Why Use Engineered Lumber?
The benefits
A lot of engineered products came about for two reasons: they are easier to install, and they do more. In just about any industry, a product that can do more, easier, and faster will quickly find a use.
For example, compared to a floor joist, a web truss won’t tip over easily when you set it down and can be quickly nailed down. That big flat surface is also much easier to put a floor on. You don’t need to drill because all the openings are already in place for plumbing, ductwork, and electrical wiring. Everything about them is easier and faster when it comes to framing a house. The same is true of I-joist, as the openings are usually pre-cut or easy to pop out. Click here to learn more about engineered lumber.
Where not to use engineered lumber
While these products have countless great applications, there is one area where caution should be exercised… the crawlspace.
For example, when laying out the crawlspace framing, builders consult the span table for an I-joist, which shows it can span up to 16 feet. Using it at the full 16 feet pushes the I-joist to the maximum of its designed capacity.
However, nothing is ever perfect in construction, and crawlspaces are rarely ideal. As a result, humidity often becomes a common issue.
No lumber products do well in high humidity. Many problems arise for wood products in areas with relative humidity over 60% (see other post on crawlspace humidity). Certain engineered products can have even greater problems with humidity due to their reliance on adhesives for their strength and ability for mold and fungus to fester.
Therefore, when an I-joist operates at its maximum capacity but outside of its intended environmental conditions, it won’t perform as designed.
What we often see is these products degrade faster in high humidity environments and start to deflect or fail much sooner.
So should you use it or not?
Yes, there are big advantages to engineered lumber. It’s easy to quickly install, better mechanical access, and bigger spans for more open areas.
Only one of these advantages translates to the flooring system over a crawlspace, which is the speed of install.
The mechanical access offers minimal advantage for drain lines, since electrical and ductwork can be run more easily and often faster beneath the joists. Additionally, framing over a crawlspace—especially one with higher risk—reduces the number of masonry piers required. Although, very few homeowners, if any, would desire or need a more open crawlspace.
However, the solution is not to just frame the floor over the crawlspace with dimensional lumber and move on. The solution is to build the house with a crawlspace where humidity is managed. Then everything in and living in the home (crawlspace included) will have improved outcomes.
