Denver’s design snow load for a new roof is 43 pounds per square foot, the citywide figure the city’s own residential code sets on the older engineering basis that most Colorado building departments still use for permits. That number isn’t the snow sitting on your roof this winter. It’s the input an engineer or truss manufacturer works from when a house is built or re-roofed. If you’re pulling a permit anywhere else in the state, the figure that matters is whatever your own county or city building department publishes, because Colorado’s snow load climbs fast with elevation and there is no single number for the whole state.
What is the ground snow load in Colorado?
ASCE 7-16, the edition IRC/IBC 2021 makes applicable in most states, doesn’t put a number on Colorado at all. The entire state falls inside what ASCE calls a case-study (CS) region on that map, meaning the terrain climbs too fast and too unevenly for one contour line to mean anything useful, and a site-specific determination is required instead. That isn’t a gap in this page, it’s how the system actually works here: Colorado’s snow load gets decided address by address, not state by state.
Denver’s own residential code fills that gap for the city with a citywide design value of 43 pounds per square foot, on the older ASD (allowable stress design) basis most Colorado departments still build permits around. That’s the number a Denver plan reviewer checks against and the number a truss manufacturer builds to. Outside Denver, the same national blank applies, and the working figure comes from whatever the local building department has adopted for its own elevation and site.
None of this is the load that actually reaches a rafter. Ground snow load is the load on flat open ground. The code applies exposure, thermal and slope factors before it converts that number into a roof design load, and for an ordinary heated house with a sloped roof the working figure lands close to 0.7 of the ground number, lower still on a steep roof.
ASCE 7-22 maps the same Denver point at 54 pounds per square foot on a strength-level basis, roughly 38 psf translated to the older ASD basis. That is not more snow falling on Denver. The two editions use different load factors underneath the same physical hazard, and IRC/IBC 2021, the code most Colorado departments are actually enforcing, still runs on 7-16. Treat 7-22 as the edition coming down the pipe, not as today’s answer.
How much snow can a roof hold in Colorado?
There’s no single figure that answers this, because it depends on the roof’s pitch, its exposure to wind, and what the snow sitting on it has actually turned into.
From ground load to roof load
Starting from Denver’s 43 psf ground figure and applying the roughly 0.7 conversion the code uses for an ordinary sloped roof gets you to roughly 30 pounds per square foot as a working design load, less on a steep roof, and that’s a Denver number only. Elevation changes this fast across the Front Range and into the mountains, and a building department at a higher site will publish a higher figure. For a sense of how much higher these design figures can run in an even colder, snowier territory, see Northwest Territories’ roof snow load and wind rules.
Depth is not weight
Fresh, light powder runs roughly 5 to 7 pounds per square foot for every foot of depth. Settled or wet snow runs two to three times that. A layer of ice on top of either adds more weight than its thickness suggests. That’s why a foot of dry January snow and a foot of heavy March snow are not the same load, even though They Look Identical from the ground.
Drift is where roofs actually get overloaded, not flat accumulation. Snow piles against a parapet or a wall, below a dormer, inside a roof valley, or on a lower roof section next to a taller wall, and the local load in that pocket can run well past the flat design figure the rest of the roof was built for.
Signs a roof is carrying too much
- Interior doors that suddenly stick or won’t latch
- New cracks appearing in ceiling drywall
- A ridge line that looks like it’s sagging when viewed from the street
If you see any of that, the safe response is to rake accumulated snow from the ground using a roof rake, working from the eaves. Climbing onto a snow-loaded roof to shovel it is how people get hurt, and it doesn’t tell you anything a licensed engineer or your building department can’t tell you faster and more safely.
What wind speed must a roof withstand in Colorado?
Denver’s basic design wind speed under ASCE 7-16 is 107 mph, and that figure means something specific: a 3-second gust measured at 33 feet in open Exposure C terrain, for Risk Category II, the classification that covers ordinary houses. That is not a sustained wind, and it is not what a weather forecast means when it reports a wind speed. ASCE 7-22 maps the same Denver point at the same 107 mph, so this is one of the few figures in the state’s code data that isn’t shifting between editions.
That number is what drives a shingle’s wind-rating class, the nailing pattern a roofer is supposed to follow, how the sheathing gets fastened down, and the uplift connections tying the roof structure to the walls below it. Edges, rakes and ridges take the worst of it, because that’s where wind uplift concentrates, and it’s why those areas fail first on an underbuilt roof.
Colorado is inland and isn’t a hurricane-prone coastal region, so the wind-borne debris glazing and shutter requirements that apply along the Gulf and Atlantic coasts don’t attach to a Colorado permit the way they do on the coast. That’s a real cost a reader here isn’t required to plan for. This figure is Denver’s alone. A county at a different elevation or terrain exposure can carry a different basic wind speed on its own building department’s records, so check there before assuming the Denver number applies to your address.
Does Colorado require an ice barrier under the shingles?
An ice barrier is a self-adhering membrane installed under the shingles, running from the edge of the eave up far enough to clear the interior wall line. It doesn’t stop snow from sitting on the roof. Its job is to stop meltwater from getting under the shingles and into the deck once an ice dam has already formed at the eave.
Why the conditions here are real
NOAA’s 1991-2020 climate normals put Denver’s coldest-month mean daily minimum at 18.4°F, cold enough to keep an unheated eave well below freezing for stretches of the winter. Paired with a design snow load meant to account for weeks of accumulation sitting on a roof, the basic setup for ice damming, sustained snow cover over a structure with a cold eave and a warmer attic above it, is present in this territory. That doesn’t mean every roof forms a dam, only that the ingredients are here.
The dam itself forms because heat escaping from the living space into the attic melts snow from underneath, the meltwater runs down the roof deck, and it refreezes once it reaches the colder overhang past the exterior wall. The refrozen ice backs water up under the shingles above it. The membrane is a backstop that protects the deck once that’s already happening. Only air sealing and attic insulation stop the dam from forming in the first place, so a reader who installs the membrane and does nothing about attic heat loss has bought protection against the symptom, not the cause.
Who actually sets the rule here
Colorado has no statewide residential building code. No state agency administers one, and state law only requires a locality that chooses to update any of its own codes to also adopt a reasonably current energy code. A county or city that leaves its adopted codes untouched isn’t required to add anything new, including an ice-barrier rule. That means whether an ice barrier is mandated at your eave, and how far up the roof it has to run, is decided by your own county or city building department, not by a single statewide document. Some states write that requirement straight into a statewide amendment. Pennsylvania‘s code does exactly that, covered in Pennsylvania’s roof snow load and wind rules. Colorado works differently, so the only reliable answer for your address is the one your local building department gives you.
What roofing material suits Colorado best?
No material is simply “best” here. The honest answer depends on how a given option responds to Denver’s wind and snow figures and to the climate zone a given county falls into, and each option trades one advantage for a different cost.
| Material | What matters under Denver’s loads | Trade-off |
|---|---|---|
| Architectural asphalt shingles | Carry a published wind-rating class tested against gust speeds like Denver’s 107 mph figure | Rating only holds if nailed to the pattern it was tested with |
| Standing-seam metal | Sheds accumulated snow well, reducing sustained roof load | Shed snow lands somewhere, so it must be directed away from doors, walks and driveways |
| Slate or concrete tile | Very durable surface | Its own dead weight adds directly to whatever snow load the structure already carries |
Where wind governs the design, the fastening and the underlayment matter more than the shingle itself. A shingle rated for a high wind speed nailed with a substandard pattern performs at the lower standard, not the one printed on the package.
The 2021 IECC divides Colorado’s 64 counties into four climate zones: 34 counties in zone 5B, 13 in zone 7, 12 in zone 6B and 5 in zone 4B. That split matters here because it selects the attic insulation levels a county’s energy code calls for, and thicker attic insulation is exactly the fix that keeps heat from escaping into the attic and starting the ice-dam cycle described above. A zone 7 county and a zone 4B county are calling for different insulation depths, so check your own county’s table rather than assume one figure covers the state. If you’re weighing materials for the first time, the broader overview at Roofing is a reasonable place to start before narrowing down to what these local figures actually require of a given roof.