step 7: Install Ridge Cap and Flashing

Ridge Cap:

• Install ridge vent (if used) before cap
• Overlap metal ridge cap panels
• Fasten into ridge blocking through furring strips
• Seal end caps with butyl tape or roofing sealant

Final Flashings:

• Install vent pipe boots (rubber or metal)
• Flash chimneys with step flashing and counterflashing
• Add closure strips at eaves (block gaps between ribs)

Step 8: Final Inspection

Quality Checks:

• All fasteners tight and sealed
• No gaps in panel overlaps
• Ridge cap secure
• Flashings watertight
• Trim pieces installed and sealed
• Ventilation openings clear

Building Inspection: Schedule final inspection per permit requirements.​

Materials and Tools Needed

Materials (2,000 SF Roof)

Labor (if hiring pros): $3,000–$6,000 (overlay saves $2,000–$5,000 vs. tear-off)

Tools Required

• Circular saw or metal shears (panel cutting)
• Cordless drill/impact driver
• Chalk line and tape measure
• Rafter square
• Ladder and roof jacks
• Safety harness and anchors
• Metal roofing screws with neoprene washers
• Furring strip fasteners (3″ deck screws)

Ventilation Requirements

Critical: Trapped moisture between metal and shingles causes rot and mold.​

Ventilation Strategy:

1. Ridge Vent: Install vented ridge cap (continuous exhaust)
2. Soffit Vents: Ensure adequate intake at eaves
3. Air Gap: Furring strips create 1–2 inch ventilation channel beneath metal
4. Ratio: 1 sq ft net free area per 150 sq ft of attic space (balanced intake/exhaust)

Without Proper Ventilation: Condensation forms on underside of metal, degrading shingles and deck.​

Building Codes and Permits

Code Compliance:

• Most jurisdictions allow 2 total roof layers (1 existing + 1 overlay)
• Some high-wind zones prohibit overlay
• Fire-rated assemblies may require tear-off
• Building permit typically required

Before Starting:

• Contact local building department
• Submit plans showing furring strip layout, ventilation design
• Schedule inspections (typically after decking repairs, before final)

Failure to Permit: Can result in fines, forced tear-off, insurance claim denials.​

Common Mistakes to Avoid

1. Skipping furring strips → Uneven surface, no ventilation, screw pullout
2. Installing over damaged shingles → Hidden rot worsens, future leaks
3. Wrong screw placement (not into furring strips) → Fasteners pull out
4. Inadequate ventilation → Trapped moisture, condensation, rot
5. Ignoring code requirements → Permit violations, insurance issues
6. Over-tightening screws → Crushed neoprene washers, eventual leaks
7. Poor panel alignment → Water infiltration at overlaps

FAQ

How much does it cost to install metal roofing over shingles?
$10,500–$20,800 for a 2,000 sq ft roof (materials + labor). Overlay saves $2,000–$5,000 vs. tear-off and replacement.

Do I need furring strips to install metal over shingles?
Yes. Furring strips create ventilation gaps, provide flat fastening surface, and prevent moisture trapping. Skipping them voids most warranties and causes rot.

Can I DIY metal roof installation over shingles?
Yes, if you have roofing experience, proper safety equipment, and a simple roof. Exposed-fastener panels are most DIY-friendly. Hire pros for standing seam systems.

Will installing metal over shingles void my warranty?
It depends on the manufacturer. Some allow overlay with proper preparation (furring strips, ventilation); others require tear-off. Verify before purchasing materials.

How long does metal roofing over shingles last?
30–50 years with proper ventilation and installation. Lifespan matches standard metal roof installations when done correctly.

Do I need a permit to install metal over shingles?
Yes, in most jurisdictions. Contact your local building department to confirm requirements and schedule inspections.

What if my shingles are damaged?
Repair localized damage or tear off entirely. Installing over widespread damage conceals problems and leads to costly future repairs.

Conclusion

Installing metal roofing over shingles saves time, money, and environmental waste when conditions are right: sound structure, good shingles, code compliance, and proper ventilation design. Furring strips and synthetic underlayment are non-negotiable for creating a ventilated, flat surface that prevents moisture trapping. While overlay installation reduces costs by $2,000–$5,000, attempting it over damaged shingles or without adequate ventilation leads to expensive failures. Always verify local codes, obtain permits, and prioritize proper preparation for a metal roof that lasts 30–50 years.

Rinuom Danuom

Roofing content specialist with 5+ years researching U.S. residential and commercial roofing. Has documented 200+ projects covering installation costs, material selection, contractor vetting, and DIY guides for homeowners across all climate zones.