.png){kind=small}
Home Additions Built to Belong to Your House
Cosman Construction designs and builds home additions across Boulder County — led by Alex Cosman, who manages every project from the first design conversation through final permit sign-off.
Boulder's housing stock tells the story well — ranch homes from the sixties, split-levels from the seventies, bungalows that haven't changed since the neighborhood was built. When families outgrow those floor plans, moving isn't always the answer. A well-designed addition gives you the space you need without leaving the neighborhood, the schools, or the home you've already invested in.
We handle the full addition scope under one contract — structural modifications, kitchen expansions, primary suite additions, existing home integration, and the complete planning and permitting process Boulder County requires. Every project starts with a detailed design, a written scope, and a real estimate before any work begins.
Homeowners across Boulder, Longmont, Lafayette, Louisville, and the surrounding Front Range have trusted us with their most significant home investments — and they come back because having one team think through both the new space and how it connects to everything existing makes a real difference. Schedule a conversation with Alex to get started.
What We Build
.jpeg)
Why Hire a Design Build Company for Your Home Addition
Home additions almost always require an architect for design and permitting drawings, a structural engineer for load calculations and foundation work, and in some cases a civil engineer for site grading or drainage — before a contractor is even in the picture. On a traditionally contracted project, hiring and coordinating those professionals is the homeowner's responsibility.
With Cosman Construction, that coordination is handled for you. We work directly with architects, structural engineers, and civil engineers as needed — assembling the right team for your addition and managing every professional relationship under one contract so the architect, engineer, and builder are aligned from day one.
An Addition Is Too Significant to Figure Out as You Go
With a project of this scale, the planning is where the budget gets protected. An addition that isn't fully resolved before construction begins will cost more, take longer, and create integration problems that are expensive to fix after the fact. We resolve every structural, design, and permitting decision before the first tool comes out.
Step 1: Consultation & Design
We start on your property — assessing the existing structure, site constraints, setback requirements, and what the addition needs to achieve before any design decisions are made. From there we produce full architectural drawings, a written scope, and a real estimate so you know what the project costs before you commit to anything.
Step 2: Project Begins
Once design is finalized, permits are in hand, and engineering is signed off, construction begins on a defined schedule — foundation, framing, rough-ins, exterior envelope, and interior finishes — each with a target date. Alex is on-site and reachable throughout, and any change that affects scope, timeline, or cost gets communicated before it affects the project.
Step 3: Project Completion
Alex walks every square foot of the finished work against the original scope — structural connections, integration details, finishes, and mechanical performance. Anything that doesn't meet standard gets corrected before your walkthrough. Permits closed, inspections handled. We're done when there's nothing left on the list.
A note on the design phase: You're not locked into completing construction with us. If you take the design we've produced and work with another contractor for the build, that's completely your call. If you choose to move forward with us, the design fee is credited toward the project cost.
