TECHNICAL
BULLETIN
TB-854
July 2015(Expires 8/2017)
Vent Holes for 16"
TJI®
230 Joists
In roof applications there are often requirements to provide venting in the ceiling cavity between the insulation and sheathing to
transfer moisture from the air space to the exterior. In TJI® roof joist applications, these requirements are most commonly achieved
with 1x4 strapping between the joist and roof sheathing. Occasionally, builders address ventilation requirements by installing vent
holes in the webs of the TJI® roof joists.
This document outlines the special design and hole installation procedures that are required when vent holes are drilled into the
webs of TJI® roof joists.
Design Procedure
The 2.5" diameter vent holes drilled into the webs of TJI® roof joists will reduce the shear capacity of the member. To design the
vented TJI® roof joist, use Javelin® and design the 16" TJI® 230 roof joist member based on span and loading conditions of the
specific application. Next, verify that the member is adequate by checking the result column of the Javelin® output for the following:
Property
Result Column
Bending, Deflection, Reaction
Pass and 100% or less
Shear
Pass and 70% or less
Hole Installation
When drilling the vent holes into the webs of TJI® joists, care must be taken to ensure that the holes are properly located and the
TJI® joist flanges are not damaged. Vent holes shall be located along the top of the member with knock-out-holes along the bottom
of the member. The following table and figure provides guidelines for locating 2.5" vent holes along the TJI® roof joist.
Dimension
Vent Hole Diameter
2 ½"
Spacing Along Member(1)
12"
Center Line of Vent Hole to Top of
Flange
3 ⅛"
1"
22
1"
38
Hole Property
12"
12"
Vent Hole
12"
12"
Knock-out-hole
(1) Minimum hole separation from web joints and joist bearing is not required
The area provided by these vent holes may not be sufficient for some roof configurations, and the designer must verify that the
venting outlined in this document meets section 9.19.1.2 (Vent Requirements) of the 2010 National Building Code of Canada.
If you have any questions, please feel free to contact your Weyerhaeuser representative.
Venting procedures in this document apply to 16"
TJI® 230 roof joists only.
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