Can a Metal Roof be Installed Over Shingles?

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Putting a new metal roof over existing shingles can be done, though it’s not always advisable. Depending on the structure, condition, number of layers, and the roof’s position, it is possible to install metal over shingles. Here are some things to check when determining whether a metal roof can be placed on top of shingles.

Structural Concerns of Having Metal Installed Over Shingles

Weight Load Capacity

First, it is essential to determine if the roof structure can handle the weight of the additional metal roofing. A new asphalt shingle roof will typically weigh between two and four pounds per square foot. However, metallic roofing is denser, with a range of 1.25 to 6 pounds per square foot for household use, which is heavier than shingles.

This extra load must be accommodated by the roof decking since the structure could sag in the long run. If in doubt about the stability of the existing architecture, consult a structural engineer to check if beams, rafters, and sheathing can carry the weight of a metal roof placed on top of shingles.

Roof Slope and Pitch

A steep-pitched roof is also required to place metal over shingles because successive layers must be installed at the correct angle. A shed roof made of metal should have a minimum slope that will allow for the proper shedding of water. If the roof has a low pitch, the water might stand and enter the seams in the roof. This risk is higher when insulation is underneath the metal roof and other layers. A good rule of thumb is to use a 4:12 pitched roof or steeper when using a metal over shingle.

Existing Roof Condition

Never place a metal roof on bad, worn, or decaying shingles. Any problems with the shingle layers underneath will immediately be worsened by the new metal roof. The first thing to do is to have a professional conduct a general roof assessment.

Look for:

• Shingles that are either damaged, missing, cracking, curling, or that are improperly nailed
• Portions of the roof deck that are accessible or can be observed
• Stains, mold, and mildew from the growth of mold

If there are any damaged or rotten areas, replace shingles in those locations before putting metal roofing on.

Ventilation Considerations

Attic Ventilation

Another consideration with all retrofit roofing is that condensation can form between shingles and a metal layer if attic ventilation is inadequate. Before installing an attic ventilator, check for code compliance with existing soffit and rooftop vents. More ventilation will help reduce condensation and moisture in the room.

Exhaust Vent Spacers

It is appropriate to use vent spacers when they overlay the shingles with metal roofing. These flashings help prep plumbing and exhaust vents to allow for adequate clearance courtesy of the new metal roof. Check to see that the vents have sufficient clearances to perform effectively without interference from the new roof.

Location Features Prior to Placing Metal on Shingles

Climate Conditions

Layering metal over shingles is also dependent on the area’s climate. In hot regional areas, heat that accumulates can cause melting of the roofing asphalt on the hottest of days. Also, in snowy regions to the north, it is advisable to clad with a waterproof layer beneath MCT to prevent ice damming. Consider environmental conditions before concluding whether to overlay the shingle with a metal roof.

Building Codes

Most places can only allow a second layer of roofing before one has to strip the entire roof off. Do not assume that some kinds of metal roofing systems are acceptable when, in fact, there are regulations that are overly laid in the jurisdiction.

Homeowner’s Insurance

Insurance companies must be consulted about the possibility of raw increases or limitations on putting metal on top of shingles. Peculiar constructions may have consequences, such as the contractors being denied compensation in case of damages in the future.

Tips to Bear in Mind When Installing Metal Roofing Over Shingles

If erecting a metal roofing system over shingles, ensure that you follow the manufacturer’s suggestions on layering application procedures.

Here are extra pro tips as well:

• Apply larger panels of vertical seam metal roofs to contain fewer seams
• Add an underlayment system for improved wind uplift rating
• Ensure that all vertical and horizontal joints, intersection joints, and other penetrating joints are sealed, as well as the edges of the nails and other fastenings
• Ventilate between the original roof and new panels
• Consider using a professional for installation, and avoid long-term issues, especially when placing overlay over shingles with metal roofing panels

The Bottom Line – Is Installing Metal Over Shingles Worth it?

Overlaying with metal can work if underlying shingles are solid, the roof structure can still support the load, and the homeowner assiduously follows the dictum of ventilation and protective measures during the process. However, problems can be expected along the line with moisture risks which is why complete tear-off is the best, even though it is the most costly method for metal roofing. Properly consider the strengths, weaknesses, opportunities, threats, and rules concerning the installation of metal over asphalt shingles; then you will be in a position to decide whether the idea will be worth it.