Is a garage conversion cheaper than a new ADU in Houston?

Usually. A 2026 Houston market guide estimates about $60,000 to $110,000 for a garage conversion versus about $140,000 to $220,000 for a new 600 sq ft detached unit. A garage with a poor slab, or one that must be raised for floodplain rules, narrows the gap.

What makes a Houston ADU cost more?

Floodplain elevation, foundation design for the soil, long sewer or electrical runs, a second story and historic district design requirements are the most common reasons a Houston ADU costs more than the published range.

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How much does an ADU cost in Houston?

Updated October 2026

As of October 2026, a 2026 Houston market guide puts a garage conversion at roughly $60,000 to $110,000 and a new 600 sq ft detached unit at about $140,000 to $220,000 all-in. Foundation and elevation work, utility runs and finishes move the number most. We price your lot in a written, itemized quote.

What do published estimates say?

No public body tracks Houston ADU prices. These are the most relevant published figures we found, as of October 2026:

Detached unit, 600 sq ft, Houston: about $140,000 to $220,000 all-in (Harbert Group, 2026).
Garage conversion, 400 to 600 sq ft, Houston: about $60,000 to $110,000 (Harbert Group, 2026).
Attached addition, Houston: about $100,000 to $160,000 (Harbert Group, 2026).
Garage-to-ADU conversion, national: about $58,000 to $173,000, averaging about $115,000 (Angi).

These are estimates from a brokerage guide and a national cost site, not bids. Read them as a starting range.

What pushes a Houston ADU above the range?

Elevation. In the 500-year floodplain, new construction must sit two feet above the 500-year flood elevation, which can mean a raised slab or pier foundation.
Soil. Foundation design follows the engineer's read of the site; poor soil adds concrete and steel.
Long utility runs. A sewer line to the back of a deep lot, or a new electrical service.
Second stories. A garage apartment adds stairs and heavier framing.
Historic review. In a city historic district, design requirements can raise material costs.

What does it cost before construction starts?

Survey, deed restriction research, design, structural engineering and permit fees all come before the first shovel. A Pearland conditional use permit or a Heights historic review adds application work. We list each of these on your quote.

Wood framing during construction: New house construction with wooden framing and scaffolding

Why do two similar ADUs cost so differently?

It depends on what is under and around the lot. Two 600 sq ft cottages can differ by tens of thousands of dollars if one needs fill and a raised slab and the other sits on dry ground near the sewer. That is why our price comes only after a site visit, in writing.

Check what your lot allows

Guides cover the general rules. For your address, we check restrictions, flood zone and city rules, then give you a written, itemized price.