Although wooden windows have a unique character and beauty all their own, some owners struggle to justify keeping them when the issue of refurbishment arises. When historic buildings intended to see an extended service life confront the issue of window repair, modern advances in chemistry may be able to provide a long-lasting remedy.
Acetylated wood is a sustainable, non-toxic, environmentally-friendly product made from managed growth trees. The chemical structure of the wood is changed by using acetic anhydride, which is made from acetic acid, more commonly known as vinegar in its highly diluted state. This product has existed in the form of cellulose acetate, or acetylated wood pulp, since the 1930s and has long been used for products such as photographic film and playing cards. However, advances in technology have finally made the process of acetylation more efficient. Acetylated wood is manufactured by Accsys Technologies PLC and is marketed as Accoya wood.
Dimensional lumber becomes much more stable after undergoing the acetylation process. The molecules that absorb water, called free hydroxyls, are replaced by the acetyl group of molecules found in acetic anhydride and wood actually loses its ability to absorb water. As a result, wood can neither swell nor shrink, making it ideal for windows and doors. No matter the climate or the weather, windows and doors won't stick because humidity has been factored out of the equation. This stability allows the wood to be 30% more thermally efficient than other wood products.
Due to the improved stability of the wood, coatings such as paint or varnish can last three to four times longer than with traditional wood products. In addition, the enzymes used in the process render the acetylated wood indigestible to insects as well as microorganisms, such as fungi. The wood treated in this process is also virtually rot-proof.
Acetylated wood has been used on projects all over the world, ranging from lighthouses and bridges to siding and bulkheads along canals. The lifespan of this type of wood when used for exterior applications is guaranteed for 50 years for above ground use and 25 years in-ground or with freshwater contact. The expected lifespan of window frames made from this type of wood ranges between 77 to 90 years, with maintenance only being required every 10 to 12 years.
Historic sites are a perfect application for this wood. For example, when the United Methodist Church in Mobile, Alabama, needed to have new windows manufactured, they chose acetylated wood. The total lifetime cost was the deciding factor for this project, rather than the initial expense. The U.S. Park Service also chose Accoya wood when President Theodore Roosevelt's home, Sagamore Hill, needed renovation. The reduction in maintenance as well as its environmentally friendly nature were factors in that decision. The expected lifespan and lack of maintenance for acetylated wood make it a sound choice for the decades to come.
In addition, this green building material is Cradle to Cradle (C2C) Gold certified and it can contribute several points towards the U.S. Green Building Council's LEED certification. It's also Forest Stewardship Council (FSC)-certified for its chain of custody from managed plantations. Acetylated wood is a CO2 negative product through out its lifespan, is completely biodegradable and recyclable. Between the ecological benefits and the superior performance of acetylated wood, this is the wood of the future.
- Linda Childers
