Metal Roof Over Shingles Methods
There are three ways to put metal over an existing shingle roof, and a fourth answer that is sometimes the right one.
Standing Seam Over One Layer of Shingles
The most common recover lays new underlayment over the shingles and fastens standing seam panels with concealed clips through to the deck. Under the 2021 International Residential Code, standing seam systems that carry the roof loads straight to the building's structure, without relying on the old roof for support, don't require the existing covering to be removed. The clips still have to reach solid wood, so the roofer should check the deck from the attic for soft or delaminated sheathing first.
Metal Panels on Battens Over Shingles
Some installs fasten wood battens or metal purlins over the shingles and attach the panels to those. The code allows metal panels on solid or spaced sheathing, or on spaced supports when the roof covering is designed for them, so ask whether the panel's installation instructions cover a batten system. Battens leave an air space between the old roof and the new one. Ask how that space is closed or vented at the eaves and ridge, because open ends let in insects and wind-driven rain.
Exposed-Fastener Panels Over Shingles
5V crimp and ribbed panels can also go over shingles, screwed through the panel face. The screws pass through the old shingles before reaching wood, so screw length and the deck underneath matter more than usual. Lapped panels also have minimum slope rules of their own, set out on Metal Porch Roofs. On a house close to salt water, the fastener metal decides how long this roof lasts, which is covered on Metal Roof Repair.
Tear-Off Before the Metal Goes On
Sometimes the honest answer to "can metal go over my shingles" is no. The code defines a roof replacement as removing the old layers down to the deck, and a tear-off is the only way to see and repair the decking, re-nail it and seal it. The full tear-off job is on Metal Roof Replacement.
Why Charleston homeowners call Charleston Metal Roofing Co.
- Estimate at no cost to you
- Metal, seam and fasteners named on paper
- Your request goes to a single local roofer
- Referral is free; you pay only the roofer you hire
Metal Roof Over Shingles Code Limits
The 2021 International Residential Code, adopted in South Carolina with state changes, says when a recover is not allowed:
Two or more layers already
If the roof already has two or more applications of roof covering, it has to come off.Wet or deteriorated
A roof that is water-soaked, or deteriorated so far that it can't serve as a base for more roofing, can't be covered.Slate or tile
A recover isn't permitted over slate, clay, cement or asbestos-cement tile.Wood shakes are different
Metal panels and metal shingles are permitted over an existing wood shake roof under the code's separate shake rules.Structural load
The roof framing has to carry the new covering plus the material and equipment loads during installation.
The city permit for a metal roof needs the manufacturer's specifications, and the permit details are on Metal Roof Replacement. If those specifications don't describe installation over an existing roof, that's a reason to ask more questions.
Metal Over Shingles or Tear-Off in Charleston
Skipping the tear-off saves the labor and the disposal of old shingles, and keeps the house covered on the day work starts. In Charleston, three things weigh on the other side.
Hidden decking
Termite risk in the city is rated "Very Heavy" in the building design criteria. Soft wood under old shingles stays hidden under a recover, and the clips are only as good as the wood they grip.Wind programs
The IBHS FORTIFIED hurricane checklist requires removing all existing roofing and re-nailing the deck, and the top tier of the SC Safe Home grant needs that designation. Deck nailing matters in a city that designs for hurricane winds (see Hurricane Metal Roofs), so check SC Safe Home Roof Upgrades before you choose a recover.
A recover makes most sense on a roof with one sound layer of shingles, a dry deck and no plans for a wind grant. A porch roof, a garage or a rental house that needs a dry lid at a lower price are the usual examples. On a main house where the deck has never been seen since it was built, paying for the tear-off buys certainty about what the new roof is fastened to.
Metal Over Shingles Quote Questions
Layer count
How many layers are on the roof now, and how the roofer checked.Deck check
What they saw in the attic, and how soft spots will be handled.Method
Direct over underlayment or on battens, and the batten material and spacing.Instructions
Whether the panel maker's instructions cover installation over an existing roof.Edges
How the drip edge, rake trim and flashing handle the extra thickness at the edges.Underlayment
What goes between the old shingles and the new panels, and its standard (see Metal Roof Insulation and Ventilation).Tear-off price
A second price for a full tear-off, so you can compare the two.