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Wood I-Joist floor framing © Daniel FriedmanWood I-Joist Definitions, Installation, & Connections

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Wood I Joist Installation & Inspection Guide.

This article defines "wood I-Joists" and illustrates the uses and installation of wood I-Joists used in residential building floor and roof construction.

We illustrate the use of wood I-joists with a plywood or OSB center used in floor and roof structures and we include illustrated details of the use of framing connectors to tie I-Joists to rim joists, beams, girders, steel girders, and also I-joist roofs to a wood-framed wall.

This article series describes wood products used in construction including engineered lumber, OSB, and Plywood products.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Wood I-Joists Used in Floor & Roof Construction

Wood I Joists atop a built-up laminate beam roof support © Daniel Friedman at InspectApedia.com

[Click to enlarge any image]

Article Contents

Above: wooden I-joists set atopo a built-up laminate wood beam supporting a roof.The 2x4 blocking along the beam sides was added to permit covering this beam with drywall. We later removed the blocking and left the beam exposed as an architectural feature in this home addition.

Below you can see the finished laminate girder as it was left exposed in the finished space. The building inspector thought we were nuts but I like it and so do the building occupants.

Wood laminate girder supporting roof left exposed © Daniel Friedman at InspectApedia.com

Wood I-Joist Applications: Floors & Roofs

Wood I Joist in preparation for use in floor or roofing © Daniel Friedman at InspectApedia.com

Our photo above 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.

Definition of I-Joist

Unlike conventional wood or metal trusses that are made of triangular supports between continuous top and bottom members, a web truss or wooden I-Joist uses a solid center member, usually comprised of oriented strand board (OSB).

You can see the OSB center component and flat 2x4 lumber forming the I-joist top and bottom chords in our photo above.

The top and bottom chords of a wood I-joist may be conventional framing lumber such as a 2x4 or the truss chords may be made of laminated veneer lumber (LVL).

Our second photo (below) 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]

Older I-Joists using Plywood

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).

Wood I Joist in preparation for use in floor or roofing © Daniel Friedman at InspectApedia.com

Above: view of stampings on the chord of wood I-trusses used in both floors and roofs.

Connections of Wood I-Joist Floor Structure to Rim Joist & Corner Connnections

Wood I-Joist connection to rim joist & corner construction © Daniel Friedman at InspectApedia.com

Click to enlarge the image above for a sharper view of the I-joist hanger used to connect the end of the roof or floor I-joist to the rim joist of this building. At the bottom of the photo you'll also see the bolted corner connection specified by both the architect and the local building inspector.

Notice that we include solid blocking at the end of the I-joist behind the joist hanger. Where the floor was cantilevered and occasionally for other structural reasons we also added solid wood blocking between I-joists, visible in the top of the photo.

Below you can see the connection of I-joists at a supporting floor girder over a garage.

I Joists abutting a center girder © Daniel Friedman at InspectApedia.com

Wood I-Joist Blocking / Bracing

For roofs or floors constructed using I-joists, to increase the structure's stiffness or rigidity, I-joists blocking is used at the center of the I-joist spans. I-joist blocks are best cut and installed during initial framing of the floor or roof system.

I-joist blocking inserted between I-joists at a New York construction project (C) Daniel Friedman at Inspectapedia.com

Details of I-joist blocking are at WOOD I-JOIST CROSS BLOCKING / BRACING - separate article

Connections of Wood I-Joist Roof Structure to Wood-Framed Stud Walls

Blocking details at I-Joists over the wall top - these I-joists support the roof © Daniel Friedman at InspectApedia.com

Above you can see the use of cut I-joists as solid in-fill or blocking between the roof I-joists where they sit atop the wall top plate.

Connection of Roof Wood I-Joists to Supporting Walls

Connection of wood I-joist for roof at top of supporting wall © Daniel Friedman at InspectApedia.com

Above you see part of our steel tie-strap nailed to the top of the I-joists that will support the roof. This connecting strap must wrap the top of the I-joist and is also nailed to the side of the I-joist before it is carried down past any blocking for nailing to the structural supporting wall framing as well.

Below you can see some of the nails through the framing connector to the side of the I-joist top chord as well as to the solid blocking in-fill at the end of the roof I-joist.

Framing connector nailing requirements at side of I-Joist for roof © Daniel Friedman at InspectApedia.com

Below we illustrate the completion of connections for the metal strapping tying the wood I-joist roof structure to the wood-framed stud wall of this building.

You can see that I nailed the connecting strap to both the double top plate of the supporting stud wall and then down past thte top plate to the stud itself.

Framing connector between roof I-joist and stud wall © Daniel Friedman at InspectApedia.com

These framing connections assure both the connection of the I-Joist to the stud wall and also the connection of the building's stud wall top plate to the vertical studs in the wall body. I can testify it was a hell of a lot of nailing, all by hand.

I don't like trying to shoot framing connector nails through a power nailer. The chance of a backfire and a nail in the eye are just too great.

Below Eric Galow is starting to nail down the roof sheathing to our now personally-secured wood I-joists.

Nailing roof sheathing to the I-joist roof structure © Daniel Friedman at InspectApedia.com

Connection of Wood I-Joists to Supporting Beam or Girder

Below you can see more framing connectors used to tie these roof I-joists to a built-up laminate beam that supports a canti-levered portion of the roof structure.

We tied all of these framing straps to the back or less-viewed side of the laminate beam to permit the beam to be left exposed in the room below.

Wood I-Joist connection to wood beam supporting a roof © Daniel Friedman at InspectApedia.com

Below you can see how this same framing connector runs up and is nailed to the side of the wooden roof I-Joist. Click to enlarge these photos to count the number of nails used.

Connection of roof wood I Joist to beam © Daniel Friedman at InspectApedia.com

Below you can see a tip for getting along with the building inspector. Even though it was not required to nail the final tip of the framing connector to this side of the I-Joist, we left it exposed so that the building inspector would have no doubt that we had carried each framing connector strap up over the top of the wooden I-Joist for this roof.

We also included photos of the nails into the top of the I-joist to document that important connection that was later hidden by the installation of roof sheathing. I showed those photos earlier on this page.

Framing connectors, roof to wooden I-Joist to supporting beam © Daniel Friedman at InspectApedia.com

Wood I-Joists Atop or Connected to Steel Beams

Wood I Joist in preparation for use in floor or roofing © Daniel Friedman at InspectApedia.com

Wood and steel roof and floor trusses are discussed separately

at TRUSSES, FLOOR & ROOF and also

at TRUSS UPLIFT, ROOF.

I_Joist floor support © Daniel Friedman at InspectApedia.com

Our wood I-joist photo (Minnesota, 2007) above 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.

I-Joist to Steel Beam Connectors

Steel joist hangers to connect a wood I-joist to a steel beam or girder are offered by Cullen, Simpson, TriForce, Ozco and other suppliers listed below.

Installation may be as shown in our photo above, with the hangers supported by and welded or bolted to the steel I-beam, or a wood filler may be installed inside the I-beam, bolted to the I-beam, and to which conventional wood-fastener joist hangers may be attached.

Shown below: Triforce Wood-to-Steel connectors joining open-web wood trusses to a steel beam.

Triforce wood to steel i-beam connectors cited & discussed at Inspectapedia.com

StiffClip joist hanger from TSN The Steel Network - cited at InspectApedia.com

Cutting Holes in Joists, Rafters, Studs, or the Web of Wood I-Joists

This discussion has moved

to CUTTING HOLES in WOOD I-JOIST WEBS, JOISTS, RAFTERS, STUDS

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