Tuesday, November 6, 2012

Why Do Windows Fail?

Foggy Windows, Failed Sills
Vinyl window replacement and repairEvery thermal double pane window eventually fails - there is no such thing as a life-time thermal pane window. Wood framed windows tend to last 20 to 25 years (if well maintained). Newer, high-end wood/aluminum clad windows last about this long too and are improving every year. Older aluminum frame windows have typically lasted 15 to 20 years. Vinyl framed windows may make it 15 years if they have standard box spacers, even longer if they have a high quality Low-e. However most newer vinyl framed windows have a low-quality Intercept Spacer, along with thin vinyl frames and these windows begin failing in 5 to 8 years due to extreme thermal expansion.

Thermal Expansion
Seattle window glass replacementSunshine is the biggest cause of window failure, which is why your south and west facing windows usually fail first. Sunshine causes both a process known as “solar pumping" and the hardening of the sealant that forms the seals of the window.

When sunshine hits a double pane window the air inside heats up significantly, (think of a car on a hot day!) causing the sealed window unit to expand and push air out through the semi-permeable seals. In the evening, the window cools and contracts, drawing tiny amounts of air—and humidity—with it.

Day after day, year after year, this cyclical expansion and contraction occurs, stressing the window seals and filling the air space with moisture. Manufacturers expect and plan for solar pumping. Built into every thermal pane window frame is silica desiccant to absorb the tiny amounts of moisture inevitably drawn into the window. The desiccant, however, has a limited capacity and lifespan. In a standard box spacer (see image above) the desiccant is inside the hollow spacer. In an Intercept Spacer, very little desiccant is used. Read more about Intercept spacers here.

Seattle foggy window failure repair Desiccant Failure or Seal Failure
At some point the window desiccant will have absorbed all the moisture it can hold and that is the day a hazy, misty bluish fog clouds your glass window pane. From this point on the window begins deteriorating rapidly. If left untreated, the trapped condensation and moisture quickly corrodes the inner window glass surfaces, eventually leaving mineral deposits and a permanent white silica haze.

Wood Windows
Weathervane window repair and replacement The biggest cause of early failure in wood framed windows is lack of maintenance. Every two years the exterior seam where the glass meets the wood needs to be caulked and the frames painted. Otherwise, rain hits the glass and runs down between the wood and the glass, pools at the bottom of the IGU (Integrated Glass Unit) and rots both the seal of the IGU and the wood frame of the window.

In the picture at right, see how the bottom sill and wood stop is rotten and warped. A simple well-placed bead of caulk could have prevented this and saved the homeowner several thousand dollars in premature window failure.

Extend Window Life
Anything that makes a window hot shortens it's life. Don't park a patio barbecue under a window. You'd be surprised how many deck windows we've had to replace due to the heat abuse from a barbecue! Use external sunshades rather than inside drapes to protect the window from heat (inside drapes trap heat between the glass and drapes). Be aware that solar film - while useful in many places - significantly increases the heat inside a double pane window and always voids the manufacturer's warranty for the window.

For a free window consultation, call us today!  425-643-4444