The boys are back from another raising in South Carolina and are getting ready for our next project, a glulam job in Pennsylvania. We have gotten a lot of requests for glulams lately, and I thought I’d write a blog about this particular building medium.
Glulams, or glued laminated timbers, are highly engineered beams that are designed with several things in mind. They can be graded for extremely high stresses or for minimal spans. This is engineer-speak to me, and relates to how the boards are layed up. The only thing I can speak knowledgeably about is that if it is a 24F designation it has an allowable bending stress of 2400 psi.
All of this is to say that glulams are really really strong. Because of how they are constructed they typically only lend themselves to steel joinery, as opposed to traditional mortise and tenon joinery as is typical with heavy timbers. The choice to use glulams is both an aesthetic and a structural decision: some people like the look of the individual striations of the laminations and the steel, and the strength of the glulams is measurable and quantifiable. Engineers love to have actual numbers with which to work.
As far as the look of the glulams goes there are several options that clients have. First is the species of wood involved. We have worked with Douglas fir glulams, southern yellow pine glulams, western red cedar glulams, and port orford cedar glulams.
Another option is the curve of the glulam. If there is a sizeable curve in the beam it may be better to use a glulam rather than a beam that is sawn with a bandsaw. There are a couple of reasons for this: the beam that is sawn will be by its very nature weaker than a glulam that was designed for that curve and glued with that particular radius. The other reason is that there is a lot of waste in a beam that is sawn to a curve.