Littleton, CO Accessory Structures: ADU Impact Fees (2026)

Two sections work together. Section 10-1-1.7(C)(3) of the Unified Land Use Code states that each dwelling unit requires payment of the city's land development impact and sewer tap fees. Section 1-14-3(D)(2)(d) of the City Code then sorts accessory construction into two groups. An accessory building of a residential use, or an addition to an existing dwelling unit, is exempt from the impact fee. The exemption ends when the addition contains a bedroom, bathroom, kitchen facilities and a separate entrance for ingress and egress. At that point the structure is treated as an additional residential unit and the fee is charged. A finished ADU with all four features falls on the fee side of that line.

The dollar figures sit in Table 1-14-3(a). The Single Family row prints $1,237.93, $1,055.11, $801.01, $432.80, $2,247.14, $2,615.80 and $8,389.79. The Multiple Dwelling Unit row prints $812.31, $692.33, $525.61, $284.00, $1,474.53, $2,028.35 and $5,817.13. In both rows the last figure equals the sum of the six before it, and the table header splits the rate into multimodal improvements, museum, library, police facilities and transportation components. Section 1-14-3 does not say which residential row an ADU is billed under. Section 1-14-3(E) gives the Finance Director or their designee the power to decide use classification questions, based on precedents, similar situations, relative impacts, trip generation rates and employees per demand unit, so confirm the row with the Finance Director's office before you budget.

Timing is set in two places. Section 1-14-3(C) says the fee is paid at the time the building permit is issued, unless a development agreement specifies an earlier time, and that it is in addition to any other fee, tax or charge required by the Code. Section 1-14-3(H) fixes the rate at the amount in effect when a complete building permit application is accepted. Section 1-14-3(I) subjects the rates to an annual inflation factor set by the Finance Director, and the section's history line lists amendments through Ord. 04, Series of 2026, effective February 17, 2026.

The fee is only one cost of the ADU path. Section 10-1-1.7 requires a building permit, a deed restriction recorded with the County Clerk and Recorder before that permit issues, and no more than one ADU per lot. Detached ADUs top out at the principal dwelling's floor area or 1,000 square feet, whichever is less.