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Room additions & ADUs

Home Additions

Room additions, ADUs and second stories — engineered, permitted and matched to your house. Add the space your family needs without leaving the neighborhood you love.

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Home Additions by The J Hammer Inc in the Los Angeles area

Grow your home instead of moving

When an LA family outgrows its house, moving means giving up a low property-tax basis and a neighborhood you love. Adding square footage is usually the smarter math — and California’s ADU-friendly laws have made it more achievable than ever. The J Hammer designs and builds additions and accessory dwelling units that look original to the house and pass inspection.

Three ways to add space

  • Attached room addition — a primary suite, a bigger kitchen and family room, or a home office that flows with the existing house. Foundation, framing, roof tie-in, HVAC extension and full finish.
  • Garage conversion ADU — the budget door into ADUs, because the structure, slab and roof already exist. Insulation, kitchen, bath and a separate entrance turn it into a permitted dwelling.
  • Detached ADU — a ground-up backyard unit with its own foundation and utilities: real rental income or multigenerational housing.

The permit reality

Additions go through standard plan check; ADUs ride a state-streamlined process most LA-area cities must approve within set timelines. Either way you need engineering, Title 24 energy compliance and a contractor who has run the gauntlet before. We handle drawings, calcs and the whole process end to end — it is half the job.

Matched to your home

A good addition does not look added. We match rooflines, stucco texture, window style and trim so the new space reads as part of the original house — inside and out. And permitted square footage appraises, so the investment shows up when you sell.

Planning your budget?See typical home additions price ranges
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Licensed & insured · LIC #1045849Get a free estimate for your home additions project
Our recent work

Real projects across SoCal.

Good to know

Home Additions FAQs

How much does a home addition or ADU cost?
Room additions run roughly $350–$650 per square foot; garage-conversion ADUs $90,000–$150,000; detached ADUs $180,000–$350,000. Exact pricing depends on your lot and scope.
Do I need permits for an ADU?
Yes, but California has streamlined ADU approvals and most cities must approve within set timelines. We handle drawings, Title 24 and the full permit process.
Can an ADU be a rental?
Yes — a permitted ADU can be rented and produces real income in the LA market. Permitted is the key word; unpermitted units subtract value and complicate every sale.
Will the addition match my house?
That is the goal. We match rooflines, stucco, windows and trim so the new space looks original, not bolted on.
Ready when you are

Let's talk about
your home additions project.

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