How to recess engineered I-joists for a curbless shower

Last updated: November 13, 2026

Key Takeaways

• Lower the shower pan while keeping the joist system engineered, not improvised.
• Frame the recess as a supported opening and follow the joist maker’s exact reinforcement detail.
• Web stiffeners, rim joists, and LVL members are the usual tools that prevent a weak spot.
• A generic article often says to “just notch the joists,” which is usually the wrong approach here.

Recessing engineered I-joists for a curbless shower means cutting and reinforcing the floor system so the finished shower floor can drop below the rest of the bathroom without weakening the joists. In this guide to how to recess engineered I-joists for a curbless shower, do not cut an I-joist blindly; consult a structural engineer and use the joist maker’s allowance. The steps below settle what can be cut, what must stay, and when the floor needs web stiffeners, rim joists, or LVL reinforcement.

What has to be true before you touch an engineered I-joist

Picture this: you’re staring at an open floor framed with TJI joists, and the shower footprint sits right between a rim joist and a load-bearing wall. You want a lower pan, but the joist web is already doing the job the flanges can’t do alone. Here’s the catch: the recess only works if the joist layout, span, and load path still make sense.

The first question is not “how deep can I cut?” It is “is this joist even a candidate for a notch or cut under the manufacturer’s rules?” Engineered I-joists are not usually treated like sawn lumber, so consult the joist manufacturer or an engineer before cutting. Their webs, flanges, and glue lines are part of a tested system, and the rules for a TJI joist shower recess come from the manufacturer’s span tables and hole charts, not from habit on site. For example, the APA and manufacturer literature require member-specific details, not field guesswork.

A curbless shower usually needs a framed drop, often around 1 to 2 inches of recess in the finished structure, but the exact amount depends on the assembly above the joists. That assembly may include subfloor, underlayment, mortar, waterproofing, and tile. The structural part must be planned around all of that, not after the tile guy shows up.

• Check the joist stamp, series, and size.
• Find the manufacturer’s hole and notch guide for that exact member.
• Confirm where plumbing, heating, and blocking will land.
• Flag any joist that carries a point load, spans unusually far, or sits near a bearing.

If the joist size or series is unknown, stop and identify it first. A generic “I-joist” answer is how floors get overcut. For manufacturer guidance, start with the APA’s engineered-wood resources and the joist maker’s published span tables.

Can you cut an engineered I-joist for a shower recess?

You can cut an engineered I-joist for a shower recess only in the locations and shapes the manufacturer allows, and only if a structural engineer signs off when the field condition is outside the published limits. That is the whole game.

For most jobs, the safe path is not a full freehand recess across several joists. It is a framed opening that transfers load around the lower area. The joists at the shower edges often need headers, blocking, or a boxed-out frame so the lowered section is supported without hacking away at the web wherever it seems convenient.

The best mental model is that the joists should stay intact where they do the spanning, while the drop happens in the framing between them or by local reinforcement where the manufacturer allows it. A recess that ignores that rule can leave the flange carrying load it was never meant to carry. IRC framing rules and manufacturer details both point back to the same idea: follow the approved load path.

Use these checks before any cut:

1. Read the joist guide. Look for hole size, hole location, end cut, and notch rules for your exact TJI or other engineered joist.
2. Map the recess. Mark the shower footprint and decide whether the drop crosses one joist bay or several.
3. Locate bearings. Keep cuts away from supports unless the manufacturer gives a specific detail.
4. Plan load transfer. Use rim joists, doubled headers, or LVL reinforcement where the opening interrupts the normal span.
5. Confirm the finish build-up. The recess must be deep enough for the tile package, not just the pan.

A common mistake is treating the web like sacrificial filler. Consult the joist manufacturer’s guide or a structural engineer before assuming a cut is acceptable. The web is part of the engineered system.

How to recess engineered I-joists for a curbless shower

You recess engineered I-joists by framing the dropped area as a supported opening, then reinforcing any cut members with the manufacturer’s required details and an engineer’s layout. The goal is a lower subfloor that still carries dead load, live load, and tile without bounce.

Picture this: you have the shower footprint marked, the subfloor pulled, and the joists exposed. The work now is careful carpentry, not demolition. The opening may be small, but the structure around it needs to act like a frame, not a pile of cut ends. In a curbless shower, the recess is only as good as the framing that surrounds it.

Start with the perimeter of the recess. Where the lowered area meets the normal floor, install solid blocking or headers so the edge of the drop has support. If a joist must be interrupted, the loads often need to jump to a neighboring joist with LVL reinforcement, double members, or a framed transfer detail. The exact fix depends on span, load direction, and what the joist maker allows.

Use this sequence:

1. Confirm the joist series, span, and allowable cut detail from the manufacturer’s guide.
2. Mark the shower recess on the framing and keep the layout square to the joists.
3. Install temporary shoring if the framing will be opened over more than one joist bay.
4. Add headers or doubled members at the recess edges so the load has a new path.
5. Cut only the approved web area, if the detail allows a cut at all, and keep the flange intact unless a specific detail says otherwise.
6. Install web stiffeners where required by the joist maker, especially near concentrated loads or cut areas.
7. Check the finished depth against the pan, mortar, waterproofing, and tile package before closing the floor.

A framed recess is often cleaner than a field-cut recess. It takes more planning, but it gives you a floor that feels solid under tile. For a curbless shower, that extra planning usually pays off in less rework.

Where web stiffeners, rim joists, and LVL reinforcement fit

Web stiffeners, rim joists, and LVL reinforcement are the parts that keep a recess from turning into a weak spot. They each solve a different problem, and mixing them up wastes time and can still leave the floor underbuilt.

Picture this: one side of the opening lands next to a rim joist, the opposite side lands under a partition wall, and the shower curb is gone. The lowered area now needs edge support, not just a hole in the floor. Here’s the catch: the outside edge of the recess often sees more stress than the center of the opening.

Web stiffeners are there to help the joist web carry loads where the web has been cut, not to replace a bad layout. They are commonly used at openings, near bearings, or where the manufacturer specifies them after a hole or end cut. If the joist guide calls for stiffeners, use the exact material and fastening pattern it names. Guessing here is bad carpentry.

Rim joists matter when the recess lands at the perimeter of the building or near a framed edge. A rim joist can help tie the ends of the joists together, but it is not a magic fix for a bad opening. If the shower drop sits near the edge of the floor, the rim joist may need to stay continuous or be doubled into a stronger boundary detail.

LVL reinforcement comes in when the load path needs a stronger member than a regular I-joist edge can provide. LVL is dense, straight, and predictable, which is why it is often used as a header or transfer member around a recess. It is not a free pass to ignore span tables; it is part of the engineered fix.

Use this rule of thumb: if the opening changes the way a load travels, the framing around the recess needs to be designed, not improvised. That is especially true in a curbless shower, where the finished floor height is set by structure as much as by tile.

What a generic shower recess article gets wrong

A generic article tells you to “just notch the joists” and move on. That advice is too broad for engineered lumber, and it can lead to a failed framing detail.

The biggest miss is pretending all I-joists behave the same. They do not. TJI joists, other engineered I-joists, and LVL members each have their own span, hole, and end-cut limits. A detail that is fine on one series may be wrong on the next. If the layout changes from a single-bay recess to a multi-bay recess, the framing method changes too.

Another bad habit is ignoring the finish build-up. A curbless shower is not just “lower than the room.” The recessed area has to fit the drain, slope, waterproofing, mortar bed if used, underlayment, and tile. If the recess is too shallow by even a small amount, the finished floor can end up proud of the bathroom floor, which defeats the point.

A third mistake is leaving the plumber to solve the structure. Plumbing needs space, yes, but the structural opening has to be planned first. If a drain line, trap, or pipe chase lands in the same zone as the joist cut, the framing and plumbing need to be coordinated before any saw touches wood.

• Don’t cut first and ask later.
• Don’t assume a joist can be notched like dimensional lumber.
• Don’t use a rim joist as a substitute for a proper header.
• Don’t close the floor until the recess depth matches the full assembly.

The safe version usually looks boring, which is a good sign when you are building a curbless shower recess.

What should I ask the engineer or lumber supplier before cutting?

You should ask for the exact joist allowance, the approved reinforcement detail, and the conditions that void the detail. That is the short list that saves the most time.

Picture this: you are holding the framing plan and the engineer wants the joist series, span, spacing, and the shower footprint. That is normal. The answer has to match the exact member, not a generic I-joist from a catalog picture. One missing detail can change the whole method.

Bring these facts to the conversation:

1. The joist manufacturer and series, such as a TJI line.
2. Joist depth, spacing, and span.
3. The exact shower location and recess size.
4. Whether the recess hits a bearing wall, beam, or rim joist.
5. Whether there are plumbing lines, ducts, or wires in the same bay.
6. The planned finished floor build-up above the lowered framing.

If the answer is “install web stiffeners and a framed transfer detail,” get that in writing or on a stamped detail if your project requires it. If the answer is “do not cut this member,” believe it. A different layout or a different drain location is cheaper than repairing a floor that bounces or cracks tile.

For a broader framing sequence, this page sits under the main curbless shower subfloor preparation guide, which covers the build-out around the recess without repeating the structural rules here. That helps keep the shower layout aligned from framing through tile.

Can you notch engineered I-joists for a shower?

You can notch an engineered I-joist only where the manufacturer specifically allows it, and most shower recesses should not rely on random notching. The safer answer is usually a framed opening with approved reinforcement, not a hand-cut notch in the flange or web. If the detail is not in the joist maker’s guide, stop and get a structural engineer review before cutting.

A shower recess is not the place to copy a dimensional-lumber rule. I-joists are engineered members, and their strength depends on the flanges, web, and connection details working together.

How much can you cut an I-joist flange?

You should cut an I-joist flange only to the amount the manufacturer allows, and in many cases the flange is the part you must protect most carefully. Flange cuts are far more serious than web cuts because the flange carries major bending stress. If the recess seems to require flange removal, that is usually a sign the framing plan needs to change.

Even a small flange cut can force a redesign. The safe move is to treat the flange as off-limits unless the published detail says otherwise, and to confirm the detail with the joist manufacturer or a structural engineer.

Drafted with AI; not yet reviewed by a person.