Your shingles are done, you want steel this time, and the question is whether the old roof has to come off first. Under Wisconsin’s dwelling code it does not, as long as one sound, dry layer is up there. The catch is the deck, which nobody will see once the panels are on.
What Wisconsin allows under a metal roof, and the fourth condition the code leaves out
The roof has to meet three conditions the state sets and a fourth we add. SPS 321.28(6) caps it at one sound, dry layer and bars shake, slate, and tile; the asphalt roof-over guide quotes the section in full. Metal falls under SPS 321.28(5), which defers to the manufacturer’s instructions, so on a roof-over the panel’s guide is the code, and the City of Eau Claire’s one written roofing rule says the same: roofing goes on per the manufacturer’s specifications. A re-roof is a dwelling-code alteration, and inside the city it is a permit job we pull. Central States’ guide tolerates two existing layers; Wisconsin does not, and the stricter rule controls.
On your roof:
- The layer count. Two means a tear-off. The model code some states use lets a self-supporting standing seam system skip the layer limit; Wisconsin’s does not. Count layers at the drip edge.
- Whether it is leaking today. The Metal Construction Association’s retrofit paper (the MCA, the metal building trade group) says a leaking roof means a tear-off or added underlayment; on a house, a tear-off.
- What the panel goes over. Shake, slate, and tile are barred; most houses here are asphalt, which is the surface the over-shingle procedures in the table below are written for.
- What the deck will hold a fastener at. The code does not write this one down: the shingles stay, so nobody sees the deck. The MCA’s checklist has the installer walk for spongy spots and, where the deck is in doubt, run a fastener pull-out test looking for at least 80 pounds of resistance. Suspect decking gets torn off so it can be checked. What turns up under the shingles goes by the age of the house, which the decking guide breaks down; on a recover nobody gets to look. Weight stacks as well: the framing carries shingles, strips, and steel, McElroy caps the whole recover at 3 pounds per square foot added, and the panels weigh roughly half what the asphalt under them does, so the MCA has the installer look for sag before the strips go down.
Why yes here when we tear off on every shingle replacement? The case against a second shingle layer is trapped heat aging the new shingles, plus the hidden deck. Heat is the asphalt problem; what wears on steel is the gaskets and the finish. The hidden deck carries over, so the answer is sometimes.
How a metal roof goes on over shingles, step by step
The sequence is Central States’ Panel-Loc Plus procedure, with the MCA, McElroy, and MBCI (another panel maker) adding detail.
- Flatten and clean the old roof. Curled or lifted shingles get nailed down or cut away and the roof swept clean. Cut away too many and the MCA says added underlayment restores what the old roof lost.
- A slip sheet over the shingles. Thirty pound felt or synthetic over the whole roof, keeping the abrasive shingles off the back of the panel; McElroy requires a barrier on any direct-attach job.
- High-temperature membrane at the eaves and valleys. Polyguard puts a metal roof’s service environment at 240 to 265 F and rates its own high-temp membrane to 260 F, which is what the eave and valley membrane under steel must carry. The slip sheet handles abrasion; this is the ice-dam protection.
- Furring strips fastened to the rafters. The panel picks the method, and on the Panel-Loc Plus we install on houses the guide says strips, so that is what the estimate names: 1x4 strips horizontally every two feet on center over the slip sheet, panels screwed to them, fastened by the MCA’s rule to the rafters, not just the sheathing. McElroy and MBCI allow direct attachment instead, screws driven through the shingles at least half an inch into the deck. McElroy calls that the economical method and furring the flatter one; on a house flat is the point. Copper-treated lumber must not touch steel, so treated furring gets a barrier under the panel.
- Panels, trim, and snow retention. From here it is a metal roof like any other; the metal roofing page covers clips, trim, and snow guards.
Will the shingles show through the steel, and will the roof sweat?
Steel acts like a mirror and telegraphs bumps in the deck or shingles through the panel, worst on flat-pan standing seam over high-profile shingles, per the MCA. The makers call it cosmetic: Central States says distortion from an uneven substrate, debris, or protruding nails is not a defect, and McElroy says oil canning, the waviness in the flat of a panel, is no cause for rejection. So the fix is in the panel and the strips: a ribbed panel shows it less than a flat pan, and the furring lifts the panel off the shingle texture, which is what Central States says the strips are for.
Sweat is the other question. Central States warns that panels over open framing on a heated building drip condensation, which is the pole barn case. The MCA advises solid sheathing and underlayment between purlins and the structure, and a house already has the sheathing. Whether sound underlayment is still under shingles at the end of their life is something the attic look settles at the estimate; where it is gone, the slip sheet stands in. The MCA also describes above-sheathing ventilation, air in at the eave and out at the ridge between the two roofs, credited with less summer heat gain and fewer ice dams. Central States claims nothing of the kind for its strips. The one over-shingle system built for that airspace is McElroy’s 138T, which holds a three-quarter inch airspace with corrugated metal at the ridge, hips, and headwalls, with testing McElroy cites showing up to 30 percent less heat transfer. That airspace does not replace attic ventilation, which still has to meet the code ratio.
Which metal panels can go over shingles
Fewer than the sales pitch suggests; the split runs along the standing seam line.
| Panel | System | Over shingles, per the maker |
|---|---|---|
| Central States Panel-Loc Plus | Exposed fastener, 29 or 26 gauge | Written procedure: felt or synthetic, then 1x4 furring |
| McElroy Max-Rib | Exposed fastener, 29 or 26 gauge | Solid deck or open framing; barrier required |
| McElroy 138T Shingle Recover | Standing seam, 24 gauge | Built for it, with the three-quarter inch air gap |
| Central States Horizon-Loc | Standing seam, 26 gauge | Solid decking with felt or synthetic; no over-shingle procedure |
| ABC Seamless | Steel roofing | Solid decking with underlayment; no over-shingle procedure |
The panels with a published procedure are the exposed-fastener lines, plus McElroy’s 138T from the maker we use on commercial roofs. The residential standing seam we put on houses is specified over solid decking, which is why it starts with a tear-off.
What a metal roof over shingles costs in Eau Claire
The roof-over price is the exposed-fastener band, $9,000 to $15,000, the same band a ribbed-panel job lands in on a budget residential roof, with a roof-over toward the lower end of it because the tear-off labor comes out and the slip sheet and strips go in. Standing seam on a house means a tear-off first, at $14,000 to $24,000 on an average house and $20,000 to $35,000 on a larger or steeper roof. McElroy credits the recover with the tear-off, the labor, and the disposal that never happen; we do not put a figure on the difference, because trim and the deck move the number more.
The estimate visit settles the layer count at the drip edge, the walk for soft spots, and the look from the attic, so a roof that fails any of those is quoted as a tear-off before you sign. What can still change is a soft spot the walk missed: the strips stop, you see it, and the job is rewritten as a tear-off with a decking allowance before it goes further.
What you take on is an exposed-fastener roof on the house: the mid-life re-gasket pass the screw gaskets need, and a ribbed profile where we would otherwise steer a house to standing seam. We will do it where ribbed steel was the plan anyway and the roof is dry, single-layer, and firm underfoot. Where the deck is soft or the house wants standing seam, we say so at the estimate and quote the tear-off.