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Energy Code Requirements for Heating an Accessory Building
Larimer County has allowed unheated detached accessory buildings to be built on monolithically poured slabs that do not extend down below frost line. As long as the structure remains unheated the frost force moves horizontally below the foundation causing no frost heave problems. However, once the structure is heated the frost force moves upward on the heated structure causing frost heave damage. To protect against frost uplift, a shallow frost foundation system may be used, which calls for slab perimeter insulation protection. The energy code states that the slab perimeter insulation shall be R-10 for 2 feet. (vertical, horizontal or both)
Be aware that section M1401.3 of the 2006 International Residential Code & Section 312.1 of the International Mechanical Code requires heating and cooling equipment to be sized based on heating loads calculated in accordance with ACCA Manual J or other approved heating and cooling calculation methodologies.
Below are heating and cooling loads approved in Larimer County for accessory buildings and some listed exemptions. If you are pulling a heating permit for an accessory structure you need to give us information on whether the structure is on a shallow monolithic poured slab and slab perimeter insulation is being added or the foundation extends below frost line (30 inches in Larimer County). Also indicate how you are meeting the energy code by marking one of the methods listed below.
Larimer County has new energy code regulations in Chapter 11 of the 2006 International Residential Code adopted effective October 2, 2007. There are exceptions to the energy code on accessory buildings.
Accessory buildings. Fully enclosed accessory buildings and attached garages not containing habitable space may be conditioned subject to the following thermal and envelope criteria:
- Such spaces meet the criteria for thermal isolation and any HVAC equipment installed therein is sized for a peak design load assuming a maximum Winter Indoor Design Dry-bulb Temperature of (60oF) and a minimum Summer Indoor Design Dry-bulb Temperature of (80oF).
- The walls are insulated with insulation having a minimum R-value of R-13.
- The roof/ceiling is insulated with insulation having a minimum R-value of R-30.
- Windows have a maximum U-factor of .45 & in total do not exceed 10% of the floor area.
- Doors have a minimum R-value of 3 and are sealed to prevent infiltration to the extent practical as determined by the building official.
Exceptions: The following accessory buildings need not meet the requirements 1-5 above.
- Accessory/Agricultural buildings heated or cooled in their interior for short periods of time and switched with a timer of 2 hours or less.
- Accessory/Agricultural buildings which are neither heated nor cooled by regulated fuel or electrical energy. (Examples of non-regulated fuels are wood, wood pellets, corn cobs, & waste oil)
- Accessory/Agricultural buildings that have restricted thermostats limiting heat to 50° F