Your house was engineered and inspected against Alberta’s snow load code. The detached garage next to it may not have been.
Every winter brings at least one story of a garage roof, a carport, or a sunroom addition giving way under snow while the main house next to it looks completely normal. That pattern is not random. It comes down to which structures on a property were actually built and reviewed to the same standard, and which ones were added later, by a different builder, under a different set of assumptions.
This article walks through the structures worth watching specifically this winter: older detached garages, flat or low-slope carports, sunrooms and three-season additions, and the spots where snow from a taller roof dumps onto a lower one. It also covers the warning signs worth taking seriously, and what to do, and not do, if a structure starts to look distressed.
Why the Detached Garage Is Often the Weakest Link
Your house was almost certainly built to the snow load requirements in effect at the time, and inspected against them. A detached garage on the same property, especially one built decades ago or without a permit at all, was sometimes framed lighter, with smaller rafters, wider spacing, or a roof pitch never checked against the same standard. It sits on the same lot, under the same snow, with a different margin of safety.
That gap widens the older the structure is. A garage built decades back, then reroofed once or twice without anyone reassessing the framing underneath, can be carrying years of snow load it was never engineered against with confidence. A permit record, if one exists, at least tells you the structure was reviewed at the time. Without one, you are relying on how the building has performed so far, not on knowing it was built right.
Flat and Low-Slope Carports: Built to Hold Snow, Not Shed It
A carport with a flat or very low-slope roof does not shed snow the way a steeper roof does, and unlike a properly detailed flat roof on a house, many older carports were never built with the membrane, drainage or structural capacity a genuine low-slope system requires. Snow accumulates on top and stays there, adding weight through the winter instead of shedding in stages.
Wet, heavy snow is harder on a structure than the same depth of dry powder, and a Chinook that partially melts a snowpack on a flat carport roof, only for it to refreeze overnight into a denser layer, can leave more total weight up there than the original snowfall did. A carport with a flat or barely sloped roof deserves specific attention before winter, not the same casual glance you might give a steep-pitched garage roof next to it.
Sunrooms and Three-Season Additions: Lighter Framing, Bigger Glass
Sunrooms and three-season rooms are usually built with lighter framing than the main house, often with a significant portion of the roof or upper walls given over to glass rather than solid framed structure. That design works well for what these rooms are meant to do, bring in light without the weight and cost of full house construction, but it leaves less structural reserve for a heavy snow load than the main roof beside it.
A sunroom roof designed for a specific, moderate snow load can be pushed past its margin by an unusually heavy or wet snow year, particularly if the room sits under an area where snow from a taller adjacent roof also lands on it. Check your sunroom’s roof condition specifically each fall rather than assuming that because the main house roof looks fine, the addition attached to it is equally fine.
When the Main Roof Dumps Snow Onto a Lower Structure
A lot of additions, sunrooms and even attached garages sit lower than the main roofline, which means snow sliding off a steep upper roof section does not stop at the edge. It lands on whatever lower roof sits directly below. This is a common and often overlooked load source: the lower structure absorbs not just its own snowfall, but a concentrated dump from everything that slides off the roof above it.
This matters most after a Chinook, when a steep roof section sheds a large slab of partially melted, refrozen snow all at once rather than a light dusting settling gradually. If you have an addition, garage or sunroom positioned directly beneath a steeper roof section, watch that specific spot after a big melt-and-refreeze cycle, since it can accumulate far more depth than what actually fell from the sky that day.
Drifting Against the House Wall Changes Where the Weight Sits
Wind rarely distributes snow evenly across a property. It picks snow up from open, exposed areas and deposits it against whatever obstruction it meets first, frequently the wall of the house itself, or the corner where an addition meets the main structure. A drift building up against a wall does not just sit on the ground. It can pile against and partially load a lower roof section in a way flat, even snowfall never would.
This is worth watching specifically at inside corners, where two walls or two roof sections meet at an angle, since wind tends to deposit the deepest drifts right there. A drift that looks impressive in the yard is one thing. A drift built up directly against a lower roof edge is a different, more specific concern worth a direct look.
Warning Signs Worth Taking Seriously
Most structures under real distress give some warning before anything fails outright, and knowing what to watch for matters more on an older garage, carport or addition than on a house built and inspected to current code.
- A ridge that looks visibly sagging or wavy when viewed from the side or from a distance
- Walls that appear to bow outward, especially near the top where they meet the roof
- Doors or windows in the structure that suddenly stick or no longer close properly
- New creaking, popping or cracking sounds during or after a heavy snow load
- Cracks in drywall, block or framing that were not there before winter
Any one of these on its own is worth a look. More than one together, especially after a heavy or wet snowfall, is worth treating as urgent rather than something to check next weekend.
If a Structure Looks Distressed: What to Do and What Not to Do
If you see any of the warning signs above, do not go up on the roof of that structure to inspect it or attempt to clear snow yourself. A roof already under structural stress is exactly the surface most likely to fail under the added weight of a person standing on it, and that risk applies whether the structure is a garage, a carport or an attached addition.
The safe move is to stay off, and stay out from directly underneath the structure, and call a professional to assess it before anyone goes near it again. If the distress looks severe, visible sagging or active cracking, treat it the same way you would treat any structural emergency and get it looked at right away rather than waiting to see if it gets worse on its own.
Pre-Winter Checks Worth Doing on Every Ancillary Structure
Before the snow starts, walk your property and look at every structure that is not the main house, since that is where attention typically drops off. Check the detached garage roofline for existing sag, look at a flat carport roof for standing debris or ponding that suggests drainage problems before snow arrives, and check where a sunroom or addition meets the main house for any existing gap or damage.
If any of these structures has never had its framing or roof condition assessed, and you cannot find a permit or engineering record for it, this fall is a reasonable time to have someone knowledgeable take a look, before it is carrying a full winter’s snow load and any weakness becomes much harder to address safely.
The House Isn’t the Structure to Worry About. The Rest of the Property Is.
A well-built, code-compliant house handles a typical Calgary winter without much drama, which is why homeowners stop worrying once the main roof looks fine. The structures actually worth watching are the ones built to a lighter standard, without a permit, or years apart from the house with different assumptions baked into the framing.
If your property includes an older detached garage, a flat-roofed carport, or a sunroom you are not confident was built with today’s snow loads in mind, get it looked at before winter rather than after a heavy snowfall forces the question. For a broader look at how your property’s various roofs, main house included, are holding up heading into the season, Calgary residential roofing services and options is worth a look before the snow piles up anywhere you cannot easily check.
About the author: this article was contributed by Angel’s Roofing, a Calgary residential roofing company certified through GAF, IKO, Malarkey, Euroshield and VELUX. Angel’s Roofing crews assess detached garages, carports and additions with the same attention given to the main house roof.
