Downsizing replacement windows is usually a problem with renovations and repairs. Sometimes it coincides with an effort to improve the energy efficiency of a house. A window needs to be replaced and the homeowner discovers that they will have to special order a window to exactly match their opening. Instead they will opt for putting in a standard-sized window to save some bucks. Or maybe they will go with the size that is on sale.
If the difference is small this may not have a big impact on the look of the house, but I have repeatedly seen where homeowners opt for a window that much smaller, and the symmetry and proportion that made the home pleasing is now compromised.
It is even more of a tragedy when the original window was unique and special in some ways. For instance Gothic windows, with their pointed arches, are not likely to be standard fare for your typical window company. They will have to be made to order. This will cost, but they add to the aesthetic value of a home. They make it unique and lovely. Replacing them with standard rectangular windows may save money now, but it will permanently reduce the value of the home.
Sometimes smaller replacement windows are required in order to effect a change to the interior. When we rebuilt our kitchen we had to reduce the size of a window because the original went down to low to allow the counter to pass under it. Our sink was going to go where the window was located and we couldn't set our sink as low as the base of the window. The solution was to fill in the bottom part of the window frame and go with a smaller window.
In our case that window did not align with any other windows, nor did changing it effect the balance or symmetry of the house. It was something we put careful thought into, but I would say that many people do not fully consider the external effects of their internal changes.
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