Modern Buildings: A Guide to Engineered Wood Products

Sept. 23, 2019
Tim Duffy says that developing a deeper understanding of engineered construction products is necessary to making informed fireground decisions.

National Fire Protection Association (NFPA) 220: Standard on Types of Building Construction, defines the types of buildings based on combustibility and the fire-resistance rating of their structural elements. Type III “Ordinary”, Type IV “Heavy Timber” and Type V “Wood Frame” all have structural wood components utilizing combustible materials (wood).

Separating buildings into five categories can aid you in your initial on-scene size-up, but a deeper understanding is required to make informed decisions.

From the fire service perspective, engineered wood products are engineered for structural applications and are made by combining wood strands, lumber, veneer or other wood fiber with glue. Understanding the strengths and weaknesses of these products, as well as where they might be found should be a priority for every firefighter.

While every product may not be covered here, the following list will provide readers with information about the more commonly found engineered wood products:

Glulam

Glued laminated lumber is made up of wood laminations that are bonded together with adhesives. The grain of the laminations runs parallel to the length of the member. Glulams are used as posts, beams, headers, and girders and aresometimes found in exposed locations in vaulted ceilings, churches or other commercial applications. This product is often used in newer Type IV buildings.

Wood “I” Joist

Wood “I” joists use sawn or structural composite flanges and plywood or OSB webs bonded together with adhesives. The wood “I” joist is fairly easy to recognize due to its shape and is frequently used as a floor or ceiling joist. Some buildings that have long roof spans may have this product used as a rafter, however it is not very common. The relatively thin when materials, which provide most of the strength, are the weak link of this product causing early failure when exposed to heat or fire.

OSB

Orient Strand Board is an engineered wood product made from wood strands and heat-cured adhesives arranged in cross-oriented layers. This product is typically used as a subfloor as well as wall and roof sheathing and may have a waterproof or flame-resistant coating
.

Structural Composite Lumber (SCL)

LVL, PSL, OSL, LSL are all examples of structural composite lumber with similar characteristics. These products are created by layering veneers, strands or flakes with adhesives to form a large billet which is then sawn into specific sizes. These products may be fastened alongside one another and used as headers, beams, valley and hip rafters or as a stand-alone member as a joist or rafter. The mass of these products is equal to or greater than traditional wood members and tests performed on LVL products by the USDA (1) and Warren Lane (2) found that failure time was similar to sawn lumber.

Recognizing the presence of engineered wood products is not only imperative to ensure firefighter safety but also required in order to select appropriate strategies and tactics. Engineered wood products are not going to disappear, in fact, they are sought after and constantly improving. It is up to us, the fire service, to delve deeper and become engaged students of building construction.

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