Wildfire Hazard Mitigation Requirements For New Construction

R324.1 Purpose. The purpose of this entire section is to establish minimum standards for design and construction of new buildings or portions thereof for the protection of life and property from wildfire.

R324.2 Scope. Within the wildfire hazard area, as defined in footnote #1 to table R905.16, all new building construction and all additions equal to or greater than 50% of the total square footage of the original structure shall comply with the provisions of this section. New building construction shall include all new structures.

Exceptions: Loafing sheds, private & detached greenhouses and similar structures.

R324.3 Alternate Materials and Methods of Compliance. The provisions of this section are not intended to prevent the use of any material or method of compliance not specifically prescribed by this section, provided any alternate has been approved and its use authorized by the building official. The building official may approve any such alternate, provided it is found that the proposed design is satisfactory and complies with the provisions of this section and this code and that the material method or work offered is, for the purpose intended, at least the equivalent of that prescribed in this section in suitability, effectiveness, fire resistance, durability and safety.

The building official shall require that sufficient evidence or proof be submitted to substantiate any claims that may be used regarding use of the alternate. The details of any action granting approval of an alternate shall be recorded and entered in the files of the Building Department.

R324.4 Definitions. For the purpose of this section, certain terms are defined as follows:

Combustible - a material that fails to meet the acceptance criteria of Standard Method of test for determination of non-combustibility in building materials.

Combustible construction - a type of construction that does not meet the requirement for noncombustible construction.

Defensible space - a natural or man-made area, where woody vegetation capable of allowing a fire to spread unchecked has been treated or modified to slow the spread and reduce the intensity of an advancing wildfire, and to create an area for fire suppression operations to occur.

Fire-resistive construction - construction designed to resist the spread of fire.

Fire-resistive rating - is the time that the material or construction will withstand the standard fire exposure as determined by a fire test made in conformity with the standard methods of fire tests of buildings construction and materials.

Fire-retardant-treated wood - any wood product impregnated with chemicals by a pressure process or other means during manufacture, and which shall have a flame-spread index of not over 25.

Fire separation - a construction assembly that acts as a barrier against the spread of fire.

Firewall Assembly- a type of fire separation of noncombustible construction which subdivides a building or separates adjoining buildings to resist the spread of fire and which has a fire-resistance rating and structural ability to remain intact under conditions for the required fire-rated time.

Flame-resistant material - material that has been modified in its chemical composition by impregnation, coating or has inherent composition that makes the material resistant to ignition and combustion when exposed to a small ignition source.

Flame retardant - is an approved chemical compound or mixture which, when applied in an approved manner to any fabric or other material will render such fabric or material incapable of supporting combustion.

Flame-spread index (FSI) - a relative index describing the surface-burning characteristics of building materials. The test used to establish FSI evaluates the flame spread over the building material surface when exposed to a test fire. The rate at which flame spreads across the specimen is compared on a scale of 0 for inorganic reinforced cement board, to 100 for red oak." The following table identifies the flame-spread index and Flame Spread Classification:

Fuel - combustible material.

Noncombustible - materials that meet the acceptance criteria of Standard Method of test for determination of non-combustibility in building materials.

Noncombustible Construction - a type of construction in which a degree of fire safety is attained by the use of noncombustible materials for structural members and other building, assemblies.

One-hour Fire-resistive Construction - will "withstand the standard fire exposure" for one hour "as determined by a fire test made in conformity with the standard methods of fire tests of building construction and materials".

Slash - unusual concentrations of downed fuel resulting from such natural events as wind, fire, or snow breakage or such human activities as timber harvesting, road construction, or building construction.

Wildfire Hazard - the relative likelihood that a fire, once started, will become disastrous. Disastrous means the destruction of life and improved property.

Wildfire Hazard Area - that area in Larimer County prone to wildfires as identified on the county's Wildfire Hazard Area map.

Wildfire mitigation - any action taken to eliminate or reduce the long-term risk to human life and property from wildfire.

Wildfire Mitigation:

R324.5 Fire-Resistive Construction. Fire-resistive construction on all new structures shall be one of the following types:

1. One-hour fire-resistive shell shall provide not less than one-hour fire-resistive construction at all exterior walls, EXCLUDING ALL OPENINGS AND DECKS.
1. Exterior siding materials shall have a flame-spread classification of Class III or better.

Exceptions: Log homes using solid logs with a minimum tip diameter of 6 inches for exterior wall construction and 8 inches for roof beams, purlins and supporting columns may be considered as one-hour fire-resistive construction.

R324.6 Defensible Space. Defensible space in compliance with current Colorado State Forest Service guidelines shall be required on all new construction in the Wildfire Hazard Area. For additions to or changes in character of the occupancy or use in existing buildings, the defensible space shall be provided around the entire building.

R324.7 Evaluation. Evaluation of the defensible space will be based upon:

1. Current Colorado State Forest Service standards and guidelines, and
2. Site specific vegetation and topographical characteristics.
3. The Building Official may allow alternatives to the Colorado State Forest Service Standards and Guidelines based on specific site conditions.

R324.8 Completion. The defensible space must be completed prior to the applicant receiving a certificate of occupancy.

R324.9 Liquid Propane Gas. Liquid propane gas facilities installed in the Wildfire Hazard Area shall comply with the current County requirements for installation of liquid propane gas facilities and it is recommended that the tank be located in the defensible space or on the same contour or downhill from the structure.

R324.10 Alternate Designs. The building official may approve other alternate designs provided it meets the requirements of Section R 104.11.

R324.11 Wildfire Fees. Fees shall be assessed in accordance to Larimer County wildfire assessment and inspection fee schedule.

R324.12 Appeals. Appeals of interpretations made by the building official relative to the application of this section shall be made to the Board of Appeals.

R324.13 Maintenance. Defensible space areas created as required by this chapter or other referenced documents within the Larimer County Wildfire Mitigation Plan are to be maintained by the property owner. No re-planting or new planting of trees, shrubs or other vegetation that would violate the defensible space requirements of this section shall be permitted.