Article and photos by Gregory Havel
When a structure is built using I-joists, there are no natural openings provided for running pipes, cables, and ducts, as there are in open-web trusses. Electricians, plumbers, and air-conditioning installers have to make their own openings, as will the do-it-yourself owner.
Most I-joists are designed and installed according to the ASTM D5055, Standard Specification for Establishing and Monitoring Structural Capacities of Prefabricated Wood I-Joists, which includes Section 6.6.3 on web openings, and the recommendations of the Wood I-Joist Manufacturers’ Association (WIJMA) www.i-joist.org. Model building codes, as well as state and local codes, may also apply NFPA 5000, Building Construction and Safety Code, 2009 edition. Chapter 45.5.5 incorporates by reference ASTM D5055, as does the International Residential Code, 2009 edition, (International Code Council) in Chapter R502.1.4.
According to the WIJMA document Establishing Shear Capacities for Prefabricated I-Joists with Holes, the amount of web material that may be removed safely varies with the dimensions and materials of the top and bottom members of the I-joist; the material, thickness, and height of the web; the type and strength of connections between the members and the web; and the size and shape of the hole (Photo 1).
(1)
According to WIJMA,
- Holes not exceeding 1/3 of the depth of the web in any dimension are acceptable in most I-joists, and they may be round, square, or rectangular.
- Holes must be placed in the center third of the vertical depth of the web.
- Round holes reduce the strength of the web less than square or rectangular holes.
- Holes larger than 1/3 of the depth of the web in any dimension may need the approval of the manufacturer or a registered engineer before they are cut and may require reinforcement of the I-joists as designed by the manufacturer.
- Always follow the design recommendations of the I-joist manufacturer and any applicable state or local building codes, whichever is most stringent.
The WIJMA document does the following:
- Recommends that holes not be cut or drilled in the web within 24 inches of the end of the I-joist or within 24 inches on either side of the bearing point if the joist is cantilevered.
- Prohibits any web holes within six inches of the bearing point, because holes of any size in these locations significantly reduce the strength of the I-joists.
- Permits vertical web joints (splices) to intersect circular holes at any point
- Allows vertical web joints to intersect square or rectangular holes only on one vertical side of the hole.
- Recommends that the space between multiple holes be at least the diameter or largest dimension of the largest hole.
The complete document is a free download at http://i-joist.org/shear%20with%20holes.pdf.
(2)
Holes in I-joist webs must be cut or drilled. In Photo 2, the holes were pounded through the webs with a hammer, which can weaken the webs. These holes are of irregular sizes and shapes that have not been tested by ASTM D5055. This method also makes it difficult to keep the hole in the middle third of the web as required. At this construction site, the building inspector required the contractor to repair these web holes as the joist manufacturer recommended in writing and to drill new holes at a new location.
Manufacturer’s instructions are usually included with each shipment or bundle of I-joists; they include information on permitted web hole sizes, shapes, locations, and spacing; prohibited locations for holes; and the procedure for obtaining approval of any modifications not covered in the instruction booklet. Some manufacturers mark acceptable locations for web holes on each I-joist. Others provide “knock-outs” or three-sided pre-cuts for holes in the web in acceptable locations, shapes, and sizes.
A good working relationship with the local building inspector will instill in firefighters some confidence that the I-joists were installed with permits and inspections and were done correctly; and will allow firefighters to contact the building inspector if they have visited a construction site and observed something that isn’t right. No matter how conscientious your building inspector is, it is possible to miss details. These kinds of details are visible only during certain stages of construction, will be concealed for the rest of the building’s life, and could lead to an early structural collapse at a fire incident, or even if no fire is present.
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Subjects: Building construction for firefighters, I-Joists
