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How many trees to build a house?

There are many good reasons to take care of your home and saving trees is one of them. Good maintenance helps protect the environmental investment that was made in your home. Sustainability folks refer to this as the embedded environmental footprint of the home. This footprint signifies that in addition to the monetary cost of your home, constructing it extracted a toll on the environment.

Land had to be cleared, prepared and dedicated to a house rather than the natural environment. Materials had to be mined and manufactured into useable components all of which took labor and energy to produce. The making of concrete, glass, petroleum, metals, plastics, fiberglass, paint, asphalt, appliances and wood products all extract costs on the environment and many of these are non-renewable. Let’s take a deeper look at just one example of the environmental costs to build an average home. The number of trees that went into its construction.

Save a tree, take care of your home.

Today lumber comes in pre-cut, ready to use pieces of wood that no longer resemble the trees from which they came. But that wasn’t always the case. Houses were originally built by folks who had to actually harvest the trees themselves. Knowing how many and of what size to cut was important. It is way too easy today to forget that lots of trees are needed to build our homes.

Board Footage

Learning about board footage is a simple exercise in forestry that we can use to determine the number of trees needed for the lumber used in our home.

The amount of wood in a tree is referred to as board footage. A board foot is 1”x12”x12”. Since there are 12 board feet in every cubic foot, you just need to determine the volume of a tree to understand its useful wood yield. Since most lumber comes from cylindrical shaped, coniferous trees, you can do this by measuring the height of the tree and multiplying by its average cross-sectional area.

Image of tree falling operation
Old growth trees

The height of a tree can be calculated very accurately from the ground by using a tape measure and basic trigonometry (yes, you finally get to use some high school math,) or more roughly by measuring shadows. Learning how to do this is a fun exercise and videos and descriptions can be readily found online. For our purposes we will simply use the average height of currently harvested trees which is eighty feet.

Next is to determine the diameter of the tree. Foresters use a standard place to measure diameter at chest height, or about 4.5 feet above the ground. Using a tape measure and the formula Diameter=Circumference/3.14 you can calculate the area of the diameter of the tree. You’ll need to divide the diameter by 2 to get the radius for the rest of the calculations, and you’ll want to divide this radius by 12 put it in feet rather than inches! From this area we can figure out cubic feet using Cubic Feet=(Area x Height)/4, where 4 is used to account for the taper of the tree from the base to the top. With this volume known, all you have to do is multiply it by 12 to get board feet!

Now that we know how to figure out the amount of wood per tree, we just need to know how much wood we will need to understand how many trees we will need to cut down.

Mature Trees Needed Per Home

The precise amount of lumber required to build a wood-framed house varies slightly across the nation, but a good average would be 6.3 board feet for the structural framing in every square foot of house. According to the Census Bureau, the average American home built in 2013 was 2,600 square feet, meaning it would have required 16,380 board feet of lumber to build!

Image of felled tree on hillside
Logging

What does that mean in trees? For the sake of discussion, consider an average mature fir or pine tree with a height of 80’ and a diameter of 2’. Using the calculation detailed above, you will find that its lumber yield is about 754 board feet. And if you require 16,380 board feet to frame the average home, almost 22 mature firs will be needed.

Another 22-24 trees will be needed for the rest of the house and its finishes. Hardwood floors, cabinets, siding, roofing, paneling etc. could more than double the number of trees needed to complete the home. In total building an average size home today will consume forty-four mature trees.

The Surprisingly High Value of Trees

The problem with trees is it takes a long time to make one. To put the environmental value into perspective, each 80’ tall fir tree takes about 6 decades to grow to that size. Forty-four of these beautiful trees represents 2,640 tree/years of growth. All this for just a single average American home. To be available today, these trees must have begun growing just after World War II.

The sacrifice of trees is a big investment environmentally to make in a structure that perhaps through a combination of fickleness, change of fashion and poor care may only last 50 years. From a trees perspective every year a structure can be extended, counts–times 44!

In early times, the presence trees furnished us with two of life’s essential requirements, food and oxygen. As humans evolved and migrated, trees also provided additional necessities such as energy, shelter, medicine, tools and transportation in the form of ships. Trees contribute directly to the environment by providing oxygen, improving air quality, climate amelioration, conserving water, preserving soil, and supporting wildlife. During the process of photosynthesis, trees take in carbon dioxide and produce the oxygen we breathe.

Trees help to control climate by moderating the effects of the sun, rain and wind. Leaves absorb and filter the sun’s radiant energy, keeping things cool in summer. Trees also preserve warmth by providing a screen from harsh wind. In addition to influencing wind speed and direction, they shield us from the downfall of rain, sleet and hail. Trees also lower the air temperature and reduce the heat intensity of the greenhouse effect by maintaining low levels of carbon dioxide.

According to the U.S. Department of Agriculture, “One acre of forest absorbs six tons of carbon dioxide and puts out four tons of oxygen. This is enough to meet the annual needs of 18 people.” Trees, shrubs and turf also filter air by removing dust and absorbing other pollutants like carbon monoxide, sulfur dioxide and nitrogen dioxide. After trees intercept unhealthy particles, rain washes them to the ground.

It took sixty years to grow the trees for the lumber needed for your average home today. Post-harvest replanting continues to increase and the industry is very conscious of sustainability of the yield. Still, trees are slow to replace and it’s common now that thousands of acres burn up every summer. How many will be left for tomorrow’s homes?  

More benefits of trees will be discovered, and their role will continue to expand to satisfy the needs created by our modern lifestyles. Bottom line, make sure you build your home to last, then maintain it properly to make the most out of the trees and other materials that went into it.

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