Seattle Energy Code
Chapter 13

Building Envelope

**Form Building Envelope Checklist (ENV-CHK)**

1301 Scope: Conditioned buildings or portions thereof shall be constructed to provide the required thermal performance of the various components according to the requirements of this chapter. Unless otherwise approved by the building official, all spaces shall be assumed to be at least semi-heated.

EXCEPTIONS:

  1. Greenhouses isolated from any conditioned space and not intended for occupancy.
  2. As approved by the building official, spaces not assumed to be at least semi-heated.
  3. Unconditioned Group U occupancy accessory to Group R occupancy.
  4. Unstaffed equipment shelters or cabinets used solely for personal wireless service facilities.
  5. Parking lot attendant booths no larger than 100 square feet, provided that the roof insulation is R-21 minimum and the wall insulation is R-13 minimum, unless otherwise allowed by Section 1310.

1302 Space Heat Type: For the purpose of determining building envelope requirements, the following two categories comprise all space heating types:

Electric Resistance: Space heating systems which use electric resistance elements as the primary heating system including baseboard, radiant and forced air units where the total electric resistance heat capacity exceeds 1.0 W/ft2 of the gross conditioned floor area.

EXCEPTION: Heat pumps and terminal electric resistance heating in variable air volume distribution systems.

Other: All other space heating systems including gas, solid fuel, oil and propane space heating systems and those systems listed in the exception to electric resistance.

1303 Climate Zones: All buildings shall comply with the requirements of the appropriate climate zone as defined herein.

ZONE 1: Climate Zone 1 shall include all counties not included in Climate Zone 2.
ZONE 2: Climate Zone 2 shall include: Adams, Chelan, Douglas, Ferry, Grant, Kittitas, Lincoln, Okanogan, Pend Oreille, Spokane, Stevens and Whitman counties.

SECTION 1310 - GENERAL REQUIREMENTS

The building envelope shall comply with Sections 1311 through 1314.

1310.1 Conditioned Spaces: The building envelope for all conditioned spaces (as defined in Chapter 2) shall also comply with one of the following paths:

  1. Prescriptive Building Envelope Option Sections 1320 through 1323.
  2. Component Performance Building Envelope Option Sections 1330 through 1334.
  3. Systems Analysis. See Section 1141.4.

1310.2 Semi-Heated Spaces: All spaces shall be considered conditioned spaces, and shall comply with the requirements in Section 1310.1 unless they meet the following criteria for semi-heated spaces. The installed heating equipment output, in Climate Zone 1, shall be 3 Btu/(h·ft2) or greater but not greater than 8 Btu/(h·ft2) and in Climate Zone 2, shall be 5 Btu/(h·ft2) or greater but not greater than 12 Btu/(h·ft2).

For semi-heated spaces, the building envelope shall comply with the same requirements as that for conditioned spaces in Section 1310.1.  However, semi-heated spaces shall be calculated separately from other conditioned spaces for compliance purposes.

EXCEPTION: For semi-heated spaces heated by other fuels only, wall insulation is not required for those walls that separate semi-heated spaces (see definition in Section 201.1) from the exterior provided that the space is heated solely by a heating system controlled by a thermostat with a maximum setpoint capacity of 45 °F, mounted no lower than the heating unit.

Figure 13A - Building Envelope Compliance Options

1311 Insulation

1311.1 Installation Requirements: All insulation materials shall be installed according to the manufacturer's instructions to achieve proper densities, maintain clearances and maintain uniform R-values. To the maximum extent possible, insulation shall extend over the full component area to the intended R-value.

1311.2 Roof/Ceiling Insulation: Open-blown or poured loose-fill insulation may be used in attic spaces where the slope of the ceiling is not more than 3/12 and there is at least 30 inches of clear distance from the top of the bottom chord of the truss or ceiling joist to the underside of the sheathing at the roof ridge. When eave vents are installed, baffling of the vent openings shall be provided so as to deflect the incoming air above the surface of the insulation.

 
Where lighting fixtures are recessed into a suspended or exposed grid ceiling, the roof/ceiling assembly shall be insulated in a location other than directly on the suspended ceiling.
 
EXCEPTION: Type IC rated recessed lighting fixtures.
 
Where installed in wood framing, faced batt insulation shall be face stapled.
 
1311.3 Wall Insulation: Exterior wall cavities isolated during framing shall be fully insulated to the levels of the surrounding walls. When installed in wood framing, faced batt insulation shall be face stapled.
 
Above grade exterior insulation shall be protected.
 
1311.4 Floor Insulation: Floor insulation shall be installed in a permanent manner in substantial contact with the surface being insulated. Insulation supports shall be installed so spacing is not more than 24 inches on center. Installed insulation shall not block the airflow through foundation vents.
 
1311.5 Slab-On-Grade Floor: Slab-on-grade insulation installed inside the foundation wall shall extend downward from the top of the slab a minimum distance of 24 inches or to the top of the footing, whichever is less. Insulation installed outside the foundation shall extend downward a minimum of 24 inches or to the frostline, whichever is greater. Above grade insulation shall be protected.
 
EXCEPTION: For monolithic slabs, the insulation shall extend downward from the top of the slab to the bottom of the footing.
 
1311.6 Radiant Floors: (on or below grade) Slab-on-grade insulation shall extend downward from the top of the slab a minimum distance of 36 inches or downward to the top of the footing and horizontal for an aggregate of not less than 36 inches.
 
If required by the building official where soil conditions warrant such insulation, t The entire area of a radiant floor shall be thermally isolated from the soil. Where a soil gas control system is provided below the radiant floor, which results in increased convective flow below the radiant floor, the radiant floor shall be thermally isolated from the sub-floor gravel layer.
 
1312 Glazing and Doors
 
1312.1 Standard Procedure for Determination of Glazing and Door U-Factors: U-factors for glazing and doors shall be determined, certified and labeled in accordance with Standard RS-31 by a certified independent agency licensed by the National Fenestration Rating Council (NFRC). **CAM 403; Website NFRC ** Compliance shall be based on the Residential or the Nonresidential Model Size. Product samples used for U-factor determinations shall be production line units or representative of units as purchased by the consumer or contractor. Unlabeled glazing and doors shall be assigned the default U-factor in Table 10-6.
 
1312.2 Solar Heat Gain Coefficient and Shading Coefficient Visible Transmittance: Solar Heat Gain Coefficient (SHGC) and Visible Transmittance (VT), shall be determined, certified and labeled in accordance with the National Fenestration Rating Council (NFRC) Standard by a certified, independent agency, licensed by the NFRC. **CAM 403; Website NFRC **
 
EXCEPTIONS: 1. Shading coefficients (SC) or solar heat gain coefficient for the center of glass shall be an acceptable alternate for compliance with solar heat gain coefficient requirements. Shading coefficients or solar heat gain coefficient for the center of glass for glazing shall be taken from Chapter 31 of Standard RS-1 or from the manufacturer's ((test)) data using a spectral data file determined in accordance with NFRC 300.
 
2. For the purposes of 1323, Exception 1, visible transmittance for the center of the glazing assembly shall be taken from Chapter 31 of Standard RS-1 or from the manufacturer's data using the data file determined in accordance with NFRC 300.
 

Note that using the exception for the SHGC for the center-of-glass does not give the full credit for the overall product (including the frame) that the NFRC-certified SHGC does. Though the SHGC for the frame is not zero (the ASHRAE Handbook of Fundamentals indicates that the SHGC can range from 0.11-0.14 for metal frames and from 0.02 to 0.07 for wood/vinyl/fiberglass frames), the SHGC for the frame is invariably lower than that for the glass. Consequently, an NFRC-certified SHGC will generally be lower.

Conversely, the VT for the center-of-glass overstates the VT for the overall product (including the frame).  The VT for the frame is zero.  Consequently, an NFRC-certified VT will always be lower.  For this reason, Exception 2 to Section 1312.2 is only applicable to Exception 1 in Section 1323.  It is not applicable to other sections.
 
1313 Moisture Control
 
1313.1 Vapor Retarders: Vapor retarders shall be installed on the warm side (in winter) of insulation as required by this section.
 
EXCEPTION: Vapor retarder installed with not more than 1/3 of the nominal R-value between it and the conditioned space.
 
1313.2 Roof/Ceiling Assemblies: Roof/ceiling assemblies where the ventilation space above the insulation is less than an average of 12 inches shall be provided with a vapor retarder. (For enclosed attics and enclosed rafter spaces, see Section 1203.2 of the International Building Code.) Roof/ceiling assemblies without a vented airspace, where neither the roof deck nor the roof structure are made of wood, shall provide a continuous vapor retarder with taped seams.
 
EXCEPTION: Vapor retarders need not be provided where all of the insulation is installed between the roof membrane and the structural roof deck.
 
1313.3 Walls: Walls separating conditioned space from unconditioned space shall be provided with a vapor retarder.
 
1313.4 Floors: Floors separating conditioned space from unconditioned space shall be provided with a vapor retarder.
 
1313.5 Crawl Spaces: A ground cover of six mil (0.006 inch thick) black polyethylene or approved equal shall be laid over the ground within crawl spaces. The ground cover shall be overlapped 12 inches minimum at the joints and shall extend to the foundation wall.
 
EXCEPTION: The ground cover may be omitted in crawl spaces if the crawl space has a concrete slab floor with a minimum thickness of 3-1/2 inches.
 
1314 Air Leakage
 
1314.1 Building Envelope: The requirements of this section shall apply to building elements separating conditioned from unconditioned spaces. Exterior joints around windows and door frames, openings between walls and foundation, between walls and roof and wall panels; openings at penetrations of utility services through walls, floors and roofs; and all other openings in the building envelope shall be sealed, caulked, gasketed or weatherstripped to limit air leakage.  Building Envelope: The following areas of the building envelope shall be sealed, caulked, gasketed, or weather-stripped to minimize air leakage:
  1. joints around fenestration and door frames,
  2. junctions between walls and foundations, between walls at building corners, between walls and structural floors or roofs, and between walls and roof or wall panels,
  3. openings at penetrations of utility services through roofs, walls, and floors,
  4. site-built fenestration and doors,
  5. building assemblies used as ducts or plenums,
  6. joints, seams, and penetrations of vapor retarders,
  7. all other openings in the building envelope.   
1314.2 Glazing and Doors: Air leakage for fenestration and doors shall be determined in accordance with NFRC 400 or AAMA/WDMA/CSA101/I.S.2/A440. Air leakage shall be determined by a laboratory accredited by a nationally recognized accreditation organization, such as the National Fenestration Rating Council, and shall be labeled and certified by the manufacturer. Air leakage shall not exceed 1.0 cfm/ft2 for glazed swinging entrance doors and for revolving doors and 0.3 cfm/ft2 for all other products.  Doors and operable glazing separating conditioned from unconditioned space shall be weatherstripped. Fixed windows shall be tight fitting with glass retained by stops with sealant or caulking all around.
  
EXCEPTIONS:
  1. Openings that are required to be fire resistant.
  2. Field-fabricated fenestration and doors that are weather-stripped or sealed in accordance with 1314.1.
  3. For garage doors, air leakage determined by test at standard test conditions in accordance with ANSI/DASMA 105 shall be an acceptable alternate for compliance with air leakage requirements.
  4. Units without air leakage ratings produced by small business that are weather-stripped or sealed in accordance with 1314.1.
1314.3 Building Assemblies Used as Ducts or Plenums: Building assemblies used as ducts or plenums shall be sealed, caulked and gasketed to limit air leakage.
 
1314.4 Recessed Lighting Fixtures: When installed in the building envelope, recessed lighting fixtures shall by Type IC rated, and certified under ASTM E283 to have no more than 2.0 cfm air movement from the conditioned space to the ceiling cavity. The lighting fixture shall be tested at 75 Pascals or 1.57 lbs/ft2 pressure difference and have a label attached, showing compliance with this test method. Recessed lighting fixtures shall be installed with a gasket or caulk between the fixture and ceiling to prevent air leakage.
 
1314.5 Loading Dock Weatherseals: Cargo doors and loading dock doors shall be equipped with weatherseals to restrict infiltration when vehicles are parked in the doorway.
 
1314.6 Vestibules: Building entrances that separate conditioned space from the exterior shall be protected with an enclosed vestibule, with all doors opening into and out of the vestibule equipped with self-closing devices. Vestibules shall be designed so that in passing through the vestibule it is not necessary for the interior and exterior doors to open at the same time. Interior and exterior doors shall have a minimum distance between them of not less than 7 ft when in the closed position. The exterior envelope of conditioned vestibules shall comply with the requirements for a conditioned space. Either the interior or exterior envelope of unconditioned vestibules shall comply with the requirements for a conditioned space.
 
EXCEPTIONS:
  1. Building entrances with revolving doors.
  2. Doors not intended to be used as a building entrance.
  3. Building entrances in buildings that are less than four stories above grade and less than 10,000 ft2 in area.
  4. Doors that open directly from a space that is less than 3000 ft2 in area and is separate from the building entrance. 
SECTION 1320 - PRESCRIPTIVE BUILDING ENVELOPE OPTION
 
1321 General: This section establishes building envelope design criteria in terms of prescribed requirements for building construction.
 
1322 Opaque Envelope: Roof/ceilings, opaque exterior walls, opaque doors, floors over unconditioned space, below grade walls, slab on grade floors and radiant floors enclosing conditioned spaces shall be insulated according to Section 1311 and Tables 13-1or 13-2. Compliance with nominal R-values shall be demonstrated for the thermal resistance of the added insulation in framing cavities and/or insulated sheathing only. Nominal R-values shall not include the thermal transmittance of other building materials or air films.
 
For metal frame assemblies used in spaces with electric resistance space heat, compliance shall be demonstrated with the component U-factor for the overall assembly based on the assemblies in Chapter 10.
 
Area-weighted averaging of the R-value is not allowed. When showing compliance with R-values, the minimum insulation R-value for all areas of the component shall comply with Table 13-1. When calculating compliance using U-factors, area-weighted averaging is allowed. Where insulation is tapered (e.g. roofs), separate assembly U-factors shall be calculated for each four-foot section of tapered insulation.
 
EXCEPTIONS:
  1. Opaque smoke vents are not required to meet insulation requirements.
  2. For prescriptive compliance only,
    1. For glazing areas that are 30% and less of the gross wall area, the The insulation of the perimeter edge of an above grade floor slab which penetrates the exterior wall may be reduced to R-5 provide that the glazing U-factor is reduced by U-0.05 below that required by Tables 13-1 and 13-2.
    2. For glazing areas that are 30% and less of the gross wall area, the insulation of the perimeter edge of an above grade floor slab which penetrates the exterior wall may be left uninsulated provide that the glazing U-factor is reduced by U-0.10 below that required by Tables 13-1 and 13-2.
  3. For roofs with continuous rigid insulation on the top of the roof, the insulation R-value may be averaged for compliance with minimum prescriptive R-values only, provided that both:
    1. the minimum insulation is no less than R-5 (but not including area within 6 inches of each roof drain), and
    2. the area-weighted average insulation is R-50 (in lieu of R-30).

1323 Glazing: Glazing shall comply with Section 1312 and Tables 13-1 or 13-2. All glazing shall be, at a minimum, double glazing. In addition, all glazing assemblies shall have at least one low-emissivity coating unless the glazing assembly has an overall U-factor that complies with the values in Table 13-1.

EXCEPTIONS:

  1. Vertical glazing located on the display side of the street level story of a retail occupancy or where there is a street level transparency requirement in the Seattle Land Use Code provided the glazing
    1. (i) is double-glazed with a minimum 1/2 inch airspace and with a low-e coating having a maximum emittance of e-0.40 in any type of frame or
      (ii) has an area weighted U-factor of 0.60 or less. (U-factor calculations shall use overall assembly U-factors. When this exception is used, there are no SHGC requirements), and
    2. has a visible transmittance of (i) 0.60 or greater for the center of the glazing assembly in any type of frame or
      (ii) has an area-weighted visible transmittance for the overall assembly including the frame of 0.52 or greater for fixed glazing and 0.44 or greater for operable glazing. Visible transmittance shall be determined in accordance with Section 1312.2, and,
    3. does not exceed 75% of the gross exterior wall area on the display side of the street level story. However, if the display side of the street level story exceeds 20 feet in height, then this exception may be only used for the first 20 feet of that story.

      When this exception is utilized, separate calculations shall be performed for these sections of the building envelope and these values shall not be averaged with any others for compliance purposes. The 75% area may be exceeded on the street level, if the additional glass area is provided from allowances from other areas of the building.
  2. Single glazing for ornamental, security, or architectural purposes shall be included in the percentage of the total glazing area, U-factor calculation and SHGC as allowed in the Tables 13-1 or 13-2. The maximum area allowed for the total of all single glazing is 1% of the gross exterior wall area.

1323.1 Area: The percentage of total glazing (vertical and overhead) area relative to the gross exterior wall area shall not be greater than the appropriate value from Tables 13-1 or 13-2 for the vertical glazing U-factor, overhead glazing U-factor and solar heat gain coefficient selected.

1323.2 U-Factor: The area-weighted average U-factor of vertical glazing shall not be greater than that specified in Tables 13-1 or 13-2 for the appropriate area and solar heat gain coefficient. The area-weighted average U-factor of overhead glazing shall not be greater than that specified in Tables 13-1 or 13-2 for the appropriate area and solar heat gain coefficient. U-factors for glazing shall be determined in accordance with Section 1312. **CAM 403; Website NFRC **

1323.3 Solar Heat Gain Coefficient: The area-weighted average solar heat gain coefficient of all glazing shall not be greater than that specified in Tables 13-1 or 13-2 for the appropriate area and U-factor. **CAM 403; Website NFRC **

EXCEPTIONS:

  1. Glazing separating conditioned space from semi-heated space or unconditioned space.
  2. Vertical glazing which is oriented within 45 degrees of north shall be allowed to have a maximum solar heat gain coefficient SHGC-0.10 above that required in Table 13-1.
  3. For demonstrating compliance for vertical glazing only, the SHGC in the proposed building shall be allowed to be reduced by using the multipliers in the table below for each glazing product shaded by permanent projections that will last as long as the building itself.
Projection factor SHGC Multiplier
(All orientations
except North-oriented		 SHGC Multiplier
(North-oriented)
0 - 0.10 1.00 1.00
<0.10 - 0.20 0.91 0.95
<0.20 - 0.30 0.82 0.91
<0.30 - 0.40 0.74 0.87
<0.40 - 0.50 0.67 0.84
<0.50 - 0.60 0.61 0.81
<0.60 - 0.70 0.56 0.78
<0.70 - 0.80 0.51 0.76
<0.80 - 0.90 0.47 0.75
<0.90 - 1.00 0.44 0.73

 

 

 

 

 

 

 

Projection factor (PF) is the ratio of the horizontal depth of the external shading projection (A) divided by the sum of the height of the fenestration and the distance from the top to the bottom of the farthest point of the external shading projection (B), in consistent units. (See Exhibit 1323.3).

Exhibit 1323.3

SECTION 1330 - COMPONENT PERFORMANCE BUILDING ENVELOPE OPTION
**Form Envelope UA Calculations (ENV UA)**

1331 General: Buildings or structures whose design heat loss rate (UAp) and solar heat gain coefficient (SHGC * Ap) are less than or equal to the target heat loss rate (UAt) and solar heat gain coefficient ( SHGC * At) shall be considered in compliance with this section. The stated U-factor, F-factor or allowable area of any component assembly, listed in Tables 13-1 or 13-2, such as roof/ceiling, opaque wall, opaque door, glazing, floor over conditioned space, slab on grade floor, radiant floor or opaque floor may be increased and the U-factor or F-factor for other components decreased, provided that the total heat gain or loss for the entire building envelope does not exceed the total resulting from compliance to the U-factors, F-factors or allowable areas specified in this section.

EXCEPTIONS: 

  1. Compliance is also allowed to be shown using Standard RS-32.
  2. The prescriptive approach in Section 1323 may be used for that portion of the building envelope that complies with Exception 1 to Section 1323.

1332 Component U-Factors: The U-factors for typical construction assemblies are included in Chapter 10. These values shall be used for all calculations. Where proposed construction assemblies are not represented in Chapter 10, values shall be calculated in accordance with Chapters 23-30 in Standard RS-1 listed in Chapter 7, using the framing factors listed in Chapter 10. For envelope assemblies containing metal framing, the U-factor shall be determined by one of the following methods:

  1. Results of laboratory measurements according to acceptable methods of test.
  2. Standard RS-1, listed in Chapter 7, where the metal framing is bonded on one or both sides to a metal skin or covering.
  3. The zone method as provided in Chapter 25 of Standard RS-1, listed in Chapter 7.
  4. Effective framing/cavity R-values as provided in Table 10-5A.

When return air ceiling plenums are employed, the roof/ceiling assembly shall:

a. For thermal transmittance purposes, not include the ceiling proper nor the plenum space as part of the assembly; and
b. For gross area purposes, be based upon the interior face of the upper plenum surface.

1333 UA Calculations: The target UAt and the proposed UAp shall be calculated using Equations 13-1 and 13-2 and the corresponding areas and U-factors from Table 13-1 or 13-2. For the target UAt calculation, the overhead glazing shall be located in roof/ceiling area and the remainder of the glazing allowed per Table 13-1 or 13-2 shall be located in the wall area. Where insulation is tapered, separate assembly U-factors shall be calculated in accordance with Section 1322. **Form Envelope UA Calculations (ENV UA)**

1334 Solar Heat Gain Coefficient: Solar heat gain coefficient shall comply with Section 1323.3. The target SHGCAt and the proposed SHGCAp shall be calculated using Equation 13-3 and 13-4 and the corresponding areas and SHGCs from Table 13-1 or 13-2. **Form Envelope UA Calculations (ENV UA)**

EQUATION 13-1 - Target UAt **Form Envelope UA Calculations (ENV UA)**

EQUATION 13-2 - Proposed UAp **Form Envelope UA Calculations (ENV UA)**

EQUATION 13-3 - Target SHGCAt **Form Envelope UA Calculations (ENV UA)**

EQUATION 13-4 - Proposed SHGCAp **Form Envelope UA Calculations (ENV UA)**

TABLE 13-1 - BUILDING ENVELOPE REQUIREMENTS FOR CLIMATE ZONE 1

TABLE 13-2 - BUILDING ENVELOPE REQUIREMENTS FOR CLIMATE ZONE 2

Last Updated: January 9, 2008