Cost per square foot is too blunt for an ADU or garage conversion budget

Square-foot pricing can help test an early concept, but it is not reliable enough to define an ADU or garage-conversion budget by itself. Utility work, existing structure, site access, foundation or slab conditions, permits, energy requirements, fire separation, windows, HVAC, plumbing, and finish level can change the total without changing the floor area.

ADUs and conversions have different cost structures

A ground-up detached ADU may require new foundation, framing, roofing, exterior finishes, and utility connections. A garage conversion reuses an existing shell but can require floor, moisture, insulation, opening, fire-separation, window, and structural work to make the space legally habitable. Applying one unit rate to both hides those differences.

Site and utility work does not scale neatly with area

A short utility route on an accessible site can be very different from a project that crosses paving, requires a service upgrade, or has limited excavation access. Many of those costs are driven by the route and existing infrastructure rather than the ADU’s square footage.

For early budgeting, carry site and utility items separately instead of burying them inside the building unit rate.

Existing conditions matter more in a conversion

Garage slab elevation, moisture, cracks, ceiling height, framing, roof condition, electrical service, and the former vehicle opening can all affect conversion scope. A low per-square-foot assumption is not useful until the team knows which parts of the existing structure are actually suitable to reuse.

Finish level can distort unit-rate comparisons

Cabinetry, appliances, plumbing fixtures, flooring, windows, lighting, and bathroom finishes can vary widely. If two projects use different selection levels, their unit prices say as much about the finish package as they do about construction efficiency.

Normalize finish assumptions before comparing completed projects or contractor proposals.

Use unit pricing only after separating major work packages

Break the project into design and engineering, permits and fees, site work, utilities, structure, enclosure, mechanical and electrical systems, interior finishes, owner selections, and contingency. Once those pieces are visible, cost per square foot can be used as a reasonableness check rather than as the primary estimating method.

Ask what the number excludes

When a contractor or online source gives a unit price, ask whether it includes design, permits, utility upgrades, trenching, demolition, appliances, landscaping restoration, temporary conditions, and final closeout. A number with major exclusions is not comparable to a turnkey project budget.

Replace the generic rate as soon as site information is available

The right time to stop relying on a unit rate is when the property, utility paths, layout, and construction scope can be documented. DreamPrint’s ADU and JADU guide covers the larger feasibility process. For a property-specific estimate and buildable scope, continue to the ADU construction service.