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.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Wood I-Joists Used in Floor & Roof Construction

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

[Click to enlarge any image]

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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

Wood I-Joist Applications: Floors & Roofs

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 © Daniel Friedman at

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

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

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

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

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

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

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

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

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

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

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

Wood I-Joists Atop Steel Beams

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

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

Our wood I-joist photo 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.

Cutting Holes in the Web of Wood I-Joists

Generally it is permitted to cut round holes in the center of the web of a wood I-joist, depending on the specific guidelines of the I-joist manufacturer. You should never cut nor notch the top or bottom chord. The rules for allowable hole size depend on the I-joist dimensions and also on where in the run of the wood I-joist the hole is to be cut. For example, no holes may be permitted near the ends of wood I-joists.

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 © Daniel Friedman at

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Continue reading at FRAMING CONNECTORS & JOIST HANGERS for a discussion of special fasteners used when framing with wood I-joists,or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.



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