Timber Grading

Don Pendergast

Don Pendergast, NELMA Northeast timber grader

“They still call it Black Monday,” says Don Pendergast, standing over a 10″ x 16″ timber, 48′ long. He’s trying to grade a yard full of timbers destined for the Lewis Conservation Center while a wannabe April O’Neil peppers him with questions about his 20 year career grading wood for NELMA, the New England Lumber Manufacturer’s Association. He’s grading tie beams for the “Meetinghouse,” one of five timber frames that will make up the Center. A marriage of traditional design and modern engineering, the frame is a reproduction of the 1722 East Derry Meetinghouse, clad in enormous glass panels nearly running sill to plate.

The timbers, with their #2 pencils sharpened,

The timbers, with their #2 pencils sharpened,

The LewCon crew has been working ten hour days, and weekends, to meet the client’s March deadline. They need this timber to be graded to the engineer’s specs so that they can start cutting. These tie beams have to make a grade of #2 or better, over 47 feet, which leaves us a whole foot of wiggle room. Pendergast walks to the end of the timber and locates the pith, the center of the former tree’s bole, or trunk. For stability’s sake, the pith should centered in the timber too. Knots radiate from the pith in a cone shape, reflecting the tandem growth of branch and bole. He’s looking at overall wood displacement, which means that a knot at the center of the wide face of the timber is more acceptable than the same knot at the edge. To receive a #2 grade on a 16″ wide timber, a sound knot’s diameter must be less than 8 1/8″. Unsound knots must be half that. He’s looking for shake, where the grain appears to be de-laminating; skips, of the planer; and splits. He’s looking for the slope of grain, which must be 1 in 6. He’s looking for torn grain, stains and wane. He’s looking for pitch pockets, he’s looking for unsound wood, which, if present, must be evenly scattered, and no more than 1/6th the width of the face. These are the requirements for a grade of #2. If we were going for select structural, the knots alone would need to be half that size. It takes four of us just to roll each timber, and Pendergast inspects all four faces.

Pendergast assesses a knot

Pendergast assesses a knot

Pendergast’s grading territory contains all of Maine and part of New Hampshire. It’s customary for him to spend only a few hours grading at each site; he was headed to Lovell, ME after meeting with us in Nottingham, NH. With prodding, Don’s telling us about his days inspecting sawmills, before he started grading timbers. Most mills have trained graders that grade the stock on-site. Dan asks, “What’s to keep the mill from inflating its grades?” Pendergast says that the grade is a guarantee, and that the grader, or mill who employs him, is liable if the timber fails. It’s that, and Don Pendergast. Pendergast used to visit mills for NELMA, inspecting stock to be sure that it met grade. He’d inspect a pallet of stock on the floor for sale, after the mill’s graders had done their work. Since grading relies on “the common sense and good judgement of the grader,” 5% of a mill’s stock is permitted to be below grade. If more than 7.4% is found to be below grade, then the lumber must be held, re-graded, and attain no more than 5% below grade. On Black Monday, Pendergast was inspecting a mill, and encountered stock that was 14% below grade. He held 865,000 board feet of lumber from sale.  “It screwed up my whole week,” Pendergast said. He rented a hotel room, and every morning for a week he’d check the stock that had been re-graded the previous day. There was enough material to fill 31 tractor trailer loads.

Grade stamp

Grade stamp, and yes, that’s a #1 below it

All of six tie beams passed, and two even made #1. In addition to tie beams, Pendergast graded rafters, braces, plates and posts for the nearly 50′ x 70′ meetinghouse frame. The stock was so big that we’d had to go all the way to Currier Farms in Danville, VT to source it. Ultimately, all but three of the timbers made the grade. Fortunately, we ordered extra.

One thought on “Timber Grading

  1. Pingback: Lickety Lantern Brasen Hill Barn | Preservation Timber Framing

Leave a Reply

Your email address will not be published. Required fields are marked *