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Last month, we started to share some of the wealth of information about windows that can be found on the National Trust for Historic Preservation website. We continue this month to examine why original windows are worth saving.

Reason #1: Old Windows are Built with High-Quality Materials

Wood windows made prior to the 1940’s are likely to be made from old growth wood. Why does this matter? Old growth wood has distinct physical characteristics that can make it superior to new materials. For instance, this wood is denser and more durable, rot resistant, and dimensionally stable than modern wood. Also, wood used to make windows constructed prior to the 1940’s was most likely harvested locally, making it better suited for local climate conditions.

Modern wood derived from tree farms grows fast due to management practices and the application of fertilizers. This is not necessarily bad because we need a steady supply of lumber for all sorts of uses. However, when it comes to selecting wood for windows, speedy growth is not always better. Fast-growing wood not only has growth rings that are further apart, but also a higher percentage of earlywood or sapwood. This earlywood is rich in sugars. Wood with more widely-spaced growth rings is less dense and therefore not as durable. The sugars feed the tree as it grows, but are also attractive to insects who don’t care if the wood is a live tree branch or your window sill.

The slower and more naturally the tree is allowed to grow, the denser the structure. This results in a stable, dense wood that mills well, holds paint and stain well, is not as attractive to insects, and has natural rot resistance thanks to a higher percentage of latewood.

What does this mean for older windows? In short, a new wood window will not last as long as the original. What about mahogany or other hard woods? They may be an option, and will tend to be denser and of higher quality than plantation-growth southern yellow pine, for example. However, these high-grade wood products can be expensive. Also, if window replacement is being considered for sustainable reasons, it is far greener to retain and repair an existing window than to have timber shipped thousands of miles to be manufactured into a new product.

Reason #2: Old Windows “Fit” Their Openings

Historic windows were made and custom installed to fit their specific window openings. Each opening is probably a little bit different, especially because natural materials react to their environment. For example, wood typically shrinks during dry weather and will swell with increased humidity. Older windows may have shifted and changed with their openings as the building aged. After 100 plus years, they may no longer be exactly square, but they still fit the opening.

If new stock replacement windows are installed in historic openings, there is very little chance that they will fit well. The resulting gaps around the windows will be just as – if not more – drafty as the historic windows that were tossed. Often, the size difference between the stock window and the historic window opening is compensated for by reducing the overall size of the opening. The result is a smaller window, less light, distorted proportions, and trim that doesn’t match the opening.
Do we have your attention? Reasons 3 & 4 to follow in August…..

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