Code watch: When is a home not a residence? When codes come into play
What do authors of the international codes consider residential buildings? A single-family home? A two-story townhouse with a grade-level entrance? A two-story apartment building? A three-story assisted living facility? The answer depends on the code you use.
The first two—single-family homes and townhouses three stories or less in height, with independent means of egress—fall within the scope of the 2006 International Residential Code. The next two fall within the scope of the 2006 International Building Code.
The distinction between residential and commercial becomes slightly different, however, in the 2006 International Energy Conservation Code. In the IECC, the provisions for residential construction apply to Use Group R-2, apartment buildings and condominiums, and Use Group R-4, assisted living facilities, as well as Use Group R-3, one- and two-family homes and townhouses of three stories or less in height. Therefore, the code officials would consider all of the buildings listed above residential, and thus subject to requirements in Chapter 4 of that code. These include more stringent U-factor limits for fenestration than those given in Chapter 5 for commercial construction.
As the next cycle of code development begins, energy use and comfort to occupants emerges as questions the IECC committee will have to address. The committee asks: When should a residential space meet the more stringent building-envelope requirements of a single-family home, and when should it be permissible for application of less stringent requirements?
Under the 2006 IECC, the more stringent building-envelope requirements always apply to all four of the types of buildings listed above. For commercial buildings, the code offers less stringent provisions for the building envelope and more complicated provisions for the building’s mechanical and lighting systems.
A number of code-change proposals will challenge this practice during the 2006-07 IECC code-change cycle. One proposal defines the residential buildings covered in Chapter 4 of the IECC as low-rise residential buildings, and establishes more stringent opaque building-envelope requirements for residential buildings covered in Chapter 5. The requirements for fenestration in these buildings would not change, however, from this proposal.
Many people argue that the energy-use patterns of all residential spaces are similar, regardless of where the residential space is located. These include peak demand for energy during evenings and weekends, and relatively heavy introduction of heat and moisture into the space via cooking, dishwashing, laundering and showering. These use patterns prove distinctly different from most commercial spaces, where the peak energy loads usually occur during the daytime, and the amount of warm, moist air generated per cubic foot of occupied space is usually considerably less than that generated in residential occupancies. Some argue that since use of the space is similar, regardless of the building type, the building envelope requirements should also be similar. This does not recognize that the mechanical and lighting systems must meet many more stringent requirements in all buildings built under Chapter 5, including high-rise residential buildings.
Another proposal would permit the design and construction of low-rise residential buildings conforming to the requirements contained in Chapter 5 for commercial buildings, as long as they meet every requirement, including those for the mechanical and lighting systems. This would permit less stringent U-values in most climate zones, while possibly requiring more stringent solar heat-gain coefficient values and again requiring more complicated-heating, ventilation and air-conditioning and lighting systems in most buildings.
A third proposal simply seeks to clarify types of buildings the code classifies as residential, and therefore subject to the requirements of Chapter 4.
Solar heat-gain coefficent ratings on residential fenestration products look to be one of the “hot topics” for residential window manufacturers this cycle. Although no proposals would change the prescriptive U-factor requirements for residential windows, several proposals seek to change their SHGC.
Some of these proposals lower the residential SHGC in Southern climate zones, in some cases allowing an increase of the SHGC if projecting overhangs exist above the fenestration. The concept of raising the maximum SHGC for a window when there’s protection from an overhanging projection is already present in the IECC fenestration provisions for commercial construction. These proposals only address climate zones 1 to 3—South Florida through Alabama—and provide SHGC ranges of 0.25 to 0.61.
Other proposals lower the maximum SHGC of residential glazed fenestration in climate zones 1 and 2, and establish minimum SHGC for residential glazed fenestration in climate zones 6 to 8—Wisconsin through Alaska. Establishing minimum SHGC in the Northern climate zones would increase the amount of solar heat gain experienced through the glass, a change many consider beneficial in these climates.
A third proposal would permit the slight increase of U-factors in climate zones 6 to 8 when the use of glazing with higher SHGC occurs. The maximum U-factor permitted under this proposal would be 0.40, with a corresponding glazing SHGC of 0.51 to 0.58.
The SHGC used for standard design, when performance-based design for residential construction is used, serves as the primary focus of another proposal. At the present time, the SHGC assumed for performance-based design is basically 0.40 in all climate zones. This can be beneficial to manufacturers of products with SHGC significantly lower than 0.40, particularly in Southern climate zones. The proposed change would vary the SHGC assumed for the standard design in climate zones 1 to 3 with the SHGC of the proposed design, if that proposed SHGC is within the range of 0.30 to 0.40. Such a proposal would remove some of the benefit of providing low SHGC products in these climate zones.
A proposal allowing the Canadian rating system, combining the SHGC, U-factor and air-infiltration rate into one equation, is currently in front of the committee. The committee considered a similar proposal last cycle but the proposal was not successful.
Maximum fenestration rating
During the last code update process, quite a bit of committee time was spent discussing various combinations of U-factor and SHGC caps on residential fenestration, when performance-based design is used under the IECC and IRC. A different set of requirements were established in the two codes, resulting in the caps on these factors being different in the single-family home and two-story townhouse—discussed at the beginning of this article—than caps for the two-story apartment building or three-story assisted living facility. For example, in climate zone 5, in Chicago, there would be no cap on U-factor or SHGC for the single-family home or the townhouse, but a U-factor cap of 0.48 would apply to fenestration in the two-story apartment building or the three-story assisted living facility.
The committee has received proposals to correct that discrepancy by either changing the requirements in the IECC or IRC. It has also received two proposals to remove the fenestration caps from both the IECC and the IRC.
The committee will hear all of these proposals, together with other proposals for windows and doors, during the 2006-07 International Code Council Code Development Hearings Sept. 20-30 in Lake Buena Vista, Fla.