Patios & Hardscape in Arvada, Colorado

Two Arvadas, geologically

The city runs east-to-west across a real transition, and where your house sits changes how we build.

East of Highway 93 — the plains portion. Expansive claystone, the standard Denver-metro condition. The Colorado Geological Survey calls expansive soil the state's most costly geologic hazard for exactly this ground: smectite clays that swell as much as 20 percent by volume with water and exert force up to 30,000 pounds per square foot. It doesn't move dramatically. It moves unevenly, season after season, and uneven movement is what breaks hardscape.

Along Ralston Creek and Clear Creek. The terraces here are Pleistocene alluvium — sand, cobble, gravel. Better draining, slower digging, and a genuinely different base design conversation.

West of Highway 93. The ground starts climbing toward the foothills. More grade, more rock, more walls and steps in the design. Arvada's own design-criteria page notes that elevation varies west of Highway 93 for exactly this reason.

We dig a test hole before we design a base. That's not thoroughness theater — the right base depth on cobble alluvium is a different number than the right base depth on claystone.

Permits: 4 feet, and the surcharge clause matters more

Arvada publishes it plainly: a permit is required for retaining walls over 4 feet, measured from the bottom of the footing to the top of the wall, or for any wall supporting a surcharge, and engineered stamped structural plans are part of the submittal.

The measuring point matters. Bottom of footing — not from the dirt you can see. A wall that looks like 3½ feet of exposed face can be over the threshold once you count the buried base course and the leveling pad. We measure it right, and we pull the permit when it's needed.

And "surcharge" is common, not exotic: a patio, a driveway, a slab, or a parked car above the wall is a surcharge, and it kills the exemption regardless of height.

Frost, and what the base has to do

Arvada's adopted design criteria list a 36-inch frost depth and a 30 psf snow load. The metro's weathering classification is Severe.

Your patio doesn't get dug to 36 inches — it isn't a foundation. What it gets is a base that doesn't hold water: 6 to 8 inches of compacted CDOT Class 6, placed in 3-to-4-inch lifts with every lift compacted, geotextile separation over clay subgrade, ¼ inch per foot of fall away from the house, and a rigid edge restraint on every free edge.

That's the spec. Here's the long version, and here's what happens when it's skipped.

What we build in Arvada

Paver patios and flagstone on the clay side. Retaining and seat walls out west where the grade demands them — drained, permitted, engineered. Walkways and steps that hold a consistent rise on a sloped lot. Get an estimate.