|Walk into any local lumberyard to get a standard 2-by-4 stud, and you'll find that it's been graded to indicate to you, the buyer, that each particular piece of wood has been deemed structurally safe for construction. And if you were building a stick-framed house, you would never trust the soundness of your home to a product that wasn't certified, right? So why should log homes be any different? Yet, each year, prospective log home-owners buy untested, ungraded timbers from sawmills in the name of saving money on the biggest structural (and most visible) component of their homes, and the results can be devastating.
"The consumer has to be concerned with purchasing logs that don't meet national grading standards," says Dana Delano, director of sales and marketing for Ward Cedar Log Homes in Houlton, Maine. "Slope of grain, knots per foot and soft knots can weaken a log's structural strength. You may be able to get cheaper logs from a sawmill or log home manufacturer that doesn't grade, but you don't have the assurance that these logs will perform under the stress load of your completed home."
So what does all this mean? According to Rich Horn, sales manager for Northeastern Log Homes, the idea of log grading dates back to the initial meeting of what was to become the Log Homes Council (www.loghomes.org) in the 1970s.
"In November 1976, there was an emergency meeting of log home manufacturers, because there was scuttlebutt that log homes might get coded out of existence due to energy and structural-stability concerns," he explains. "The industry was rude and crude in those days—from a design-and-engineering point of view. So, this group of log-home company owners and presidents gathered to address this issue so the industry could move forward. The need to grade logs came out of this meeting. The challenge was that every company had its own profile, making standardization difficult. A New York City engineer named Steven Winter came up with the concept of the 'in-scribe rectangle' measured on the end grain of a cut timber. Now the grading rules could be applied to any log, no matter if it was round or rectangular. It was a real breakthrough because it put everyone on an equal playing field."
"Our industry needed a program that was comparable from one manufacturer to the other," adds Mark Feder, vice president of sales at Ripley, West Virginia-based Appalachian Log Structures, who holds a Bachelor's of Science degree in Forestry from West Virginia University.
And thus, the Log Homes Council's log grading program (American Society for Testing and Materials Standard D3957 Standard Methods for Establishing Stress Grades for Structural Members Used in Log Buildings) was born. A stress grade is a set of maximum "defects" that is allowed in logs or timbers after they've been manufactured. Size of knots, slope of grain, decay, checks and insect issues are all part of that set. And it's important to keep in mind that these criteria should not only apply to logs used in the walls, but for ridge beams, purlins, rafters—all structural wood components.
"Grading doesn't have anything to do with beauty of the logs; it has to do with structural integrity for construction," reminds Scott DeBerry, market development manager for Bronson, Florida-based BK Cypress Log Homes. "If you're worried about the aesthetics, look at photos of finished homes and check out sample logs. That's the best way to judge the look of the product."
How to Tell if Logs are Graded
"There's a protocol to retest a log package to make sure that it's on grade," says Rich. "There are requirements to be correct and there are consequences if a company doesn't meet that standard. They may have to replace inferior logs that were passed through, and the company could even lose its grading certificate number (i.e., lose their license) if they allow inferior logs to slip through beyond the allowable amount.
What's Acceptable and What Isn't?
Knots. Size of knot dictates the strength of the material. The larger the knot, the weaker the wood. Both size and clustering are factors.
Slope of grain. Grain should be as parallel to the length of the log as possible. Once it deviates, it can lose strength and become more susceptible to splitting or cause a structural defect after seasoning.
Species. Species are not compared against each other. Each is judged individually on its own merit. But some species more easily meet grading criteria than others. Yellow poplar, for example, typically doesn't meet the minimum standard, according to Mark, because it has a large knot structure and too much slope in the grain, and it loses moisture fast (meaning it has a tendency to check severely). Yellow poplar used to be ok to build a log home with, because the logs were taken from old growth and virgin timber with lots of heartwood; but today, it's not a desirable species for log home construction.
Moisture content. This component doesn't always factor into log grading; however the Log Homes Council is lobbying to make moisture content declaration part of the standard. Currently, there are provisions that companies should indicate a log's moisture content from green (freshly cut timber) to dry (seasoned timber) and kiln-dried logs should have a moisture content of less than 19 percent. One level is not superior to another, but it should be specified so proper construction measures can be taken.
Are Logs Required to Be Graded?
Think of it like this: if you were going to build a stick-framed house, you would have to build it out of graded material. The same applies to log home construction. You don't want to build with a log that's ungraded. It's a structural component of your home. You want to build with the best materials. Graded logs can be slightly more expensive than non-graded logs, but the assurance of quality is worth it. As Rich says, "Companies that participate in the structural grading program always say, 'This made our product better.'"