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W H Y C A N ‘T W E B U I L D A
P E R F E C T H O U S E ?
This
is the second part of a continuing YOUR HOME series that looks at the various
challenges faced during the life of any home. Many people expect a perfect home, whether buying a brand new
or a “used” home. With that
expectation, they will be disappointed.
There simply is no such thing as a perfect house. To
start with, what is perfect? To
each owner and builder, that probably means something different. Is being precisely square, level, and
plumb perfect? Are smooth, uniform,
unblemished finishes perfect? Is an
expected service life of 100 years perfect?
Is a virtually maintenance-free exterior perfect? If any of these criteria define a perfect
house for you, then you will be disappointed. We
suspect that Mother Nature and Mother Earth get a good laugh at our futile
efforts to build the perfect house.
There are probably endless reasons why building the perfect house is
an impossible goal. We believe the
following to be the most fundamental: 1.We
build our houses on the ground! Mother
Earth (the ground) is unpredictable. 2. We
build most of our houses with wood.
Wood is organic. Mother Nature
did not design wood to be a predictable, reliable building material. It is dimensionally unstable and changes
shape as it ages and as temperature and humidity change. In this issue, we
explore this topic in more detail. 3. We
use human beings to build our houses!
Human beings are not perfect.
Further, there seem to be fewer and fewer skilled human beings
available to help build houses. 4. We build our houses outside! That’s the worst practice of all!! The same Mother Nature that gives us
imperfect wood with which to build our houses then throws unpredictable
weather at us while we build. In this issue, we’ll look at the effect of
building our homes with wood. Ever
since man began to build his own shelter and stepped out of the world of cave
dwelling, wood has been an important part of those structures. For the log cabins of our earliest
settlers and the tepees of American Indians, wood was an essential part of
construction. Even in the centuries-old stone buildings of Europe, wood was
still an important part of the roof structures and, often, the floors. In
certain climates, alternatives have evolved, but none have endured to the
point of replacing wood as the material of choice. Each has clear disadvantages and are very dependent on certain
environments for durability. These
include the adobe and straw bale structures of the Southwest and the igloos
of northern Alaska and Antarctica. Throughout
various parts of the world, there are certainly other variations but the one
most common material that repeats itself over and over through different
cultures and different centuries is wood. Its
attractiveness lies in its availability, relative lightweight (as compared to
metals and stone) making it easier to work with, and the relatively simple
tools required to prepare it for use (cut and shape it) as well as assembling
it into a structure (nailing and screwing). Wood
comes in many different forms, species and ratings. This article is not intended to provide an understanding of the
choices of wood in construction, either now or in the past. Instead, the article attempts to explain
why the use of wood in the majority of our homes prevents us from building
the perfect house. As
noted above, any such discussion must first define what is meant by
perfect. In our experience, in
today’s world, perfect means, among other things, without visual flaws. In an average home, that means no cracks,
no blemishes in flat painted surfaces, no separations in the joints between
separate pieces of wood trim, doors that open and close smoothly from season
to season, etc. For each homeowner
the definition of a perfect home is likely to be different. Wood is Material of Choice Wood
continues to be the material of choice for most residential
construction. During the last decade
there have been some new wood-based products introduced that generally fall
under the heading of engineered lumber. TJI, Trus-Joist, glu-lam and
micro-lam are examples of product names of material in this category. Waferboard and Aspenite and similar
“plywood substitutes” can be
considered engineered lumber or structural composition board. The big difference between conventional
timber framing components and engineered lumber is the fact that engineered
lumber is processed by using smaller pieces of lumber and gluing them
together to create a larger usable timber framing member or construction
component. It’s Organic Standard
timber, while it continues to be one of the most economical materials to use,
is easy to work with, light weight and generally readily available, has one
significant flaw as it relates to building the perfect home. It is organic! Mother
Nature, in her vast gardens and forests throughout the world, grows
trees. The growth of those trees is
affected by weather variations from season to season, severe weather events
(hurricanes, floods, etc.), and geographic influences. The quality of any tree to be converted to
useful construction lumber is also dependent on the type of tree and its
age. As is to be expected in a free
enterprise, market-driven economy, those trees that produce the best
construction lumber are also typically the most expensive. Unfortunately, the framing that is not
visible once the home is complete is one area where savings is often
targeted. Thus, lower quality lumber
is often used for framing. In addition, since it is an organic material,
wood is not dimensionally stable. What
is wood? When it is still a tree (a
large plant, to botanists), wood is a growing, living entity, primarily
xylem. According to Webster’s, xylem
is a complex tissue in the vascular system of higher plants that consists of
vessels, tracheids or both usually together with wood fibers and parenchyma
cells, which functions chiefly in conduction of water and dissolved
minerals and also for support and
food storage. Xylem constitutes the
woody element of a tree. If you are
wondering, parenchyma cells, again, according to Webster’s, are a tissue of
higher plants that consists of thin walled photosynthetic or storage
cells. Add to that mix some
cellulose, which forms the walls of the cells. Cellulose, by the way, is a type of glucose (sugar). And to complete the mix, add water. Just as a healthy living human body is
mostly water, a healthy living spruce tree, for example, is about 50 percent
water. Wow, and you thought wood was,
well, just a piece of wood. It Shrinks! As
long as all of the normal functions of life in an organic entity such as a
tree are active and healthy, the water is an important part of maintaining
that health. As soon as the tree is
cut down, it dies as an organic entity and the cellular structure and
dependance on water take on significantly different characteristics. Most importantly, the water no longer
serves a function and the systems that were dependent on the water become
inactive. Without an ongoing source
and use for the water, it dries out, and the moisture content (percent of the
DRY weight of the wood that is water) begins to decrease. The
timber industry has established that 19% moisture content is an acceptable
level for a piece of lumber to be used in construction. This is referred to as surface-dry or kiln-dried
lumber. In most timber industries,
drying lumber in kilns is no longer common.
The term, however, has survived.
There is also a standard in some forestry organizations that dictates
that a piece of lumber sold for construction purposes must be at 15% moisture
content or less. In other words,
when that piece of lumber arrives on the construction site, there is still
some water in it. Over
the first few years after that piece of lumber is used in your home, the wood
will shrink. As the moisture leaves
the wood, the cellular structure must shrink to compensate for the absence of
that water. Eventually,
it will reach equilibrium with its ambient conditions which will vary
according to the climate, part of the country, how the home is occupied,
other available sources of moisture, etc., etc. Typically, that piece of lumber will reach equilibrium with its
surrounding conditions at somewhere between 8 and 12% moisture content. Thus, there will have been a change in
moisture content between how it arrived on the site and where it finally
reaches equilibrium. Sometimes, the
moisture content will even go up temporarily depending on how the material is
handled on the site and whether it is exposed to rain, high humidity,
etc. For this reason, better
contractors will often bring finished lumber into the house and allow it to
sit there for several weeks or months so that it reaches equilibrium with the
surrounding conditions before it is cut and put in place. This is the best technique for getting the
best results from a wood floor or quality wood trim, for example. It is Not Homogenous There
is yet another reason why wood is not dimensionally stable. It is not a uniform, homogenous
material. The grain structure (those
faint lines you see in a piece of wood which represent the layers of wood
that have developed through the years of growth) will vary from season to
season. Also, for various reasons,
imperfections will develop, such as knots and pitch pockets (accumulation of
sap in certain spots within the wood).
These imperfections contribute to the dimensional instability of a
piece of wood. They also contribute
to the reasons why wood will twist, warp and/or split after it has been put
in a home. As it dries out, the
influence of each of these imperfections will take on different levels of
significance within that piece of wood. Wood
will continue to be an important part of residential construction well into
the foreseeable future. Wood
continues to be a material that provides a sense of quality and feel in a
home. While we have many composite
products that are replacing such things as wood trim, cabinetry, and doors,
the homes people dream about still have a lot of wood. Framing,
of course, will remain predominantly wood, all of which is, in our opinion,
as it should be. It is simply
important to realize that as long as we do use wood, it will be impossible to
produce a perfect home. Along with
the various other reasons noted in this series of essays, the use of wood
simply makes it impossible to meet the standards of perfect often considered
by many homeowners today. Is there an answer to this apparent
dilemma? Yes, to maintain a
reasonable level of expectation for the homes that we build. Criterium
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