ConstruBay

Home Additions · Marin County

Home Additions
in Marin County

Primary Suites, Great Rooms and Second Story Additions

Sometimes the best home is the one you are already in — expanded. A well-designed addition adds space, value and functionality without the disruption of moving. ConstruBay manages every phase of Marin County home additions — engineering, permits, construction — with fixed-price accountability.

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Addition Types

01

Primary Suite Addition

Add the primary suite your home deserves. Bedroom, bathroom, walk-in closet, private deck. Engineered for Marin's hillside conditions.

02

Great Room Addition

Expand your living and dining space with an open great room addition designed for Marin's indoor-outdoor lifestyle.

03

Second Story Addition

Add a full second story or partial upper level. Structural engineering and planning department approvals managed entirely by ConstruBay.

04

Garage Conversion

Convert an underutilized garage into living space — guest suite, home office or ADU. Often the most cost-effective addition in Marin County.

2026 Pricing

ScopeInvestment RangeTimeline
Primary Suite 400–500 sq ft$285,000 – $385,00014–18 weeks
Great Room 300–500 sq ft$225,000 – $375,00012–16 weeks
Second Story Addition$450,000 – $750,0006–10 months
Garage Conversion$150,000 – $280,0003–5 months

FAQ

How much does a home addition cost in Marin County?

Home additions in Marin County range from $285,000 for a primary suite addition to $600,000+ for a second story or great room addition. All quotes include engineering, permits, materials and our 10-year warranty.

How long does a home addition take in Mill Valley?

Home additions typically take 4–8 months depending on scope. Marin County permits add 4–12 weeks to the beginning of every project.

Does ConstruBay handle addition permits in Marin County?

Yes. We manage all permits from application to final approval including structural engineering and planning department approvals required for additions in Marin County.

Do you build second story additions in Marin County?

Yes. We build second story additions throughout Marin County. These projects require structural engineering and often design review — we manage the entire process.

Start Your Addition Project

Fixed-price proposal within 5 business days. Every addition starts with a free site visit and property assessment.

Start Your Addition Project
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