June 12th, 2014
How Long Should A Window Last?
Several weeks ago, I received a phone call from a homeowner who was rather upset about his wood windows. The windows were still functioning well with the exception of the insulating glass, which was imploding, causing the glass to visually distort. “Why are you calling me?” I asked, and “where did you get my name?” He went on to explain that he was researching the cause of this implosion effect and came across several articles that I had written years ago about argon retention. He wanted to file a lawsuit against the manufacturer to force him to come out to his home and install new insulating glass units in all of his 38 windows. I asked him what he wanted from me, and he replied, “I want you to be my expert witness in court.” I asked him how old his windows were, and he replied, “My windows are only 18 years old!” My response to him was, “They have served you well – now go buy new windows!”
So, how long should a window last? Well, in his case, the windows were still performing fine except for the insulating glass. This implosion was due to the argon. “Why did we ever start putting argon in the insulating units in the first place, he asked, and exactly how was this causing implosion?
Any physical chemist will tell you that if you cram molecules of the same type within a confined area, the laws of nature are such that these molecules will try to escape. This is called entropy. Entropy is a measure of the randomness of molecules in a system. Spontaneous changes in isolated systems occur with an increase in entropy. Molecules like to go from orderly mode (packed within an isolated space) to a random mode, or a higher degree of entropy. In a nutshell – the argon molecules want to get out!
Ok, so back to the original question: why do we try to defy nature by forcing a bunch of argon molecules to stay together in close quarters? At two pennies a liter, the cost of gas filling with argon is modest while it results in a nice jump in thermal performance, I explained. High speed gas fill machines are quite common these days. This means we can fill IG units very efficiently translating to a significant value for the consumer.
So, what have we learned in the past 18 years? I explained to him that at the time these windows were being built, the window industry was just getting started with argon. We were just beginning to understand the permeation characteristics of argon through IG sealants and how, due to the law of partial pressures, argon moves from inside to outside faster than air permeates from outside to inside an IGU thereby resulting in a negative pressure over the years. This is the cause of the deflection and visible distortion. The question to ask is “how long will this take to happen? Will it happen in 1 year, 5 years or 18 years?”
Well, if it happens in a single year or even in as few as 5 years, I would say we have a problem, since most homeowners expect their windows to last much longer than 5 years. However, if it takes 18 years to develop, then I would argue that this window system did not fare too bad at all. There are many other ways for a window to fail. Seals eventually fail due to the effects of hot- cold temperature cycling, heat, UV aging and wind loads. When seals fail, so does weather tightness. Water vapor creeps in, glass seals fail, and fog obscures the view. Once the view is obscured, a window is not doing what it is intended to do, that is, provide a view, so it must either be repaired or replaced. Hardware also fails, and then there is the question of whether or not a replacement part can be found after all those years. I also get quite a few phone calls regarding window parts. I can’t tell you how many calls I have gotten from homeowners wanting me to help them source parts for a 20 year old casement window, sash locks and even screen parts. This makes be believe that many homeowners expect their windows to last well beyond 20 years, and indeed modern frame designs are quite capable of doing so. It just boils down to repair costs and availability of compatible components to repair their windows. Sometimes I just say to them, “Call a guy named Murph at Strybucs!”
If one does a little research, most building industry sources will say that window glazing (IG) should last at least 20 years, and the window itself should last from 30 to 50 years. Maybe so, but based on the advances made in window technology in the last 20 years, I would say that 20 years from now, I will be replacing my windows not because of failure, but rather obsolescence!