A metal roof goes on in a fixed order: tear-off and deck repair, then membrane and underlayment, then the trim around the edges and in the valleys, then the panels, then the closures, the flashings at chimneys and pipes, and the ridge. Every step covers the one before it. So the day to check a layer is the day it goes on, not the day the crew packs up. Here is the order, and what you can see at each stage while it is still visible.
The order, from the deck up
Sheffield Metals, a metal roofing supplier, filmed a full standing seam job from start to finish, and its chapter list is a clean picture of the sequence. It runs tear-off, deck repair, underlayment, curb measurement, perimeter flashing, valley, first panels, closures, valley panels, chimney, pipe penetrations and vented ridge.
| Stage | What goes on | What you can still see that day |
|---|---|---|
| Tear-off | Old shingles come off to bare deck | Soft, stained or delaminated sheathing |
| Deck repair | New sheets where the old ones failed | How many sheets, and where |
| Membrane and underlayment | Self-adhered membrane at the eaves and valleys, underlayment over the rest | Full coverage, laps running downhill, nothing torn |
| Edge trim and valleys | Eave, rake and valley metal | Straight lines, trim fastened before any panel sits on it |
| Panels | Panels laid across from the first edge | Clean cut ends, no metal filings left on the finish |
| Closures and flashings | Foam or metal closures, then chimney and pipe flashings | Every pipe and chimney has its own detail |
| Ridge | Vented or closed ridge cap | Whether the attic is meant to vent through it |
The layers below the panels decide most of what the roof does for decades, and you see them only briefly.
Tear-off first, or strapping over the old roof
Most metal jobs start the way a shingle job does, by stripping to the deck. Sheffield Metals says it “always recommends removing the existing shingles so you can properly inspect, repair, and level the roof deck.” A deck you have seen is a deck you can trust.
The other route is strapping over the old roof. MROOF, an Ontario metal roofer, describes the professional version as wood or steel strapping “fastened through the shingles into the rafters or deck,” with underlayment on top and the panels fastened to the strapping, never to the old shingles. It also notes that Ontario “generally” allows a metal overlay on one existing shingle layer, and that two layers mean a tear-off. For when that route makes sense and when it does not, see how we approach metal roofing in Collingwood.
On the day: if the deck is exposed, walk around the house before the membrane goes down and ask to see any sheet that is being replaced.
The membrane has a cold-weather floor
Panels do not care much about the temperature. The membrane under them does. The data sheet for Grace Ice & Water Shield HT, a membrane sold for use under standing seam, says to apply it “when the air, roof deck, and membrane are at temperatures of 40°F (5°C) or higher.” The same sheet says it “can be left exposed for up to 120 days” before the roof covering goes on, so a short wait for panels is not a problem. A cold week is.
That matters on a job that runs into November around Georgian Bay. If the forecast drops, ask how the crew will keep the membrane going on at or above the maker’s floor, and whether they will wait. Our post on the best season for roof replacement covers the same cold-weather question for shingles.
On the day: look at the eaves before anything covers them. The membrane should run up from the edge and sit flat, and every lap should shed water downhill.
Trim before panels
On a standing seam roof, the eave, rake and valley metal go on before the first panel. Sheffield Metals puts it plainly: perimeter flashings “take the brunt of wind uplift forces, so it’s important to get them right.” In a town where wind comes off the bay, the edge is where a metal roof is tested first.
On the day: stand back from each gable end and sight along the rake trim. It should run straight, and it should be fastened before panels hide its fasteners.
Cuts belong on the ground
This is the step homeowners rarely know to watch. Panels get cut to fit at hips, valleys, chimneys and openings, and how they are cut matters. MBCI, a panel manufacturer, says field cuts “must be cut with nibblers, snips or shears to prevent edge rusting,” and says not to cut panels “with saws, abrasive blades, grinders or torches.”
Where the cut happens matters too. Cutting throws off fine particles the trade calls swarf. MBCI says swarf can cause “permanent staining,” and that panels should never be cut “on the roof or over other metal panels.” The fix is simple: cut on the ground, then sweep or blow the filings off the finished panels.
On the day: a cut-off saw throwing sparks on a finished roof is worth a polite question. At the end of each day, look at the panels near any cut for dark specks. They lift easily that evening.
Chimneys, pipes and the ridge
Penetrations take the most care, because each one needs its own flashing detail from the panel maker. A chimney gets a cricket or a formed flashing. A plumbing vent gets a boot sized for the pipe. Closures fill the ribs at the eave and ridge so wind, snow and insects cannot get under the panels.
On the day: count the pipes and vents on your roof before the job, then count the flashings on the finished roof. They should match.
Do you need an air gap under a metal roof?
Not when the panels go on a solid deck over membrane and underlayment. A reply on Green Building Advisor puts it simply: “If the roofing is tight to the sheathing, there is no air to vent, no condensation to dissipate.” A gap exists when the panels sit on strapping over the old roof, and then its ends need screening at the eave and ridge. The noise question has the same answer: over solid decking, rain on metal is no louder indoors than rain on shingles.
After the panels: snow and water
A roof that sheds snow drops it at the eaves in slabs. Snow guards above doors and walkways are part of finishing the job, and the gutters underneath matter too. On a steep metal roof, a new eavestrough in Collingwood sits higher and needs tighter hanger spacing than it would under shingles.
Questions homeowners ask
Can I be home during a metal roof installation? Yes, and it helps. Tear-off is loud, but the stages you want to see happen in daylight, and a good crew expects you to look.
Can a metal roof go on in winter? The panels can. The membrane under them has a minimum temperature on its data sheet, so a winter install depends on the weather at the eaves, not the calendar. Ask which membrane is going on and what its floor is.
Who should cut the panels? The crew, on the ground, with snips, shears or nibblers. If you see sparks on the roof, ask what tool is in use and whether the filings are being cleaned off that day.
Will the job look different from a shingle replacement? The first day looks the same. After that, the trim goes on before the panels, and the finished edges are metal all the way around.
Price it, then watch it go on
Before you commit to the install, check roof replacement cost in Ontario for the local ranges on standing seam and steel shingles. Then send us the roof details or call (249) 499-0101. We install metal and asphalt, and we will price your roof both ways on one visit.