Metal Roof Over Shingles – Installing Metal Roofing Over Shingles. What to consider when putting a steel roof over asphalt shingles.
1. Metal Roofs Are Not Just In Architectural Digest Anymore
Metal roofs used to be found only on architect-designed houses. No longer a novelty, metal roofing is increasingly found on more conventional houses.
2. Metal Roofing Can Be Installed Over Your Existing Roof
Metal roofs can be installed over your existing roof without tearing off shingles. While shingle removal is the preferred route, it is also messy and raises the cost of the job.
Water vapor in conjunction with a metal roof on existing shingles is a problem. Water vapor build-up and attendant mold and rot are not reasons alone to avoid installing metal over shingles. Roofers can install a vented metal roof can be installed over existing shingles which would eliminate the vapor problem.
Also, installing the metal roof on top of furring strips (1×3’s or similar) will raise the metal and provide an air pocket between it and the shingles.
Metal Roof Over Shingles Design Ideas
3. They Are No Noisier Than Asphalt Roofing
Surprisingly, properly installed metal roofing is no noisier than any other type of roof. Metal roofing is typically installed over a solid substrate. Additionally, the attic and insulation provide a sound barrier. If you wish to install metal roofing over your existing roof, the metal roof will most likely be raised over the existing roof by means of furring strips. These furring strips will create an air pocket which will further deaden sound.
4. Metal Roofing Does Not Attract Lightning More Than a Conventional Roofs
Yes, it does seem like metal roofing would attract lighting, but this is faulty logic.
According to a technical bulletin from the Metal Construction Association, “Metal roofing does not in any way increase the risk of a lightning strike.”
Not only that, but if metal roofing does happen to get struck by lightning, it is less combustible than conventional roofing materials such as shake shingles.
As the bulletin asserts:
Because metal roofing is both an electrical conductor and a noncombustible material, the risks associated with its use and behavior during a lightning even make it the most desirable construction available.
5. Their Warranted Lives Are Equal To Conventional Roofing Products
If you live in fire-prone areas, such as Southern California, metal roofing will extinguish any embers. Insects such as termites can never eat metal roofing. Metal roofing is impervious to rot and mildew.
Because it conducts heat quickly from the sun, snow slides off more quickly than with conventional roofing.
Even so, most metal roofing manufacturers will warrant their products only for an average of 30 years, which is about the same as conventional roofing manufacturers.
6. Metal and Low-Pitched Roofs Are Like Peas In a Pod
Because metal roofing comes in larger sheets and the pieces are so tightly sealed together, you can install metal roofing on gently pitched roofs.
7. In Severe Hailstorms, They May Be Irreparably Damaged
Metal roofing will weather pea-sized hailstorms.
But if your area ever experiences severe hailstorms with larger stones, your aluminum or copper roof may get dented. Steel is harder and will fare better in the event of a hailstorm.
8. Modifying Metal Roofing Is Next-To-Impossible For Homeowners
Asphalt shingles are easy to replace because they are available at your local home improvement store and because you are working with small pieces.
Metal roofing, on the other hand, is generally available only through select retailers. Also, the large sheets are difficult to handle and fabricate unless you are a professional.
9. Ridge Venting Will Be More Obvious
On a shingled roof, the continuous ridge vent (CRV) is the strip of shingle-like material that runs the entire length of the peak of the house, masking outflow holes.
On composite roofs, you have seen this countless times but probably never noticed. One reason is because the CRV lies very flat. Also, the two materials blend in with each other so well.
On your metal roof, the CRV will be metal and will stand out a bit farther and be more obvious. However, these thick, prominent lines or ridges are inherent in metal roofs and add to their distinctive look.
Steel roofing offers many benefits over slate tiles or asphalt shingles. Metal roofing is resistant to fire, rot, and termites. Manufacturers provide 30-year warranties on metal roofing products. Installing steel roofing over existing roofing materials is fairly simple. Use furring strips to build a slat board on the roof, then mount the steel sheets to the slat board. Some consideration for vent stacks and chimneys is required during the design process. Installing a steel roof will cost approximately $60 per square foot.
Installation Metal Roof Over Shingles
Step 1 – Work Safely
Choose a day with calm weather to work on the roof. Metal roofing is very slippery when wet. Brace your extension ladder correctly when climbing onto the roof. In some cases, you can lean the metal sheets against the roof surface on the ground and lift them up from the roof while working. This is preferable to carrying large stacks of sheets up a ladder.
Step 2 – Measure Roof
Measure the surface area of the roof to predict your material needs. Add a 2 to 4 inch overhang when buying metal sheeting for the roof plane. You need enough boards to run lengthwise across the roof every 2 feet from top to bottom. You need edging and trim for the perimeter of all roof surfaces and the top ridge. You will also need preformed closures or flashing to close the roof surface around vent stacks or chimneys. Obtain several boxes of 3-inch wood screws, ¼-inch wood screws, and 1-1/4 inch roofing nails. Decide whether to use V-crimp or R-panel roofing. V-crimp does not require lap screws to install.
Step 3 – Install Slat Board
The furring strips are 1×4 pine boards. Secure them to the roof with wood screws at every 4 to 6 inches. Install the slat board as described above.
Step 4 – Install Edging
Bend the metal edging to your needs if necessary and fasten it to the roof with nails at every 4 to 6 inches.
Step 5 – Install Metal Sheets
Begin laying the metal sheets from the bottom to the top of the roof. Overlap the rises and dips if using corrugated sheets, or lay flat sheeting with a slight vertical overlap. Screw the metal sheets into the slat board with a wood screw every 2 feet along the edges. Screw the first sheet in the center as well as the edges. Use tin shears to cut gaps for pipes and exhaust vents.
Step 6 – Install Trim
Cut v-shaped notches into metal sheets and bend them to fit trim pieces to the ridge line and eave. Close the bottom of the metal roof.
Step 7 – Install Closures
Seal around gaps that were left for vents and chimneys with preformed closures or metal flashing. Secure these in place with roofing cement and screws.