Retrofits, barrier-free conversions, or a brand-new custom build, whatever project you’re tackling, the question you should be asking is, “Does it pass the 3/4 × 4 rule?”
This code requirement, embedded in ASME A17.1/CSA B44, was introduced after a series of child-entrapment tragedies, limiting the space between a landing (hoistway) door and the elevator car door to prevent small bodies from being in danger. Knowing and documenting compliance is now a must-have for obtaining permits, conducting inspections, and ensuring homeowner peace of mind.
Why the Home Elevator 3/4 x 4 Rule Compliance Matters
- Real incidents: Multiple child injuries and at least one 2021 fatality occurred when kids slipped between the doors of residential elevators with excessive gaps.
- Code response: The 2017 update to ASME A17.1 / CSA B44 capped the landing-to-car clearance at ¾ in. and required the space to reject a 4-in. sphere.
- Enforcement: Provincial authorities such as Ontario’s TSSA. And most U.S. states now flag non-compliant installs during inspection.
Decoding the Home Elevator 3/4 x 4 Rule Compliancein One Minute
| Limit | What Inspectors Do | Builder Take-Away |
| ¾-inch gap | Measure from the back of the closed landing door to the edge of the landing sill. Anything > 19 mm fails. | Frame and shim jambs tight; verify after doors are hung. |
| 4-in. sphere | Push a 102 mm ball between the landing door and the car door/gate at all heights. If it passes, the site fails. | Choose door packages (or space guards) that physically block a 4-in. object at every point. |
Landing vs. Car Doors: Identifying the Critical Gap
- Landing (Hoistway) Door – A builder-supplied swing door that usually matches the homes’ other interior doors.
- Cab Door or Gate – Supplied with the elevator cab; may be full-height sliding door panels or accordion gate.
- Critical Gap – The distance between the back of the landing door and the sill edge. That’s the space subject to the ¾-in. / 4-in. limits.
Field check: Close the landing door, pull the threshold trim, and measure straight back to the sill. If you’re anywhere near ¾ in., plan for mitigation now, not at the final stage.
What does a landing/hoistway door look like?
A landing door, often called a hoistway door, is the hinged door you see from the hallway. In many custom homes, it matches other interior doors, installed by the builder or trim carpenter. It may be power-operated, but more often it’s a manual swing door.
Inside the cab, Cambridge Elevating supplies a second barrier: the elevator car door or gate. This can be a full-height sliding panels or an accordion (bi-folding) gate, and it may also be manual or powered, depending on the model and budget.
Models affected by the 3 ⁄ 4 × 4 rule: Elmira, E50, and Heritage all use a separate landing door plus a car door, so the gap between them must meet the ¾-inch / 4-inch compliance test.
Cambrian is the exception; it features two sets of sliding panels; one set serves as the landing door and the other as the car door, inherently eliminating the gap issue.
Why the home elevator 3/4 x 4 rule compliance zeroes in here: The safety code measures the space between these two independent doors. If that “critical gap” exceeds ¾ in. or admits a 4-in. sphere, the installation fails inspection.
Where exactly is the critical gap?
The gap inspectors care about is the distance from the back of the closed landing door to the edge of the landing sill, the point where finished flooring stops and the elevator shaft begins. That’s the start of the running clearance between the building and the moving cab.
- Measure here first: Close the landing door, remove the threshold trim if installed, and put a tape measure straight back to the sill edge.
- Any reading over ¾ in. or a spot where a 4-in. sphere can slip through must be fixed with tighter framing, space guards, or switch to full-height sliding doors.
Getting familiar with these two door types and the slim space between them helps builders frame accurately, avoid costly rework, and sail through the 3/4 × 4 inspection.
Solutions for New Builds and Retrofits
Meeting the home elevator 3/4 x 4 rule compliance comes down to choosing the proper interlock and prepping the hoistway correctly, especially for the E50, Elmira, and Heritage models.
New Construction
If you’re building new, you’ve got a clean slate:
- Frame your hoistway properly (e.g., 50″ x 50″ for the E50),
- Use the Atlas Interlock, and
- Hang the door with ¾” of clearance behind it.
When done right, this setup automatically complies with the code. No baffles. No surprises.
Understanding Your Interlock Options
There are two main types of interlocks used in residential elevators:
Atlas Interlock (Recommended)
- Clearance: Door must have exactly ¾” of space behind it when closed.
- Handles: Only low-profile or inset handles can be used; anything that sticks out more than ¾” will block the lock.
- Door Baffles: Not needed, as long as the spacing and handle depth are correct.
This is the cleaner, simpler install, especially for new builds. Just follow the specs, and you’re code-compliant from the start.
Honeywell Interlock (Fallback Option)
- Clearance: The door is mounted 3″ from the jamb’s inside edge, and the lock itself is deeper (2¼”).
- Handles: Standard passage or dummy handles are allowed.
- Door Baffles: Mandatory. Every landing door must have a baffle to close the gap and meet the ¾” rule.
Honeywell setups are common in retrofits or situations where the Atlas requirements weren’t followed, but they do require more components and precise measurements.
Cambridge Elevating Advantage
- Complete Compliance Guidance – We supply every dimension, interlock position, and gap requirement you need, whether the job uses full-height sliding doors (already compliant) or accordion gates that call for baffles.
- Two Door-Baffle Options – If a baffle is required, choose either our 3-inch metal guard or a clear acrylic model, both ship ready to install and meet the ¾-inch / 4-inch rule.
- Builder-Friendly CAD Files – Each package includes CAD drawings that flag jamb thickness, shim zones, and rail-wall details so framing crews can hit code on the first try.
What if My Elevator Doesn’t Meet the ¾″ x 4″ Rule?
If your elevator doesn’t comply with the ¾″ x 4″ rule, typically due to excess space between the car door and the swing door, you’ll need to install door baffles to bring it up to code.
This often happens when:
- A Honeywell Interlock is used instead of an Atlas,
- The swing door isn’t hung with the correct spacing,
- Or landing entrances weren’t framed according to spec resulting in door frames being needed.
What Is a Door Baffle?
A door baffle is a safety component mounted on the back of a swing door. Its purpose is to reduce the gap between the closed door and the hoistway, helping you meet the safety code.
To comply, baffles must:
- Fill the gap behind the door to ensure no more than ¾″ clearance remains,
- Be at least 11″ tall,
- And have a 70-degree sloped top to prevent anyone from standing or placing objects on them.
Cambridge Baffle Options
We offer two pre-made baffle solutions:
- Standard 3″ Baffle
- Premium Clear Baffle (with stainless steel standoffs)
- You can also build a custom (DIY) baffle, as long as it meets the above code requirements.
If you’re unsure whether your elevator setup needs a baffle or which type to choose, our Project Management team is here to help. Just call 1-800-265-3579.
Builder Checklist for Home Elevator 3/4 × 4 Rule Compliance
When it comes to meeting code, we don’t just sell elevators, we offer complete, code-compliant solutions.
Here’s how we help you get it right:
Atlas Interlock System:
Our go-to solution for clean, code-ready installs, when doors are hung properly, this setup ensures compliance with the ¾” rule, no extra hardware needed.
Expert Support & Clear Documentation:
Our dedicated Project Management team works with you at every step, from planning to final inspection, and our detailed CAD drawings make it easy for framing crews to hit spec on the first try.
Flexible Safety Options:
If your site needs adjustments, we offer two types of door baffles, standard and premium, to help you meet safety requirements without rework.
Codes, Inspectors & Paperwork
- Canada: CSA B44-19 adopted by all provinces; Ontario OBC (Ontario Building Code) references plus TSSA field bulletin.
- U.S. states: Nearly all adopt ASME A17.1 (2016 or later). Always confirm the edition with the local elevator authority.
- Submittals you’ll need: shop drawings, gap-mitigation hardware sheets, measurement photos, and the final inspection tag.
Cambridge Elevating Support for 3/4 × 4 Compliance
- Pre-build consults—layout reviews and model selection to meet space & noise goals.
- Door baffles — factory-made guards that ship ready for installation and bring accordion-gate systems into 3⁄4 × 4 compliance.
- Dealer network: Identical support across Canada & the U.S. through certified CE dealers.
Schedule a Code-Ready Project Review
Avoid failed inspections and last-minute retrofits. Contact Cambridge Elevating today for a free, code-ready review of your next elevator project, and ensure home elevator 3/4 x 4 rule compliance before framing even begins.
