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Kamloops, BC
Metal suits this climate — but a panel expands and contracts across a sixty-degree annual range, and everything that matters about the roof follows from how the system lets it move. Including where the snow lands when it lets go.
Steel and aluminium expand when they warm and contract when they cool. On a short length that is trivia. On a roof panel running unbroken from ridge to eave, across the temperature range Kamloops actually sees, it is the single fact the entire assembly has to be designed around.
City of Kamloops — climatic design temperatures
January design temperature (1%): −28 °C · July design drybulb (2½%): 34 °CCity of Kamloops Building By-law No. 11-80, Climatic Data table.
That is a design range of roughly sixty degrees between the coldest winter condition and the hottest summer one — and the panel surface in direct July sun runs hotter still than the air temperature the table describes. Every one of those degrees moves the metal, in a cycle that repeats daily through the shoulder seasons and annually through the extremes.
Nothing about that is a defect. Metal is a genuinely good roof for this climate. But it means the right question to ask a roofer is not steel or aluminium, and not what colour. It is: how does this system let the panel move?
There are two broad ways to hold a metal roof down, and they answer the movement question very differently.
Exposed-fastener systems screw through the face of the panel into the structure below, with a rubber or neoprene washer under each screw head making the seal. They are simpler, faster and cheaper. The catch is that the panel still wants to move, and now it is pinned. Over thousands of cycles the panel works against the screw shank, the hole elongates slightly, and the washer — which is the actual weatherproofing — gets compressed, chewed and eventually sun-perished. On a roof of any age the honest maintenance item is that the fasteners are a wear part.
Concealed-clip systems, of which standing seam is the common form, hold the panel with clips hidden inside the raised seam. Many clips are designed so the panel can slide against them. The fastener never penetrates the weather surface at all. It costs more, and it is the answer that actually addresses the movement rather than resisting it.
“Fastener back-out” means something different here. The phrase also shows up in asphalt shingle roofing, where it describes nails working proud as the deck expands and contracts beneath them — that mechanism is covered on the roof repair page.
On a metal roof the driver is not the deck. It is the panel itself sliding against a fastener that is holding it still. Same words, different physics, different fix — and a roofer who explains which one they mean is worth listening to.
Visible waviness in the flat part of a metal panel is called oil canning. It is almost always cosmetic rather than a failure, it is more obvious on wide flat pans, in low sun, and in darker colours, and it can be reduced with striations, narrower panels or a backer. It is worth raising before installation, because it is a legitimate disappointment afterwards and a difficult one to fix. It is not a leak and not a structural problem.
This is the difference between a metal roof in a brochure and a metal roof in Kamloops, and it is the part worth thinking hardest about.
Asphalt shingle is rough. Snow sits on it, compacts, and melts off gradually. Metal is smooth, and it conducts heat from the building below, so a layer of meltwater forms between the snow and the panel. At some point the friction holding that slab in place stops being enough — and the whole accumulation comes off in one sheet, usually with no warning and usually on the first warm day after a cold stretch.
A roof that sheds snow cleanly is often sold as a benefit, and structurally it is one. The problem is entirely about what is underneath. Over a driveway, a front step, a gas meter, a heat pump, a deck railing, or the spot where a car is parked, a sheet release is a genuine hazard and a real source of damage claims.
The standard answer is snow guards — devices fixed to the roof that break the slab up and let it release in manageable amounts. They need to be specified as part of the roof rather than added later, because on a standing seam roof they should clamp to the seam rather than penetrate the panel. Ask where they are going before the quote is signed, and walk the perimeter of the building thinking about where people and equipment actually are.
Three local conditions push in metal’s favour and one complicates it.
Rain noise is the objection people raise most and the one that matters least — over a solid deck with underlayment, a metal roof is not meaningfully louder than anything else. Condensation is the real consideration. Metal is cold on a clear winter night, and warm moist air reaching the underside of a cold panel will condense on it. That is an attic ventilation and vapour-control question rather than a roofing-material question, and a good installer will raise it before you do.
If you are still deciding whether the existing roof is finished at all, a written inspection answers that first. If the old roof is definitely done, the material decision sits inside the wider replacement conversation. And if metal is already on the building and something is wrong at a seam or a penetration, that is a repair.
Tell us what’s on the roof now and what you’re considering, and we’ll pass it to a local Kamloops roofer.
It suits the climate well. The dominant ageing force on roofing here is ultraviolet exposure rather than persistent moisture, and a finished metal panel does not embrittle and shed granules the way an asphalt shingle mat does. The trade-offs are cost, the need to design for thermal movement, and planning for snow releasing off the roof in sheets.
Exposed-fastener panels are screwed through the face of the metal, with a washer under each screw head making the seal. Standing seam holds the panel with clips hidden inside a raised seam, so nothing penetrates the weather surface and the panel is free to move as it expands and contracts. Standing seam costs more and addresses thermal movement rather than resisting it.
Because the panel moves and the screw does not. Across a wide annual temperature range the metal expands and contracts against the screw shank, which can elongate the hole and compress or perish the washer that is doing the actual sealing. On exposed-fastener roofs the fasteners are a wear part and should be inspected rather than assumed.
Yes, and usually all at once. Metal is smooth and conducts heat from the building, so meltwater forms under the snow and the accumulation releases as a sheet with little warning. That is fine over open ground and a hazard over a driveway, a doorway, a gas meter, a heat pump or a deck. Snow guards break the release up and should be specified as part of the roof.
It is waviness visible in the flat area of a panel and it is almost always cosmetic rather than a failure. It shows up more on wide flat pans, in low sun and in darker colours, and it can be reduced with striations, narrower panels or a backer. Raise it before installation, because it disappoints people afterwards and is awkward to correct.
It depends on weight, not on material. The City exempts reroofing that does not alter the dead loads or slope of the existing roof structure, and most metal roofing is lighter than the asphalt it replaces, so it commonly falls inside that exemption. Structural work such as new skylights or dormers is a separate trigger. Confirm your specific project with the City.