Wood I-Joist floor framing © Daniel Friedman Wood I-Joist Photos, Product Definitions & Descriptions

This article defines "wood I-Joists" and illustrates the uses and installation of wood I-Joists used in residential building floor and roof construction. This article series describes wood products used in construction including engineered lumber, OSB, and Plywood products. Also see FRAMING CONNECTORS & JOIST HANGERS for a discussion of special fasteners used when framing with wood I-joists.

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Wood I-Joists Used in Floor & Roof Construction

Our photo (below left) illustrates wood I-joists used in construction of building floors and roofs. You will observe that the center web of the I-joist is constructed of OSB sheathing material that we illustrated just above. Our second photo (below right) shows common lumber markings found on the solid wood top and bottom chords of wood I-joists. [Click any image to see an enlarged, detailed version]

Wood I Joist in preparation for use in floor or roofing (C) Daniel Friedman Wood I Joist in preparation for use in floor or roofing (C) Daniel Friedman

Engineered wood floor trusses (photos above and below) such as I-Joists originally were constructed using a plywood web beginning in 1977, and modified by by Trus-Joist in 1969 to use laminated veneer lumber (LVL) and OSB-like laminated wood fiber web (shown in photos above left and below in combination with a steel beam).

I_Joist floor support (C) Daniel Friedman

Watch out
: common construction defects involving wood I-Joists include improper size or placement of holes cut in the I-joist web to permit installation of wiring, plumbing, or ductwork.

Improper location or size of holes, notches, or even removal of the center web can cause substantial weakening of the structure and are violations of both the manufacturer's instructions and building codes.


Below our photos of I-joists used to support a building floor illustrate how the builder avoided most cuts in the i-joist webs: flex duct and plumbing were laid out to move between I-joists rather than through them, and where an HVAC duct trunk line had to run at right angles to the I-joists the builder suspended it below the I-joists.

This was a much better solution than we found at a different job where the builder removed entire sections of I-joist web to run large rectangular HVAC ducts!

Wood I Joist in floor or roofing (C) Daniel Friedman Wood I Joist in preparation for use in floor or roofing (C) Daniel Friedman

Our wood I-joist photo at above right illustrates the use of doubled or paired wood I-joists and special steel connectors (I-Joist hangers) designed to support doubled I-joists where they abut a girder or beam.

Wood and steel roof and floor trusses are discussed separately at TRUSSES, FLOOR & ROOF and at at TRUSS UPLIFT, ROOF.

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