Insulated Glass (IG) Failure
Insulated glass (sometimes called “double-pane glass”) is the assembly of two separate panes (called “lites”) of glass over a spacer frame to form a hermetically sealed air space between the lites. The air space provides a far greater impediment to thermal transfer between the interior and exterior sides of the building wall, improving building comfort and reducing heating and cooling costs.
When the sealant(s) separating the IG unit’s sealed air space are breached, the unit has failed. (Note: nothing lasts forever. Anything over 20 years’ service would be termed a respectable life cycle, not a failure.) IG failures are usually visible: the presence of condensation or discoloration of the glass within the air space or rust along the edge of the IG unit where the spacer meets the glass are common signs of an air space breach.
When the compromised IG unit was manufactured, a desiccant was encased within the air space to absorb and continuously hold the humidity trapped inside during assembly and sealing. When the sealed edges are breached, additional humidity from the outside air slowly invades the IG unit air space and saturates the interior desiccant. As more moisture enters, condensation and visible glass damage are often observable. When breached, an IG unit cannot be repaired. It must be replaced with a new IG unit custom-made to the exact size of the unit to be replaced.
Central Oregon Glass Tips:
- You can save money on an IG unit replacement at any glass shop if the unit is in a sash that can be removed and brought in to the shop to be measured.
- Many people find do-it-yourself IG replacement to be, in hindsight, a regrettable decision. We recommend you contact your preferred glass shop for both the measure and installation of IG units.
Low Emissivity (Low-E) Glass:
Standard clear glass is highly emissive, meaning it is excellent at radiating thermal energy. Put another way, radiant heat goes right through glass. Low-emissivity glass, a microscopically thin, transparent coating of reflective metals, reduces both the loss of heat from a heated space and the gain of heat from the sun. It’s materials technology that works. No heated or cooled space should have windows without Low-E glass.
There are many variations of Low-E glass. (See the Glass Class titled “How Low-E Glass is Made”.) For purposes of consumer decision-making, however, U-value and Solar Heat Gain Coefficient (SHGC) are important to understand.
U-value refers to the measured effectiveness of glass to radiate heat back into a heated space. All u-values, for all materials, are expressed as values between 0 and 1. 1 is a perfect thermal conductor, where inside temperature is fully radiated to the outside forming a “thermal short circuit”. Aluminum, for example, has a u-value of 1.00, one of the reasons that old aluminum windows are so cold in the winter. Insulated glass made of two lites of clear glass has a u-value of .70 (meaning 70% of heat that contacts the glass radiates through the glass to the exterior). In Central Oregon, consumers should purchase Low-E glass IG units with a u-value of .30 or less.
SHGC is a measure of a glass’s ability to keep ultraviolet sunlight from penetrating into a building. As with u-value, SHGC is expressed as a value of 0-1 with lower numbers indicating better ultraviolet radiation prevention. In Central Oregon, SHGC is critically important, especially in southern and western window exposures. Installing the wrong glass can cost money and create very uncomfortable living spaces. Consumers should purchase IG with a SHGC of .40 or less.
Central Oregon Glass Tips:
- Many glass shops feature a Nippon Sheet Glass Low-E product that performs poorly in SHGC. Central Oregon Glass rarely uses this glass type and then only in specific, targeted applications. Be sure your glass provider is using high-performance Low-E glass.
- Low-E glass normally has a very slight tinted appearance, visible from the building exterior but essentially invisible when looking through the glass from the interior. Different varieties of Low-E glass have differently-colored tints. If avoiding color appearance from the exterior is important to you, be sure that your glass provider is using the same Low-E product as the glass it is replacing.
How Low-E Glass is Manufactured:
Low-E glass is standard clear glass with a microscopically thin, transparent coating of reflective metals applied to one side. There are two manufacturing methods used to coat Low-E glass.
Pyrolytic Chemical Vapor Deposition Low-E Glass: sometimes called a “hard coat”, this coating is applied to raw glass as it is cooling from its molten form to its solid form on the raw glass manufacturing line. The coating molecules are tin-based and are mechanically bonded to the still-hot glass. This manufacturing method is relatively inexpensive, but all pyrolytic products lag in thermal performance, particularly SHGC.
Magnetron Sputter Vacuum Deposition (MSVD) Low-E Glass: also called sputter-coated or soft coat Low-E glass, this coating is applied to finished glass in a vacuum chamber. The coating molecules are silver-based and can be applied in several microscopic layers to achieve targeted performance levels. A plasma is created and positively charged ions bombard the negatively-charged silver source material with sufficient force to dislodge atoms of the source and “sputter” it onto the surface of the glass. While soft coat Low-E glasses vary in performance among varieties, they generally outperform hard coat products, especially in SHGC.
Central Oregon Glass Tip:
- Unless you have a specific application for Low-E glass with good u-value performance and poor SHGC performance, make sure your glass provider is using a good soft coat Low-E in your home or business. If you think a higher (lower-performing) SHGC might be for you, be sure you have a glass provider that understands and will provide the technical expertise you need to inform your decision.
Replace the Window or Replace Just the Glass?:
When window glass becomes broken, damaged or when an IG unit has failed, consumers face the decision of whether to replace the glass or to replace the entire window – glass, sash, frame, window trim and all.
In cases of residential aluminum windows the best answer is always to replace the entire window (see the Glass Class titled “Aluminum Windows”).
Unless your wood or vinyl windows are in poor condition overall, it is almost certain that the best option is to replace the glass only into the existing window sash and frame. This is true because, while the replacement IG may sometimes be as expensive as an entirely new window, the time and material cost required to install an entirely new window is far greater than to replace just the glass. A rule of thumb is that replacing just the glass is about half the cost of a window replacement.
What might change the economics? Many windows have two glass panels (example: slider windows where one half slides and the other side is fixed. If both glass panels are broken or failed, it may be possible to replace the entire window for about the same price as replacing the two glass units. If the window needs other repairs in addition to glass replacement, such as new rollers or balances, the price might edge enough closer to a full window replacement that starting new is desirable.
Central Oregon Glass Tips:
- If you have uncertainty about whether to replace glass or the entire window, ask your glass provider to quote your job both ways. Some glass shops do not do window replacements, so get a window quote from another company to allow you to make an informed decision.
30 years and longer ago, residential window frames and sash were often constructed of aluminum. While rigid and long-lasting, there is no material in the world more poorly suited for window frames than aluminum.
For example, in winter when outside temperatures are cold, the aluminum perfectly conducts the outside temperature into the building interior. That’s why rooms with aluminum windows are cold in the winter and homes with aluminum windows are so expensive to heat.
In addition to personal discomfort and higher than necessary utility bills, aluminum windows can damage the walls within which they are installed. First, they often leak so when rain or other water hits them it can seep down from the leaky window and begin to damage the wood framing. Second, because the frames can be so cold in the winter when the inside room temperature is warm (or trying to be), water condensation can be a big problem. Water collects on the cold aluminum, then drips down into the wall cavity with dry rot or other damage done.
Residential aluminum windows are bad windows, plain and simple, and there’s no way to make them good. (Note: aluminum windows are fine in places like Hawaii, but the information covered in Central Oregon Glass Class bulletins is customized to the Central Oregon climate.)
New, high efficiency windows can be a significant investment. But when aluminum windows are replaced with energy-efficient windows, personal comfort improves and you can feel the difference. The financial return often takes more than five years, but heating and cooling costs decline. And while you may not have or be developing surrounding wall damage, you are unlikely to know if you are. Such damage is often not observable until the old window is removed.
Central Oregon Glass Tips:
- If you have aluminum windows and are able to replace them, do so. There is no argument in support of aluminum residential windows vs. windows constructed with vinyl, wood or other modern, thermally efficient materials.
- Make sure your glass or window contractor makes a written contract that clearly defines the project and also establishes a process by which contingencies can be managed. The contract should establish, at a minimum, how repair of dry rot will be conducted and how the additional repair work will be fairly priced.
- If your home or building was constructed in 1978 or before, the existing paint must be tested for lead content before any work commences. If lead exists, by Oregon law the work must be performed by a contractor with additional licensing for lead paint abatement. For contractors, the fine for disturbing lead paint without a lead paint abatement license is severe. For the client, improper handling of lead-based paint risks the health of family, pets and neighbors.