Energy efficiency considerations in window replacement projects

All photos courtesy Hoffman Architects Inc.

by Craig A. Hargrove, CDT, RRC, AIA, LEED AP
At some point, windows reach the end of their useful life. The question is, how does a building owner know whether it is advisable to defer a window project another year or two, or to call in a design professional right away? At what point is window replacement inevitable?

The first thing to consider is the comfort of building users. Most complaints about office environments involve thermal comfort, often originating at deteriorated windows. Leaks at window openings are obvious indicators of compromised performance, but more subtle problems, such as difficult operation or drafts, may also become troublesome. (While safety is the primary consideration in any building assembly, systemic failure of the structural integrity of properly designed, installed, and maintained windows is usually indicative of a severe state of advanced deterioration. Most window assemblies will generally reach a condition prior to this where a host of other factors—many of which are discussed in this article—will point to the obvious need for replacement.)

To keep occupants comfortable, a certain amount of energy must be added to or removed from the building interior by the heating and air-conditioning systems. This thermal load can become much higher in buildings with inefficient windows, as HVAC systems run overtime to meet the demand of excess heat transfer through the fenestration.

Correct window replacement can improve aesthetics, daylighting, and views, while reducing operating cost.

The cycling of temperatures and the migration of moisture from one day or season to the next can manifest at windows in the form of:

  • shrunken gaskets and seals;
  • warped, faded, or displaced frames; and
  • etched or fogged glass.

As glazing becomes scratched, distorted, or clouded, building occupants may complain of compromised views, along with bothersome glare that can affect daylighting schemes.

Another factor to consider is maintenance and cost control. As windows age, it may become increasingly difficult and cost-prohibitive to find replacement parts. Keeping up with the needs of older windows is more demanding, as maintenance personnel spend hours responding to user complaints. (While windows have generally become more thermally efficient, increased maintenance efforts over time are generally the result of deterioration and failure of window components [e.g. gaskets, seals, and hardware] rather than shortcomings in the original design.) Protecting building infrastructure from environmental infiltration and chasing after damage can become a strain, and the cost of ongoing problems adds up.

As with any capital improvement, aesthetic appeal is also a driving force. New windows can add equity to a commercial property, and also present a way to dramatically improve the building’s appearance.

Energy efficiency is not often a precipitating factor in the decision to replace aging windows. However, once user comfort, maintenance demands, and aesthetics conspire to make window replacement unavoidable, a window project offers the opportunity to improve energy efficiency and reduce operating costs. Whether owners pay for these expenses themselves or pass them along to tenants, energy savings can be a compelling consideration when designing new windows.

New window systems must comply with the requirements of the local code governing that jurisdiction. Any code that has adopted the International Energy Conservation Code (IECC) as 
a foundation also, by extension, uses a version of American Society of Heating, Refrigerating, and 
Air-conditioning Engineers (ASHRAE) 90.1-2013, Energy Standard for Buildings Except Low-rise Residential Buildings, as a reference standard. However, IECC identifies its own path to compliance, and adopting municipalities often further modify those requirements to meet their own, local needs.

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