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Second-Story Addition in Centennial

Licensed second-story addition services for Centennial and Arapahoe County. Double your living space without moving.

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Second-Story Addition

Double your living space without moving

Local Service

Second-Story Addition Services in Centennial, Colorado

Autotelic provides professional second-story addition services throughout Centennial and the surrounding Arapahoe 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 Centennial (south Denver metro) or nearby communities, our team delivers quality workmanship backed by Colorado licensing and full insurance coverage.

Permits & Licensing

Permits in Centennial

Centennial building permits, inspections, and contractor license approvals are handled by the city's Building Division. Permits and contractor licenses must be applied for online through the city's Self-Service Portal, and we handle that process as part of every project. Authority: City of Centennial — Building Division.

Permit Thresholds

Centennial permit thresholds

Code reference
In Centennial, Colorado, building permits for residential remodel work are governed by the 2021 International Residential Code (IRC) Section R105 (adopted via Centennial Municipal Code Chapter 18 – Building Regulations, per Ordinance 2023-O-06 and related adoptions of the 2021 I-Codes).Section R105
Code reference
Typically exempt work (aligning with IRC R105.2 exemptions, with local application) includes:
Code reference
One-story detached accessory structures (e.g., sheds) ≤200 sq ft.
Code reference
Fences ≤7 ft high; retaining walls ≤4 ft high (measured from bottom of footing).
Code reference
Prefabricated swimming pools <24 inches deep.
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Window awnings projecting ≤54 inches.
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Decks ≤200 sq ft, ≤30 inches above grade, and not attached to the dwelling.
Use tax (not collapsed into a single rate)
City of Centennial Use Tax of 2.5% applied to the actual cost of materials, plus Arapahoe County Use Tax of 0.25% applied to the actual cost of materials.

Codes are amended regularly — verify current requirements with City of Centennial — Building Division.

Zoning & ADU

Centennial zoning & ADU quick facts

Code reference
Centennial, Colorado (Arapahoe County) Land Development Code (LDC, Chapter 12 of the Municipal Code) governs zoning. New districts were adopted in 2024; the city’s zoning descriptions page notes that details should be verified in the current LDC (Municode).
Code reference
The most commonly referenced single-family residential districts for established neighborhoods are the Neighborhood Conservation (NC) subdistricts (NC5, NC6, NC9, NC12, NC18); newer or redevelopment areas use Suburban Residential (RS), Auto-Urban Residential (RA), and Urban Residential (RU).
Code reference
Residential development standards in RS/RA/RU/AG/NI generally reference LDC Division 3-4 (Residential Neighborhood Development Standards) and Division 3-5 (Housing Palette); non-residential summaries on the city site are not directly applicable to single-family additions/ADUs/garages.
ADU permitting (LDC § 12-3-603(H) and related sections)
Yes, permitted as an accessory use in AG, RS, RA, RU, NC (all subdistricts), and NI districts (plus limited commercial districts on single-family lots only).§ 12-3-603
ADU max size (LDC § 12-3-603(H))
≤ 50% of the principal dwelling’s footprint (exterior wall polygon on the ground), or the full existing attic or basement area (including internal stairwell) without any expansion of those spaces.§ 12-3-603
ADU height (LDC § 12-3-204 and § 12-3-603(H))
Attached/interior: same as the primary dwelling in the district.§ 12-3-204
Detached
17 ft maximum.
ADU setbacks (LDC § 12-3-301 and Table 12-3-301)
Same minimum setbacks as principal structures in the underlying district (no reduction allowed).§ 12-3-301

Codes are amended regularly — verify current requirements with City of Centennial — Building Division.

Energy Code

Centennial energy code quick facts

Code reference
Centennial, Colorado, has adopted the 2018 IECC (with the 2021 I-Codes package) as its energy code, with no mention of Denver-specific overlays such as the Denver Green Code or Energize Denver.
Code reference
This is enforced by the City’s Building Division under Ordinance No. 2023-O-06 (adopting the referenced codes by reference, effective as part of the 2021/2023 code update package).Ordinance No. 2023-O-06
Code reference
Centennial is in Climate Zone 5B.
Code reference
The code applies to alterations, additions, and remodels per IECC Chapter 5 (existing buildings), with the prescriptive requirements of Chapter 4 (or equivalent U-factor/UA paths) generally applying to new or modified portions of the thermal envelope.
Code reference
Key prescriptive requirements relevant to remodels/additions (drawn from 2018 IECC Table R402.1.2 and related sections for CZ 5; these are the base code values with no local amendments identified that alter them):
Ceiling/attic insulation
Minimum R-49 (or equivalent U-factor ≤ 0.026).
Adopting reference
2018 IECC R402.1.2 (Table R402.1.2).
Wood-frame wall insulation
R-20 cavity or R-13 cavity + R-5 continuous insulation (or equivalent U-factor ≤ 0.060).
Ordinance No. 2023-O-06Source: centennialco.gov

Codes are amended regularly — verify current requirements with City of Centennial — Building Division.

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When a second-story addition makes sense

A second-story addition adds bedrooms, a primary suite, office space, or other living area without expanding the home’s footprint. It is often considered when side-yard setbacks, lot coverage limits, a detached garage, or outdoor living priorities make a rear or side addition less practical. In the Denver metro, many homes on smaller lots or in established neighborhoods face those constraints. Vertical expansion can preserve yard space while increasing finished square footage, but it is a structural project—not a cosmetic remodel. The existing foundation, first-floor walls, floor framing, and roof system all have to support new loads.

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What the work typically includes

Scope varies by home and design, but second-story additions commonly involve: - Structural evaluation of the foundation, bearing walls, and first-floor framing - Temporary protection and weatherproofing while the existing roof is opened or removed - New floor framing, exterior walls, windows, and a new or modified roof - Stairs or stair reconfiguration to reach the new level safely and code-compliantly - Exterior finishes that tie into existing siding, masonry, or stucco - Electrical, plumbing, and HVAC extension into the new space by licensed specialty trades - Insulation, drywall, flooring, and interior finishes - Updated smoke/CO detection and means-of-egress details required for the new sleeping or living areas Some projects build over an existing single-story wing; others raise a portion of the home and rework the roof lines around the addition. Matching floor elevations, stair placement, and exterior proportions early reduces costly redesign later.

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Structural and design checks before you commit

Before drawings are finalized, the existing structure needs a clear assessment. Key questions include whether the foundation and first-floor bearing lines can carry the added dead and live loads, whether posts, beams, or sistered joists are required, and how lateral loads (wind and seismic design categories applicable locally) will be handled in the new wall and roof diaphragm. Denver-metro housing stock ranges from mid-century ranches to newer two-story production homes. Older homes may need more framing reinforcement, foundation work, or selective demolition to create clean bearing paths. Design also has to address head height at stairs and eaves, window placement for light and egress, and how the addition reads from the street so massing does not overwhelm the original house. Energy code requirements affect wall and roof assemblies, window performance, and how the new conditioned space connects to the existing thermal envelope. Those choices should be settled in design, not improvised in the field.

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Living in the home during construction

Second-story work is disruptive. Opening the roof, removing ceiling finishes below bearing lines, and running new stairs often affect the main living level. Dust control, temporary weather barriers, and phased access plans matter as much as the finish schedule. Some households relocate for part of the build; others stay and wall off work zones. Expect periods without normal use of rooms under the addition, intermittent utility shutoffs when trades tie in new systems, and restricted yard or driveway access for material staging. A written phasing plan—what stays occupied, where temporary protection goes, and how the home is dried in—should be part of project planning.

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Permits and coordination in the Denver metro

Second-story additions require building permits and plan review. Submittals typically include architectural and structural drawings, and may include energy compliance documentation and public-tree or zoning clearances depending on the property and scope. Roof structure, stair geometry, egress windows in sleeping rooms, guardrails, and smoke detection are common plan-review focus areas. A municipally licensed Denver general contractor coordinates the project, permit process, inspections, and licensed specialty trades such as electrical, plumbing, and HVAC. Individual trade permits are pulled and inspected under those specialty licenses as required by the city or county. HOA architectural review, if applicable, runs in parallel with municipal permitting and should be started early so exterior materials and height are not reworked after permit drawings are complete.

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Cost factors without a one-size number

Second-story addition cost is project-specific. Major drivers include: - Structural reinforcement needed at the foundation and first floor - Size and complexity of the new level, including roof form and exterior finish matching - Stair location and whether existing halls or rooms must be reconfigured - Extent of work required on the level below for beams, posts, or ceiling repair - Mechanical strategy—extending existing HVAC versus adding capacity or zoning - Window and exterior material choices - Site access, temporary protection, and whether the household will occupy the home during construction - Local permit, design, and engineering requirements Because those variables differ by house, proposals should follow on-site evaluation and schematic design rather than a generic per-square-foot assumption.

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How to prepare as a homeowner

Clear goals help the design team size the addition correctly: who will use the space, whether a full bath is required, storage needs, and whether future resale layout matters as much as immediate use. Gather any existing plans, survey work, prior remodel permits, and HOA guidelines before the first site visit. Also note known issues—settlement cracks, past roof leaks, undersized electrical service, or aging HVAC—that could surface when the structure is opened. Sharing those details early keeps structural and mechanical scope realistic.

FAQ

Common questions

Can my existing foundation support a second story?

Not always without reinforcement. A structural evaluation looks at foundation type and condition, soil bearing assumptions, and how new loads transfer through the first floor. Some homes need added footings, beams, posts, or wall reinforcement; others can accept the load with more limited framing upgrades. That determination belongs in design, before demolition.

Will we need to move out during a second-story addition?

It depends on the roof opening sequence, stair work, and how much of the main level is affected. Some owners stay with temporary barriers and phased work; others relocate during demo, framing, and dry-in. Ask for a phasing and protection plan so occupancy expectations are explicit.

Who handles the trade permits and licensing?

A municipally licensed Denver general contractor coordinates the project and inspections. Licensed specialty trades handle electrical, plumbing, HVAC, and other regulated scopes, including the trade permits those disciplines require.

How long does a second-story addition usually take?

Duration depends on size, structural complexity, weather during roof-open work, permit review time, and finish level. Design and permitting often take a substantial period before construction starts. Construction itself commonly spans several months once work begins; your schedule should be built from the actual drawings and municipal review timeline, not a generic estimate.

Do second-story additions require new stairs?

Most do, unless an existing stair already lands where the new floor can connect cleanly. Stair placement affects hallways, closets, and rooms on the first floor, and the stair must meet current code for rise, run, headroom, and guards. Resolve stair location in schematic design because it drives both structure and daily circulation.

What surprises homeowners most on these projects?

Conditions hidden above ceilings and in bearing walls—older framing, prior undocumented remodels, or limited capacity for new point loads—are common discovery items once the structure is opened. Exterior matching, temporary weather protection, and the amount of first-floor repair under new beams are also easy to underestimate without thorough design.

Service Area

Serving Centennial and Arapahoe County

We serve Centennial, 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 Centennial project.

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