Hi Old Guy,
We have recently moved from Toronto to a small town north of the city, after purchasing a century home. We love the house but most of the windows have blurry or wavy glass on the lower section of the glass panes. The salesman told us that hundred year old glass tends to sag over the years forming these patterns. Is this true, and should we keep the original windows or replace them?
I live in a century home myself and we had similar saggy glass window panes. The first winter ice was forming on the inside of our single pane original windows, not to mention the fact that there were some pretty brisk drafts. We decided to replace them with up-to-date thermal pane glass – not nearly as charming, but much more comfortable. Like you, I was told by several people that over the years glass tends to slump or sag due to gravity and it forms clear but wavy patterns at the lower portion of the window over time. However, after doing some research about this, it turns out they were wrong.
Once glass is formed into its solid state it stops flowing and holds its shape forever. The patterns you see were formed by the way the glass was manufactured years ago. Molten glass was poured onto large cooling tables where it was allowed to spread as it cooled and solidified and was later cut into window panes. The glass was always thicker at the spot where it was poured. The thicker edge, which often looked wavy, was always placed at the bottom of the window frame for stability. The choice to replace your original windows is up to you. If you opt for new ones, you’ll notice a big difference in comfort and energy savings. Many manufacturers can produce replacement windows that are excellent reproductions of your originals. (You might want to note that some municipalities have restrictions on what changes you can make to century homes.) Enjoy your new old home.
The Old Guy.