Detached ADUs ($100K–$300K+)
A separate, fully self-sustaining structure — own kitchen, bath, HVAC, electrical, and entrance. Best for true independence: aging parents who want their own space, college kids returning home, or a long-term rental income stream.
Greenville County zoning around detached ADUs is specific and not the same as the city's. Setbacks, lot coverage, and septic capacity all matter. We walk the lot before any design conversation to tell you what's actually possible.
Attached ADUs / mother-in-law suites ($25K–$100K)
Shares an external wall with the main home. Often called a mother-in-law suite. Shares utilities for cost efficiency. Best when you want close family proximity without the full standalone build.
Easier to permit than detached, fits more lots, and tends to look more naturally part of the home. The trade-off: less acoustic privacy and shared mechanical capacity.
Internal ADUs (varies — often $40K–$150K)
Carved out of existing home space — basement conversion, above-garage suite, or repurposed wing. No new footprint, just a code-compliant secondary unit inside what's already there. Cost depends entirely on what's currently there and what code requires (egress, ventilation, kitchen plumbing).
How to choose
Start with your lot. Septic capacity and zoning will narrow the field before you fall in love with a plan. Then consider goals: independence, rental income, family proximity, or just more flexible space. Resale value is best preserved with detached or attached ADUs that look intentional from the street.
Bottom line
All three classifications can add resale value when designed and permitted properly. The wrong choice for your lot or goal becomes an expensive backyard shed. Free feasibility consult: site walk plus written zoning and septic review delivered as a one-pager — no contract required.
