Although there have been many breakthroughs in new building materials, there is still nothing that can quite take the place of the natural beauty of wood. Wood is perhaps the oldest building material known to man, and is still just as much in demand today as it ever was. Wood is cheap, easy to shape and handle, and renewable.
However, there are limitations in regards to wood in its natural state. For one thing, cross sectional area of a given beam or column is limited to that of the tree from which it is taken. Structural beams and columns must have a sufficiently high second moment of area, and as such, often have rather large cross sectional areas.
When trees are felled without regard to whether or not they are being replaced, we pave the way towards a world where wood will no longer be affordable and available in the way it is today. But even though we plant trees to replace those we cut down, we all know that trees don’t just “grow up” overnight. At the same time, demand is in no way declining.
This is when smart people who saw the handwriting on the wall came up with a brilliant solution – modern glued laminated timber, aka glulam. By gluing many smaller fragments of wood together, a larger component can be produced. In fact, the size of the component is only limited by handling and transportation constraints.
Glulam removes two major limitations: First, it allows us to produce large structural components with relatively small and young trees, removing the dependence on larger, older trees. Second, natural wood has a tendency to warp, twist, crack, shrink, expand, etc, as moisture enters or leaves, potentially causing serious problems for any structure.
Glulam is considerably more stable in this respect, as well as has significantly higher strength and stiffness properties when compared with its natural counterparts. Wood in its natural state is full of small defects – primarily in the form of knots – which significantly lower the load-bearing capacity.
A beam’s second moment of area is based on an “ideal” specimen, meaning one in which there are no defects. If defects are taken into account, a given specimen’s load-bearing capacity can easily be reduced by half. Glulam not only reduces the negative impact of such defects, but also has a higher elastic modulus than natural wood.
Glulam is typically used for beams, columns, and other structural and framing components that are hidden beneath the finished surface of a building or house. They can however, also be used for exterior or more visible applications as well if coated. Whether to use glulam or natural wood is a matter of personal preference, cost, availability, and design.
For those who are interested in more detail on glulam connections and related information, I’m linking to a PDF I found very helpful with images and diagrams detailing a wide assortment of joints and connections, as well as examples of what not to do: Glulam Connection Details