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Can You Put a Metal Roof Over Shingles? A Complete Guide for Homeowners
Can you put a metal roof over shingles? It seems simple enough—avoid the mess and expense of a full tear-off, while upgrading to a modern, long-lasting metal roof. But is it really that straightforward?
In this comprehensive guide, we’ll dive deep into this question and cover everything you need to know before making your decision.
What Is a Metal Roof Overlay?
A metal roof overlay is exactly what it sounds like—installing a new metal roof directly over an existing layer of shingles. This method avoids the time, labor, and disposal involved in tearing off the old shingles.
It’s a popular option among homeowners who want to save money or minimize disruption. However, it’s not always the right solution for every home.
Is It Legal to Install Metal Over Shingles?
Yes, in many locations, local building codes allow you to install a metal roof over one layer of shingles. The key word here is one. Most building codes do not allow more than two layers of roofing materials due to weight and safety issues.
Before making any plans, it’s important to:
- Check your local building codes.
- Verify that your home has only one existing layer of shingles.
- Ensure the roof structure is sound and capable of supporting the added weight.
If you’re unsure, a qualified roofing contractor can inspect your home and help guide the decision.
Advantages of Installing a Metal Roof Over Shingles
1. Cost Savings
Skipping the tear-off process saves significantly on labor and disposal fees. Removing old shingles can add thousands of dollars to a roofing project, depending on the size and condition of the roof.
2. Faster Installation
Tear-off can add one or more days to the project timeline. By installing over existing shingles, you shorten the project duration, allowing for quicker weatherproofing and less disruption.
3. Environmentally Friendly
Keeping the old shingles out of landfills is a greener option. Metal roofing is already eco-conscious because it’s often made from recycled materials and is itself recyclable at the end of its lifespan.
4. Added Insulation
The old shingles can serve as an extra insulating barrier, helping with noise reduction and temperature control, particularly in colder climates.
5. Durability
Metal roofs are known for their long life. With proper installation, you can expect 40 to 70 years of protection. Adding them over shingles doesn’t shorten their life, assuming moisture and ventilation issues are addressed.
Disadvantages and Potential Risks
1. Hidden Roof Damage
By skipping the tear-off, you may be covering up problems like rotted decking, water damage, or mold growth. These issues won’t go away—and over time, they could worsen and compromise your new roof.
2. Moisture Trapping
If moisture becomes trapped between the metal panels and the old shingles, it can lead to condensation, mold, and even structural damage. This is especially problematic in areas with high humidity or poor attic ventilation.
3. Irregular Surface
Old shingles may be curled, cracked, or uneven. Installing metal panels over an uneven surface can cause the panels to warp, oil-can (appear wavy), or not sit flat, which can affect both appearance and performance.
4. Added Weight
Although metal roofing is lightweight, adding any material on top of existing roofing adds weight. If your home’s framing wasn’t designed to handle this, it could lead to sagging or structural strain.
5. Void Warranties
Some manufacturers void warranties if the metal roof is installed over shingles. This is because they can’t guarantee performance over a non-ideal substrate.
Structural and Code Considerations
Before installing a metal roof over shingles, it’s essential to ensure the structure is sound. Here’s what needs to be checked:
Roof Deck Condition
The roof deck (usually plywood or OSB sheathing) must be in good condition. If it’s soft, warped, or water-damaged, it may not support the new roof. You can’t assess this without removing the shingles—one of the main trade-offs of overlaying.
Roof Load Capacity
Every roofing system adds weight. Your home’s framing needs to support the additional load without causing sagging or other issues. In some cases, a structural engineer may be needed to perform calculations or provide recommendations.
Number of Shingle Layers
Most building codes prohibit more than two layers of roofing. If your home already has two layers, including the original shingles, you’ll need to tear off at least the top layer before installing anything new.
Local Permits and Inspections
You may need a permit to re-roof your home, especially when adding a different roofing material. Some municipalities also require an inspection after installation to ensure compliance with safety and fire codes.
Installation Methods
There are two primary ways to install metal over shingles:
1. Direct-to-Deck Installation
This involves placing the metal panels directly over the shingles using screws. It’s quick but doesn’t address underlying irregularities. Without proper underlayment, it can lead to issues like oil-canning or moisture entrapment.
2. Strapping (Purlins or Battens)
This method involves installing wood purlins or battens over the shingles, then securing the metal panels to the wood. This provides a flatter, more ventilated base and improves airflow under the metal roof.
Benefits of Strapping:
- Allows for vented airspace to reduce condensation.
- Smooths out irregularities in the shingle surface.
- Improves screw hold by giving fasteners a solid grip.
Strapping is more labor-intensive and slightly more expensive but results in a more durable installation.
Underlayment Is Still Required
Even though shingles offer some weather resistance, you still need underlayment between the shingles and the metal roof. Popular options include:
- Synthetic underlayment: Lightweight, durable, and resistant to tearing.
- Ice and water shield: Required in colder climates to prevent ice dams.
- Felt paper: The traditional, affordable option—though less common today.
The underlayment adds a moisture barrier, provides cushioning, and improves long-term performance.
Common Metal Roofing Materials Used in Overlays
When installing metal over shingles, the choice of metal roofing system matters. Here are the most popular types:
Standing Seam
- Look: Sleek, modern panels with concealed fasteners.
- Lifespan: 40–70 years.
- Cost: Higher upfront, but excellent durability and low maintenance.
- Ideal For: Homeowners seeking a long-term, high-performance solution.
Corrugated Metal Panels
- Look: Classic wavy design with exposed fasteners.
- Lifespan: 25–40 years.
- Cost: More affordable than standing seam.
- Ideal For: Budget-conscious installations with a simpler appearance.
Metal Shingles
- Look: Mimics traditional roofing like slate or cedar shake.
- Lifespan: 40–60 years.
- Cost: Similar to standing seam, but with a more traditional aesthetic.
- Ideal For: Homeowners who want the performance of metal with the look of shingles.
Cost Comparison: Overlay vs. Tear-Off
| Installation Type | Average Cost per Square Foot | Total Cost for 2,000 Sq. Ft. Roof |
|---|---|---|
| Metal over shingles | $7 – $11 | $14,000 – $22,000 |
| Full tear-off + metal | $9 – $14 | $18,000 – $28,000 |
Note: These are estimates. Actual costs vary depending on location, labor, metal type, roof complexity, and additional materials like insulation or ventilation.
When You Should Not Install Metal Over Shingles
While there are many advantages, overlaying is not always the right call. Avoid installing metal over shingles if:
- Your roof has more than one layer of shingles.
- You suspect or know of roof deck damage.
- You live in a high-humidity or hurricane-prone area.
- You’re planning to sell your home soon, and potential buyers may be wary.
- Manufacturer warranties require full tear-off for coverage.
Maintenance Tips for Metal Overlays
Once your metal roof is installed over shingles, proper maintenance will ensure it lasts decades:
- Inspect twice a year: Check for rust, loose fasteners, or signs of water intrusion.
- Clear debris: Keep gutters clean and remove leaves from the roof surface.
- Seal penetrations: Watch for leaks around vents, chimneys, and skylights.
- Check attic ventilation: Ensure the space under the roof is properly ventilated to reduce condensation risks.
Final Thoughts: Should You Do It?
Installing a metal roof over shingles can be a smart, cost-effective solution if the existing roof is in good shape and all building codes are followed. It reduces waste, saves time, and avoids the mess of a tear-off—while giving your home a long-lasting, attractive roofing system.
However, it’s not without risks. Hidden damage, moisture problems, and warranty voids are real concerns. That’s why it’s crucial to have a professional roofer evaluate your current situation.
