Stricter Energy Codes Reduce Requirements for Operable Windows

Julie Ruth
June 18, 2015
COLUMN : Code Arena | Codes & Standards

How important is it to you to be able to open an exterior window and bring fresh air into an interior space you are occupying? Would you consider buying or renting a home that did not have operable windows? If you did not have operable windows in your kitchen or living room would it bother you?

The 2015 International Building Code and 2015 International Residential Code requires interior, habitable spaces to be ventilated by either natural or mechanical means. If natural ventilation is to be used, operable openings to the exterior are required that are equal in area to 4 percent of the floor area to be ventilated. For example, a total of 80 square feet of exterior, operable openings are required to ventilate a 2,000-squarefoot area. These openings are to include operable windows, doors, skylights, louvers and “other openings to the outdoors.”

The builder has the option of providing mechanical ventilation of the space, rather than natural ventilation. The 2015 International Mechanical Code provides the requirements for mechanical ventilation of interior, occupied spaces.

These requirements are not new. They have been in the International Codes and its legacy codes for decades. What is new is that, due to the increased energy efficiency of new construction, the air infiltration (leakage) rate through the building envelope has been dramatically reduced.

A Ventilation Issue 

It used to be relatively safe to assume that sufficient natural ventilation occurred through the building envelope of residential construction so that mechanical ventilation wasn’t required. But that is no longer the case, particularly for low occupancy buildings of wood frame construction.

For example, in your own home, you do not need to open the windows to have enough oxygen for you and your family to breathe. Enough outside air leaks in through the building envelope and enters when the exterior doors are opened to meet that need. The same is often true of relatively small office buildings, retail stores, warehouses and factories. Typically, a mechanic heating and ventilation system is not put into place until a building becomes large enough that it is desirable to be able to control the flow of air to specific spaces, condition some spaces and not others, etc.

The 2015 International Mechanical Code, however, requires the use of mechanical ventilation for dwelling units that meet the air leakage criteria for low-rise residential spaces of the 2015 International Energy Conservation Code. Although there are many jurisdictions that adopt and enforce the International Mechanical Code but not the International Energy Conservation Code, there are several others that do.

The question then becomes, if a builder is not required by the code to put in operable windows, will they? Certainly the builder is going to respond to what the marketplace wants. Some parties believe that operable windows are not going to go away. The reasoning is that codes do not need to mandate them for people to want them, and if people want them, builders will provide them.

There is certainly evidence that this may be the case. For example, although the 2015 IBC and 2015 IRC also require natural lighting of spaces via exterior glazed openings, an exception is given for spaces with sufficient artificial lighting. In most buildings, the artificial lighting provided is sufficient to meet this requirement and exterior glazed openings are not required, but they are still commonly provided.

Some people enjoy being able to open their windows and get some fresh air into an interior space when the exterior conditions warrant it. Others go from heating season to air conditioning with no pause in between to bring in fresh air.

Will this new provision of the 2015 International Mechanical Code affect the demand for operable windows in residential buildings? That is a question that has yet to be answered.

Code Arena is brought to you by the America Architectural Manufacturers Association. Julie Ruth may be reached through AAMA at 847/303-5664 or via e-mail at