Wasatch Snow Load and What It Does to a Roof

September 2026

April snow is a different animal than January snow

The calls do not come in January. They come in the first week of April, after a storm parks over the valley and drops a foot of wet snow on a roof that already had eight inches of old pack sitting on it. Somebody hears a noise in the night, or a door upstairs stops closing right, and they go outside in the morning and look up at a roofline that is not quite the shape it used to be.

Powder is light and it blows off. Spring snow is wet, it grabs, and it sits there taking on rain. Two snowfalls that look the same depth from the driveway can differ by a factor of four in what they weigh, and the roof does not care what it looked like.

How much a roof is actually carrying

Snow load gets measured in pounds per square foot of roof area. Fresh dry snow runs somewhere around four to seven pounds per foot of depth. Settled snow, a week old and compacted, runs two or three times that. Saturated spring snow, or an old pack that has taken rain on top of it, can run twenty pounds per square foot per foot of depth or worse.

Put numbers on a real roof and it gets your attention. A thousand square foot slope under two feet of wet settled snow is holding fifteen to twenty tons. The framing was designed for a load, and the design load in Salt Lake County is not the one up in Wasatch County or on the higher benches, where the ground snow load is heavier.

So a roof built correctly for Salt Lake City is not automatically adequate in Midway. Same builder, same plan, different number in the code.

Why the weight is never even

If snow sat in a uniform blanket this would be simple. Wind moves it and roof shape catches it, and the drifts land in predictable places carrying three or four times what the open field carries.

• Against a taller wall. A garage roof against a two story wall, an addition against the main house. The drift grows all winter and never gets sun.
• In valleys. Two slopes funneling into one line, snow sliding down both into the same channel.
• On the lee side of a ridge. Wind lifts snow off the windward slope and dumps it past the peak, so the two sides of a roof carry very different loads.
• Below a dormer or a chimney. Anything sticking up creates a pocket behind it.
• Where an upper roof sheds onto a lower one. The serious one. A metal upper slope releasing its pack onto a shingled porch roof delivers the load as an impact.

When we get called out on a structural concern in the middle of winter, we are looking at those five places. The open field of the roof is almost never the problem.

What overloading does, in order

Roofs rarely collapse without warning. They complain first, and the complaints are readable if you know them.

Deflection

The framing bends. Sight along a ridge line from the ground and look for a sag in the middle. Inside, look at a ceiling line against a wall, or a door that suddenly will not latch in February and works fine in June. That is the roof structure moving under load and telling you.

Cracking at connections

In an attic under heavy load you can sometimes hear it, a series of sharp reports as fasteners work in the wood. Look at where rafters meet the ridge and where truss webs meet the chords. Split wood at a gusset plate, or a plate that has started to back out of the truss, means that joint is being asked for more than it has.

Trusses are engineered assemblies and they do not take kindly to modification. A remodel that cut a web to run ductwork, or a collar tie removed for attic storage, turns an adequate roof into an inadequate one, and nobody notices until the heavy year.

Everything the water does

Weight is only one way snow gets to you. The other is meltwater: heat escapes the house, the pack melts from underneath, the water runs to the cold overhang and freezes into a dam, and standing water backs up under the shingles. We have written about that in detail elsewhere on this site.

The two problems feed each other. A pack that keeps melting and refreezing gets denser and heavier than fresh snow ever was. Ice runs about fifty-seven pounds per cubic foot, so a foot of it on a low slope porch roof is a serious load on framing sized for snow.

The parts that fail before the framing does

Long before a structure is in trouble, snow takes out the accessories, and this is most of what we replace in the spring.

Gutters come first. A gutter is hung to carry water, not a sliding pack of ice. When a slope releases, the load hits the gutter on its way off and pulls hangers out of the fascia or folds the front edge down. That exposes the fascia and the deck edge to everything that comes off after.

Fascia and the first few inches of deck go next, usually because the gutter came off, or because water has been backing up behind ice at the eave and soaking the edge for a few winters.

Skylight curbs and chimney crickets take the load on their uphill side. A cricket is the small peaked structure that diverts snow around a chimney. Where somebody skipped it, the chimney holds a pack against itself all winter with flashing as the only thing between that and the attic.

Most of what we fix in April was not broken by weight. It was broken by a pack in motion, and it happened at the eave.

What you can do about it

Snow retention, where it belongs

Snow guards hold the pack in place so it melts off gradually instead of releasing in one slab. On a metal roof they are close to mandatory over a doorway, a walkway, a driveway where you park, or a lower roof. Metal is slick and lets go without warning, and a slab of wet snow off a second story roof is enough to hurt somebody.

On asphalt, the shingles hold snow reasonably well on their own and retention is more selective. Where we add it is above an entry or above a lower roof that would take the impact.

Get the heat out of the equation

Air sealing the attic bypasses and balancing intake and exhaust venting is the highest value winter work on most houses here, and it is cheap next to everything else in this article. A cold attic means the pack sits as snow instead of rebuilding itself as ice, and less water works under the shingles at the eave.

Know your roof’s weak corner

Every house has one. Walk around yours after a storm and find where the snow piles deepest. That is the spot to watch in a heavy year, and on a lot of houses it is the garage roof against the main wall. Better to know before the April storm than during it.

Clearing it, carefully

If a load has to come off, a roof rake worked from the ground at the eave is the safe version, best done in the first day after a heavy wet storm while the snow is loose. Once the pack sets, raking gets aggressive and takes granules with it.

Do not climb up there. A loaded roof is slick, the edges are invisible under snow, and a shovel on cold asphalt tears shingles. If a load has to come off a steep or high roof, that is a call, not a Saturday project.

Low slopes and flat roofs

Flat roofs do not shed. Everything that lands stays until it melts or gets removed, a blocked drain turns snowmelt into a pond, and standing water at eight pounds per gallon on a deck already carrying snow is how low slope structures get into trouble.

Anyone with a low slope section, and that includes plenty of mid-century houses across the valley, should have the drains and scuppers cleared before the first storm and checked mid-winter. If nobody has been up on yours, that is worth a note on our contact page before November.

Questions we get about snow on roofs

How much snow is too much on my roof?

Depth is the wrong measure, because water content changes everything. Four feet of dry powder can be lighter than eight inches of saturated spring snow. The useful signal is behavior rather than depth: a visible sag along the ridge, doors or windows that stop operating in winter, new cracks at ceiling corners, or cracking noises from the attic. Any of those and stop looking at the depth and make a call.

Is a steep roof safer under snow load than a shallow one?

Generally yes, because it sheds. A steep slope lets the pack slide off before it builds, which is why the historic mountain houses up in Wasatch County are pitched the way they are. The tradeoff is that everything the roof sheds lands somewhere, so steep roofs need thought about where the snow goes and what is standing underneath.

Do I need snow guards on an asphalt shingle roof?

Usually only in specific spots. Asphalt has enough surface texture to hold a pack most of the time. Where we add retention is over a front entry, over a walkway, and above any lower roof that would take an impact load. Blanketing a whole shingled roof with guards is rarely money well spent.

My gutters bent under ice. Is that a roof problem or a gutter problem?

Both, and fixing only the gutter means doing it again. Bent gutters usually mean either a pack releasing onto them or ice backing up at the eave, and the second one points at attic heat. We replace the gutter and then talk about why it happened, because a new gutter under the same conditions bends the same way.

Can you tell if my framing is adequate for where I live?

We can look at what is up there, tell you what we see, and flag anything obviously modified or distressed. Where a real structural question exists, a residential trussed roof in an area with a heavy ground snow load and visible deflection, the right answer is a structural engineer, and we will say so. We are roofers and we know the line.

Should I clear my flat roof after every storm?

Not after every one, but keep the drains clear and pay attention after a wet storm or a rain-on-snow event. A blocked drain on a low slope roof is the fastest way to turn a manageable snow load into standing water, and standing water is heavier than the snow was.

Where to start

If something about your roof changed this winter, a sag, a door, a bent gutter, a stain, the right time to look at it is now while the evidence is fresh. Spring is when we do the repairs, and the ones we plan in February go better than the ones we discover in June.

Call (801) 382-8898 and tell us what you noticed, or write it out on our contact page and we will come look. We work out of Salt Lake City across the Salt Lake valley and up into the counties around it, twenty-seven years in the trade and eight of them under the Hancock Signature name, and we know which houses up here carry snow badly. If it turns out you need an engineer rather than a roofer, that is what we will tell you, and we will not sell you a roof to solve a framing question.