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THORNTON SERVICES
Second-Story Addition in Thornton
Licensed second-story addition services for Thornton and Adams County. Double your living space without moving.
- Full Design Lifecycle
- Construction & Tenant Finish
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Local Service
Second-Story Addition Services in Thornton, Colorado
Autotelic provides professional second-story addition services throughout Thornton and the surrounding Adams County area. Full second-story additions across the Denver metro with structural engineering, framing, roofing, and complete interior build-out. Commercially licensed and insured. Whether you're in Thornton (one of Colorado's fastest-growing cities) or nearby communities, our team delivers quality workmanship backed by Colorado licensing and full insurance coverage.
Permit Thresholds
Thornton permit thresholds
- Code reference
- This applies to residential remodels and is governed by the city’s adopted codes (2024 International Residential Code, 2024 International Existing Building Code, and related codes with local amendments, effective for applications on or after July 1, 2025).
- Code reference
- Attached decks of any height; any deck serving the main exit door; decks with attached roofs; decks/porches 200 sq ft or larger; any deck or porch in the front yard.
- Code reference
- Fences over 7 ft tall; retaining walls over 48 inches (measured from bottom of footing; engineering required).
- Code reference
- Room additions; attached/detached garages; accessory buildings larger than 200 sq ft.
- Code reference
- Detached decks less than 200 sq ft and less than 30 inches above grade that do not serve the main exit door.
- Code reference
- One-story detached accessory structures less than 200 sq ft.
- Code reference
- Fences 7 ft tall or less.
- Code reference
- Painting; minor roofing repair (one square or less); replacement of less than 100 sq ft of asphalt shingles.
Codes are amended regularly — verify current requirements with **The Building Inspection Division of the City of Thornton (Colorado) issues residential building permits.
Zoning & ADU
Thornton zoning & ADU quick facts
- SFD-L — Minimum Lot Area
- 6000 sfSFD-L
- SFD-L — Minimum Lot Frontage
- 60 ftSFD-L
- SFD-L — Front Setback (min)
- 20'SFD-L
- SFD-L — Side Interior Setback (min)
- 5'SFD-L
- SFD-L — Side Setback Abutting Street (min)
- 20'SFD-L
- SFD-L — Rear Setback (min)
- 15'SFD-L
- SFD-L — Lot Coverage (max)
- 85%SFD-L
- SFD-L — Building Height (max)
- 35'SFD-L
Codes are amended regularly — verify current requirements with **The Building Inspection Division of the City of Thornton (Colorado) issues residential building permits.
The build sequence for a Second-Story Addition project
This service is a component of How a Home remodel project works in Thornton.
Energy Code
Thornton energy code quick facts
- Code reference
- 2024 International Energy Conservation Code (IECC), including the Colorado Model Electric Ready and Solar Ready Code (with local amendments), effective July 1, 2025.
- Code reference
- This is adopted by reference in Thornton City Code Sec. 10-174 (with amendments in Sec. 10-175), along with the 2024 International Existing Building Code.§10-174
- Code reference
- Permit applications submitted on or after July 1, 2025, must comply.
- Code reference
- No specific local numeric amendments to prescriptive requirements (e.g., R-values, U-factors, or air-sealing thresholds for Climate Zone 5B) or details on remodels/additions beyond the base 2024 IECC + state model code are identified in available sources.
Codes are amended regularly — verify current requirements with **The Building Inspection Division of the City of Thornton (Colorado) issues residential building permits.
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What a second-story addition covers
A second-story addition in the Denver metro adds habitable floor over an existing house: new floor structure, stairs, roof, windows, and usually electrical, mechanical, and plumbing. The existing foundation and walls have to carry the extra load. A municipally licensed Denver general contractor coordinates the project, design professionals, and licensed specialty trades. Cost is project-specific and depends on structure, roof, and how much of the first floor is opened.
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Structure and zoning height
City and County of Denver Community Planning and Development treats second-story additions as structural review items that exceed IRC prescriptive limits. The residential permitting guide asks for a letter of structural integrity sealed by a design professional who personally inspected the existing foundation and building (DBCA 133.3). Zoning height is measured in feet and stories from the front and rear base planes (Denver Zoning Code Sec. 13.1.2). Plans should show allowed versus proposed height.
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Permits and who coordinates the work
Additions typically need zoning, building, and Sewer Use and Drainage (SUDP) reviews, plus electrical, mechanical, and plumbing when those systems change. Denver Energy Code Chapter 5 [RE] applies to additions. Cities and counties license general contractors. Colorado has no statewide general contractor license. Autotelic acts as a municipally licensed Denver general contractor and coordinates licensed specialty trades plus the design professionals required for the project.
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What buyers should prepare
Target rooms, existing drawings if any, roof and attic photos, and known foundation concerns.
FAQ
Common questions
Do second-story additions need a Denver permit?
Yes. CPD requires building, zoning, and typically SUDP, with structural review because the work exceeds IRC prescriptive limits.
Who handles second-story permits and licensing?
A municipally licensed Denver general contractor coordinates the project, design professionals, and specialty trades. Colorado has no statewide general contractor license.
Can the existing foundation take a second story?
Only after a design professional inspects it. CPD asks for a sealed structural-integrity letter for second-story additions.
How is height measured?
In feet and stories from the zoning front and rear base planes, not just from the sidewalk.
What information helps define scope?
Desired rooms, existing drawings, foundation notes, landmark status, and city or county.
Service Area
Serving Thornton and Adams County
We serve Thornton, CO and all surrounding Denver metro communities. Our team is based in Denver and operates throughout the Front Range, from Castle Rock to Longmont and everywhere in between. Contact us for a free estimate on your Thornton project.
How It Runs
01
Survey
02
Design
03
Build
04
Verify
DESIGN SERVICES
Discovery & Site Analysis
Needs + preference programming, site survey, as-built documentation, feasibility.
We walk, measure, and photograph your property — existing conditions, utilities, structure, and constraints. You get the as-built documentation and feasibility read that every later decision rests on.
Learn more →Concept Design & Space Planning
Schematic design, floor plan studies, layout options.
Your scope becomes schematic floor plans you can compare side by side — circulation, daylight, adjacencies, and what each option does to the budget. Layout decisions happen on paper, where changes are cheap.
Learn more →Architectural Design & 3D Renderings
Design development, materials + finishes, photorealistic visualization.
The chosen concept resolves into materials, finishes, fixtures, and lighting — with the automation layer drawn in. Photorealistic renderings let you walk the space and adjust before anything is priced.
Learn more →Construction Documents & Permitting
Full CD sets, structural + MEP engineering coordination, permit-ready drawings.
Approved designs become coordinated architectural, structural, and MEP sheets — the set your jurisdiction permits from and trades build from. We submit, track, and answer review comments.
Learn more →CONSTRUCTION
New Construction & Custom Homes
Ground-up homes and light commercial, dirt to keys.
Ground-up residential and light commercial builds — foundations through finishes, including modular and steel construction. One accountable builder from dirt to keys.
Learn more →Remodels & Additions
Kitchens, baths, basements, pop-tops, whole-home.
Kitchens, baths, basements, pop-tops, and whole-home renovations that respect the house you already have. We handle structure, permits, and the dust.
Learn more →Commercial Tenant Finish & Build-Outs
Shells to working spaces — retail, office, restaurant, school.
Raw shells become working spaces — showrooms, offices, restaurants, schools. Dealer-spec finishes, code compliance, and opening dates held.
Learn more →ADUs & Modular Construction
Backyard cottages, garage conversions, factory-built homes.
Backyard cottages, garage conversions, and factory-built homes — zoning, design, permits, and set. Denver’s ADU rules are a specialty, not a surprise.
Learn more →Outdoor Living & Patio Structures
Decks, pergolas, and dining patios built for Colorado weather.
Decks, pergolas, and dining patios engineered for Colorado sun, snow, and hail — structure, shade, and drainage done right the first time.
Learn more →TECHNOLOGY
Smart Home Automation
Lighting, shades, climate, audio, security — one interface.
Whole-home control of lighting, shades, climate, audio, and security from a single interface — Crestron, Lutron, Savant, and Control4 designed in, not bolted on.
Learn more →A/V Systems
Theaters, distributed audio, video walls, commercial sound.
Theaters, distributed audio, video walls, and commercial sound — designed, installed, and tuned by the same team for over 20 years.
Learn more →Control Systems
Custom programming — scenes and schedules that fit the space.
Every subsystem brought into one elegant interface — custom programming for homes and venues, with scenes and schedules that match how the space is actually used.
Learn more →Networking & Edge Compute
Enterprise Wi-Fi, structured cabling, racks, on-prem compute.
Enterprise-grade Wi-Fi, structured cabling, racks, and on-premise compute — the backbone that makes everything else reliable, including our own Barbot platform.
Learn more →Solar & Energy Storage
Solar arrays, Tesla Powerwall, EV charging — certified install.
Solar arrays, Tesla Powerwall, and EV charging designed and installed by a Tesla Energy Certified team — roof, electrical, and app in one scope.
Learn more →Let's design your perfect Second-Story Addition together
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