Additions & ADU Construction — Northern Hills Construction

Remodeled bathroom space by Northern Hills Construction. Sonoma county

Build With Confidence. Renovate With Precision.

Create more space, increase home value, and adapt your property to changing needs with professional additions and Accessory Dwelling Unit (ADU) services across Sonoma, Napa, Marin, San Francisco, and Oakland counties. Northern Hills Construction handles design coordination, permitting, construction, and closeout so your addition or ADU is delivered on time, on budget, and built to last.

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What we build

Home additions — master suites, second‑story additions, garage conversions, sunrooms.
Accessory Dwelling Units (ADUs) — detached, attached, or garage‑conversion ADUs for rental income, family, or office use.
Kitchen and bath expansions — open layouts and functional flow improvements.
Room repurposing — convert underused spaces into livable, code‑compliant areas.

LIC# 1115098

Lets Build your Dream Home!

Interior finish work and cabinetry installation

Our process (clear, predictable, and owner‑focused)

Discovery & Feasibility — site review, zoning check, and preliminary budget.
Design & Permitting — coordinate architects/engineers, prepare permit sets, submit to local jurisdictions.
Preconstruction — finalize scope, schedule long‑lead items, and set milestones.
Construction — managed trades, weekly progress updates, safety and quality inspections.
Closeout — punch list completion, final inspections, warranties, and O&M manuals.

Typical timeline: small additions 8–12 weeks; ADUs 4–9 months depending on design complexity and permitting. Typical contingency: 5–10% for residential projects.

What to expect in your estimate

Itemized scope — labor, materials, allowances, and permit fees.
Milestone payments — tied to deliverables (mobilization, framing, finishes, closeout).
Change‑order policy — written approvals with cost and schedule impacts.
Warranty & closeout — workmanship warranty and full documentation at handover.

Residential Builders Near You and what to expect when hiring a builder/ GC

Framing service by Northern Hills Construction

Owner checklist before you start

Confirm budget range and financing options.
Gather property documents: plot plan, existing floor plans, and utility locations.
Decide on primary use (rental, family, office) to guide design and code choices.
Reserve contingency funds and set realistic timeline expectations.

Owner checklist before you start

Confirm budget range and financing options.
Gather property documents: plot plan, existing floor plans, and utility locations.
Decide on primary use (rental, family, office) to guide design and code choices.
Reserve contingency funds and set realistic timeline expectations.

The Importance of quality construction and communication.

Proof of quality

Portfolio — view recent additions and ADUs to evaluate craftsmanship and finishes.
References — client testimonials and job‑site visits available on request.
Licensing & insurance — fully licensed, bonded, and insured for Bay Area projects.

General Contracting Essentials: The Complete Flagship Guide for Homeowners and Business Owners

Services

concrete footings and foundations by NHC

Interior remodeling by Northern Hills Construction

Northern Hills Construction portfolio

Frequently asked questions

Do ADUs require separate utility meters? Utility requirements vary by jurisdiction; we evaluate options and coordinate with providers.
Can I rent my ADU immediately? After final inspection and certificate of occupancy, ADUs are typically rentable; local short‑term rental rules may apply.
Will an addition increase my property taxes? Additions can affect assessed value; consult your assessor for specifics.

NHC Portfolio

Why choose Northern Hills Construction for additions and ADUs

Local permitting expertise — we navigate Sonoma County and Bay Area permit processes to reduce approval time.
Family‑owned accountability — direct owner involvement and consistent on‑site supervision.
Sustainability and resilience — energy‑efficient systems, wildfire‑resilient materials, and long‑term durability.
Turnkey project management — from preconstruction planning through final inspections and as‑built documentation.

Brandyn Miller, CA

I couldn't be more impressed with their work! From the initial consultation to the final walk-through, the team was professional, attentive, and truly dedicated to bringing my vision to life.

General Contractor Services for Additions & ADUs

Northern Hills Construction provides full‑service general contracting tailored to additions and ADUs across Guerneville, Santa Rosa, Sebastopol, and the greater Bay Area. We combine hands‑on construction experience with local permitting knowledge so your addition or ADU moves from concept to certificate of occupancy with minimal friction and predictable costs.

Services

Core Services We Deliver for Additions and ADUs

As a full-service general contractor, we offer a wide range of services to cater to all your construction needs, Take a look at our General Contracting Service pages for Santa Rosa, and Sebastopol

Site evaluation & feasibility — Zoning, setbacks, lot coverage, and utility checks to confirm what’s buildable.
Design coordination — Work with your architect or our partners to translate ideas into permit‑ready plans.
Permitting & agency coordination — Prepare and submit permit packages, attend plan check meetings, and manage inspections.
Turnkey construction — Framing, structural work, MEP rough‑ins, finishes, and systems integration handled by vetted trades.
Project management — Scheduling, procurement of long‑lead items, subcontractor coordination, and weekly progress reporting.
Cost estimating & transparent budgeting — Itemized estimates, allowances, and change‑order controls to protect your budget.
Closeout & warranties — Final inspections, as‑built drawings, O&M manuals, and workmanship warranties at handover.

Local Expertise That Matters

Working in Sonoma County and nearby Bay Area communities requires familiarity with local codes, wildfire‑resilience standards, and utility provider requirements. Northern Hills Construction’s experience in Guerneville, Santa Rosa, and Sebastopol shortens approval timelines, avoids common permit pitfalls, and ensures your ADU or addition meets both code and community expectations.

Permitting, Code Compliance, and Wildfire Resilience

We prioritize early code review and wildfire‑resilient design choices—ember‑resistant vents, noncombustible cladding options, and defensible‑space recommendations—so your project is safer and more insurable. We also manage Title 24 energy compliance and coordinate any required utility upgrades to prevent last‑minute delays.

How Our Additions & ADU Process Works

Discovery & budget — Site visit, zoning check, and preliminary cost range.
Design & permits — Coordinate drawings, submit permits, and track approvals.
Preconstruction — Finalize schedule, order long‑lead items, and set milestones.
Construction — Managed trades, quality inspections, and weekly updates.
Closeout — Punch list completion, final inspections, and delivery of warranties and as‑builts.

Sustainability, Value, and Long‑Term Performance

We recommend energy‑efficient systems, durable materials, and design choices that reduce operating costs and increase resale value. Whether your ADU is for rental income, multigenerational living, or added workspace, we focus on solutions that deliver long‑term return and lower maintenance.