On most Colorado roofs, snow is a morning problem. It falls overnight, the sun hits the shingles, and by noon the downspouts are running. The storms worth worrying about are the other kind. They come in cold, sit on the north side of the house for days, and pick up another layer before the first one is gone. If your roof was already tired, that's when it starts showing you where.
Here's how snow load on a roof in Colorado plays out over one storm, then one week, then one full season, and what each stage does to a roof with some years on it.
The storm: the first two days
Snow doesn't all weigh the same. Dry powder, the kind you can blow off a windshield, is mostly air. Wet snow, the kind that packs into a snowball without trying, holds far more water at the same depth. A foot of one and a foot of the other are very different loads on your rafters. We won't guess at numbers here. The design snow load your house was built to comes from the building department that permitted it, and the engineering standard behind those figures is published by the American Society of Civil Engineers.
It also doesn't land evenly. Wind and roof shape move it around before it ever settles.
- Valleys collect snow sliding off two slopes at once.
- Low-slope sections (porch roofs, patio covers, the flat-ish addition someone built later) hold snow instead of shedding it.
- North faces stay shaded, so their snow outlasts everything on the south side.
- Dormers, chimneys and any spot where a lower roof meets a taller wall catch drifts. Wind scours the upwind side and dumps it on the downwind side, sometimes much deeper than what's on the open slope.
During the storm itself, an older roof mostly reveals problems it already had. A cracked rubber boot around a vent pipe. Step flashing that's pulled away from the chimney. Shingles whose seal strips let go years ago. Snow sits right on top of those spots and waits.
The week: heavier without getting deeper
This is the stage people miss. The snowpack shrinks a little each day, so it looks like things are getting better.
They aren't. Sun melts the surface, the water soaks down into the pack and refreezes, and the whole layer gets denser. Less height, same or more weight. If another storm drops fresh snow on top, or worse, a bit of rain falls on it, the old pack acts like a sponge.
Underneath, a second thing is happening. Warm air leaking from the house into the attic heats the roof deck and melts the bottom of the snow. That meltwater runs down to the eaves, which hang out past the warm walls and stay cold, and it freezes there. Do that for a week and you've got an ice dam: a ridge of ice along the gutter line with a pool of water backed up behind it, working its way under the shingles.
Newer roofs usually have ice and water barrier, a sticky membrane, along the eaves to catch that water. Plenty of older roofs have a single narrow strip or none at all. In the Town of Castle Rock, a re-roof now has to include ice and water barrier and drip edge at the eaves and rakes, which tells you how much the town cares about this exact failure.
Icicles hanging off one section of gutter and not the rest usually point to a warm spot in the attic above it: a bathroom fan venting into the attic, a can light, a gap around an attic hatch. Fixing that is often cheaper than fighting the ice every winter.
The season: freeze, thaw, repeat
One storm rarely breaks a roof. A whole winter of them can.
Every freeze-thaw cycle pushes water a little deeper. It gets into a nail hole, freezes, and opens the hole a hair wider. Brittle shingles crack where they bend over the ridge. Granules loosen and wash into the gutters. And decking that got wet in December can stay damp under a snowpack for weeks, which is long enough for oriented strand board to swell at its edges and start coming apart in layers. Plywood holds up better but softens too. Nails rust.
By spring, a roof that looked fine from the driveway in October can have soft spots you'd feel underfoot. Small damage like a lifted section or a leaking pipe boot is usually a straightforward roof repair. If you're in unincorporated Douglas County (Highlands Ranch, Franktown, Sedalia, Perry Park and the rest), a repair larger than one roofing square, which is 100 square feet, needs a permit from the Douglas County Building Division.
What it looks like from the attic
You can learn a lot with a flashlight and a few minutes in the attic after a long cold stretch. Stay on the joists. Look for:
- Dark stains or damp patches on the underside of the decking, especially under valleys and near the eaves.
- Frost on the tips of roofing nails poking through. When it warms up, that frost drips, and people mistake it for a leak.
- Decking that dips between rafters like a hammock.
- Rafters that aren't straight when you sight down them, or a fresh split in the wood, the kind that looks bright instead of gray.
- A ridge line that sags in the middle when you look at the house from the street.
A freshly cracked rafter, a ceiling that's started to bow, or new popping and creaking during a heavy snow are reasons to keep people out of that part of the house and call someone that day. Don't go up on the roof to fix it yourself.
Raking: when it helps and when it hurts
A roof rake can help. It can also do more damage than the snow.
It helps on single-story roofs and low-slope sections you can reach from the ground. Pull down the bottom few feet above the eaves, which takes weight off the overhang and removes the snow that would otherwise melt and feed an ice dam. Leave an inch or two on the shingles. Scraping down to the surface tears off granules and can crack cold, stiff shingles.
It hurts in a few predictable ways:
- Using a metal blade, or one without rollers, that gouges the shingles.
- Raking from a ladder, or climbing onto a snowy roof at all.
- Chipping at an ice dam with a hammer or ice pick. You'll cut the shingles long before you clear the ice.
- Pulling snow off an upper roof onto a lower one, which just moves the load somewhere weaker.
- Swinging an aluminum pole anywhere near the service line coming into the house.
If the snow you're worried about is up high, on a two-story slope or behind a dormer, raking from the ground won't reach it, and that's a sign to have someone look rather than improvise.
After the melt
Spring is the honest time to judge an older roof. The snow's gone, the damage it hid is visible, and you can decide calmly instead of during a leak. A roof inspection from us is free, and if the roof isn't safe to walk, a drone inspection gets eyes on the valleys and north slopes without anyone on the shingles. We'll tell you plainly if it just needs a repair, and we won't suggest an insurance claim for damage that isn't there.
If the decking is soft in more than a spot or two, or the shingles are cracking across whole slopes, patching usually stops making sense, and that's when a conversation about roof replacement is worth having before next winter's first storm that refuses to melt. Our shop is at 282 Malibu St in Castle Rock, and the number is 303-500-1667.