2024-25_NTCA_Reference_Manual_dig_dwnld

Glossary of Terms for Engineered Wood Products

Blocking Panel – Cut from I-Joists, the blocking panel is placed between and perpendicular to the I-Joists. It functions to evenly distribute vertical loads from above when placed over load bearing walls, provides lateral support to keep I-Joists in a true vertical position, and also transfers lateral shear forces from the floor system into the supporting members below. Cantilever – An unsupported overhang of joists extending beyond the load bearing support wall of a building. Joists should be supported laterally by blocking panels at the bearing wall nearest the cantilevered end to prevent rollover. In general, the cantilever length should be 1/4 of the adjacent span or more to prevent “humps” in the floor that may negatively affect your tile installation. Flanges – The top and bottom rectangular components of an I-Joist that are either sawn lumber or structural composite lumber, such as laminated veneer lumber (LVL). The top flange is of the same type and grade of material as the bottom flange. The net flange size depends on the material used. Glue Laminated Timber – also known as glulam, is composed of selected laminations of lumber glued face to face and primarily used in commercial construction. I-Joists – An “I” shaped engineered wood structural member. I-Joists are prefabricated using sawn or structural composite lumber flanges and wood structural panel webs, bonded together with exterior-type adhesives. Due to their unique shape and geometry, they require specific construction details to perform properly. Rim Board – A rectangular board ranging from 1 in. (25 mm) to 1-1/2 in. (38 mm) thick placed perpendicular to the I-Joists at the perimeter of the building. It functions to evenly distribute vertical loads from above when placed over load bearing walls, provides lateral support to keep I-Joists in a true vertical position, and also transfers lateral shear forces from the floor system into the supporting members below. Rim Joist – Similar to Rim Board, an I-Joist can be placed perpendicular to the I-Joists at the perimeter of the building. It functions to evenly distribute vertical loads from above when placed over a load bearing wall, provides lateral support to keep I-Joists in a true vertical position, and also transfers lateral shear forces from the floor system into the supporting members below.

Squash Block – 2 in. x 4 in. (51 mm x 102 mm) or 2 in. x 6 in. (51 mm x 152 mm) lumber cut to a vertical length of the depth of the I-Joist plus 1/16 in. (2 mm) and placed adjacent to I-Joists beneath load bearing walls to transfer concentrated loads above to the load bearing wall below. Structural Composite Lumber (SCL) – Rectangular sections produced by combining strands or veneers of wood together with exterior type adhesives. Common types are laminated veneer lumber (LVL), parallel strand lumber (PSL), and laminated strand lumber (LSL), which can be used as beams, joists, or the flanges of I-Joists. Webs – The wood structural panel serving as the vertical center component of an I-Joist. Can be plywood or oriented strand board (OSB). All panels are classified as Exposure 1 or Exterior and are 3/8 in. (10 mm) in thickness or greater. Web Stiffeners – A wood block that is used to reinforce the web along the vertical axis of an I-Joist where the web is in jeopardy of buckling out of plane or the web of the I-Joist is in jeopardy of knifing through the I-Joist flanges. There are two kinds of web stiffeners; bearing stiffeners and load stiffeners. They are differentiated by the applied load and the location of the gap between the slightly undersized stiffener and the top or bottom flange. Load stiffeners are located between supports where significant point loads are applied to the top flange of an I-Joist. The 1/8 in. (3 mm) gap is at the bottom flange of a load stiffener. Bearing stiffeners have the gap located adjacent to the top flange. They are used at supports where significant point loads exceed the joist’s bearing capacity. The bearing stiffener transfers load directly into the bottom flange and increases the joist’s bearing capacity. Wood Structural Panels – Used as the subfloor and/or underlayment in wood floor construction, this category includes softwood plywood, hardwood plywood, oriented strand board (OSB) and particle board. Knock-outs – A 1-1/2 in. (38 mm) diameter perforated hole located at equally spaced intervals along the web of an I-Joist. The knockout is intended to provide plumbers and electricians access holes for wiring or small diameter pipes without having to drill holes or check manufacturer’s literature to determine where holes can be placed. The knockout can be removed by lightly tapping the plug with a hammer.

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NTCA Reference Manual | 2024 / 2025

Chapter 2 | Substrates