Installation of a 2-head GREE FreeMatch R32 heat pump in Saint-Michel (Jardins-de-Napierville RCM)

A metal roof cannot be drilled into or walked on just anywhere, and it does not hold snow like a shingle roof.

Let us clarify at the outset, because the name is a trap and the municipality itself dealt with it 140 years ago: this Saint-Michel is in the Jardins-de-Napierville RCM, in Montérégie. The post office was also called La Pigeonnière from 1854 to 1880, then Saint-Michel-de-Napierville—and the Commission de toponymie explains why in full: the change was intended “to eliminate any ambiguity with another Saint-Michel, in the Bellechasse region.” The parish was established in 1853, the municipality in 1855, and its status changed from parish municipality to municipality on December 10, 2011.

Almost the entire territory is in a permanent agricultural zone, and here again the Commission de toponymie is precise about what distinguishes Saint-Michel from its market-gardening neighbors: “Nowadays, the main crop is potatoes.” The Saint-Michel-Archange Church, at 1786 Rue Principale, is listed in the Répertoire du patrimoine culturel du Québec—inventoried, which is neither a designation nor a citation, and we say this because the distinction quickly disappears in sales copy.

We installed a GREE FreeMatch R32 2-head wall-mounted heat pump on a house with a metal roof. In rural Quebec construction, that is almost the rule—and it is a subject on which homeowner-oriented documentation is surprisingly sparse.

What was installed

Values taken directly from data sheet X610068B. Two matching heads for two comparable zones; each operating alone is 46% above the 8,190 BTU/h modulation floor, providing some flexibility during the shoulder seasons. This unit also has the best COP in the range, 4.19. And, as we now do systematically: this capacity-and-distribution combination has already been used elsewhere in our series. What distinguishes this page is not the technical data sheet—it is the roof.

Four types of sheet-metal roofs, and one question to ask

People talk about a “sheet-metal roof” as though it were a single thing. There are four types, and they do not behave the same way as soon as you want to attach anything to them.

• Snap-lock standing seam (snap-lock): the panels are secured to the substrate with concealed clips, and the female fold snaps onto the male fold. No exposed screws.
• Mechanically seamed standing seam (mechanically seamed): same principle, but the seam is mechanically seamed on site. This is the system suitable for the lowest slopes and the one manufacturers recommend where temperature variations are significant.
• Exposed-fastener panel (profiled or corrugated sheet metal): the panels are screwed through their face, with visible sealing washers. This is by far the least expensive format and the most common on agricultural buildings.
• Stamped steel shingle or tile: interlocking elements that are nailed down.

One question determines everything else: are the fasteners concealed, and does the panel float?

And here is the trap that fools the most people, including contractors: there is a nail-strip profile (nail strip) that looks like a standing seam, has concealed fasteners, but is nailed directly to the substrate and does not float. It looks like a standing seam without behaving like one. Relying on appearance here means choosing the wrong fastening method.

What attaches to a standing seam, and how

The seam clamp: tighten, don’t drill

On a standing seam, you do not have to drill into the roof — and you must not. The market solved this problem long ago, driven by the solar industry, with seam clamps (seam clamps).

The mechanism is simple and worth understanding. The two-piece clamp grips the vertical fold of the seam, then set screws are tightened until they mark — dent — the seam metal without piercing it. This indentation creates the mechanical grip. The roof’s watertight skin is never pierced.

One technical detail determines everything, and it is rarely explained: set screws must have rounded tips, never hollow tips. A hollow tip cuts through the paint and protective coating on the seam — and what follows is corrosion, then a discussion about the warranty.

As for the warranty, let’s be precise. Clamp manufacturers maintain that a properly designed and installed clamp preserves the roof warranty. But the governing document is the roof manufacturer’s own warranty, not the clamp manufacturer’s, and it must be verified on a project-by-project basis. We will not write “it doesn’t void the warranty” as a general fact — we will write that you need to read the right warranty before tightening anything.

As for load, the rule is published and simple: the service load must never exceed the published anchorage strength for the clamp, and that strength is specific to the seam profile, metal, and thickness. There is no generic value. We therefore will not publish one — it is exactly the kind of figure that travels from one website to another while losing its conditions along the way.

On an exposed-fastener panel, you have to drill — and know where

A panel with exposed fasteners has no protruding seam to clamp. There is nothing to tighten. You drill, and the only question is what you are drilling into.

Manufacturers of supports for this type of roof are categorical: the fastener passes through the panel and goes into the load-bearing structure—decking, purlins, or wood or steel trusses—and never into the sheet metal alone. Watertightness is provided by a non-hardening butyl sealant applied at the factory, housed in a recess that protects it from ultraviolet radiation.

Remember the short version: with standing seams, clamp and do not drill; with exposed screws, drill and reach the structure.

Thermal movement, and the mistake to avoid

This is the most subtle point of the subject, and the one we most often see ignored.

A standing-seam roof with sliding clips is designed to move. The panels are fixed at a single point along their length and slide everywhere else within the clips, independently of the supporting structure. One manufacturer puts it plainly: whenever you prevent the roof from doing what it was designed to do—move—you risk damaging the panel, not only aesthetically but also in terms of watertightness.

The consequence for equipment follows from this: two adjacent panels slide independently. A frame or rail rigidly bolted to clamps installed on several different panels ties those panels together and works against the system. The load is then transferred to the seams and clips.

We owe the reader a clarification: the principle—that a panel must remain free to move, and that restraining it damages it—is published by manufacturers. The consequence for equipment spanning several panels, however, is an engineering inference that we stand behind, not an instruction we read somewhere. We therefore treat it as such: by limiting the spans between panels and asking the roof manufacturer rather than deciding on our own. Nor will we publish a coefficient of expansion or a movement value in millimeters: we have found none that we can cite.

Walking on it

A sheet-metal roof can be walked on, but not just anywhere. Manufacturers’ guidance is consistent: place your foot on the flat of the panel, above a structural support, and never on a rib or a seam. Wear soft-soled shoes, and make sure nothing is caught under them—a grain of gravel crushed into the finish will stay there.

The reason is more serious than an appearance concern: on a standing-seam roof, the seam is precisely what the entire waterproofing and fastening strategy relies on. A crushed seam is not a cosmetic defect; it is a compromised anchoring surface.

What the municipal by-law adds, and what we cannot say about it

Three verified findings about Saint-Michel's by-laws, and two refusals.

Zoning by-law 2022-301 contains a subsection titled, word for word, “Air conditioner, heat pump, and generator and mechanical equipment”, within its section on accessory structures and equipment. The equipment is therefore named. ⚠️ We were unable to read the text of this subsection—the document cuts off beforehand, on three attempts—and we will publish no setback, no screen, and no height drawn from text we have not read.

By-law 2022-304 on permits and certificates is instructive because of what it does not say: its list of work requiring an authorization certificate names solar panels, geothermal systems, and wind turbines—but not air-source heat pumps. This absence has been verified. The same by-law sets the issuance period at thirty days from receipt of a complete application. The most plausible reading is that the outdoor unit falls under the permit for accessory structures—this is our interpretation, not a quotation, and it can be confirmed at 450 454-4502.

And one point that directly bears on this page's subject: by-law 2022-307 on PIIAs includes, among its objectives, limiting the visibility of mechanical equipment from the public right-of-way, with an explicit requirement for rooftop equipment. We report this objective without citing the article number because we were unable to confirm it, and we note that it applies only to the areas subject to it.

As for noise, nothing: nuisance by-law 128-2 is distributed as a scanned document without a text layer. No threshold, no measurement point, no hours. We will not invent decibel limits for this municipality.

Snow on a metal roof does not slide down; it breaks loose.

It is the second half of the issue, and the one that physically moves the equipment.

The trigger is not the cold; it is the thaw

Contrary to intuition, metal roofing holds snow quite well as long as it is cold. The problem comes with the thaw—and the clearest technical description we found identifies the conditions: with around 25 centimetres of accumulation and a temperature of 0 to 2 °C, a layer of water forms on the roof surface, friction collapses, and the avalanche starts moving.

Read these two figures and picture a February in Montérégie. These are not exceptional conditions; they are the normal conditions during a thaw.

The difference from an asphalt shingle is a difference in kind, not degree. A rough mineral surface holds snow and lets it flow slowly, in chunks. A smooth metal roof releases it all at once, as a slab. The wording used by people in the trade is blunt, and we quote it as is: everything in its path will be destroyed.

Our Les Cèdres page covered the case of snow sliding off a roof onto a ground-level unit, and we will not revisit it here. What metal roofing adds is that the event is no longer gradual and is triggered not by accumulation, but by melting. A clearance calculated for gradual shedding is worthless against a slab.

The installation implication

It can be summed up in one sentence: never place an outdoor unit, refrigerant line, or condensate pipe in the path of snow shedding from a metal roof overhang. And if the roof has no snow guards, that is the first thing to put on the table—before the model, before the price.

Snow guards, and what must not be claimed

Snow guards (or snow fences) are the countermeasure. A Quebec green-building reference considers them “very important” on a metal roof, especially above doors, and distinguishes the pad-style model from the continuous bar, which is sturdier and more expensive.

Two honest cautions. First, “very important” is an opinion, not a requirement: we found no Code article requiring snow guards, and we have seen Code-compliance claims from vendors, which we will not repeat. Second, we will publish no snow-load value taken from a commercial website.

However, one verified detail neatly closes the loop with the first half of this page: on a standing-seam roof, snow guards are fastened to the seams, exactly like equipment clamps, and therefore do not interfere with the panels’ contraction and expansion. Glued models, on the other hand, are not recommended: when they tear away, they take the paint and protective coating with them, and corrosion follows.

The same logic therefore governs both problems — what is attached to a metal roof and what keeps snow from sliding off it are fastened in the same way, for the same reason.

One last thing, and it has nothing to do with the roof

The Régie du bâtiment du Québec has published a reminder worth repeating: installing a wall-mounted air-conditioning unit requires a contractor holding the appropriate subcategory — 15.10 for refrigeration, or 15.9 for small refrigeration systems when the cooling capacity does not exceed 20 kW, plus subcategory 16 for electrical work if electrical work is required. The Régie associates installations performed outside these rules with concrete dangers, including fire. The licence number can be verified in the registry, and it is the subcategories you need to read—not merely whether the number exists.

What this page adds to the previous one

Our Mont-Saint-Hilaire page covered a unit installed on a sloped, shingle roof and showed that rules written for flat roofs cannot be applied to it. This page covers a metal roof and a unit that is not installed on it: the question is no longer “how do you keep it on the slope?” but “how do you attach it without drilling, and how do you keep it from ending up underneath in February?”

At AirGreen, we install, maintain, and document HVAC systems in Saint-Michel, Napierville, Saint-Édouard, Saint-Cyprien-de-Napierville, Sainte-Clotilde, Saint-Chrysostome, and throughout Jardins-de-Napierville, as well as in Montreal, Laval, Longueuil, on the North Shore, and on the South Shore. If your home or building has a metal roof, mention it during the first call: the roof type changes the fastening method, and the fastening method changes the quote.