Accessory Living Areas

With the passage of Colorado House Bill 24-1152, which went into effect on June 30, 2024, Larimer County no longer requires applicants to go through a planning process before applying for an Accessory Living Area building permit.  There are some new requirements before a building permit application will be accepted, so please review the information below.  The planning division will still be part of the building permit review process and applicable Land Use Code requirements will still apply.

An Accessory Living Area (ALA) is defined as finished space attached to or part of (e.g. basement) a single-unit dwelling or a detached building that is intended and designed to be occupied as a separate living unit than that of the primary single-unit dwelling and clearly accessory to the single-unit dwelling on the lot. A single-unit dwelling that includes contiguous living space intended to be occupied by a single living unit is not considered an accessory living area.


Larimer County Land Use Code §3.4.5.A - Accessory living areas are required to comply with the following or an appeal may be required. Please contact the On Call Planner at planning@larimer.org for more information.

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  1. Lodging Facilities, as defined in §20.2.4.C, Lodging Facilities, are prohibited within an accessory living area. The accessory living area shall not be rented for 30 days or less as a short-term rental unit as regulated by §3.3.5.B, Short-Term Rental. 
  2. A tiny home on wheels fixed to a temporary foundation approved by the Larimer County Building Department may be used as an accessory living unit.
  3. The accessory living area may be occupied by one additional living unit, separate from the principal dwelling unit.
  1. Unless otherwise noted in this §3.4.5.A., an accessory living area in a detached building or in a portion of a residence that is attached with no direct access from the primary residence is allowed as a use by right. 
  2. Building permit applications are required for accessory living areas and are subject to all standards contained herein and all applicable impact fees, including transportation capital expansion fees.
  1. One accessory living area is permitted per lot.
  2. The total square footage of the accessory living area shall comply with the standards in Table 3-15 below.

Table 3-15: Accessory Living Area Maximum Size by Lot Area

Lot Area (sq. ft.)

Maximum Total Area of Accessory Living Area
(lesser of) [1][2]

Up to 15,00075 percent of the square footage of the single-unit
dwelling or 900 square feet
15,000 to 100,00075 percent of the square footage of the single-unit
dwelling or 1,000 square feet
Greater than 100,00075 percent of the square footage of the single-unit
dwelling or 1,200 square feet

Notes:

[l] The total square footage of the single-unit dwelling excludes any basement areas,
finished or not.
[2] Exceeding the maximum total area of an accessory living area requires approval by the
Board of County Commissioners through the appeals process in §6.7.2.

  1. The Director may approve an accessory living area in an existing structure that exceeds the maximum total area requirement in Table 3-15 if the accessory living area is clearly incidental to the principal dwelling unit and meets one or more of the following criteria:
    1. The existing structure is recognized as contributing to the historic, rural, or neighborhood character of the area;
    2. The interior configuration of the existing structure is arranged in a manner that the space to be used as the accessory living area cannot feasibly be divided in conformance with the size requirements; or 
    3. There are unusual physical circumstances or conditions in the design of the existing structure that affect the total allowed area.
  1. The single-unit character of the property shall be maintained.
  2. One additional off-street parking space shall be provided for the accessory living area.
  3. If the accessory living area is located in a detached building, to the maximum extent practicable it shall be located within 300 feet of the primary residence.
  4. If the accessory living area is attached to the primary residence, the accessory living unit entrance must be located on another façade leaving only one entry visible on the front façade of the primary residence.

Things to Consider Before Applying for a Building Permit

  1. Water & Sewer Verification: 
    It is the applicant’s responsibility to verify an adequate water and sewer source is available. Prior to submitting a building permit for an Accessory Living Area, the applicant must obtain approval from their utility service providers. Please see the utility approval handout. A completed version of this form must be submitted with your building permit. You may contact the Health Department for septic information, but pre-approval is not required for septic systems. However, you may need to enlarge or replace your system to accommodate additional bedrooms.
  2. Fire Protection: 
    Fire Sprinklers may be required in new structures. The Lyons Fire Protection District and Estes Valley Fire Protection District require fire 
    sprinkler systems in new homes. This requirement may also be listed on your subdivision plat.
  3. Engineering Fees: 
    Transportation fees will be collected to offset the impact of additional vehicles on the roadway system. Per Section 15.1.7 and 15.1.8 of 
    the Land Use Code, Transportation Capital Expansion Fees (TCEF) are required for Accessory Living Areas and are based on livable square 
    footage. The applicable TCEF fee shall be paid prior to the issuance of the building permit. Refer to our website for more information and 
    an estimated price per square foot: https://www.larimer.gov/engineering/development-review
  4. General Engineering Conditions:
    • In most cases, Larimer County Engineering Department will require that the accessory living area utilizes the same access as the 
      primary dwelling on the property. For questions contact eng-permits@co.larimer.co.us.
    • There shall not be modifications to the existing drainage patterns on the property as the result of the addition of an Accessory Living Area. If significant grading changes are expected, the applicant shall work with their Professional Engineering Team to ensure no adverse impacts on surrounding property.
    • An ALA is not allowed within any Zone AE (Floodway) Floodplain Overlay District
  5. Building Code Requirements
    • Under Larimer County’s adopted building codes, an Accessory Living Area (ALA) is subject to all the same requirements as a principal dwelling unit: structural integrity, wildfire hazard mitigation, fire separation from garage/barns, exiting, emergency exits from bedrooms, light, ventilation, sanitation, energy efficiency including insulation, windows, water/space heating efficiency and lighting controls, minimum 70 sq. ft. habitable rooms, minimum 7’ ceiling height, etc. An ALA requires at least one exit directly to the exterior that does not lead into a garage/barn. Newly constructed dwelling units require a radon mitigation system and radon testing, prewiring for a Solar Photovoltaic system and for an Electrical Vehicle charger if there is an attached garage or carport. In most of unincorporated Larimer County, wind and snow loads exceed code prescriptive rules, so structural plans must be drawn and stamped by a licensed Colorado Professional Engineer.
    • Fire Impact fees may be due, as well as the Transportation Capital Expansion fees.
    • To save you the time and expense of drawing up plans and proceeding down a possible dead end, we will not initiate a building permit without the signed water/sewer form from the appropriate utility district or Colorado Division of Water Resources.
    • For more information and guidance, please consult our Building Staff on Call at (970) 498-7660 or by email to Building@larimer.org.