The long-awaited International Green Construction Code (IgCC) has been published. The International Code Council, the organization that produces building codes widely used in the United States, such as the IBC and IECC, produced the IgCC. Development began in 2009 with the American Institute of Architects on board as a sponsor. The International Association of Lighting Designers (IALD) was represented on the drafting committee and testified at all code development hearings. Along with our IALD colleagues, Lam Partners Principals Keith Yancey and I were intimately involved in the development of the electric and daylighting related provisions of the code. For more on green building codes, see my February 2010 article Will Green Building Codes Leave You Seeing Red?.
So now the question is, will the IgCC be widely adopted? One school of thought is that many municipalities are clamoring for a green building standard written in enforceable code language. The other asks why a municipality would add another very complex code to the enforcement responsibilities of their already overstretched inspectional services departments. Me? Well, I’m skeptical that IgCC will take off, especially considering the anti-regulatory tone in our political discourse these days. But don’t listen to me; I was surprised by the wildfire success of LEED.
What does this have to do with daylighting? Well, did you know that the IgCC has a mandatory provision requiring minimum daylighting of buildings? Surprise! We’re not talking about daylight responsive lighting controls to save energy; we’re talking about buildings having to be designed to ensure a minimum amount of daylight into the building. This is not a code requirement we are used to in the US.
So how does it work in IgCC? First, the requirement only applies to these building and space types:
- Office, Higher Education, Labs
- Retail (single-story and larger than 10,000 square-feet)
- Manufacturing and Warehouse
- Library reading areas, Transportation waiting areas, Exhibit halls, Athletic areas.
The IgCC says that in one-or-two story buildings, 50% of your floor area has to be daylighted and 25% in buildings three-floors and up. The trick is defining “daylighted”. IgCC does this with two options: a prescriptive method and a performance method. If your project is required to have a daylighted area larger than 25,000 square-feet, you must use the performance method.
Let’s look at the prescriptive method first. It defines your daylighted area based on the height and width of your windows and skylights. Then, assuming you have a sufficient daylighted area, you determine if you have a high enough “effective aperture” (EA). EA is just your window area multiplied by glass transmittance, divided by the daylighted area. The more window area you have and the higher transmission your glass is, the more daylight will enter. The minimum EA is given in a table and is based on the sky type for your location. There is also a nasty looking formula that lets you reduce the required daylighted area based on exterior shading obstructions, such as other buildings.
The performance method requires daylight computer modeling of the project. Simply put, the performance requirement says that you have to show that you will have at least 300lux and not more than 4500lux in the daylighted area. You show this under clear sky on the equinox for the either 9:00AM or 3:00PM.
Easy, right? Truthfully, both the prescriptive and performance requirements are more complicated than I have led you to believe and this will be especially true when applied to complex architecture. In many cases, designing a building to meet these requirements will require a daylighting design expert, and likely one with expertise in daylight computer modeling software. Those of us who deal with the LEED daylighting credit will find these daylighting requirements familiar, but if IgCC takes off we are going to have to pay attention to daylighting from the very beginning of the building design process. It’s one thing to say, “Hey, let’s see if we can get a LEED point.” With IgCC we’ll be saying, “If I don’t site, mass, and fenestrate my building properly, I’ll be in violation of code.”
Photo credit: Stephen M. Lee (1), Glenn Heinmiller/Lam Partners (2), Lam Partners (3)