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Short Summary
Main recommendation: Convert an existing detached garage with alley access into a simple, affordable 400 sq ft one-bedroom/one-bath ADU, using a basic layout, plug-in appliances where local code allows, and space-saving details. The speaker's all-in cost was about $30,000, largely offset by his own labor, and he suggests planning for roughly $100 per square foot.
Key Points
- The garage was a good candidate because it had alley access, high ceilings, and access to utility infrastructure, including a sewer line running beneath it.
- The layout is intentionally simple: a 20x20 footprint with a one-wall galley kitchen, a 5x8 bathroom, and a small bedroom with closet.
- Space is maximized with a pocket door in the bathroom, a barn door on the bedroom, vertical storage, and a drop-ceiling storage loft.
- Brightness and perceived size are boosted through a window on every wall, light wall colors, a bright white ceiling, recessed lighting, and dimmers.
- Each unit gets its own HVAC mini split and in-unit washer and dryer, which the speaker says helps compete with typical shared-wall apartments.
- Flooring is hardwood in general, but the speaker uses luxury vinyl plank (LVP) here because the unit sits on a slab on grade.
Details Worth Noting
- Concrete instructions:
- Assess the garage for alley access, ceiling height, and proximity to the sewer line before committing.
- If the sewer lateral must be replaced, expect to cut concrete and dig about four feet down; the speaker did this to run a new lateral from the main house to the alley, which made adding a bathroom straightforward.
- Where zoning does not allow a full kitchen, use plug-in appliances such as a two-burner induction cooktop on the bar top, since the jurisdiction in this example did not require 220-volt wiring for the kitchen.
- Use a 10.1 cubic foot apartment-size fridge and stock standard cabinets; the speaker had custom poplar cabinets made and painted them in place for a roughly 10-day turnaround.
- Cut a prefabricated granite countertop slab (about nine feet) using the same method as plywood with a diamond blade, and use a 15-gauge stainless over-mount sink to hide the cut marks.
- Use a prefabricated fiberglass shower surround in the 5-foot-wide bathroom with a 30-inch vanity, and a pocket door to avoid losing floor space.
- Install a 12,000 BTU Daikin mini split (about $3,000 installed) per unit, rated to heat and cool up to 600 sq ft.
- Add small storage touches such as hooks, belt hangers, and a 24-inch-tall drop-ceiling storage loft over the bathroom and closet.
- Put lights on dimmers, which the speaker says costs only about $20 more per switch.
- Alley setback here was only three feet, which the speaker treated as a demarcation line rather than a true rear yard.
- Ideal parking setup: parking in the alley, so tenants can access the unit from the alley without interacting with the front house.
- Cost breakdown: about $30,000 all-in for the 400 sq ft unit, with much of that offset by the speaker's own labor. He estimates roughly $75/sq ft at a bare minimum for a very handy owner, but recommends planning around $100/sq ft.
Bottom Line
A garage conversion can produce a functional, bright ADU on a tight budget, but success depends on the site's infrastructure, local zoning rules, and the owner's ability to handle much of the labor.
