ADU rules in Columbus

Columbus has no accessory dwelling unit use. A second home on a lot is the Two-Family Residential use, which CLDO §3-4(b) defines to include 'two detached single-family units on a single lot'. Table 4-3 permits that use by right only in R-2 (Two-Family), R-3 (Multiple-Family), O (Office) and UC (Urban Commercial), and by special permit in LC, B-1 and B-2; it is not listed at all in AG, RR, R-1 (Single-Family) or NTR. An owner in the ordinary R-1 district would have to rezone to R-2 first, as several 2026 applicants did.

An attached second unit (a duplex conversion, or a two-unit townhouse) falls under the same Two-Family Residential use in CLDO §3-4(b), so it follows the same district gate: by right in R-2, R-3, O and UC (R-2 allows townhouses only as two-unit townhouses), by special permit in LC, B-1 and B-2, and not allowed in AG, RR, R-1 or NTR. The code has no internal or basement accessory apartment use, and the residential accessory-use list in §6-8(a) contains no dwelling.

Because the second unit is a principal dwelling under the Two-Family use, no accessory-unit size cap applies; the only floor is the 400 sq ft minimum in the §2-7 dwelling unit definition. Table 4-4 caps building coverage at 50% and impervious coverage at 65% in R-2 and R-3 (55% in R-1), with a 36 ft height limit and 15 ft front and rear and 7 ft interior side yards; R-1 to R-3 have no minimum lot area. Two detached units must be at least 14 ft apart under §6-3(b). The §6-8(a)(1) rule that no detached accessory building may exceed 35% of allowable lot coverage, and the 20 ft peak height for accessory buildings (Table 4-4 Note 3), govern garages and sheds, not the second dwelling.

Neither the Two-Family Residential definition in §3-4(b) nor the two-single-family standards in §6-3(b) require the owner to live on the property, at application or afterward. Both units may be occupied by tenants.

Table 9-1 requires 2 off-street spaces per dwelling unit for Two-Family Residential (and for duplexes), so adding a second unit adds 2 spaces. Under §6-3(b)(2) a detached second dwelling must also be served by a driveway at least 10 ft wide leading from a public street adjacent to the lot.

In R-2, R-3, O and UC the Two-Family use is permitted by right: the Building Official issues a building permit after administrative site plan review (§12-2 requires site plan review for all uses before a building permit; §12-6(b)). In LC, B-1 and B-2 it needs a special use permit under §12-3, which goes to a Planning Commission hearing and a discretionary City Council decision. In R-1, RR and AG the use is not available without rezoning, which is a legislative City Council action.

The Two-Family use is an ordinary residential use with no rental, occupancy or separate-sale restriction in the CLDO. The bed and breakfast definition in §3-7(c) and Note 1 to Table 4-3 exempt 'short term rental of residential property in compliance with LB57' (Neb. Rev. Stat. 18-1758), so a nightly rental is not treated as a bed and breakfast or lodging use. City Code §111.16 counts short-term rentals of 30 days or less as lodging facilities subject to the city's lodging facility occupation tax; the code has no short-term rental license or registration.