Why Lumber Grade Can Make or Break Your Post-Frame Building
July 28, 2015
Lumber grade is often overlooked in post-frame construction – but it might just be the most important part. That’s why it’s crucial to use Machine Stress-Rated (MSR) lumber – whose strength is tested by a machine – rather than relying on the standard estimation called Visual Grade lumber.
Most people think little of their lumber. In their eyes, lumber is lumber. What’s the big deal where it comes from?
In reality, the type of lumber you use can have a huge impact on the strength of your building. Over the past 10 to 20 years, the quality of lumber has deteriorated due to the rise in fast-growth, farmed lumber, as opposed to stronger, slower-growth natural lumber. In fact, the National Lumber Grading Association has determined that the design strength of visually graded #1 SYP lumber is 25% weaker than its rated value.
That’s why we urge everyone to use only MSR lumber for every component of their post-frame build. But before jumping into the advantages, let’s further define the difference between the two rating systems.
Defining Machine Stress-Rated and Visual Grade lumber
Every tree that gets cut for dimensional lumber goes to a saw mill, where it is cut into boards. But how these boards are evaluated varies widely between two different processes:
*Machine Stress-Rated (MSR) lumber – This lumber is run through a machine that tests the strength of each board using either a mechanical bending process or a process similar to an ultrasound that tests wood density and structure. This test tells you the exact amount of stress a piece of lumber can handle. This is also referred to as (MEL) Machine Evaluated Lumber.
*Visual Grade lumber – This is the old industry standard for lumber used. Rather than being tested by a machine, it’s rated based on certain visual inspections, including:
*Number, size, and position of knots and holes
*Bark on edges
*Checks and splits
*Twisting, bowing, and warp
*Species of wood
It’s also common practice in the lumber industry for rejected MSR lumber to be used as visually graded lumber. Thus, some visual grade lumber sold today is actually lumber that didn’t make the MSR or MEL grade.
Now that you have a clear understanding of the differences, we’ll explain three of the primary advantages of only incorporating MSR lumber into your post-frame building project.
Three Key Advantages of Only Using MSR Lumber
1. Minimum strength of your building’s structural components is known – The elements – primarily wind and snow – constantly put stress on buildings. Over time, that stresses your lumber. The more force placed on your building, the stronger your lumber must be to withstand it.
The only way to ensure that your building will remain standing in the face of these elements is to know your building’s minimum strength. Using MSR lumber in the engineering and design process provides you the minimum strength of every piece of lumber used in your building. So, once it’s built, you know it’s going to remain durable.
2. Prevents weak links in your build – Visually graded lumber and lower quality splicing techniques have less stiffness and strength. In post-frame construction, one “weak link” among your building components can cause a catastrophe.
This is especially critical in structural elements, such as columns and trusses. Using MSR lumber eliminates any weak links so you can feel confident that your building is structurally sound, through and through.
3. Reduces regular maintenance expenses – Environmental and climatic effects can stress and fatigue your lumber. With a stronger and stiffer MSR grade your building’s susceptibility to required maintenance will be much lower.
The stronger a structure starts out, the longer it will last before maintenance is required. Over the years you will save a significant amount of money by utilizing stronger MSR lumber up-front in the building process.
Don’t base your building’s durability on an estimated strength of the structure. When contracting an engineering and design team for your next post-frame construction project, be sure they only use MSR lumber, so you can reap all the advantages that accompany it.