Image

Engineered-wood, I-joists work differently than dimensional lumber concerning mid-span holes and notching.

I-Joist Intricacies

Engineered-wood, I-joists work differently than dimensional lumber concerning mid-span holes and notching.

  • Image

    http://www.builderonline.com/Images/tmp157D%2Etmp_tcm138-974455.jpg?width=1111

    true

    1111

    Image

    Harry Whitver

    1. Get the Guide

    All I-joist manufacturers publish “specifier’s guides” that include illustrated hole charts and allowable notching of the I-joist chords and web. The guides are free and available at local lumberyards that stock I-joists, as well as by online download. Use the guide to design floor and roof assemblies, educate framing crews, and inspect their work.
  • http://www.builderonline.com/Images/tmp157E%2Etmp_tcm138-974457.jpg?width=1116

    true

    1116

    Image

    Harry Whitver

    2. Use the Holes

    The center webs of some I-joists feature perforated knock-out holes at acceptable locations for small plumbing pipe or electrical conduit runs through the floor frame without affecting the floor’s performance or structural integrity and eliminating the need for extra chases. Consider these locations before cutting new holes in the web.
  • http://www.builderonline.com/Images/tmp1580%2Etmp_tcm138-974463.jpg?width=1115

    true

    1115

    Image

    Harry Whitver

    3. Hole Chart

    This hole chart for iLevel’s residential I-joists, found in its specifier’s guide, is based on a table that calculates how far and how large a square or rectangle hole can be cut from the ends of the joist (never less than 1 foot or within certain zones of the web) and from each other to maintain designed performance and structural integrity.
  • http://www.builderonline.com/Images/tmp1581%2Etmp_tcm138-974465.jpg?width=1111

    true

    1111

    Image

    Harry Whitver

    4. Notching No-Nos

    The ends of I-joists can be cut, including bevels and birdsmouths, to accommodate various roof rafter and eave soffit designs. There are limitations, namely bevels that extend beyond the inside face of the wall and birdsmouth cuts that set the thin center web directly onto the top plate without support from the bottom chord and/or a block.

Engineered-wood I-joists are arguably a better-performing and more resource-efficient option to solid-sawn 2x10 and larger roof and floor joists, what with their longer span capabilities, stiffness, stronger load capacities, superior structural integrity in fluctuating climate conditions, and more efficient use of timber.

But there are other, more subtle differences in their on-site applications compared to their solid-sawn counterpoints, including how and where framers are allowed to cut holes in the thin web of an I-joist for mechanical runs and whether and where the chords of these long-span beams can be notched. An improper hole or notch can result in squeaky floors, or far worse.

I-joist manufacturers and suppliers go to great lengths to make sure designers and framers understand those limitations—in some cases designing floor and roof systems on their behalf to mitigate miscuts—but they still come across improper holes and notches in the field.

Consider these tips for I-joists, and consult your local I-joist supplier for more details.