Note the tight growth rings of the old growth pine from 1918 compared to those of the pine currently being harvested.
When wooden sash windows were crafted in the eighteenth and nineteenth century, pine was the wood of choice. It was plentiful, easy to work with, and most importantly, it was very strong and durable.
The pine used then is what is now called, “old growth.” This refers to virgin forests, where the trees being harvested were hundreds of years old.
Old growth pine bears no resemblance to the pine that is harvested now, which is usually only 10-20 years old.
By way of comparison, old growth pine typically had 30 growth rings per inch. The pine produced by modern lumber companies might only have 3-5 rings per inch.
Characterized by a very tight, straight grain, this is what gives this type of wood its strength. These trees grew very slowly in dense forests where there was great competition for light. Because of this, the growth rings were very tight in these trees. In addition to making the wood strong, there are other benefits.
Because the trees tended to have more growth from summer to fall, as opposed to spring or early growth, this added a natural rot resistance. In addition, because the wood is harder and drier than modern lumber, termites are less of a problem. The wood-gnawing pests prefers soft and mushy wood, which is easier to chew.
Wood is not stable, as witnessed by windows and doors that become swollen with humidity during the summer months and become difficult to operate. Also, this instability and physical movement of the wood in turn causes coatings to fail. Once there’s a crack in the paint, moisture seeps in and this allows rot to begin growing.
However, old growth pine doesn’t expand or contract very much due to its very tight grain. This makes it a much more stable material. This lumber is ideal for windows and doors since they are expected to move freely. This lack of swelling and shrinking of the old growth pine greatly contributes to the longevity of the integrity of the paint on the window sashes.
This allows them to remain in better condition for a longer period with less frequent maintenance required than most modern wood windows.
The tight, straight grain also give old growth wood greater strength than modern wood. This translates into being able to handle greater stress loads, which is of importance especially in large sash windows.
Sash windows crafted from old growth pine are irreplaceable. The wood can only be salvaged from old buildings. The forests where it grew were decimated by harvesting, primarily during the Industrial Revolution. By the 1940’s, these forests were for the most part gone.
Before deciding to replace original wood sash windows, it’s important to realize that the wood they were constructed of is irreplaceable. It’s a far superior material to any modern growth wood.
RELATED POSTS:
Sapele mahogany (Entandrophragma cylindricum) is a durable hardwood grown in Africa. With its straight grain, it has long been used for the fabrication of windows and doors.