URBAN WILDLAND INTERMIX CODE (UWIC)
GUIDELINES FOR BUILDING PLAN CHECK

At the request of the Fire Districts throughout the County, the Board of Supervisors adopted an ordinance that allowed us to implement new regulations for reducing fire hazards associated with wildfires in the rural areas. If your new residential development is proposed in an area mapped as the State Responsibility Area, your structure must be constructed in a manner complying with the Urban Wildland Intermix Code. Implementation of these new requirements have raised many questions and these guidelines are provided to give the applicant a better understanding of Ignition Resistant Construction requirements when submitting plans for a building permit. Once the applicant has received an IR rating from the Fire authority, the designer is then required to incorporate all of the related UWIC ignition resistant features into the building design prior to plan submittal. Please include the IR rating on the cover sheet of submitted drawings. This information should be located in the Project Data section along with occupancy group and construction type of the building. Many builders are not thoroughly familiar with the UWIC code requirements, so it is important to provide complete details and specifications on the plans to aid in the construction. For more information please download:
Excerpts from the Urban Wildland Intermix Code   
Graphic Detail IR-1 Ignition-Resistant Construction    
Graphic Detail IR-2 Ignition-Resistant Construction    

FREQUENTLY ASKED QUESTIONS

1. Q: Sections 504.7 & 505.7 state that, " . . . the area below the structure (such as a deck) shall have all under floor areas enclosed to within 6 inches of the ground . . ." Does this mean that an enclosure wall needs to be constructed with one-hour materials on both the outside and the deck underside or interior side of the wall?

   A: The deck enclosure is only required to have fire resistive construction on the exterior, vertical side. If the deck is enclosed, only the top side of the deck (surface) is required to be of one hour materials.

2. Q: Sections 504.10 & 505.10 state that, "Attic ventilation openings shall not be located . . . between rafters at eaves . . . " Does this mean that there are to be no vent openings in the blocking between rafters, even though the eaves are enclosed per 504.3 and/or 505.3?

   A: Ventilating eave overhangs will be allowed, but not through the soffit. One method is to utilize a metal perforated strip vent in the fascia up behind a noncombustible gutter. Another acceptable method to ventilate the eave would be to vent from on top of the roof with an approved under the shingle strip type vent, or a sheet metal eyebrow vent. Drilling the frieze blocks will be acceptable as long as the soffit is protected with 3/4; solid material (IR2) as called for in sections 505.10, and 1 HR. (IR1) per section 504.10.

3. Q: Section 505.3 states that, "Combustible eaves, fascias and soffits shall be enclosed with solid materials with a minimum thickness of 3/4 inch." What does 3/4 solid material mean?

   A: "Solid material" means wood or other similar conventional products, installed in a manner that will not allow any gaps or spaces for fire to develop. Even materials installed in a tight manner will shrink in time and create gaps. Plywood with 3/4 battens protecting the joints, or similar material with tongue and groove joints are acceptable.

4. Q: Section 504.10 and 505.10 states, " . . . vents through roofs shall not exceed 144 square inches each." Does this mean ridge vents and other strip venting need to be broken into pieces such that not one vent exceeds 144 square inches? Also, should there be a minimum separation between individual vents?

   A: Strip type vents are not required to be divided into 144 sq. inch segments. The intention is for large openings to be limited to 144 square inches.

5. Q: May cantilevered decks and porch coverings be treated the same as a soffit, or should we always use the much more restrictive appendages and projection section?

   A: A cantilevered deck or porch overhang may be treated as a soffit as long as it does not project more than 48" out from the exterior wall.

6. Q: What materials are allowed to be specified for exterior guardrails and stair handrails? Heavy timber, noncombustible, one-hour, ... or can we allow standard wood railings?

   A: Guardrail and stair handrail construction need not be fire resistive. Standard 2x2 pickets and 2x4 construction are acceptable.

7. Q: Regarding stairways, is there an acceptable alternative to construction being of one-hour-materials/noncombustible/heavy timber? The Heavy Timber code section requires columns to be 8x8, and beams to be 6x10. The code is silent with respect to HT exterior stairs. Some applicants are choosing to leave stairways off of the plans. The result is a potentially less fire resistive stairway being added at a later date, or even worse, no stairway ever constructed at all. Could exterior stair stringers and treads possibly be constructed of 4x12 lumber? What about trellises or arbors?

   A: Exterior stair stringers and treads may be built of 4x12 (minimum) lumber in conjunction with heavy timber deck or one-hour rated deck construction. Trellises and arbors may not be allowed on decks or attached to buildings with habitable uses unless of full heavy timber or fire resistive construction.

8. Q: If an upper floor deck is directly over a deck below, and there is a descending slope greater than 10 percent, does the upper floor deck need to be enclosed per 504.7 and 505.7 as well?

   A: If the upper deck is completely within the footprint of the lower deck, then any fire would be deflected; therefore the upper deck does not need to be enclosed to the ground, but it must be constructed to meet the same fire resistive requirements including the under side of the deck itself.

9. Q: Should a new habitable structure that is attached to an existing dwelling by only a roof structure be referred to Fire for an IR rating? Does Fire consider these attached or not?

   A: Fire considers these types of structures as attached, just like a room addition to an existing structure, so no IR determination is required.

10. Q: Should existing structures that are being converted from non-habitable uses (with an occupancy classification other than R3) to an occupancy classification of R3 habitable space be referred to Fire for an IR rating?

    A: If the structure is detached and being converted to habitable space, then yes, it requires an IR rating. Attached conversions are treated as additions and do not require an IR rating.

11. Q: Since the UWIC ordinance only applies specifically to new residential dwellings, why are habitable accessory structures that are not formal dwelling units referred to Fire for an IR rating determination?

    A:Because when the habitable structure is residential in nature it is given the same occupancy classification as a dwelling. R3. Therefore, it has been determined that if the proposed structure is new development and a residential occupancy it must meet the UWIC requirements.

12. Q: The definition of a single family dwelling is a residential building with a kitchen. A building used as a sleeping room without a kitchen is not an SFD. Should the ordinance be amended?

    A:No, The ordinance should not be amended because the proposed habitable space would be used for sleeping, and would therefore require an IR rating.

13. Q: An application for a two-story garage is classified as a mixed occupancy building. The occupancy is correctly assigned as U1/R3. The R3 upstairs is shown on the plans as non-habitable storage. What are the requirements for UWIC?

    A: The two-story garage building only needs an IR determination from Fire if the use on the second floor is shown as habitable. A complying stairway (for floor space having more than 5 ft. of headroom) and an occupancy separation for the floor/ceiling assembly is still required. The difficulty of converting the second floor to habitable at a later date should be understood. Removing the siding to create a one-hour exterior wall in the future could prove to be expensive.

14. The UWIC ordinance states that the exterior walls of the building must be constructed with one-hour materials on the outside, or be of approved noncombustible materials. What are approved noncombustible materials? Who approves them and where can I find out what they are?

    A: Recognized testing labs and evaluation services provide approvals of materials. These materials must be tested in accordance with the standards published by the American Society of Testing Materials (ASTM). The California Building Code provides a definition of "noncombustible" in section 215. It states that the standard for noncombustible materials is ASTM E136. One example of a noncombustible material is Hardiboard. These products are classified as noncombustible in accordance with ASTM E136 and have a flame spread rating of 0 and a smoke density rating of 5 in accordance with ASTM E84. In addition, the test data must be listed as approved by the ICC evaluation service (ICC ES). The legacy report number for James Hardie Building Products is NER-405. Therefore, the product is an approved noncombustible material. If an applicant wishes to propose a building product as noncombustible, this is the type of criteria we need them to submit to show that it has been tested and is approved. After review of the submittal, the Building Official may allow approval.

15. Q: I am extensively remodeling my house. At what point would I be required to go to the Fire agency for an IR Rating and meet all the provisions of the UWIC?

    A: The requirements apply to new residential development and to remodeled dwelling construction deemed to be replacements where more than 75% of the exterior walls are being replaced. It does not apply to room additions.

HEAVY TIMBER CONSTRUCTION

If you choose to meet the UWIC provisions for heavy timber construction, the structural members must, at very minimum be sized and joined as per Type IV construction of the California Building Code, Section 605.6. Please refer to the CBC section for the entire text. The following excerpts are listed here for guidance:605.6.2 Columns. Wood columns may be of sawn timber or structural glued-laminated timber not less than 8 inches in any dimension when supporting roof or floor loads except as specified in Section 605.6.4. Columns shall be continuous or superimposed and connected in an approved manner. As the code specifies the size of members as "nominal" sizes, the actual net surfaced sizes may be used. For example, a nominal 8"x8" member will actually net 7-1/2"x7-1/2" which meets the intent of the code.

605.6.3 Floor framing. Beams and girders may be of sawn timber or structural glued-laminated timber and shall not be less than 6 inches in width and not less than 10 inches in depth.

605.6.4 Roof framing. Roof framing that does not support floor loads shall have members not less than 4 inches in width and not less than 6 inches in depth.

605.6.5 Floors (we are applying this section to exterior decks). Floors shall be without concealed spaces. Floors shall be (A) of planks, splined or tongue and groove, not less than 3 inches in thickness covered with 1-inch tongue and groove flooring laid crosswise or diagonally, or 15/32-inch wood structural panels, or (B) of planks not less than 4 inches in width set on edge close together and well spiked, and covered with 1-inch flooring or 15/32-inch wood structural panels. The lumber shall be laid so that no continuous line of joints will occur except at points of support. Floors shall not extend closer than 1/2 inch to walls. Such 1/2 inch space shall be covered by a molding fastened to the wall and arranged so that it will not obstruct the swelling or shrinkage movements of the floor. Corbelling of masonry walls under floors may be used in place of such molding.

605.6.6 Roof decks. Roofs shall be without concealed spaces and roof decks shall be of planks, splined or tongue-and-groove, of not less than 2-inch thickness, or 1-1/8" tongue-and-groove wood structural panels with exterior glue, or of a double thickness of 1-inch boards with tongue-and-groove joints, or with staggered joints, of lumber not less than 3 inches in nominal in width, set on edge close together and laid as required for floors.

605.6.7 Construction Details. Girders and beams shall be closely fitted around columns, and adjoining ends shall be cross tied to each other, or intertied by caps or ties, to transfer horizontal loads across the joints. Wood bolsters may be placed on top of columns which support roof loads only. Where intermediate beams are used to support a floor, they shall rest on top of girders, or shall be supported by ledgers or blocks securely fastened to the sides of the girders, or they may be supported by approved metal hangers into which the ends of the beams shall be closely fitted.

The joinery of all wood members should be tightly fit in order to eliminate points of ignition.

Please provide drawings that include cross references, specific designs, dimensions, materials, and notations that thoroughly explain the code required construction methods in detail.

The decision to incorporate heavy timber construction in lieu of one-hour-fire-resistive-construction, or of approved non-combustible materials, means that the construction must meet the intent of the code to provide fire protection for the building. Heavy timber construction is considered to be "slow burning" because it is open structural framing without concealed spaces and without sharp projections or rough surfaces, which are more easily ignitable. It is considered to provide fire protection equivalent to one-hour in certain building applications (from the UBC Handbook).

We appreciate designers that take the time to prepare complete and thoroughly detailed plans. The final design should provide the builder with enough information to install this heavy timber design to code standards. If the layout is complex and requires an engineered design, please include calculations and drawings that are stamped and signed in ink by an architect or engineer licensed in California.