Wood is the most environmentally friendly of all structural building materials available today because it is renewable and sustainable.  However, timber does have many limitations when it comes to constructing a home.

First of all, while it is renewable, it takes a long time to grow a tree of suitable size to provide trusses, sheathing, and framing lumber; builders and architects are further limited in the maximum size of components that can be milled from most mature trees.  Lumber warps, splits, and is studded with knots and other blemishes which have both structural and aesthetic ramifications.  Then there is the environmental issue of harvesting enough wood to meet the need for building materials while maintaining sufficient forests to maintain oxygen and moisture levels in the atmosphere.

While there was initially a lot of reluctance among builders to forego the old and familiar, more and more homes are being built at least partially with a lumber bi-product, engineered wood.  These products are manufactured through processes that use recycled wood, waste wood such as chips, strands, even sawdust, to produce framing lumber, joists, and paneling.

Engineered wood can be made from any kind of tree - hard or soft - and the lumber is generally straighter and stronger than milled lumber.  It is also more consistent than the products produced by nature and can span greater distances without sagging.

Engineered wood is more expensive than dimensional lumber but the total installed costs can be less because of the ease of installation, dimensional stability and higher quality.

The first engineered wood has been around for decades.  Plywood consists of veneers arranged in perpendicular layers.  The cross-laminated layers give plywood strength and stiffness.  However, over the years the safety of the glues used in the process have been questioned.  More about that later.

Another engineered wood product that is in common usage is Oriented Strand Board or OSB.  This material has become so common that most people with any interest in construction recognize it by its acronym.  OSB consists of wood strands, typically three to four inches in length, bonded with adhesives into a mat which is then layered with other mats. OSB is used as sheathing, in I-joists, and as the "bread" in the sandwich that is a structural insulated panel.

Another popular engineered product is Glulam (glued laminated timber.)   This is created by bonding together individual pieces of lumber having a thickness of two inches (50 mm) or less, end-joined to create long lengths.  These lengths or laminations are then face-bonded together to create the finished product. Glulam can be shaped into forms ranging from straight beams to complex curved members, and used in headers, floor girders, and ridge beams.  These products are also widely used in commercial construction.

There are a number of other types of engineered wood products.  We will talk about the environmental appropriateness of these products and some of their limitations later in the week.