Section 160.1 - Mandatory Requirements for Building Envelopes

(a) Ceiling and roof insulation. The opaque portions of ceilings and roofs separating conditioned spaces from unconditioned spaces or ambient air shall meet the requirements of Item 1 or 2, and 3 below:

1. Attic Roof. Roofs with an attic space shall meet the requirements of A through C below:

A. Shall be insulated to achieve an area-weighted average U-factor not exceeding U-0.043 or shall be insulated between wood-framing members with insulation resulting in an installed thermal resistance of R-22 or greater for the insulation alone. For vented attics, the mandatory insulation shall be installed at the ceiling level; for unvented attics, the mandatory insulation shall be placed at either ceiling or roof level;

B. Attic access doors shall have permanently attached insulation using adhesive or mechanical fasteners. The attic access shall be gasketed to prevent air leakage; and

C. When loose-fill insulation is installed, the minimum installed weight per square foot shall conform with the insulation manufacturer's installed design weight per square foot at the manufacturer's labeled R-value.

2. Non-attic roof. Roofs without attic spaces shall meet the applicable requirements of A through C below:

A. Metal Building - The area-weighted average U-factor of the roof assembly shall not exceed 0.098.

B. Wood framed and others - The area-weighted average U-factor of the roof assembly shall not exceed 0.075.

C. Insulation placement - When insulation is installed at the roof, fixed vents or openings to the outdoors or to unconditioned spaces shall not be installed. When the space between the ceiling and the roof is either directly or indirectly conditioned space, it shall not be considered an attic for the purposes of complying with CBC attic ventilation requirements.

Exception to Section 160.1(a)2C: Vents that do not penetrate the roof deck and are instead designed for wind resistance for roof membranes are not within the scope of Section 160.1(a)2C. 

3. Insulation shall be installed in direct contact with a roof or ceiling that is sealed to limit infiltration and exfiltration as specified in Section 110.7, including but not limited to placing insulation either above or below the roof deck or on top of a drywall ceiling.

(b) Wall insulation. Opaque portions of above grade walls separating conditioned spaces from unconditioned spaces or ambient air shall meet the following applicable requirements:

1. Metal building - The area-weighted average U-factor of the wall assembly shall not exceed 0.113.

2. Metal framed - The area-weighted average U-factor of the wall assembly shall not exceed 0.151.

3. Wood framed and others -

A. Nominal 2x4 inch framing shall have an area-weighted average U-factor of the wall assembly not exceeding 0.095.

B. Nominal 2x6 inch framing shall have an area-weighted average U-factor of the wall assembly not exceeding 0.069

C. Other wall assemblies shall have an area-weighted average U-factor of the wall assembly not exceeding 0.102.

4. Light mass walls - A 6 inch or greater hollow core concrete masonry unit shall have a U-factor not to exceed 0.440.

5. Heavy mass walls - An 8 inch or greater hollow core concrete masonry unit shall have a U-factor not to exceed 0.690.

6. Spandrel panels and curtain wall - The area-weighted average U-factor of the spandrel panels and curtain wall assembly shall not exceed 0.280.

7. Demising walls - The opaque portions of framed demising walls shall meet the requirements of Item A or B below:

A. Wood framed walls shall be insulated to meet a U-factor not greater than 0.099.

B. Metal Framed walls shall be insulated to meet a U-factor not greater than 0.151.

8. Bay or bow window roofs and floors. Shall be insulated to meet the wall insulation requirements of Table 170.2-A.

(c) Floor and soffit insulation. The opaque portions of floors and soffits that separate conditioned spaces from unconditioned spaces or ambient air shall meet the applicable requirements of Items 1 through 3 below:

1. Raised mass floors shall have a minimum of 3 inches of lightweight concrete over a metal deck or the area-weighted average U-factor of the floor assembly shall not exceed 0.269.

2. Raised wood floor shall have an overall assembly U-factor not exceeding U-0.037. In a wood framed assembly, compliance with the U-factor may be demonstrated by installing insulation with an R-value of 19 or greater.

3. Other floors - The area-weighted average U-factor of the floor assembly shall not exceed 0.071.

4. Heated slab on grade floor - A heated slab on grade floor shall be insulated to meet the requirements of Section 110.8(g).

(d) Vapor retarder.

1. In Climate Zones 1-16, the earth floor of unvented crawl space shall be covered with a Class I or Class II vapor retarder. This requirement shall also apply to controlled ventilation crawl space for buildings complying with the Exception to Section 160.1(c).

2. In Climate Zones 14 and 16, a Class I or Class II vapor retarder shall be installed on the conditioned space side of all insulation in all exterior walls, vented attics and unvented attics with air-permeable insulation.

(e) Fenestration products. Fenestration separating conditioned space from unconditioned space or outdoors shall meet the requirements of either Item 1 or 2 below:

1. Fenestration, including skylight products, must have a maximum U-factor of 0.58.

Exception 1 to Section 160.1(e)1: Up to 0.5 percent of the conditioned floor area is not required to comply with the maximum U-factor requirement.

Exception 2 to Section 160.1(e)1: For dual-glazed greenhouse or garden windows, up to 30 square feet of fenestration area per dwelling unit is not required to comply with the maximum U-factor requirement.

Exception to Section 160.1(e): Fenestration installed in buildings meeting Part 7 of the California Building Code, California Wildland-Urban Interface Code, where the building is located in Fire Hazard Severity Zones or Wildland-Urban Interface (WUI) Fire Areas as designated by the local enforcement agency.

2. The area-weighted average U-factor of all fenestration, including skylight products, shall not exceed 0.58.

(f) Installation of fireplaces, decorative gas appliances and gas logs. If a masonry or factory-built fireplace is installed, it shall comply with Section 110.5, Section 4.503 of Part 11, and shall have the following:

1. Closeable metal or glass doors covering the entire opening of the firebox; and

2. A combustion air intake to draw air from the outside of the building, which is at least 6 square inches in area and is equipped with a readily accessible, operable, and tight-fitting damper or combustion-air control device; and

Exception to Section 160.1(f)2: An outside combustion-air intake is not required if the fireplace will be installed over concrete slab flooring and the fireplace will not be located on an exterior wall.

3. A flue damper with a readily accessible control.

Exception to Section 160.1(f)3: When a gas log, log lighter, or decorative gas appliance is installed in a fireplace, the flue damper shall be blocked open if required by the CMC or the manufacturer's installation instructions.

(g) Slab edge Insulation. Slab edge insulation shall meet the following minimum specifications:

1. Insulation material alone without the facing shall have a water absorption rate no greater than 0.3 percent when tested in accordance with ASTM C272, Test Method A – 24-Hour-Immersion; and
2. Water vapor permeance no greater than 2.0 perm/inch when tested in accordance with ASTM C272; and
3. Concrete slab perimeter insulation shall be protected from physical damage and ultraviolet light deterioration; and
4. Insulation for a heated slab floor shall meet the requirements of Section 110.8(g).