insulating glass units

Maintaining insulating glass units in condos

An expert defogs the life expectancy and upkeep requirements of windows
Tuesday, February 16, 2016
By Dale Kerr

What is the life expectancy of a condominium building? It’s something of a trick question that was posed to attendees at CCI-Toronto’s Condo 101 course on building maintenance and repair.

Their guesses ranged from 35 to 100 years. The answer came from a prominent condominium lawyer: “Because the Condo Act requires condominiums to be maintained, there is no reason a condominium shouldn’t last 1,000 years.”

Of course, the key element in his statement is the requirement for maintenance. Every component of a building requires maintenance, from regular inspection and cleaning to eventual replacement, to ensure the building as a whole will last that 1,000 years.

What follows is a look at the life expectancy and maintenance requirements of windows and specifically insulating glass units (IGUs).

Insulating glass units

The most basic IGU (also called a double glazed unit) consists of two lites of glass sealed to an aluminum spacer to create a hermetically sealed, air-filled space between the lites of glass. The still air between the lites of glass provides the insulating value to the window.

The insulating value of the IGU can be improved by replacing the air with argon gas, or less commonly with krypton gas, or by replacing the aluminum spacer with a spacer made of a material that is more resistant to heat flow, such as silicone. The insulating value of the IGU can also be improved by adding additional lites of glass (and therefore air spaces) to create triple or quadruple glazed units, or by adding a low-e or other film material to the glass.

Most often, IGUs are glazed directly into the frame of the window, although in some windows IGUs are glazed into operable (sliding or swinging) sash members that are then installed into the overall window frame. The IGUs are typically glazed using a wet seal (or glazing tape — a sticky butyl material) on the exterior and a dry seal (a gasket) on the interior.

The seals prevent glass-to-metal contact, which could cause glass breakage; the exterior wet seal also prevents water from penetrating the lower window frame members, or sill tracks. Although the sills have weep holes to the exterior so that water that gets into the sill tracks can drain back to the outside rather to the inside where it can damage wall finishes.

Repair and replacement

Over time, residents may notice that there is condensation or “fogging” in the inside of their IGUs. This occurs when moisture diffuses through the seals of the IGU. Desiccant, a material that absorbs moisture, is added to the spacer bar to limit the moisture in the cavity between the lites of glass. Eventually, however, the desiccant cannot hold any more moisture and fogging appears on the interior of the IGU.

Once this happens, the IGU needs to be replaced. This typically happens after about 20 years, but it can occur earlier.

Manufacturers typically warrant their products for five years against this type of failure. However, the warranties only cover replacement of the IGU itself, not the labour for replacement. As the window itself will last longer than the IGUs, many consultants recommend carrying an annual allowance in the reserve fund starting at 10 to 15 years to allow for isolated IGU replacement.

The life of an IGU will be significantly shortened if it is allowed to sit in water. This can happen if the exterior glazing tape has failed and rain gets into the glazing cavity (the space between the IGU and the window frame). This can also happen if there is a significant amount of condensation on the inside of the windows that finds its way into the glazing cavity.

A cap bead of silicone sealant can be applied to the exterior perimeter to stop rain penetration if the glazing tape has failed. If condensation is the problem, reduce the humidity in the building and keep heavy drapes open so the warm interior air has a chance to warm the inside of the window.

Inspection and maintenance

Residents and property managers can help ensure they get the maximum life out of their IGUs and their windows by regularly inspecting and maintaining them.

A new standard (to be labelled CSA A440.5) is being developed by the Canadian Standards Association for high exposure windows, meaning windows installed in high-rise buildings or in extreme climates, such as coastal regions. It is anticipated that the standard will include a section on window maintenance. The purpose of window maintenance as stated in the draft standard is:

  • to ensure windows continue to provide long-term weather protection, security, light and ventilation;
  • to ensure windows remain in good working order;
  • to control water damage to building interiors or wall assemblies from possible leaks or condensation; and
  • to control energy consumption.

As per the standard, building residents are expected to perform periodic basic inspection and maintenance tasks for their windows.

Residents should visually inspect their windows, minimally in the spring and fall, for any damage, cracks in glass or finishes, fogging of the glass, missing or damaged weather-stripping or gaskets, damaged operating hardware (such as cranks or locks), difficult operation, staining that could be evidence of water penetration, or water standing in the sill tracks. Any problems should be reported to the building management.

Residents are also expected to clean the inside of the glass, and other interior window surfaces. In particular, sill tracks should be kept free of dirt that could affect the operation of sliding windows or that could block the weep holes. Replacing broken rollers on sliding sash will also help improve the life of the windows, as rough handling of the sash due to a broken roller can put stress on the sash that will shorten its life expectancy.

Properly maintained, windows should last a minimum of 30 years or more.

Dale D. Kerr, M.Eng., P.Eng., BSSO, ACCI, is a principal of GRG Building Consultants. With close to 30 years’ experience looking at window systems, including six years as chair and vice-chair of the CSA A440 Standard on Windows, she is an expert on window technology. Dale can be reached at GRG’s Newmarket office at (800) 838-8183.

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