Home Additions in Lone Tree, CO

An addition is the most regulated project a Lone Tree homeowner can take on. It touches the City of Lone Tree building code, the zoning code, the wildfire code the city adopted in 2026 and, on some lots, the floodplain and airport overlays. The Building Division handles the permit, but the lot’s zoning or development plan decides where the addition can go. We work through both before design is locked.

Soils Reports and Engineered Foundations

Lone Tree amends the residential code so that a permit application includes a soils test of the building site, prepared by a professional engineer registered in Colorado. A Colorado-registered engineer then designs the foundation to that soils report. On hillside, steep-slope or geologic hazard sites, the Building Official can also require recommendations from an engineering geologist.

The foundation inspection is handled differently too. Under the local amendment, it is performed by a Colorado-licensed professional engineer or registered architect, who gives the Building Official a stamped written report. We schedule the engineer’s visit as part of the foundation phase so concrete is not held waiting.

Setbacks Depend on Your Zone or Development Plan

Where an addition can sit starts with the zoning. In the city’s SR suburban residential district, general setbacks are 25 feet from a local or collector street, 5 feet on the sides and 20 feet in the rear for the main house. SR-1 lots use a 20-foot street setback with a front-entry garage and 15 feet with a side-entry garage, with 20 feet in the rear. SR-2 allows a 15-foot rear setback, not counting patios, except 25 feet along South Yosemite Street or Lincoln Avenue.

The larger-lot districts are wider. SR-E and SR-L require 25 feet front and rear and 15 feet on the sides, and SR-M requires 20 feet front and rear and 10 feet on the sides. Many Lone Tree neighborhoods are zoned PD, planned development, and there the setbacks and lot standards come from the neighborhood’s recorded development plan instead of the SR tables. We pull the right document for your lot before sketching anything.

We did not find a residential lot coverage maximum in the SR article of the city’s zoning code. If your lot is in a PD, the development plan may set one, and your HOA covenants may add their own limits.

Height Limits and What Can Project Into a Setback

In the SR district, the main house can be up to 35 feet tall, and an accessory building up to 10 feet, which the Director may raise to 20 feet. SR-3 single-family areas allow up to 50 feet. Those limits shape whether a second-story addition is possible before any structural question comes up.

Some parts of a building can reach into a required setback. Eaves, cornices, canopies, fireplaces and wing walls can extend up to 3 feet. An open, uncovered deck at ground level can extend up to 6 feet, and one more than 4 feet above grade up to 3 feet, but neither can go into a side setback. The city will not issue a permit for a structure inside an easement without written approval from the easement holders.

Lone Tree’s 2026 Wildfire Resiliency Code

In 2026 Lone Tree adopted the Colorado Wildfire Resiliency Code, 2025 Edition, and its map as Chapter 19 of the municipal code; City Council approved it on second reading on April 21, 2026. The city says the requirements are triggered by qualifying work, such as a building addition of 500 square feet or more, or replacing 25% or more of an existing roof.

The city’s staff report says that when an addition triggers the code, only the addition has to conform, not the whole house. Its basic hardening measures include Class A roof coverings, ember protection, noncombustible gutters and downspouts, vents with 1/8-inch mesh, and noncombustible surfaces in the zone from 0 to 5 feet around the building. The report estimated the map covers about 214 homes west of I-25 and most residential areas east of it.

This code is new, and we did not find a published effective date on the city’s official pages. Confirm with the city whether your address is mapped and which requirements apply before design is final.

Floodplain and Airport Overlays

If a lot falls in the city’s floodplain overlay district, a floodplain development permit is required before a building permit can be issued. Applicants start with a meeting with city planning and engineering staff, and the Director of Public Works serves as floodplain administrator. The 2026 fee schedule lists that permit at $300 for a no-impact review and $700 for a standard one.

The floodplain rules also treat any improvement costing 50% or more of the structure’s market value as a substantial improvement, which brings the whole building under the requirements. Separately, homes in the Centennial Airport Overlay Area that require noise mitigation must meet the city’s minimum sound transmission ratings for walls, roofs, windows and doors.

Design Loads for a Lone Tree Addition

The city publishes the climate numbers a new structure is designed to. Ground snow load is 30 psf, design wind speed is 115 mph in Exposure C, the seismic design category is B and the frost line is 36 inches. Ice barrier underlayment is required on roofs, and weathering is rated severe.

Floor live loads are 40 psf, or 30 psf in sleeping areas, and roof live loads are 30 psf. Attic floors are designed for 10 psf with no storage and 20 psf with limited storage. These figures go straight onto the structural drawings, and the plan reviewer checks them.

How We Sequence a Lone Tree Home Addition

We begin with the lot: zoning or development plan, setbacks, height, easements, and whether the wildfire, floodplain or airport overlays apply. The soils test and engineered foundation design follow, along with HOA design review, which the city strongly recommends before any permitted work.

The full permit set and valuation go in through the city’s online portal. Permit fees follow valuation; on the 2026 schedule, a project between $100,001 and $500,000 pays $993.75 for the first $100,000 plus $5.60 per additional $1,000, and plan review adds 65% of that fee.

After issue we excavate, pour the foundation with the engineer’s inspection and stamped report, then frame, dry in and rough in the trades for city inspection. Exterior work stays within the city’s hours, 7:00 a.m. to 7:00 p.m. on weekdays and 8:00 a.m. to 6:00 p.m. on weekends and holidays, and the finished addition goes through final inspection before we hand it over.

Common Questions

Does a Lone Tree addition need a soils report?
Yes. Lone Tree’s residential code amendment requires the permit application to include a soils test by a Colorado-registered professional engineer, and a Colorado-registered engineer designs the foundation to that report.

How close to my property line can I build an addition in Lone Tree?
It depends on your zone. In the general SR district the side setback is 5 feet and the rear setback is 20 feet for the house, and SR-1, SR-2, SR-E, SR-L and SR-M each have their own numbers. Lots in a PD zone follow their recorded development plan. Confirm your lot’s zoning with the city’s Planning Division.

Will the new wildfire code affect my addition?
It can. The city says the Colorado Wildfire Resiliency Code applies to qualifying work in mapped areas, such as an addition of 500 square feet or more, and the staff report says only the addition has to conform. The code is new, so confirm with the city whether your address is covered.

Do I need a floodplain permit for an addition?
Only if your lot is in the city’s floodplain overlay district. There, a floodplain development permit is required before a building permit is issued, and the 2026 fee is $300 for a no-impact review or $700 for a standard review.

Talk to Us About Your Project

Tell us what you need more room for and where you picture it on the lot. We will check your zoning or development plan, coordinate the soils report and engineering, work through HOA review, and manage the Lone Tree permit and inspections from foundation through final.