Install Metal Roof Over Shingles – The Ultimate Time-Saving DIY Guide
You can install a metal roof directly over existing asphalt shingles by using 1×4 furring strips or a high-quality synthetic underlayment to prevent abrasion and moisture buildup. This method is safe as long as the existing roof deck is structurally sound and local building codes permit a second roofing layer.
Ensure you use specialized roofing screws with EPDM washers and install a proper drip edge to prevent water from wicking back under the new metal panels.
Most homeowners dread the thought of a full roof replacement because of the massive mess, the cost of disposal, and the back-breaking labor of tearing off old shingles. If your current roof is reaching the end of its life but the underlying wood is still solid, you have a much better option.
I am going to show you how to install metal roof over shingles to save you thousands of dollars and days of frustrating cleanup. This approach provides a double layer of protection and can actually improve your home’s energy efficiency when done correctly.
In this guide, we will walk through the structural requirements, the essential tools you will need, and the step-by-step process to ensure your new metal roof is leak-proof and looks professional. Whether you are a weekend warrior or a seasoned DIYer, these tips will help you master this project.
Is Your Home a Candidate for a Metal Overlay?
Before you order your panels, you must determine if your house can handle the extra weight. While metal is significantly lighter than asphalt, adding a second layer of material is a serious structural decision that requires a quick inspection.
Check your local building codes first. Most jurisdictions allow for a maximum of two layers of roofing material. If you already have two layers of shingles on your house, you must strip them down to the deck before proceeding with any new installation.
Next, get up in your attic with a bright flashlight. Look for signs of water damage, sagging rafters, or rotted roof decking. If the plywood or OSB underneath is soft or crumbling, you cannot install metal roof over shingles safely because the fasteners will not have anything solid to bite into.
Finally, check the “flatness” of your current roof. If the shingles are badly curled or buckled, they will create an uneven surface. In these cases, using furring strips is mandatory to create a flat plane for your new metal panels to sit on.
Essential Tools and Materials for the Job
To get a professional result, you need the right gear. Working with metal requires specialized cutting tools that differ from standard woodworking equipment. You want clean edges that won’t rust over time.
For cutting the panels, I highly recommend electric metal shears or a “nibbler” attachment for your drill. Avoid using a standard circular saw blade, as it generates excessive heat and sparks that can damage the protective coating on the metal, leading to premature corrosion.
You will also need a high-quality impact driver with a magnetic nut setter. The fasteners used in this project are self-piercing screws with EPDM rubber washers. These washers are the only thing standing between you and a leak, so they must be driven straight and to the correct depth.
Don’t forget the safety gear. A roofing harness and high-traction boots are non-negotiable. Metal panels are incredibly slippery, especially if there is even a hint of moisture or morning dew on the surface. Always work with a partner when handling long panels to prevent the wind from catching them.
Step-by-Step Guide to install metal roof over shingles
Once you have confirmed your roof is structurally sound and you have your materials staged, it is time to start the installation. Consistency is the key to a roof that looks good and stays dry for decades.
1. Prepare the Surface and Install Underlayment
Clean the old roof of all debris, branches, and moss. If you are not using furring strips, you must lay down a layer of synthetic underlayment or a slip-sheet. This prevents the abrasive shingles from scratching the back of the metal panels as they expand and contract.
If you choose the furring strip method, screw 1×4 purlins horizontally across the roof. Space them 24 inches apart on center. This creates an air gap that provides extra insulation and a perfectly flat surface for the metal, even if the shingles underneath are bumpy.
2. Install the Drip Edge and Closures
Start at the eave (the lowest edge of the roof). Install your metal drip edge over the underlayment or furring strips. This ensures that water running off the roof is directed away from the fascia boards and into the gutters.
Place outside closure strips along the eave line. These foam strips match the profile of your metal panels. they act as a gasket, preventing wind-blown rain, snow, and insects from getting underneath the ribs of the metal once it is fastened down.
3. Squaring and Fastening the First Panel
The first panel is the most important one. If it is crooked, every subsequent panel will be off, and you will end up with a mess at the gable end. Use a string line or a large framing square to ensure the first panel is perfectly perpendicular to the eave.
Overlap the eave by about an inch to ensure water sheds into the gutter. Drive your roofing screws into the flat part of the panel, right next to the major ribs. Do not over-tighten the screws; the rubber washer should be compressed but not bulging out from the sides.
4. Overlapping and Finishing the Run
Each panel has a “lapping” edge and a “under-lap” edge. Make sure you are following the manufacturer’s directions for the overlap. Usually, this involves one full rib of overlap to ensure a water-tight seal between the sheets.
Continue across the roof, checking for squareness every few panels. When you reach the end of the roof, you may need to trim the width of the last panel. Use your shears to make a clean, straight cut, and then install the gable trim to cover the raw edge.
Choosing Between Furring Strips and Solid Underlayment
When you install metal roof over shingles, you have two primary ways to bridge the gap between the old and the new. Both have benefits, but your choice depends on your climate and the condition of your old roof. Furring strips (also called purlins) are the gold standard for DIYers. They allow for airflow between the old shingles and the new metal. This “vented” space helps keep the house cooler in the summer and prevents moisture from getting trapped between the layers.
Using a synthetic underlayment directly on top of the shingles is faster and cheaper. This is a great option if your shingles are relatively flat and in decent shape. It acts as a secondary water barrier, but you lose the benefit of the air gap for thermal regulation.
Regardless of the method, never skip the separation layer. Placing metal directly against asphalt shingles will cause the shingles to act like sandpaper. Over time, the vibration from wind will rub the protective paint off the bottom of your metal panels, leading to rust from the inside out.
Managing Flashing and Critical Seal Points
Most roof leaks don’t happen in the middle of a panel; they happen at the “penetrations” like chimneys, vent pipes, and valleys. These areas require extra attention and high-quality sealant to remain watertight.
For vent pipes, use EPDM pipe boots. These flexible collars slide over the pipe and have a metal base that you can mold to the shape of the metal ribs. Apply a heavy bead of polyurethane sealant under the base before screwing it down to the panel.
In the valleys, use a dedicated W-style valley flashing. This piece sits under the metal panels on both sides and provides a clear channel for water to flow down. Never drive screws directly through the center of a valley, as this is a guaranteed recipe for a leak.
When you reach the peak of the roof, install a vented ridge cap. This allows hot air to escape from your attic while keeping rain out. Use closure strips under the ridge cap to prevent “blow-back” during heavy storms or high-wind events.
Common Pitfalls and Pro Tips for Success
Experience is the best teacher, but learning from others’ mistakes is much cheaper. One common error is over-driving screws. If you crush the EPDM washer, it will crack and fail within a few years. Aim for a firm seat where the washer just starts to spread.
Another tip is to avoid using graphite pencils to mark your metal. The carbon in the graphite reacts with the zinc in the metal coating and can cause the metal to corrode. Use a sharpie or a specialized metal-marking chalk instead.
Always sweep the roof at the end of every day. Small metal shavings (swarf) left behind from drilling or cutting will rust overnight if there is any moisture. These tiny rust spots will bond to your new paint and look terrible, even if they don’t compromise the panel’s integrity immediately.
Keep an eye on the weather forecast. You don’t want to have half a roof exposed if a thunderstorm rolls in. Only prep the sections you can reasonably cover with metal or underlayment before the sun goes down or the clouds move in.
Frequently Asked Questions About How to install metal roof over shingles
Does a metal roof over shingles make the house hotter?
Actually, it usually makes the house cooler. If you use furring strips, the air gap acts as an insulator. Furthermore, metal reflects more solar radiation than dark asphalt shingles, reducing the heat load on your attic significantly.
Will the new roof be noisier when it rains?
This is a common myth. Because you are keeping the old shingles and the original roof decking, you have extra layers of sound dampening. Most homeowners find that a metal overlay is no louder than a standard asphalt roof during a rainstorm.
Can I install metal roof over shingles if the roof is steep?
Yes, but the safety risks increase significantly. On steep pitches, you must use roof jacks, harnesses, and specialized footwear. If you are not comfortable working at heights on a slippery surface, this is the time to call in a professional crew.
Do I need to pull a permit for an overlay?
In most areas, yes. A permit ensures that your project meets local wind-load requirements and that you aren’t exceeding the allowed number of roofing layers. Failing to get a permit can cause major headaches when you try to sell your home later.
Final Thoughts on Your DIY Roofing Project
Choosing to install metal roof over shingles is one of the smartest upgrades you can make for your home. You get the longevity and durability of metal without the nightmare of a total tear-off. It is a project that requires precision and respect for safety, but the rewards are well worth the effort.
Take your time with the layout and squaring of your first panels. If you get the foundation right, the rest of the panels will fall into place like clockwork. Remember to use the right fasteners, never skip the underlayment, and keep your workspace clean of metal shavings.
You are building a roof that will likely outlast your time in the home. Stand back, work safely, and enjoy the peace of mind that comes with a professional-grade DIY installation. You’ve got this—now get out there and start measuring!
