Stiltz Duo Alta Through-Floor Homelift: Planning Guide

What is the Stiltz Duo Alta, and where does it fit?

The Duo Alta is Stiltz's compact through-floor homelift for two stops, free-standing on two rails, with no shaft, machine room or load-bearing walls needed.

The Duo Alta is Stiltz's compact through-floor homelift. The car rides on two parallel vertical rails and passes through an opening in the floor. The drive, a self-contained rope drum with a braked gear motor, is enclosed in the car's roof space. Stiltz states that the lift is free-standing, so no load-bearing walls are required, and that it needs no lift shaft or separate machine room. When the car is downstairs, a lid closes the floor opening.

Stiltz shows these locations:

• Through the floor from a downstairs room, the most common location.
• A stairwell void to a landing. No floor opening, but the landing needs a gate and support brackets.
• A garage, with a safety enclosure on the garage level.
• A closet on one or both floors, as the layout permits.
• Under a sloped or vaulted ceiling. The rails attach to a horizontal surface, so Stiltz uses a "build-down".

Where it does not fit:

• Wheelchair users. Stiltz's wheelchair model is the Trio Alta.
• More than two stops, or more than 14 ft 9 3/16 in of travel.
• Two entrances. The Duo Alta has a single door. In the Duo range, Stiltz lists the Thru-Car for the Duo Classic only, a different model; the Trio Alta also offers a Thru-Car.
• Outdoors. The owner manual says indoor use only.
• Upper floors below 93 in of ceiling height, unless Stiltz confirms a reduced-height car for the site (section 04).

The Stiltz brochure also shows Duo Classic and Duo Vista models with different dimensions. Plan only from Duo Alta documents.

Other models are in the home elevator guides.

How does the Duo Alta compare with the Trio Alta?

The Trio Alta is Stiltz's larger, wheelchair-capable model, with a heavier rated load, a longer travel option, a wider entrance and a taller minimum ceiling.

The Trio Alta is the larger Stiltz model. The two March 2024 US specs carry the same electrical and standards wording; they differ in size, load and configuration.

See the Stiltz Trio Alta planning guide for that model.

Duo Alta choices Stiltz publishes:

• Car door: a 43 5/16 in hinged half-height door or a full-height door. The LED light curtain protects the upper half of the car with either door. Stiltz's product page lists the half-height door as standard and the full-height door as an optional extra; its FAQ says either is standard. The owner manual warns that with the half-height door a small child on the upper floor could fall into the partly lowered car. Stiltz's brochure notes that state or local regulations may require a specific type of door, so settle the door at plan review.
• Inside the car: fold-down seat and interior grab rail options.
• Controls and phone: additional remote controls; a landline phone is standard and a cell phone is an option.
• Power: an uninterrupted power supply (UPS) option.
• Car height: Stiltz's brochure says any car can be special-ordered with a cab height reduced by 4 in (100 mm) for lower upstairs ceilings.
• Color: grey (RAL 7038) is standard.

What are the Duo Alta's dimensions, capacity and speed?

The Duo Alta carries 375 lb at up to 5 7/8 in/s, with a 41 1/4 in x 31 7/8 in floor cut-out and a 93 in minimum ceiling.

Values are from the Duo Alta Technical Specification, TechSpecTrade_Duo_PA_0324_US_EN_V3.3 (March 2024), page 3. Metric appears only where that page gives it.

Notes:

• On the spec drawing, width runs parallel to the entrance and length runs front to back. Of the two external car dimensions, the drawing shows only the 28 13/16 in length.
• The spec says: "Please note that all dimensions in this document are for guidance only and must not be relied upon for construction purposes." Build from the project drawing Stiltz issues for the site.
• Other Stiltz pages give smaller footprint figures ("less than 8.5 sq ft", "under 7 sq. ft.", "less than 6 sq ft"). Lay out the room from the cut-out and car dimensions, not a footprint figure.
• An older Duo Alta spec (V3.0, 2021) is still online with different ceiling figures. Use V3.3.

What does the house need at the floor opening and ceiling?

The house needs the 41 1/4 in x 31 7/8 in cut-out, at least 93 in of upper-floor ceiling, and architect-designed framing, since Stiltz publishes no loads.

• Who cuts the opening. Stiltz's brochure says the ceiling aperture is created by a qualified contractor; its FAQ says a Stiltz Authorized Dealer does this work. State in the contract who cuts, frames and finishes the opening.

• Framing. Stiltz describes a retrofit this way: the ceiling below is opened, timber props support the joists while they are cut, a timber brace is fitted around the opening, and the upper floor is cut from a Stiltz template of the lift's footprint. That is a description, not a structural design.

  Stiltz does not publish loads for the lower floor, the rail fixings or the upper-floor framing, so the architect or engineer designs the headers and framing. The brochure also notes that in rare cases pipes or wires have to be rerouted.

• The lid. Obstruction sensors stop the lift if anything is below the car or resting on the floor lid. Plan the upstairs room so the lid area stays clear.

• Ceiling height. The spec requires at least 93 in on the upper floor. It also lists a maximum external lift height of 95 15/16 in without saying how the two figures relate, so confirm the clearance at the exact location on Stiltz's project drawing. Stiltz offers a cab reduced by 4 in for lower ceilings but does not publish the resulting minimum ceiling height.

• Stairwell and garage locations. A stairwell-void installation needs a gate at the landing and support brackets. A garage installation needs a safety enclosure, which Stiltz's range page describes as a simple shaft built around the elevator in the garage. Stiltz does not publish gate or enclosure specifications; confirm them with Stiltz and the AHJ. Stiltz does not publish a fire rating for the floor opening or lid. Ask the AHJ.

What power and controls does the Duo Alta need?

The Duo Alta needs a dedicated 220 to 240 V, 10 to 20 A circuit that stays permanently powered, plus a landline phone and hold-to-run controls.

• Supply. The spec lists 220 to 240 V and a 10 to 20 A socket; the lift plugs in. The product page says a dedicated 220 V AC line is required. Plan a dedicated 220 to 240 V circuit and receptacle.

  Do not read the spec's phrase "Plugs into a standard domestic power socket" as a 120 V outlet: the same line specifies 220 to 240 V, and the current spec publishes no 120 V option. A 2021 Stiltz of New Jersey page mentions a 110 V outlet with a step-up transformer; the March 2024 spec does not.

• Not published. Receptacle type (NEMA configuration), breaker size, phase, frequency, running current, disconnect and outlet location. Stiltz's range page mentions a 15 A outlet, which is inside the spec's 10 to 20 A range. Confirm receptacle type, breaker size and outlet location with Stiltz before rough-in.

• Keep it plugged in. The owner manual says the power plug should never be disconnected from the mains, so the emergency power supply stays charged.

• Controls and phone. A control panel in the car and two wireless remote controls serve as the landing call stations. Controls are hold-to-run: the rider keeps pressure on the control for the car to move. A key switch lets the owner lock the lift out, and the emergency stop button stops the lift and triggers the alarm. A landline phone is standard. Stiltz does not publish the phone connection requirement; confirm it with Stiltz.

• Power failure. A battery backup in the drive unit returns the car to the lower floor. On emergency power, the button that sends the lift to the upper floor is disabled. The uninterrupted power supply option allows numerous trips up and down until main power returns.

• Safety devices. Standard per the spec: LED light curtain, door interlock (the lift moves only with the car door fully closed), top and bottom obstruction sensors, built-in brake, battery backup, load sensor and door lock. The product page adds out-of-balance sensors, a fall arrest mechanism and top and bottom safety pans; the owner manual adds a slack rope sensor and auxiliary limit switches.

Can the Duo Alta go outdoors or in an unheated space?

No outdoor version is published; the owner manual limits the Duo Alta to indoor use above 5°C, so confirm an unheated space with Stiltz first.

No outdoor version is published. The Stiltz Duo Alta User Manual (UserManual_Duo_A_Feb20_US_EN_V1, January 2020) says the lift "is designed for indoor use only", that the ambient operating temperature should not fall below 5°C, that it must not run in a potentially explosive environment, and that it must never be used in a fire.

Stiltz does not publish an upper operating temperature, a humidity range, an outdoor rating or a noise level. For a garage or other unheated space, confirm with Stiltz that the location meets the manual's conditions before the design is fixed.

Which codes apply in New Jersey and Pennsylvania?

Mobility123 obtains New Jersey permits for the Duo Alta as an ASME A17.1 Section 5.3 private residence elevator; Pennsylvania excludes single-dwelling-unit lifts from its Uniform Construction Code.

What Stiltz states. Stiltz's US technical specification (V3.3, March 2024) calls the Duo Alta a "Domestic personal homelift that complies with the Machinery Directive 2006 / 42 / EC" and says the EN81 range was built in accordance with BS EN81-41:2010. Neither is a US standard, and Stiltz's public US documents state no UL listing. The code documentation for a New Jersey submittal comes through the installing dealer and is confirmed at elevator plan review.

New Jersey

• Permit. The Duo Alta is an "elevator device" under the Elevator Safety Subcode, N.J.A.C. 5:23-12, and needs a construction permit to install (5:23-12.1(e); 5:23-2.14).
• Code path. In Mobility123's New Jersey permit practice, the Duo Alta is permitted as an ASME A17.1 Section 5.3 private residence elevator. Mobility123 submits sealed layout drawings for elevator plan review, and the lift is approved on that basis.
• Edition. New Jersey's 2024 codes (IBC/2024 and IRC/2024 NJ editions, NEC 2023) took effect August 17, 2026, with a six-month grace period for permit applications under the prior code (5:23-1.6(a)). The elevator subcode uses the A17.1 edition listed in IBC/2024 Chapter 35, ASME A17.1-2022/CSA B44-22.
• Plans. Where the State has elevator subcode jurisdiction, DCA reviews the elevator plans. Layout drawings are signed and sealed by a New Jersey licensed architect or engineer. Check the town on DCA's jurisdiction list.
• Installer. A licensed elevator mechanic, or a person working under one's supervision, installs, services and maintains it (N.J.S.A. 45:14H-5a, and the licensing board's rules, N.J.A.C. 13:44M-2.1 and 13:44M-5.2(c)).
• After installation. In Groups R-3, R-4 and R-5, not accessible to the public, the lift is exempt from periodic inspection and from registration (5:23-12.3(a)5; 12.4(b)). Where DCA is the elevator subcode official, acceptance is by a sealed report from a New Jersey licensed engineer or registered architect (DCA policy SLCI-Admin 001-2020).

Pennsylvania

• A lift used only by the occupants of one dwelling unit in a solely residential building is outside the Uniform Construction Code's elevator chapter (34 Pa. Code § 405.1(b)(3)). Ask the municipal building code official about permits for the floor opening, the framing and the new circuit.
• Other lifts need a Department of Labor & Industry permit, acceptance inspection and certificate of operation (§§ 405.3, 405.5, 405.6). Pennsylvania does not adopt A17.1 Section 5.3 (§ 405.2), so ask the Department before planning a Duo Alta that occupants of more than one dwelling unit can use.

Who decides. The elevator subcode official decides whether a New Jersey submittal meets the code. The design professional designs the framing at the opening. Stiltz describes the Duo Alta as a domestic homelift, so public-building accessibility rules are not covered here. Forms, set counts and deadlines are on the NJ and PA code requirements page.

Who does what on a Duo Alta project?

The owner, architect, Stiltz dealer, electrician, GC and code officials each handle a defined stage, from feasibility and design through installation and closeout.

What mistakes cause rework?

Common mistakes include planning from marketing footprint figures, using outdated specs, assuming a 120 V outlet, and framing the opening before an engineered design exists.

• Planning from a marketing footprint figure. Figures such as "under 7" or "less than 6" sq ft produce a layout that is too tight. Plan from the 41 1/4 in x 31 7/8 in cut-out.
• Using the 2021 spec or Duo Classic drawings. The 2021 spec (V3.0) lists a different ceiling range (86 5/8 in minimum, 94 1/2 in maximum). The Duo Classic and Duo Vista have a different outline on Stiltz's brochure drawing (40 15/16 in x 29 1/8 in). Either one can leave the opening or the ceiling the wrong size. Use spec V3.3 and the project drawing.
• Assuming a 120 V outlet. The lift needs a dedicated 220 to 240 V circuit; missing it means electrical rework after the finishes.
• Skipping the ceiling check. Below 93 in the standard car does not fit, and Stiltz does not publish the minimum for a reduced car.
• Choosing the Duo Alta for a wheelchair user. Stiltz rates it for two people standing or one sitting and names the Trio Alta as its wheelchair model, so the lift may not serve a rider who stays in a wheelchair.
• Sealing the layouts before the code documentation is in hand. Stiltz's public specification cites no US standard, so the documentation for the New Jersey submittal comes through the installing dealer. Layout drawings sealed without it may need rework at plan review.
• Framing the opening without an engineered design. Stiltz publishes no loads, so framing sized without a design professional may be rejected at plan review or inspection, or need rework.

Checklists

Separate checklists cover what the architect or designer, the general contractor and the electrician confirm before and during a Duo Alta installation.

What warranty and service does Stiltz publish?

Stiltz publishes a 24-month parts warranty, no labor terms, and recommends yearly service by a trained Stiltz Authorized Dealer.

Stiltz's FAQ says: "Every Stiltz home elevator includes a 24-month parts warranty." The product page lists the same two-year parts warranty. Stiltz does not publish labor terms. Full warranty terms are available from the manufacturer or a dealer on request.

Stiltz recommends service once a year by a trained Stiltz Authorized Dealer. Its FAQ says the lifts are installed only by an Authorized Stiltz Dealer, and the owner manual says installation and service work must be carried out by an authorized Stiltz service technician.

Planning questions

Sources and revision history