Plumber Cuts an Engineered Floor Joist
During a bathroom renovation, a plumber cuts a 90 mm diameter hole through the top flange and web of a 241 mm deep engineered wood I-joist. The joist spans 4.6 m, supports a tiled shower and a bearing wall above, and is one of six at 400 mm centres. The cut is 250 mm from the end bearing and removes about half the top flange width. The plumber says the hole is “between the flanges” and fills the gap with spray foam. The homeowner reports a slight bounce and a crack in the ceiling below. The general contractor wants to cover it with subfloor the same day and move on. The joist manufacturer’s installation guide is not on site, but the joist stamp is readable. The tiled shower is already purchased and the schedule is tight.
1. What is your immediate response when you see the cut joist?
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Stop the work and do not cover the joist. The cut is not a normal plumbing penetration: it removes part of the top flange and is only 250 mm from bearing, which is likely outside the manufacturer’s permitted hole zone for an engineered I-joist. Spray foam does not restore structural capacity. Because the joist supports a bearing wall and a tiled shower, the floor above may need temporary shoring while the condition is assessed. The contractor should be told that the subfloor cannot be closed until a written repair is obtained. The joist stamp and manufacturer’s guide, or a qualified engineer if the guide is unavailable, should be used to evaluate the loss of section and the load path. The ceiling crack and bounce are symptoms that the floor system has already deflected, not cosmetic issues to ignore.
2. How would you evaluate the severity of the defect?
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The evaluation should compare the actual cut with the manufacturer’s hole chart and installation instructions for that joist series. The key facts are the joist depth, span, spacing, bearing condition, location of the hole from the end support, size of the hole, and how much top flange was removed. A hole near bearing is more serious because shear is highest there, and a top-flange cut can reduce the composite action that the joist depends on. The bearing wall above adds load, and the tiled shower is sensitive to deflection and cracking. The evaluation should also check whether the joist is cracked, whether the web is crushed at bearing, and whether adjacent joists share the load. If the manufacturer’s chart does not clearly permit the condition, a qualified engineer should provide a sealed repair or replacement detail.
3. What repair options are acceptable, and what should be rejected?
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Acceptable options depend on the manufacturer’s or engineer’s written direction. They may include replacing the joist, sistering with a designed engineered lumber member, adding a designed repair detail such as web stiffeners and squash blocks, or installing additional framing to reduce the span and load. The repair must restore both strength and stiffness for the bearing wall and tile deflection limits. Rejected options include spray foam, a plywood patch nailed over the area, or simply covering the joist with subfloor. The repair should be inspected before closure, and the tile installer should not proceed until the floor is verified. If the joist is part of a manufactured floor system, using a generic site-built repair without the manufacturer’s or engineer’s approval can void the system and leave the homeowner with a hidden structural defect.