Article #1577 - 2006 IECC Commercial Building Envelope Prescriptive Requirements

[2006 IECC]

The 2006 International Energy Conservation Code (IECC) replaces the 2003 IECC as the model energy code applicable to conditioned, commercial buildings. A commercial building is anything other than a low-rise (1-3 stories) house, condominium, or apartment (R-2, R-3, and R-4). Requirements for the building envelope fall under Chapter 5, Section 502. Compliance to ASHRAE 90.1-2004, Section 5, is also acceptable by reference in the energy code. The basic prescriptive requirements are listed below, but they are not comprehensive guidelines for compliance.

Residential Building, Group R-2: Residential occupancies containing more than two dwelling units where the occupants are primarily permanent in nature such as apartment houses, boarding houses (not transient), convents, monasteries, rectories, fraternities and sororities, dormitories and rooming houses. For the purpose of this code, reference to Group R-2 occupancies shall refer to buildings that are three stories or less in height above grade.

Residential Building, Group R-4: Residential occupancies shall include buildings arranged for occupancies as Residential Care/Assisted Living Facilities including more than five but not more than 16 occupants, excluding staff. For the purpose of this code, reference to Group R-4 occupancies shall refer to buildings which are three stories or less in height above grade.

Major Changes

Climate zones (by county) for the 2004 Supplement to the IECC, the 2006 IECC, and ASHRAE 90.1-2004.

The 2006 IECC generally streamlined and shortened the code and incorporated some significant changes. Envelope tables decreased from 37 to 1, and Climate Zones dropped from 19 to 8. Zone lines were based on political and geographical boundaries rather than heating degree days, with higher-numbered zones having colder climates. Also, because metal buildings tend to be less efficient thermally, the 2006 IECC introduced new requirements and techniques for their insulation.

Another major change sets the requirements limit of buildings to 40% glazing area, down from 50%. One single U-factor is required regardless of the glazing percentage below that. If a building goes over the glazing limit, compliance may be shown using the Total Building Performance Approach in section 506.

Building Envelope Definition

The Building Thermal Envelope is defined as what separates the building from unconditioned space. These elements include the roof/ceiling assembly, exterior walls (now defined as any wall that surrounds interior space), mass walls, and below-grade walls, fenestration, the floor assembly (where the floor is over unconditioned space), and the slab edge.

Roof Assembly

Metal frame ceiling insulation.

Roof R-value requirements are based on assembly type or insulation placement. The code recognizes that even continuous insulation above a roof deck is not continuous. If a weighted average is done, the insulation thickness may vary up to an inch. Metal buildings typically require R-19 or double layers and will always require thermal breaks.

Walls, Metal Buildings

In all Climate Zones 1-4 except Marine, metal building walls require R-13 insulation installed perpendicularly to the girts and compressed by the metal skin. In all other climates, R-13 insulation should be installed perpendicularly and continuously to the girts as well as within the framing cavity.

Walls, Mass

Mass walls are now based on mass per square foot to include walls with a mass of at least 35 lb per square foot of the wall surface area or, if the material density is ≤ 120 lb/ft³, with a mass of 25 lb per square foot.

Walls, Below-Grade

For walls more than 85% below grade, insulation must extend down 10 feet from the finished grade level or to the level of the floor, whichever is less.

Fenestration

Overhang projection

A new glazing table (502.3 Building Envelope Requirements: Fenestration) shows products and climate zone requirements. Many categories were added to reflect different site-built products in the 2006 code. In hotter climates, SHGC requirements were reduced to 0.25 with no overhangs. In Climate Zones 4 and higher, a projection factor greater than 0.25 can be substituted for a low SHGC window.

SHGC requirements for skylights are new for 2006 IECC. Skylights are limited to ≤ 3% of the roof area, and the U-factor and SHGC are based on whether the material is glass or plastic. Always try to use the NFRC 100 rating for the U-factor because the best value in the default table provided by the code is 1.05, which represents a worst-case window.

Floor/Slab

For unheated slabs, insulation is not required except in Climate Zone 8. Heated slabs require insulation in all climate zones.

Other Requirements

Moisture control for warm and humid climates.

All openings or seams in the building envelope must be sealed, and air must be allowed to escape through exhaust openings and vents integral to the building envelope. Vestibules are required for spaces greater than 3000 ft², with exemptions for Climate Zones 1 and 2.

Vapor retarders should be used in unvented framed cavities except in Climate Zones 1-3, or where moisture and its freezing will not damage the materials, or where other means approved by the local building official prevent condensation. Remember to install the retarders on the warm-in-winter side of insulation.

Compliance Software

DOE’s Building Energy Codes Program (BECP) has produced COMcheck which is a free software tool that can demonstrate compliance with the 2006 IECC and calculate trade-offs for high-efficiency mechanical equipment.

Additional Information

For more information, view the Envelope Requirements portion of the Commercial Requirements of the 2006 IECC Training Broadcast three-part series.

Code Citations*

*Copyright, 2006, International Code Council, Inc. Falls Church, Virginia. All rights reserved. 2006 International Energy Conservation Code. PNNL-SA-51649