Installing a metal roof over existing asphalt shingles is a popular and cost-effective way to upgrade or replace an aging roof. 

Rather than completely tearing off the old shingles, a metal roofing system can be installed directly over the existing roof. This saves time and money compared to a full tear-off and replacement. 

Installing over shingles also allows the insulation and decking to remain intact. 

However, proper preparations must be made, including inspection and repair of any rotted or damaged areas, removal of old nails and vents, and installation of additional underlayment. 

When correctly installed using manufacturer-approved fasteners and sealants, a metal roof can provide 50+ years of durable and energy-efficient performance.

Benefits of Installing a Metal Roof Over Shingles

The key benefits that make installing a metal roof over existing shingles a great option include longevity, energy efficiency, aesthetics, and cost savings from avoiding a full tear-off. 

Metal roofs typically last over 50 years, whereas asphalt shingles begin degrading after just 15-20 years. The long service life of metal roofing is very appealing to homeowners. 

Metal’s reflective surface also provides energy efficiency benefits by deflecting solar heat gain during summer months. 

This can lower air conditioning usage and electricity bills. Metal roofing comes in a wide range of colors, textures, and styles – from elegant standing seam panels to decorative shakes and tiles. 

Enhancing roof aesthetics increases curb appeal and home resale value. Finally, installing a new metal roof over the existing shingles saves thousands in labor and disposal costs compared to completely removing the old roof first.

Preparing the Existing Roof

To ensure proper installation and performance of a new metal roof over existing shingles, careful preparation of the roof is crucial. 

Thoroughly inspect the roof decking from the attic and repair any sagging areas or water damaged boards. 

Remove any old nails, vents, pipes, and other protrusions that could potentially puncture through the new metal roofing over time. 

Install 30lb roofing felt over the shingles as an extra moisture barrier and separation layer. Some metal roofing applications also benefit from installing roof strapping horizontally across the shingles to create a solid fastening base. 

Insulation boards may also be added on top of the shingles before the metal roofing to improve energy efficiency. 

Always follow the roofing manufacturer’s recommendations for proper underlayment products and installation techniques when preparing the existing shingled roof.

Installing the Metal Roof

When installing metal roof panels over shingles, work from bottom to top, starting with the eave drip edge around the perimeter. 

Use manufacturer-approved fasteners, typically self-tapping screws with rubber washers, driven through the metal into solid decking or strapping every 12-18 inches. 

Do not rely solely on fastening to existing shingles. Follow lap joint and sealant application instructions. 

Work up the roof installing panels in vertical rows, overlapping sides and ends per manufacturer specifications. Install ridge caps and hip/valley flashings as needed. 

Cut panels for areas like roof penetrations using tin snips or a nibbler tool. Attach vent pipes, skylights and other accessories securely to maintain a watertight roof system. 

An experienced metal roofing contractor is recommended for best results.  

Safety Considerations

Installing a metal roof involves working at heights, electrical hazards, sharp panels, and fall and slipping risks. 

Use OSHA-approved harnesses and tie-off points any time working over 6 feet up. Set up scaffolding or roof jacks properly to create a stable work platform. 

Keep areas below clear of debris that could injure anyone underneath. Wear cut-resistant gloves when handling sheet metal. 

Use extra caution during windy conditions when lifting panels. Follow all safety procedures from the manufacturer. 

Provide proper fall protection for both workers on the roof and anyone below in the potential drop zone. Take frequent breaks during hot weather to avoid heat exhaustion. Stay hydrated and use earplugs and eye protection. 

Costs and ROI

The upfront cost of a standing seam metal roof averages $6-10 per square foot installed, compared to just $1-3 per square foot for asphalt shingles. 

However, the lifespan of metal roofing over 50 years provides excellent ROI long-term. Factor in potential energy savings from a reflective roof surface as well. 

Proper installation directly affects performance and longevity. Get at least 3 contractor bids and ask for references to compare the experience. 

For a 1,500-square-foot roof, installed costs could range from $9,000-$15,000 depending on the type of metal roofing chosen. 

With metal’s durability, your new roof could easily outlast you in the home.

Maintenance

While resistant to leaks, debris, and decay, metal roofs still require some periodic maintenance. 

Inspect the roof each year, looking for any loose fasteners, separated panel laps, or damage from falling branches or storms. 

Repair as needed with sealants or screws. Keep the roof clear of leaves and other debris that can retain moisture. 

Avoid walking on the roof unnecessarily to prevent dents or scratches. Use caution when shoveling snow, as metal can be slippery. 

A properly installed and maintained standing seam metal roof provides decades of performance with minimal upkeep required.