Larimer County CO Deck Permit Rules

Larimer County Deck Permit Rules

A deck in unincorporated Larimer County needs a building permit if it is more than 30 inches above grade or serves as the house's main entry or exit, and attached decks sit on footings at least 30 inches deep. This guide covers the county's deck handout, its January 2026 snow and frost table, bracing and stair rules, and the wildfire code that now applies across the unincorporated county.

Last reviewed November 2026.

When Larimer County requires a deck permit

Larimer County's trigger is simpler than Fort Collins'. Its residential deck handout says a permit is required if either of two things is true: the deck is more than 30 inches above grade, or it serves as the main entry or exit to the structure. If neither is true, no building permit is required. Two things still apply either way: electrical work on the deck needs a county electrical permit, and the deck has to meet the Land Use Code's setback and floodplain rules, which county Planning (970-498-7679) can confirm.

Since January 1, 2026, permits in the unincorporated county are issued under the 2024 International Residential Code, with the county's 2025 Wildfire Resiliency Code alongside it.

What goes in the application

A residential building permit application.
Two full sets of plans to scale: plan view, cross sections and elevations showing footings, posts, beams, joists, ledger and connections.
Three copies of a scaled site plan.
A foundation plan stamped by a Colorado registered engineer if the location or design warrants it.

The old stone Pleasant Valley School near Bellvue, Colorado — The old Pleasant Valley School near Bellvue.

County deck construction rules

Larimer County deck handout, key numbers

Item	Rule
Lumber	Treated or naturally decay-resistant
Support	Piers or pads required
Footing depth, attached deck	At least 30 in below grade
X-bracing, attached deck	Surface 10 ft or more above grade at any point
X-bracing, detached deck	Surface 5 ft or more above grade at any point
Guard	Required over 30 in; 36 in minimum height; a 4 in sphere can't pass
Stair rise	4 in minimum to 7-3/4 in maximum; variation 3/8 in or less
Stair run	10 in minimum with 3/4 to 1-1/4 in nosing; 11 in without nosing
Handrail	More than 3 risers: continuous, graspable, 34 to 38 in above nosings

Source: Larimer County Community Development, Residential Deck Information handout. Its footing and span tables are drawn at 40 psf ground snow for elevations of 5,500 ft or less.

Snow, frost and wind by elevation

The county's Structural Design Information sheet, updated January 2026, sets the minimum frost depth at 30 inches countywide and lists ground snow by elevation on the strength basis of ASCE 7-22: 55 psf up to 5,000 feet, 70 at 6,000, 80 at 6,500, 95 at 7,000 and 110 at 8,000. Basic wind speeds run from 115 to 225 mph by the county map. A home can be built to the code's prescriptive tables only where ground snow is 70 psf or less and wind is under 140 mph, which rules out the higher foothills. Those numbers are compared with each town's in the footing depth and snow load guide.

Height matters for bracing too: a second story deck 10 feet up needs X-bracing under the county handout.

Fresh snow covering a deck and its railing, with snow-covered trees beyond — A fresh snowfall covering a deck and its railing.

The wildfire code in the unincorporated county

The county's 2025 Wildfire Resiliency Code, effective January 1, 2026, declares all of unincorporated Larimer County a wildland-urban interface area. Where its structure rules apply, a deck's walking surface has to be noncombustible, Class A rated, exterior fire-retardant-treated wood or ignition-resistant material, with composite allowed at Class B or better. What that means for a deck on an existing house is in the Larimer County wildfire code guide.

Larimer County Deck Permit: Questions

Snow on a deck railing with snowy pines and a mountain range beyond

Snow on a deck railing, mountains beyond.

Do I need a permit for a deck in unincorporated Larimer County?

Yes if the deck is more than 30 inches above grade, or if it serves as the main entry or exit to the house, according to the county's residential deck handout. If neither is true, no building permit is needed, though electrical work on the deck needs a county electrical permit and the deck still has to meet setback and floodplain rules.

How deep do deck footings go in Larimer County?

30 inches below grade. The county's January 2026 structural design table sets the minimum frost depth at 30 inches countywide, and the deck handout requires footings at least 30 inches below grade for a deck attached to the house.

What is the snow load in Larimer County?

It depends on elevation. The county's January 2026 table, on the ASCE 7-22 strength basis, lists 55 psf ground snow up to 5,000 feet, 70 psf at 6,000, 80 at 6,500, 95 at 7,000 and 110 at 8,000. Homes can use the code's prescriptive tables only where ground snow is 70 psf or less and wind is under 140 mph; beyond that, a design professional is needed.

When does a Larimer County deck need bracing?

The deck handout calls for X-bracing when an attached deck's surface is 10 feet or more above the surrounding grade at any point, or a detached deck's is 5 feet or more.

Which areas does Larimer County's building department cover?

Unincorporated Larimer County: places like Laporte, Bellvue and the foothill and rural areas outside town limits. Fort Collins, Loveland, Wellington, Timnath, Berthoud, Windsor and Johnstown run their own building departments inside their limits.