Why and Where should you use engineered lumber products?
Lets just ignore the whole category of sheet goods for this post and focus on the products used for framing.
A lot of the engineered products came about for two reasons they are easier to use (install) and they can do more.
A web truss that has a flat 2×4 on the bottom is much easier to use as a floor joist than a 2×10. The web truss wont tip over easily when you set it down and and quickly be nailed down. That big flat surface is also mush easier to put a floor on. All those openings mean no drilling is required to run plumbing, duct work and electrical wire either. Everything about them is easier and faster when it comes to framing a house. They same is basically true of I-joist as the openings are usually pre cut or easy to pop out.
The trussed and I-joists also make it much easier to make bigger rooms. Paired with LVLs, PSLs, and Gluelams and making the large open floor plans that are so popular today becomes a much easier task for the framers.
In just about any industry a product that can do more, easier and faster will quickly find a home.
These things all sound amazing, but is there anywhere we shouldn’t use engineered lumber products?
We tend to think that while these products have countless great applications there is one area where caution should be exercised, and that’s in the crawlspace.
The reason is a little multi fasciated so let us build the case.
Lets use an engineered I-joist for out example.
When laying out the crawlspace framing the span table for the joist is consulted and the builder/architect/engineer sees that the specific board they want to use can span 16ft. So they lay out the crawlspace to allow the I-joists to span 16ft. The board is used to the maximum of its designed capability.
In general crawlspaces tend to not be perfectly designed and humidity is a very common problem in a crawlspace.
When the testing is done to determine the spans and capacities for engieneered lumber products the assumetion is they will be in a limate controled environment. No lumber products do well in high humidity and many problems arriase for wood products in areas with relative humidity over 60% (see other posts on crawlspaces and humidity). But 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 interact with them.
So if you take an i-joist and put it in a situation where it is pushed to its max capacity but not in its designed environmental conditions they do not perform as designed.
What we often see is these products degrade faster in high humidity environments and start to deflect or fail much sooner. This is especially true of I-joists when compared to a web truss, due to the OSB web.
If you recall we said the big advantages to engineered lumber are it’s easy of install (faster), easier mechanical access, and bigger spans for more open areas.
Only one of these advantages fully translates to the flooring system over a crawlspace, faster. The mechanical access is a minimal gain at least for drain lines, while everything else can simply be run under the joists, which for electrical and duct work would be arguably faster. In terms of big spans and open areas, very few, if any home owners will care that they have big open spaces in their crawlspace. So only the speed at which the framing can be done and the reduction of masonry piers holds as an advantage for these products in terms of framing over a higher risk area like a 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 and then everything in the crawlspace and living in the home will have improved outcomes.
So lets talk about humidity in the crawlspace.
