The issue: drilled hole size. Structural composite lumber (SCL) manufacturers typically recommend that round hole sizes not exceed 2 inches in diameter in the beam.

A 2-inch hole may be large enough to accommodate wiring but for HVAC ductwork? Nearly impossible. HVAC contractors are faced with an improvised solution of under oraround but never through the beam.

So this picture should be welcome news to any contractor that’s longed-for a more builder-friendly approach to working with composite lumber beams in roof and floor assemblies.

A leading engineered lumber manufacturer has come up with a solution that safely allows round beam holes of up to 10-1/2 inches in diameter for a 16-inch deep beam. That’s more than five times the size of the standard 2-inch hole typically advised by manufacturers.

For years, I-joists were the go-to way to install ductwork, plumbing fixtures, and wiring through a joist. The rise of wood I-joists has challenged SCL manufacturers to come up with a safe, practical ways to permit larger holes in beams to take full advantage of the existing large hole capability of I-joists.

“We listened to our customers,” says Tomo Tsuda, P.Eng, PE, an engineer with Weyerhaeuser, the company that pioneered the proprietary large-hole solution for composite lumber beams. “Our customers said changing energy codes and the desire to run ducts in conditioned spaces such as the floor cavity made larger beam holes a growing need.”

So what changed to allow an expanded round-hole size? The breakthrough stems from a series of “destructive evaluations” of full-scale SCL beams with varying hole sizes. Engineers asked what kind of forces and failure mechanisms occur a large hole in a composite lumber beam. What role did hole location and size, beam type, and loading play in reimagining beam hole size?

“Those tests allowed us to create proprietary design procedures that now offer contractors unprecedented flexibility in floor and roof construction,” Tsuda says.

The key to creating oversized beam holes is a popular engineered lumber products sizing software program called Forte®. Forte is a free download that makes it easy for contractors to properly locate and size maximum hole dimensions without compromising structural requirements.

With Forte, contractors can create hole-sizing options of up to 2/3 of the beam’s depth. The software is designed to support an assortment of Weyerhaeuser beam products, including Trus Joist® TimberStrand® LSL, Microllam® LVL, and Parallam® PSL. Click here to learn more about enlarged round role treatments in composite lumber beams.