To install a metal roof over existing shingles, follow these key steps and considerations:

Preparation and Inspection

• Inspect the existing shingle roof to ensure it is in good condition, without soft spots, lifted, cracked, or blistering shingles. The plywood decking underneath should be solid and free of damage

• Check local building codes to confirm that installing metal roofing over shingles is allowed. Some codes restrict roofing over multiple layers due to weight concerns

Installation Methods

1. Direct Attachment Over Shingles

• Attach metal roofing panels directly through the shingles into the wood deck below. This is cost-effective and quicker since it avoids removing shingles

• Place a protective barrier such as #30 felt, synthetic underlayment, or thin foil-faced insulation between the shingles and metal panels to prevent wear from expansion and contraction

• Note that this method may reduce ventilation under the roof and can telegraph imperfections from the shingles through the metal, which affects aesthetics but not performance

2. Using Furring Strips or Battens

• Install wood furring strips (purlins) over the existing shingles, then attach metal panels to these strips. This creates a flat surface and helps with ventilation

• Use a barrier like felt or synthetic underlayment between the wood strips and metal to prevent corrosion, especially if pressure-treated lumber is used

• This method adds weight and height to the roof system and may increase costs but improves durability and appearance

Additional Tips

• Remove or cut back shingles at eaves and gable edges to properly install flashing and fasteners

• Ensure proper ventilation to avoid moisture buildup beneath the metal roof

• Consider that installing metal over shingles means you won't replace old underlayment or inspect the deck thoroughly, which can affect long-term roof performance

Summary

Installing a metal roof over shingles is possible and can save time and money by avoiding tear-off and disposal costs. However, it requires careful inspection, adherence to building codes, and proper installation techniques like using barriers and possibly furring strips to ensure durability and performance. Hiring an experienced contractor familiar with metal roof-overs is highly recommended

. This approach extends roof lifespan, adds curb appeal, and is environmentally friendly since it avoids shingle waste