Crawlspace drain under I-joists
What's wrong here?
- The bottom flanges of the I-joists have been notched, which I-joist manufacturers do not permit
- Nothing. The notches are near the end of the span and shallower than 1/6 of the joist depth
- A drain pipe may not be supported by floor joists; it must hang on its own hangers
- Holes are not allowed anywhere in an I-joist web
Show the answer and the code reference
The answer
The bottom flange of each I-joist has been notched to raise the drain, and R502.8.2 does not allow cuts or notches in I-joists except where the manufacturer permits them; I-joist manufacturers prohibit cutting or notching the flanges.
Correct choice: 1. The bottom flanges of the I-joists have been notched, which I-joist manufacturers do not permit
An I-joist gets its bending strength from its flanges: the bottom flange works in tension and the top in compression, while the thin web mainly carries shear. Cutting a flange through severs the tension chord, so the joist can lose most of its capacity at that point. R502.8.2 says cuts, notches and holes in I-joists (and in trusses, structural composite lumber and glulam) are not permitted unless the manufacturer's recommendations allow them or a registered design professional has designed for them. The sawn-lumber notch limits of R502.8.1 (1/6 of the depth, not in the middle third) do not apply, which is why a shallow notch near the support still fails.
How to fix it
Stop and get a repair detail from the I-joist manufacturer or a registered design professional; typical fixes are full-depth reinforcement or replacement of the cut joists. Reroute the drain below the joists on hangers, or through web holes sized and located per the manufacturer's hole chart.
Code references
IRC 2018 R502.8.2 — Engineered wood products
Cuts, notches and holes bored in engineered wood products, including trusses, structural composite lumber, structural glued-laminated members and I-joists, are prohibited except where permitted by the manufacturer's recommendations or where the effects of the alterations are specifically considered in the member's design by a registered design professional.
Drills citing R502.8.2IRC 2018 R502.8.1 — Sawn lumber
Notches in solid lumber joists, rafters and beams may not exceed 1/6 of the depth, may not be longer than 1/3 of the depth and may not be in the middle third of the span; end notches may go to 1/4 of the depth. These limits are written for solid sawn lumber, not for I-joists.
Drills citing R502.8.1
2024 IRC:not yet checked Confidence: low
Minnesota
Minnesota adopts the 2018 IRC with Minnesota amendments as the Minnesota Residential Code (Minn. Rules ch. 1309). No Minnesota amendment to R502.8.2 is known. DLI is adopting the 2024 IRC as the next edition; see the 2024 IRC note.
About the Minnesota Residential CodeWhy the other choices are wrong
- Nothing. The notches are near the end of the span and shallower than 1/6 of the joist depth. Those are the sawn-lumber limits in R502.8.1. I-joists fall under R502.8.2, which prohibits cuts, notches and holes except as the manufacturer allows or a design professional designs for, and I-joist manufacturers do not allow flange cuts at all.
- A drain pipe may not be supported by floor joists; it must hang on its own hangers. Pipe can be strapped or hung from joists. The problem is not how the pipe is supported but that the flanges were cut to raise it.
- Holes are not allowed anywhere in an I-joist web. Manufacturers publish hole charts that allow round and rectangular holes in the web, sized and spaced by joist depth and distance from the support. Running the drain through properly sized web holes is the usual fix.