When people think of wood, there is generally a controversy
on whether harvesting trees is worth it.
Wood use is very prominent in many phases of construction from building large
buildings to small toys for kids. Wood
is an important product in our everyday lives, but what are the positive and
negative effects of using wood in construction?
The Good
Wood has been engineered over time
to become a suitable building product for the construction of office buildings,
homes, and schools. Engineered wood refers to products that change slightly
from natural wood so that the limitations it possesses are lowered and desired
characteristics are enhanced (Zastrow). Some common engineered wood products include
plywood, face veneer, particle board, fiberboard, wood flooring, and glulam. These
products have made it possible to begin building larger skyscrapers out of wood
to decrease the carbon emission from using construction products such as cement
and metal. Using engineering technology, densified wood has been made which is
considered “as strong as steel” (Zastrow).
The Bad
As there are many good qualities of
using wood for construction, wood does have some major limitations. Some of
these limitations include warping, swelling/ shrinking, rotting, and knots that
effect the strength. As longitudinal shrinkage
is negligible, the loss or addition of moisture causes a wood to shrink or
expand in the tangential and radial directions. The tangential direction of
wood has the most shrinkage being 4-12% (Dimensional Shrinkage). To help prevent shrinkage, wood can be dried,
but this is an expensive process. Normally, wood used for homes is dried to
about 7% to help prevent the doors, drawers, cabinets, floorboards, and other
wooden material in the house from warping or sticking when opening (Dimensional
Shrinkage). Another major issue when
using wood for construction is its ability to grow fungi and begin to decay. When
fungi begin to grow on the wood, the plant cells degrade and the carbon in the
plant material is converted to carbon dioxide gas and the wood begins to lose strength
and weight (Pasanen). Wood is usually treated with preservatives, but over time
the wood is still subject to decay, especially when used outdoors. Knots of
trees form when a branch dies or is removed from the trunk of the tree. In knots,
the direction of the grain of the wood is changed which causes a decrease in strength
almost as if there was just a hole in that area.
The “Neutral”
Trees are considered carbon
neutral. This means that that carbon they can sequester carbon for a large time
period, but then emit the carbon back into the atmosphere at the end of their
life. While growing, trees can sequester as much as 48 pounds of carbon dioxide
per year and about 1 ton of carbon dioxide by the time the tree is 40 years old
(Evans). This sequestered carbon dioxide stays trapped in the tree though its
construction of buildings, paper making, wooden toys, and many other objects made
of from trees. Trees are considered
major carbon reservoirs. Many people believe that the carbon stored in trees is
completely limited from the atmosphere. However, this is not the case because carbon
is released back into the atmosphere when the tree begins to decay. Many building materials emit carbon dioxide immediately
during construction, but trees are different. This allows trees to be neutral since the
amount of carbon dioxide they emit is generally similar to the amount of carbon
dioxide they store.
Resources
“Dimensional
Shrinkage.” The Wood Database,
https://www.wood-database.com/wood-articles/dimensional-shrinkage/.
Evans, Evr. Tree Facts. https://projects.ncsu.edu/project/treesofstrength/treefact.htm.
Pasanen, Anna-Liisa, et al.
“Fungal Growth and Survival in Building Materials under Fluctuating Moisture
and Temperature Conditions.” International Biodeterioration &
Biodegradation, Elsevier, 4 Dec. 2000,
https://www.sciencedirect.com/science/article/pii/S0964830500000937.
Zastrow, Mark. “Crushed Wood Is Stronger than Steel.” Nature
News, Nature Publishing Group, 7 Feb. 2018, https://www.nature.com/articles/d41586-018-01600-6.
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