The recent trend of installing operable windows may have you wondering whether they are right for your next building project. To uncover the real story behind operable windows, Mark Lucuik, principal, Morrison Hershfield (www.morrisonhershfield.com), Ottawa, Ontario, and a 16-year veteran of the field of building science, weighs in on what you need to know in order to make an educated decision.
What are the benefits of installing operable windows?
There are two major benefits, and one is the concept of control - that an occupant has some control over his/her environment. The other benefit is the concept of natural ventilation. Air from open windows can effectively cool and ventilate (and can save on operating costs), rather than using fans that are driven by electricity.
What are the biggest concerns?
Unfortunately, there is an increased threat of water and air leakage with operable windows - you may have a crack around the perimeter of a window that could be prone to leakage, or you may have people that inadvertently leave them open in inclement weather. These concerns can often be alleviated through careful design and installation, and proper window selection.
Operable windows also can bring with them increased noise and airborne pollutants, such as exhausts, pollen, and particulates. In some locations, you might find that operable windows just aren’t all that feasible.
Also, there are a lot of the mainstream mechanical engineers who have difficulty with the concept of natural ventilation, and they perceive windows as being something they can’t control. If relying on natural ventilation, it is important to retain an engineer with sound knowledge and experience in this specific field.
How can resistance to natural ventilation be overcome?
It is important to get good and proper commissioning and to ensure that occupants understand the theory and limitations of operable window use. It is not uncommon that naturally ventilated buildings do not meet up to the expectations regarding energy - often because the people who maintain the building don’t understand how to operate the mechanical systems in relation to the windows.
So, educating building operations and management staff is essential?
Yes. Also make sure that the users are knowledgeable. It’s not as simple as “opening a window and it works.” Sometimes, if you’re on the windward side of a building and you open a window, the air will go out of that window. So, this person might open the window more, thinking, “I want more air to come in,” when really they are letting more air out.
Are operable windows more expensive than fixed windows?
Operable windows are more expensive. Expect to pay approximately 20-percent more for fully operable windows vs. fixed windows. Price also changes by type of operable window - sliders are cheaper than casements, for example. There are a lot of differences in price. I encourage owners to think holistically. If you’re offsetting mechanical costs and downsizing fans by using operable windows, that can more than pay for the premium of an operable window. If you are going to put a traditional mechanical unit up on the roof and put in operable windows, then it doesn’t make sense money-wise.
What types of buildings are not good candidates for operable windows?
Hospitals, health institutions, testing laboratories, or any other building that requires really clean air are not good candidates for operable windows. Note that these are the exceptions; most commercial, industrial, or institutional buildings should consider the use of operable windows.
I don’t think operable windows are suitable for every building in every location. But, they can certainly be utilized much more than they are now.
Jana J. Madsen ([email protected]) is managing editor at Buildings magazine.