Snow Load in Manitoba: What to Check on Your Roof, Garage and Deck Before Winter

Oct 1

7 min read

Snow load failures in Manitoba almost never happen because of one big snowfall. They happen where snow collects deeper than the rest of the roof, on a structure that was already carrying something it was not designed for. The places to check before winter are drifting zones against taller walls, valleys, low slope sections, unheated garages and shops, carports, and any deck or roof that was added on later. Structure that was built for the load and is in good condition does not need your attention. Structure that was modified, added to, or never engineered does.

People tend to think about snow load as a question of how much snow falls. It is not, really. Snow is distributed by wind long before it is distributed by gravity, and what ends up on a roof in April has very little to do with what fell in January.

The pattern we see is consistent. A roof carries fine for twenty years. Then a garage goes up next to it, or an addition changes the roofline, or a deck roof gets added, and suddenly there is a step in the roof where wind drops its load. That step collects a drift several times deeper than the open field snow around it, and it does it in the same place every single year.

None of this is exotic. It is just worth walking your property once in the fall with this in mind, because the fixes are easy in October and difficult in February.

At a Glance

Drifting, not total snowfall, is what overloads most structures here
Any place where a lower roof meets a taller wall is a drift zone
Valleys, dormer sides, and low slope sections hold more than they look like they do
Unheated garages, shops, carports, and lean tos are the most common failures
Structures added on later are the ones most often built without load in mind
Interior signs matter: sticking doors, new drywall cracks, sagging ceiling lines
Never climb onto a snow loaded roof to clear it

Where Does Snow Actually Pile Up on a Building?

Wherever the wind slows down.

The classic spot is a step in the roof. If you have a single storey section attached to a two storey section, or a garage roof running into the house wall, wind carrying snow over the upper roof drops it as soon as it hits the sheltered pocket behind the wall. That drift can be dramatically deeper than the snow on the open roof around it, and it sits there all winter because the wall shelters it from the wind that would otherwise move it.

The same thing happens on the downwind side of anything that sticks up. Parapets, large chimneys, dormers, mechanical units, and even a row of trees on the windward side all create drift shadows.

Valleys are the other collector. Two roof planes meeting at a valley funnel snow and ice into the same line, and that line is also where meltwater runs. Low slope roofs hold snow rather than shedding it, which is not a defect but does mean the structure underneath has to be up to it.

Which Structures Are Most at Risk?

Almost always the ones built without a structural design, or built for a different purpose than they now serve.

Carports and lean tos. Often the lightest structure on a property, frequently added by a previous owner, and often tied into a wall that creates a drift zone by definition.
Unheated garages and shops. No heat means no melting, so the load accumulates all season instead of shedding.
Deck roofs, pergolas with added cover, and three-season rooms. Frequently built as a summer structure and then given a solid roof later.
Old outbuildings. A shed or barn that has been standing for decades may be carrying rot at the connections even though it looks fine.
Anything with a modified roofline. Additions that create a new step, a new valley, or a new low slope area change the snow pattern for the whole building.

A heated house roof in good condition, designed and built for the region, is generally not the thing to worry about. The exception is where heat loss has created ice buildup at the eaves, which adds weight in exactly the wrong place. That is a different mechanism and we cover it in our post on ice dams on Manitoba roofs.

What Should I Check Before the Snow Comes?

Do this from the ground and from inside, not from a ladder in November.

From outside, walk the full perimeter and look for the drift zones described above. Note where a lower roof meets a taller wall, where valleys run, and where anything was added on. Then look at the structures themselves. Posts that are out of plumb, beams with a visible sag, rusted or missing connection hardware, rot at a post base, and any repair that was clearly improvised are all worth attention now.

From inside, look for the signals that a structure is already moving. Doors and windows that have started to stick in a building where they used to swing freely. New cracks in drywall, particularly diagonal cracks from the corners of openings. A ceiling or beam line that is no longer straight when you sight along it. Daylight at connections in an unfinished shop or garage.

In a garage or shop with exposed framing, you have the advantage of being able to see the structure. Use it. Look at where the rafters or trusses bear on the walls, look for splits at connection points, and look for any truss that has been cut or modified to fit something in. A cut truss is a serious issue and not a do it yourself repair.

Should I Be Clearing Snow Off My Roof?

Generally no, and if you do, not by climbing on it.

Getting onto a snow-covered roof is one of the more dangerous things a homeowner can decide to do. The surface is slick, the edge is invisible, and the structure you are standing on is the one you are worried about.

Where clearing does make sense is targeted rather than total. Reducing a specific drift against a wall, or clearing a low slope section, or pulling snow back from the eave with a roof rake from the ground, addresses the actual problem without stripping the whole roof. Total clearing is rarely necessary and can damage shingles, particularly in cold weather when they are brittle.

Chipping ice off with anything metal will damage the roof, and using a heat source to melt through an ice dam has caused more than one fire. If a structure is showing signs of distress under load, the right call is to stay out of it and get somebody to look at it.

Can Anything Be Fixed Once Winter Has Started?

Some things, but this is a job that rewards doing it early.

Reinforcing a post, adding a beam, replacing rotten bearing points, or building a proper footing under a sagging carport all involve work that is far easier before the ground freezes and before the structure is loaded. Emergency shoring is possible in winter, and we do it, but it is a temporary measure taken under worse conditions.

The planning side, on the other hand, runs perfectly well through winter, and that is the right use of the season. Our post on what construction work can still get done through a Manitoba winter covers what carries on and what waits for open ground.

Real Scenarios

You have a carport that groans and the posts look a little off plumb. Take that seriously. Out of plumb posts on a snow loaded structure are a warning, not a cosmetic issue. Get it assessed before the load comes on.

Your garage roof drifts hard against the house wall every year. That drift is not going to stop happening, so the question is whether the garage structure is built for it. This is exactly the kind of thing worth sorting out at the design stage, which we get into in our post on building a detached garage in Manitoba.

You want to add a roof over an existing deck. Do it as a designed structure, not as an extension of the deck frame. Deck framing is designed for people and furniture, not for a winter of accumulated snow plus the weight of a roof.

You run housing or facilities for a community and have a mix of buildings of different ages. Prioritize the unheated and the added on. Storage buildings, shops, garages, and anything with a lean to takes the load without any melting help, and those are the buildings that come down.

You notice a ceiling sagging mid winter. Get people out of the space and get somebody there. Do not go up on the roof to clear it.

FAQ

How much snow is too much on a roof?

There is no useful universal number, because depth is a poor proxy for weight. Wet, settled, or ice layered snow weighs far more than the same depth of fresh powder. Condition and drifting patterns matter more than a measurement.

Does a steeper roof solve the problem?

It helps, because steeper roofs shed more readily, but it does not eliminate drifting at steps and valleys, and shedding snow has to land somewhere you have thought about.

Are heat cables a fix for snow load?

No. Heat cables are aimed at ice at the eaves and drainage paths, and they do nothing about structural load. They also treat a symptom rather than the heat loss causing it.

My shop has trusses and one was cut for a light. Is that a problem?

Potentially a serious one. Trusses are engineered as complete assemblies, and cutting a member changes how the whole thing carries load. Have it looked at.

Can an existing structure be reinforced rather than rebuilt?

Often yes. Additional posts, proper footings, beam reinforcement, and connection upgrades are all common. Whether it is worth doing depends on the condition of what is already there.

Does snow load matter for fences and decks?

Less for load and more for what accumulated snow and ice do to posts and hardware over a season. Our post on choosing a fence that survives Manitoba frost heave covers what actually moves those structures.

Ready to Have Somebody Look at It?

Flip Flop Construction works on roofs, garages, shops, decks, and the structures around them across Winnipeg, Steinbach, Kleefeld, Grand Beach, and surrounding Manitoba communities, along with Red Lake, Kenora, Dryden, and remote fly in communities in Northern Ontario. Framing, roofing, concrete, and repair are all handled by the same crew, so a structural fix does not turn into three separate trades and three separate schedules.

Have a look at our roofing work, see everything we handle, and get in touch before the snow makes the decision for you.

431-777-5219 flopconstruction@gmail.com flipflopconstructioninc.com One crew, every trade, no excuses.