What is it and where should you use it?
Engineered lumber is a huge category of building products that has changed the way we build and what we can build.
A simple definition of what we mean by an engineered lumber product is anything that is made with wood that has been modified in any way beyond simply removing other wood to make a board. Or everything that is not dimensional lumber – that is the standard building material you see lining the racks of big box stores.
Lets start with the simple ones that are most common and familiar.
Pressure treated lumber – This is dimensional lumber that has been treated with chemicals to make it more resistant to mold and fugus that would cause it to rot with water and ground contact. They type of treated lumber availalbe is quite regional, in the Unites States, east of the Mississippi river we have pressure treated lumber that is green in color. It comes in sever/ ground contact and non ground contact options. High pressure like vacuum sealing is used to drive/pull chemicals into the wood to give it the desired qualities. One importate thing to note is that this is a treatment against mold and fungus, not insects. Well cover more on treated lumber in a future post.
Sheet goods – This by itself is a large and diverse category of lumber. Sheet goods are all the wood products that come in sheets. In the US, the standard size if 4ftx8ft. This is not a natural form wood takes but it does make building things far easier. In this category are things like Plywood, Oriented Strand Board (OSB), press board, and Medium Density Fiber Board (MDF). While these are used to build houses and add sheer value (rigidity, locking things together) they are not part of our structural framing so we may come back to them another day.
LVL – Laminated Venner Lumber. This product looks like plywood thats imitating a peice of dimensional lumber. They are made by laminating (gluing) long strips of wood (veneer) in differing orientations to produce boards that are two or more times stronger than a dimensional board of the same size. They also resist compression better than diemsional lumber due to the differing orentation of the wood fibers. These boards are great for creating big openings and adding lots of strength to and area with out having to use steel.
PSL – Parralell Stand lumber – these are peices of lumber made by gluing strands of lumber together under pressure that are parralell to each other. They have great compressive strength making them excellent for use as a column or post where lots of weight needs to land in one spot. They can also be built up into large dimensions and made into beams to support a large load that way. PSL’s typically cost more than LVL’s making them better for applications where they are needed for their ability to be pressure treated, or improved appearance when finishing (staining).
LSL – Laminated Strand Lumber, these are like a LVL/PSL hybrid and can look more like a peice of OSB made into a board. compared to dimensional lumber they have increased strength, stiffness and dimensional stability, but are not as strong as an LVL or PSL. They cost less than LVLs and PSLs but more then dimensional lumber. They are useful in framing when perfectly straight boards are required like framing a tall wall that will get raking light, or framing a shower where tile will be installed.
Gluelam – These beams and large structural components are a lamination of dimensional lumber. Meaning its a beam made of dimenstional lumber glued together. The provide increased strength and stiffness are are typically used to make big openings or to create uniquley shapped beams.
I-joist – This is the wooden version of the commonly recognized steel framing member. They consist of a osb web down the middle making the vertical portion of the I, and a dimensional lumber or LVL top and bottom making the flat or horizontal portion of the I. They provide increase stiffness and ability to span further distances that dimensional lumber would. Often they are designed to allow larger openings in them as well for mecanicals (duct work, plumbing and electical wires) than can be accomplised with dimensional lumber.
Web Truss – This is another floor and ceiling framing product that also mimics its steel counter part. There is typically a 2×4 laying flat running horizontally along the top and bottom with either metal (less common now) or wood webbed members making triangles between the top and bottom pieces. These trusses allow for longer unsupported spans and provide lots of openings for mecanicals.
See our next post on the draw to all these engineered products and where should they be used?