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Shrinkage: Less is More

EW: Why do you recommend woodframing in 4–5–story construction?

CN: Wood is readily available, and it has considerable strength and durability. Plus when you look at the reduced material and labor cost compared to steel or concrete, it’s much more cost competitive than concrete or steel.

EW: What about shrinkage?

CN: Shrinkage in wood is caused by high initial moisture content, with the average for lumber at 19 to 20 percent. It will shrink until it reaches its moisture equilibrium, which in most structures is around 8 to 12 percent. As it shrinks, it’s not uncommon to see a quarter of an inch of shrinkage per floor. So with a 4–5–story building that’s more than an inch of shrinkage. Ultimately it can affect shear wall performance and the structural capability of the building, causing windows to sink lower than exterior brick veneer and potentially resulting in damage to plumbing.

EW: How does LSL fit in?

CN: In wood-framed construction, the majority of the shrinkage comes perpendicular to the grain. We specify LSL for horizontal framing members in our wall plate system. Because LSL is manufactured at a lower moisture content, around 6 percent, it helps eliminate plate shrinkage.

EW: Do you see this application becoming a long-term trend?

Multi-story wood framing is going to continue because of both the economy and efficiency of these products. In British Columbia, Canada, wood-framed buildings go up to six stories, and there is testing for structures up to seven stories. But we know for a fact that lumber is going to shrink, and it’s typically going to drop down to that moisture content of 8 to 12 percent. Using LSL in wall plates to eliminate that shrinkage just makes sense.

LP® SolidStart® LSL can help reduce plate shrinkage. It’s manufactured at approximately 6 percent moisture content, less than the moisture equilibrium of most structures.

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