Building Code Model and Commentary

The International Codes developed by the International Code Council (ICC) establish standard building safety and engineering regulations and help protect critical infrastructure, which is the lifeline of a community during and after a major hazard event. Jurisdictions have the option of adopting local amendments to the International Codes that are tailored to address risks associated with hazard areas. While it is not required, adopting more stringent standards to mitigate hazards leads to safer, stronger, and more resilient communities.

The types and associated levels of risk can vary widely among communities. Amendments to the local building code depend largely on area-specific conditions and/or mitigation objectives that the community has defined relative to one or more hazards. This model has been prepared from a planner’s perspective and presents several examples where tailored building code standards, specifically related to hazard mitigation, can be implemented into local building codes. Local building officials and other hazard mitigation staff are the administrators of building codes and should take the lead role in tailoring language for your jurisdiction and selecting appropriate methodologies.

Land development and zoning codes address mostly site conditions and exterior building treatment, but rarely address what happens within the building itself before, during, or following construction. Building code standards are most effective when paired with other hazard mitigation strategies that are identified in this guide, specifically: Community Wildfire Protection Plan; Hazard Mitigation Plan; Resilience Planning; Conservation Easement; Stream Buffers and Setbacks; Stormwater Ordinance; Site-Specific Hazard Assessment; Subdivision and Site Design Standards; and Wildland-Urban Interface Code.

Text in grey shading provides model language while commentary is located in italics in the column at the right. The model language used in this document is based on existing building codes from communities around the state and nation. The language is illustrative only; consult local building officials and legal counsel to tailor language for your jurisdiction.

In 2019, the National Institute of Building Sciences released a report, Natural Hazard Mitigation Saves, that is intended to inform future code changes to make communities more resilient, help jurisdictions make decisions on what codes to adopt and enforce, and assist policymakers in developing effective federal programs that support pre-disaster mitigation. The report also includes research that helps quantify the benefits of exceeding the baseline standards found in the 2015 International Building Code (IBC) and 2015 International Residential Code (IRC). The report suggests that implementing measures in new construction to exceed select provisions in the 2015 IRC and 2015 IBC and implementation of the IWUIC saves society approximately $4 for every $1 spent on mitigation. The benefit-cost ratio increased further to $6 for every $1 spent on mitigation provided by federal mitigation grants through the Federal Emergency Management Association (FEMA), the U.S. Economic Development Administration (EDA), and the U.S. Department of Housing and Urban Development (HUD). 

The best way to mitigate risks associated with flooding is to avoid constructing in areas that are at risk for flooding. The Stream Buffers and Setbacks section and Stormwater Ordinance section of this guide provides guidance for preventing development near flood risk areas and management of on-site stormwater.

Many communities have adopted floodplain regulations as part of their land development codes that are separate from the community’s building codes. Colorado has minimum requirements for floodplain regulations that are established by the Colorado Water Conservation Board. Some Colorado standards for certain floodplain management activities exceed those required by the National Flood Insurance Program (NFIP). In those cases, the stricter of the State standards take precedence.

Addressing existing structures located in flood-prone areas is particularly challenging. Existing structures can use flood mitigation techniques (aside from avoidance of floodplain areas) including:

• Dry flood-proofing (making the building watertight to prevent water entry);
• Wet flood-proofing (making uninhabited or non-critical parts of the building resistant to water damage);
• Relocation of the building; and
• Incorporating floodwalls into site design to keep water away from the building.

In addition to the techniques above, a relatively simple approach to preventing water damage to structures is requiring gutters and downspouts on all buildings to direct water away from the foundation to prevent damage from trapped moisture. For this reason, Boulder County has adopted amendments to the IBC requiring all buildings (with exception to a few) to provide gutters or downspouts.

Note: This language can be added as a new Section 1805 in Chapter 18 of the IBC:

Dampproofing and Waterproofing

Gutters, downspouts, and downspout extensions are required on all buildings.

Exceptions:

1. Post framed buildings.
2. Buildings where, in the opinion of the building official, the gutters will become damaged by sliding snow.
3. Roofs with eaves or overhangs of six feet or greater.
4. Roofs that are constructed with internal roof drains.
5. Buildings where an approved alternate means of drainage is designed by a soils engineer or other qualified registered design professional.

Another strategy for minimizing the risk of flood through building design is by installing a vegetated roof or green roof. A green roof refers to roof surfaces that have been designed to incorporate large areas of vegetation. Green roofs provide several benefits to the community including improved aesthetics, reduced heat island effect, and retaining and reducing peak stormwater runoff during rain events. While it is common for communities to incentivize the construction of green roofs, some cities including Denver, Toronto, Washington D.C., and San Francisco, require their construction

As residential developments expand into wildland areas, people and property are increasingly at risk from wildland fire. Several preventative measures can be taken to minimize the spread of fire on the site as well as to make the building more fire-resistant. In addition to adopting local building code amendments to protect structures, the Wildland-Urban Interface Code and the Community Wildfire Protection Plan sections of this guide provide guidance for how wildfire hazards can be minimized through other measures.

Note: This language, which was taken from the Boulder County Building Code, can be added to Section 723 in Chapter 7 of the IBC:

Generally

Unless more restrictive requirements apply, the ignition-resistant construction and defensible space requirements of Section [R327] of the amendments to the IRC shall be applicable to all new buildings, additions, and repairs.

Note: This language, which was taken from the Larimer County Building Code and the Boulder County Building Code, can be added as a new Section 327 in Chapter 3 of the IRC:

Defensible Space

1. Defensible space in compliance with current Colorado State Forest Service and guidelines shall be required on all new construction in the [hazard area].
2. Any landscaping materials or natural ground cover within three feet of the exterior walls of the building shall be a non-combustible surface – no landscaping – over a weed barrier within five feet of exterior walls. The noncombustible surface should extend underneath and two feet past the dripline of decks.
3. For additions equal to or greater than [insert percentage of the total square footage of the original structure here], the defensible space shall be provided around the entire structure.
4. 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

The Building Official may allow alternatives to the Colorado State Forest Service standards and guidelines based on specific site conditions.

1. Defensible space areas created as required by this code or other referenced documents within the [community hazard mitigation plan] are to be maintained by the property owner.
2. 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.

Exterior Walls

1. Exterior walls of buildings or structures shall be constructed with one of the following methods extending from the top of the foundation to the underside of the roof sheathing:
   1. Noncombustible materials approved for a minimum of one-hour fire-resistance-rated construction on the exterior side.
   2. Approved noncombustible materials.
   3. Heavy timber or log wall construction.
   4. Fire-retardant-treated wood labeled for exterior use on the exterior side.
   5. Ignition-resistant materials on the exterior side.

Exterior Windows and Glazing

1. Exterior windows, window walls, glazed doors, windows within exterior doors, and skylights shall be tempered glass, multi-layered glazing, glass block, or have a fire protection rating of not less than 20 minutes.
2. Unless they are part of a fire-rated assembly, window frames and sashes may be constructed using any material permitted by this code. Windows with unreinforced vinyl frames or sashes are not permitted.

Exterior Doors

1. Exterior doors and garage doors shall be approved noncombustible construction, metal clad, solid core wood not less than 1 3/4 inches in thickness, or have a fire protection rating of not less than 20 minutes.
2. Windows within doors and glazed doors shall comply with exterior window and glazing standards.

Vents

1. Attic ventilation openings, foundation or under-floor vents, or other ventilation openings in vertical exterior walls and vents through roofs shall not exceed 144 square inches each.
2. Such vents shall be covered with noncombustible corrosion-resistant mesh with openings not to exceed 1/8 inches or shall be designed and approved to prevent flame or ember penetration into the structure.
3. Gable end and dormer vents shall be located at least 15 feet from property lines and shall be designed and approved to prevent flame or ember penetration into the structure.
4. Under-floor ventilation openings shall be located as close to grade as practical.

Roof Covering

Roof covering materials shall be listed Class A roof covering materials or be constructed as a Class A roof assembly. For roof coverings where the profile allows a space between the roof covering and roof decking, the space at the eave ends shall be fire stopped to preclude entry of flames or embers, or have one layer of 72-pound (32.4 kg) mineral-surfaced, non-perforated cap sheet complying with ASTM D 3909 installed over the combustible decking.

Roof Valleys

When provided, valley flashings shall be not less than 0.019 inch (No. 26 galvanized sheet gage) corrosion-resistant metal installed over a minimum 36-inch-wide underlayment consisting of one layer of 72-pound mineral-surfaced, non-perforated cap sheet complying with ASTM D 3909 running the full length of the valley.

Protection of Eaves

1. The leading edge of the roof at the fascia shall be finished with a metal drip edge so that no wood sheathing is exposed.
2. Eaves, fascias, soffits, covered decks, and covered porch ceilings shall be protected on the enclosed underside by any one of the following materials or methods:
   1. Noncombustible materials;
   2. Ignition-resistant materials;
   3. Materials approved for a minimum of 1-hour fire-resistance-rated construction;
   4. 2-inch-thick nominal dimension lumber;
   5. 1-inch-thick nominal fire-retardant-treated wood;

3/4-inch-thick nominal fire retardant-treated plywood labeled for exterior use; or

1. Any materials permitted by this code.

Gutters and Downspouts

1. Gutters, downspouts, and gutter covering devices shall be constructed of noncombustible material.
2. Gutters shall be provided with an approved means to prevent the accumulation of leaves, pine needles and debris in the gutter.

Liquid Propane Gas

Liquid propane gas containers and tanks installed in the [hazard area] shall be located within the defensible space in accordance with the International Fire Code.

Spark Arrestors

Chimneys serving fireplaces, woodstoves, barbecues, incinerators, or decorative heating appliances in which solid fuel or liquid fuel is used, shall be provided with a spark arrestor.

1. Spark arrestors shall be constructed of woven or welded wire screening of 12 USA standard gage wire (0.1046 inch) (2.66 mm) having openings not exceeding one-half inch.
2. The net free area of the spark arrestor shall not be less than four times the net free area of the outlet of the chimney.

Definitions

Defensible Space: An area either natural or manmade, where material capable of allowing a fire to spread unchecked has been treated, cleared or modified to slow the rate and intensity of an advancing wildfire and to create an area for fire suppression operations to occur.

Fire-Retardant-Treated Wood: Wood meeting the requirements of Section R802.1.5 of the IRC or Section 2303.2 of the IBC.

Heavy Timber Construction (Type IV, HT): Construction with wood framing members, columns, flooring and roof decks sized in accordance with IBC Section 602.4.

Ignition-Resistant Building Material: Ignition-resistant building materials shall comply with any one of the following:

1. Material that complies with the requirements for noncombustible materials in this section.
2. Fire-retardant-treated wood labeled for exterior use.
3. Roof assemblies containing fire-retardant-treated wood shingles and shakes and classified as Class A roof assemblies.
4. Materials currently approved by the California Department of Forestry and Fire Protection, Office of the State Fire Marshal (search categories include 8110-Decking Materials, 8120-Exterior Windows, 8140-Exterior Sidings and Sheathings, 8150-Exterior Doors and 8160-Under Eave).

Log Wall Construction: A type of construction in which exterior walls are constructed of solid wood members and where the smallest horizontal dimension of each solid wood member is at least 6 inches (152 mm).

Noncombustible: As applied to building construction material, a material that, in the form in which it is used, is either one of the following:

1. Material of which no part will ignite and burn when subjected to fire. Any material conforming to ASTM E 136 shall be considered noncombustible within the meaning of this Section.
2. Material having a structural base of noncombustible material as defined in Item A above, with a surfacing material not over 1/8 inch (3.2 mm) thick, which has a flame spread index of 50 or less. Flame spread index as used herein refers to a flame spread index obtained according to tests conducted as specified in ASTM E 84 or UL723.
3. “Noncombustible” does not apply to surface finish materials. Material required to be noncombustible for reduced clearances to flues, heating appliances or other sources of high temperature shall refer to material conforming to Item A.
4. No material shall be classified as noncombustible that is subject to increase in combustibility or flame spread index, beyond the limits herein established, through the effects of age, moisture or other atmospheric condition.

Some communities address wildfire concerns through a separate set of code standards specific to the Wildland-Urban Interface by adopting a standalone WUI Code – which is available as part of the International Code family but can also be integrated into the community’s land development code for site development issues aside from structural requirements. For more information, see the WUI Code section of this guide.

Designing buildings and structures for the direct effects of a landslide, debris flow, or rockfall is not typically cost-effective. However, many improvements can be made to a site to reduce the structural risk to debris flow and/or rockfall. The most effective ways to prevent damages from a gravity-driven movement of earth is to:

• Select non-hillside or stable slope sites for development; (avoidance)
• Construct channels, drainage systems, retention structures, and deflection walls;
• Plant groundcover to stabilize soils;
• Reinforce soils using geo-synthetic materials; and
• Avoid cut and fill building sites.

Most of these can be addressed by land development codes and engineering standards, rather than building codes. The Landslide, Mud/Debris Flow, and Rockfall section of this guide provides guidance for how land movement related hazards can be avoided.

The key strategy for protecting a building from wind damage is to maintain the structural integrity of the building envelope, 

including roofs and windows. Bracing roof trusses and gables and using hurricane straps to strengthen the connection between the roof and walls and walls and foundation will help the structure withstand lateral and uplift forces. Chapter 16, Section 1609 of the IBC and Chapter 3, Section 301 of the IRC establishes general standards based on regional climactic data for the appropriate design of buildings and structures to withstand wind loads.

Winds blowing over mountain ranges or through gorges or river valleys in some regions can develop speeds that are substantially higher than the values indicated on the map. The basic design windspeed map provided in the IBC (Figure 1609.3(1)) and IRC (Figure R301.2(4)A) identifies the Front Range Area as a “special wind region” requiring further examination for unusual wind conditions. 

In 2006 the Structural Engineers Association of Colorado (SEAC) prepared a Colorado Front Range Gust Map that several communities have adopted to supplement the basic wind design criteria found in the IBC and IRC. This map is intended provide local communities with area-specific windspeed data to inform the design of buildings and structures in the Front Range area. It is important to note, when selecting basic wind speeds in regions with a diversity of terrain, use of regional climatic data and consultation with a wind engineer or meteorologist is advised.

Larimer and Boulder counties have adopted area-specific windspeed maps depicting wind exposure categories for anticipated wind events.  

Note: This language, (similar to those found in Boulder and Larimer Counties), can be used to amend Section 1609.3 in Chapter 16 of the IBC or Section R301.2.1 in Chapter 3 of the IRC:

Basic Windspeed

1. The project engineer may designate exposure based on site specific conditions.
2. The required Wind Design Speed for a project area shall comply with the [insert name of local windspeed map here], as amended.

There are several ways in which building codes can improve a building’s resistance to seismic events. The primary focus of earthquake design is ensuring that people can safely exit a building following an earthquake. While implementing additional design measures may allow buildings to better withstand the effects of an earthquake, they are not always intended to ensure full functionality of a building following an event.

Implementing earthquake resilient construction practices can be accomplished through a variety of structural engineering measures or structural components (e.g., shear walls, braced frames, moment resisting frames, diaphragms, base isolation, energy dissipating devices such as visco-elastic dampers, elastomeric dampers, and hysteretic-loop dampers, and bracing of nonstructural components). More simple building techniques can also be used including avoiding soft stories (a multi-story building in which one or more floors have windows, wide doors, large unobstructed commercial spaces, or other openings in places where a shear wall would normally be required for stability) and bolting the sill plate of houses to the foundation.

The IBC establishes “seismic design categories” based on the spectral accelerations as mapped by the USGS and the site soils classification as determined by a geotechnical engineer. The seismic design category increases in seismic resistance as a function of a letter, seismic design category “A” is the least seismic resistant while category “F” is the highest. The most common mitigation technique used by communities to address seismic events is to require the minimum seismic design category for all types of buildings to exceed that required by the IBC. Benefits and costs of designing to exceed International Code requirements for earthquake depend on several factors including added cost of construction, building economic design life, building replacement cost, and other variables. 

Note: This language can be added to Section 1613 in Chapter 16 of the IBC:

Minimum Seismic Design Category

All buildings and structures in [insert jurisdiction name, specific hazard area, or other identifier here] shall satisfy the requirements of Seismic Design Category [insert appropriate category here (A through F)], as a minimum.