Fence installation and repair in Boulder.

Boulder's wind is in the code, and it's the highest number we build to

Most contractors talk about wind. Boulder legislates it. The city's residential building code amendments specify a three-second wind gust velocity of 150 mph east of Broadway and 165 mph west of Broadway, with topographic effects and a special wind region designation, a 40 psf ground snow load, severe weathering, and a frost line depth of 32 inches.

That's not hypothetical. NOAA's Boulder records include a 147 mph gust at the NCAR Mesa Lab in January 1971 and a January 1982 windstorm that damaged an enormous share of the city's buildings. The mechanism is a downslope windstorm coming off the Divide — the air accelerates down the mountain front and hits Boulder hard, and the closer you are to the foothills the worse it is. That's why the code splits at Broadway.

A six-foot solid privacy fence, standing in a 165 mph design wind, is an enormous structure to hold with four-by-fours. So we don't build one casually west of Broadway. Deeper posts, wider footers, three rails, and a hard push toward shadowbox or board-on-board construction that lets air through instead of catching all of it. On the worst lots, steel posts. Boulder is the place where the wind conversation isn't a sales pitch — it's the design.

• ▸150 mph design gust east of Broadway · 165 mph west
• ▸Special wind region + topographic effects — in the code
• ▸Frost line depth 32 in. per Boulder's code
• ▸Chain-link takes wind better than anything else — it's the honest recommendation here
• ▸Shadowbox / board-on-board over a solid panel, especially west of Broadway

The permit rule is the opposite of what you'd guess

Everyone assumes Boulder is the strictest permit jurisdiction on the Front Range. On fences, it isn't. Fences not over seven feet tall are exempt from building permit requirements in the City of Boulder. A normal four-to-six-foot residential fence needs no building permit here.

Permits are required in a floodplain, in a wetland, and on a historic district or landmark property. Boulder has meaningful amounts of all three, so this isn't a footnote.

The height rule is also not what people expect. Boulder does not use the 42-inch-front, six-foot-rear split that most of the metro uses. The code allows a maximum of seven feet in height for any individual fence, wall, hedge, or combination of them located within three feet of each other on the same property, measured from finished grade directly beneath to the tallest element — and it explicitly prohibits modifying the grade to gain height. On or within three feet of a property line, up to twelve feet is possible with joint agreement between abutting owners, provided the height doesn't exceed seven feet measured from the highest grade within three feet of either side of the line.

• ▸Fences not over 7 ft — exempt from building permit
• ▸Permit required: floodplain, wetland, historic district / landmark
• ▸7 ft max for any fence, wall, hedge, or combination within 3 ft of each other
• ▸Height measured from finished grade — no regrading to gain height
• ▸A fence built ON the property line needs a notarized, recorded neighbor agreement
• ▸Barbed and electric prohibited, with narrow district exceptions

The wildfire rule — Boulder's newest, and almost nobody has it

Boulder's fence code requires that newly constructed fences and walls of any height, including gates and arbors, on a lot within the Wildland-Urban Interface area comply with the city's Wildland Code. In practical terms, the city states that all new fence and gate sections built within eight feet of a structure must be constructed with noncombustible materials.

Boulder adopted the 2024 International Wildland-Urban Interface Code effective August 1, 2025. If you're in the WUI — and a lot of south and west Boulder is — that eight-foot zone against your house is not a wood fence zone anymore.

This is a serious design constraint and a serious safety one. A wood fence running up to a house is a wick. The Marshall Fire made that lesson concrete for this county in a way nobody here needed twice. What it means for a Boulder fence design is usually a noncombustible transition — metal or masonry — for the section closest to the structure, and wood or composite further out. We design it that way and we tell you why.

Boulder's build specs and the ground under them

Boulder's own fence guide is unusually specific, and the specs are worth knowing because they set a floor. Posts set in concrete a minimum of 24 inches below grade. Wood posts a minimum four-by-four, ground-contact rated. Chain-link posts a minimum inch and a half in diameter. A maximum of 30 square feet of solid fencing between posts unless the fence is engineered. At least 18 inches from any public sidewalk. Ten feet of clearance around fire hydrants.

Note the tension between two of those numbers: the fence guide's 24-inch minimum and the building code's 32-inch frost line. We build to the frost line, not the minimum — a post whose base sits inside the freeze zone is a post the ground can lift, and Boulder freezes hard.

The ground itself is Pierre Shale in much of the area between Boulder and Louisville. The Colorado Geological Survey identifies the Pierre Shale by name in its work on heaving bedrock along the Front Range piedmont, where steeply dipping sedimentary bedrock containing zones of expansive claystone comes near the surface. Expansive claystone plus a 165 mph design wind is exactly the combination that argues for depth, diameter, and a footer that sheds water.

One more Boulder-specific rule that saves arguments: a fence built on the property line requires a notarized agreement between the neighbors, recorded with the County Clerk. If you're going on the line, get the paper. If you don't want the paper, we build inside your line.

The four fences, in Boulder

Permits, height, and the HOA

Fences not over seven feet tall are exempt from building permit requirements in the City of Boulder — which surprises people who assume Boulder is the strictest jurisdiction around. Permits are required in a floodplain, in a wetland, and on a historic district or landmark property, and Boulder has meaningful amounts of all three.

Height: the code allows a maximum of seven feet for any individual fence, wall, hedge, or combination located within three feet of each other on the same property, measured from finished grade — and modifying the grade to gain height is prohibited. There's a joint-agreement provision that can allow more on a shared property line. A fence built on the property line requires a notarized neighbor agreement recorded with the County Clerk.

The wildfire rule is the one to know. New fences and walls of any height on a lot in the Wildland-Urban Interface must comply with the city's Wildland Code, and new fence and gate sections within eight feet of a structure must be noncombustible. Boulder adopted the 2024 IWUIC effective August 1, 2025. If you're in the WUI, that changes what your fence can be made of near the house.

Codes change. Verify current requirements with City of Boulder Planning & Development Services— and with your HOA if you have one — before you build. We'll walk it with you and flag anything on your lot that's going to matter.