(2015 IECC and ASHRAE 90.1-2013) Commercial Building Code (Illinois)

Last updated: 25 February 2019
2015 IECC
Application to replacement fenestration products
Where some or all of an existing fenestration unit is replaced with a new fenestration product, including slash and glazing, the replacement fenestration unit shall meet the applicable requirements for U-factor and SHGC in Table C402.4.
Building Envelope Requirements
Building thermal envelope assemblies for building that are intended to comply with the code on a perspective basis, in accordance with the compliance path described in Item 2 of Section C401.2, shall comply with the following:
The opaque portion of the building thermal envelope shall comply with the specific insulation requirements of Section C402.2 and the thermal requirements of either the R-value –based method of section C 402.1.3; the U-, C-, F-Factor-based method of Section C402.1.4; or the component performance alternative of Section C402.1.5
Roof solar reflectance and thermal emittance shall comply with Section C402.3
Fenestration in building envelope assemblies shall comply with Section C402.4
Air leakage of building envelope assemblies shall comply with Section C402.5
Prescriptive Compliance
Fenestration shall comply with Sections C402.4 through C402.4.4 and Table C402.4. Daylight responsive controls shall comply with this section and Section C405.2.3.1.
Vertical Fenestration: New vertical fenestration area that results in a total building fenestration area less than or equal to that specified in Section C402.4.1 shall comply with Section C402.4. Additions with vertical fenestration that result in a total building fenestration area greater than Section C402.4.1 or additions that exceed the fenestration area greater than Section C402.4.1 shall comply with Section C402.4.1.1 for the addition only. Additions that result in a total building vertical glass area exceeding that specified in Section C402.4.1.1 shall comply with Section C407.
Skylight area
The skylight area shall not be greater than 3 percent of the gross roof area.
In an enclosed space greater than 2,500 square feet (232 m2) in floor area, directly under a roof with not less than 75 percent of the ceiling area with a ceiling height greater than 15 feet (4572 mm), and used as an office, lobby, atrium, concourse, corridor, storage space, gymnasium/exercise center, convention center, automotive service area, space where manufacturing occurs, non-refrigerated warehouse, retail store, distribution/sorting area, transportation depot or workshop, the total daylight zone under skylights shall be not less than half the floor area and shall provide one of the following:

A minimum skylight area to daylight zone under skylights of not less than 3 percent where all skylights have a VT of at least 0.40 as determined in accordance with Section C303.1.3.
A minimum skylight effective aperture of at least 1 percent, determined in accordance with Equation 4-4.
Skylight Effective Aperture= 0.85. 𝑆𝑘𝑦𝑙𝑖𝑔ℎ𝑡 𝐴𝑟𝑒𝑎 . 𝑆𝑘𝑦𝑙𝑖𝑔ℎ𝑡 𝑉𝑇 . 𝑊𝐹 𝐷𝑎𝑦𝑙𝑖𝑔ℎ𝑡 𝑧𝑜𝑛𝑒 𝑢𝑛𝑑𝑒𝑟 𝑠𝑘𝑦𝑙𝑖𝑔ℎ𝑡 (Equation 4-4)
Skylight area = Total fenestration area of skylights.
Skylight VT = Area weighted average visible transmittance of skylights.
WF = Area weighted average well factor, where well factor is 0.9 if light well depth is less than 2 feet (610 mm), or 0.7 if light well depth is 2 feet (610 mm) or greater.
Light well depth = Measure vertically from the underside of the lowest point of the skylight glazing to the ceiling plane under the skylight.
Air leakage
The thermal envelop of buildings shall comply with Sections C402.5.1 through C402.5.8, or the building thermal envelope shall be tested in accordance with ASTM E 779 at a pressure differential of 0.3 inch water gauge (75Pa) or an equivalent method approved by the code official and deemed to comply with the provisions of this section when the tested air leakage rate of the building thermal envelope is not greater than 0.4 cfm/ft2 (0.2 L/s.m2). Where compliance is

Want to know more about this policy ? Learn moreLearn more

End uses covered
  • Building end-uses
  • Building systems
  • Space heating
  • Space cooling
  • Water heating
  • Lighting
  • Exterior lighting
  • Interior lighting
  • Building vintage
  • Building envelope