Hardscaping in Denver has to handle expansive clay and freeze-thaw. Durable patios and walls need proper excavation, a compacted aggregate base, drainage away from the house and, for walls, gravel and a drain behind them. In the City of Denver, walls over 12 inches need a zoning permit; suburbs set their own rules.
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Hardscape is a big part of Denver landscaping, both because it uses no water and because so many homeowners are replacing lawn with patios, paths and gravel gardens. The challenge is what lies underneath. Front Range clay can swell when wet and shrink when dry, and winter brings repeated freeze-thaw cycles. Patios and walls built without a proper base and drainage tend to heave, crack and settle.
Common hardscape projects
- Paver patios and walkways over a compacted aggregate base
- Flagstone patios and paths, set dry on gravel or mortared on a concrete slab
- Segmental block and boulder retaining walls to terrace sloped lots
- Steps, landings and seat walls
- Gravel and rock gardens as part of a water-wise landscape
- Fire features, subject to local rules and HOA guidelines
Building for expansive soil and freeze-thaw
A durable patio needs excavation below topsoil, a compacted aggregate base, edge restraint and a slight slope so water runs off and does not soak into the clay next to the house. Water that collects under a patio can freeze and lift it in winter, or swell the soil beneath it. Ask any contractor how deep they excavate, what base material they use, how they compact it, and which direction the finished surface drains.
Retaining walls
- A compacted gravel leveling pad, with the first course partly buried
- Free-draining gravel behind the wall and a perforated drain at the base
- Geogrid reinforcement for taller segmental walls, per the manufacturer or engineer
- A slight setback so the wall leans into the slope
Permits in the City of Denver and elsewhere
The City and County of Denver says walls over 12 inches high, including retaining walls, need a zoning permit, walls over four feet need a building permit, and retaining walls over six feet require engineering plan review. Front-yard fences are generally limited to four feet and backyard fences to six. Suburbs such as Aurora, Lakewood, Arvada, Littleton, Parker and Castle Rock, and unincorporated Douglas, Arapahoe and Jefferson counties, set their own thresholds, so check with the local building department. HOAs in Highlands Ranch and many newer subdivisions also review hardscape plans.
Utilities and wildfire
- Colorado 811 must be contacted at least three business days before digging, and private lines such as sprinkler pipes and landscape lighting are not marked.
- On wildfire-prone lots, the Colorado State Forest Service recommends hard, nonflammable surfaces such as pavers, gravel and stone within five feet of the house.
Comparing quotes
Hardscape quotes vary because scope varies. Compare excavation depth, base thickness, edge restraint, drainage, materials, haul-off, permits and warranty. A noticeably low bid often skips base depth or drainage. For more detail, see our guide to patios, walls and drainage on expansive soil, then request a hardscape company.
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Frequently asked questions
Do I need a permit for a retaining wall in Denver?
In the City and County of Denver, walls over 12 inches high need a zoning permit, walls over four feet need a building permit, and retaining walls over six feet need engineering review. Suburbs and counties set their own thresholds.
Why did my patio heave over the winter?
Usually water got into the base or the clay below it, then froze or made the soil swell. Fixes involve lifting the surface, improving the base and making sure water drains away rather than under the patio.
Are pavers or concrete better on Denver soil?
Both can last over a well-built base. Pavers flex a little and can be lifted and reset if the soil moves; poured concrete can crack if soil swells, so control joints and drainage matter.
Sources and further reading
- Colorado State University Extension
- CSU PlantTalk: Choosing a lawn grass for Colorado
- CSU PlantTalk: Expansive soils
- Denver Water: summer watering rules
- Denver Water: drought information
- Aurora Water: Grass Replacement Incentive Program
- City and County of Denver: fences and walls
- Denver Office of the City Forester: tree pests and diseases
- Colorado Department of Agriculture: pesticide applicator licensing
- Colorado Department of Agriculture: noxious weed species
- Colorado State Forest Service: Home Ignition Zone guide
- Colorado General Assembly: SB24-005 (nonfunctional turf)
- Colorado 811
- National Weather Service Boulder: Denver monthly climate normals
- USDA Plant Hardiness Zone Map
- EPA WaterSense