A vertical lift module's installation envelope is set by three physical limits: building clear height, distributed floor load, and bay/service clearance. Modula documents unit heights from 10 ft 10 in up to 68 ft 11 in for the standard Lift and Flexibox lines, 7 ft 10 in to 22 ft 11 in for the Slim, and 14 ft 7 in to 52 ft 10 in for the Pallet unit, with the Next line spanning 8 ft 9 in to 52 ft 10 in [S1].
Tray payload reaches 2,200 lb on the Lift, Pallet, and Compact Heavy units, with the Next capped at 1,102 lb per tray [S1][S2]. A unit fully loaded with maximum-payload trays concentrates a non-trivial point load and a large distributed load onto a footprint roughly 66 in (1.6 m) deep for slim units, which is why the slab and ceiling questions are answered before the order is placed [S1].
Clear Height: the First Filter on VLM Model Selection
Clear ceiling height inside the finished building is the first spec to lock, because VLM models are sold in fixed height bands, not as continuous ranges. Modula's Slim tops out at 22 ft 11 in while the Lift/Flexibox reaches 68 ft 11 in [S1]. White Systems documents a 40+ ft ceiling envelope across its Compact and PowerColumn 3 (PC3) lines, with a 2,200 lb/tray reinforced tray option on the Compact Heavy [S2].
Subtract the unit's own structural height from the finished clear height, then subtract the access bay height (Modula offers 27.36 in, 35.23 in, and 50.98 in bay options) plus the service-overhead clearance the OEM specifies for the extractor carriage and rooftop drive [S1]. The remaining vertical room is wasted if the chosen unit sits below it, and a structural problem if it sits above it. Outdoor enclosures sidestep interior clear-height limits, but they bring their own weatherproofing, climate-control, and structural attachment requirements (2025-07) [S4].
Floor Load: Concrete Slab, Reinforcement, and Point Loads
A VLM concentrates weight along two parallel rails that the extractor carriage rides between, with each loaded tray contributing its payload plus the tray's own mass to the column. With 2,200 lb trays and units holding dozens of trays, the live load on a 66 in (1.6 m) deep footprint can easily exceed the 100 lb/ft² (4.79 kPa) that a typical office slab is designed for, and a fully loaded heavy unit will push into ranges that need a structural review against the governing building code's Chapter 16 structural design provisions [S8].
Treat the slab as a structural element, not a finish surface: verify slab thickness, compressive strength (typically 4,000 psi / 27.6 MPa for industrial), and reinforcement, and verify the column rails bear on a level, continuous strip footing or a thickened slab area designed for the calculated point load [S8]. The site survey should pull existing structural drawings and mark any below-slab utilities, conduit, or underfloor drainage that the new column loads would crush.
Service Envelope, Bay Placement, and Operator Ergonomics
The access bay opening is the operator's working point and it must be sited where forklifts, pallet jacks, and conveyors can feed it without crossing pedestrian lanes. Modula offers internal, external, single, or dual delivery bay configurations with up to 3 bays total, mountable on the front, rear, or on multiple floors, and its Next line supports a picking window from 3.94 in x 2.94 in up to 98.43 in x 25.75 in for unusually small or large items [S1]. White Systems designs its bay to deliver trays at the "optimum ergonomic retrieval height", which is the goods-to-person ergonomic anchor of the whole system [S2].
Reserve floor space in front of the bay equal to at least the longest tray plus the operator's reach envelope, plus a service corridor of roughly 36 in around the non-bay sides so a technician can stand beside the column to change a drive belt, rack, or pinion. The internal extractor needs its own overhead service clearance from the top of the tallest stored tray to the ceiling; consult the OEM submittal for that exact number because it varies by tray height band [S1].
Power, Controls, and Integration Loads on the Building
A VLM's electrical service is small relative to its mechanical mass, but it still has to be planned. Modula's Slim line runs on 240V single-phase, 240V three-phase, or 48V three-phase, and the larger units draw more from standard 480V three-phase industrial service [S1]. The unit's controller (Modula's 10.4 in touch-screen Copilot, White Systems' MILO software) typically needs a dedicated circuit, an Ethernet drop for ERP/WMS integration, and a barcode-scanner connection at the bay [S1][S2].
Worth noting: White Systems documents a 4-point metal rack-and-pinion drive on all its VLM models, an alternative to the belt-driven extractors common in this product class, with the OEM claim that the rack-and-pinion design reduces stretching, slipping, and routine maintenance [S2]. For a deeper look at how a VLM's footprint and density stack up against conventional floor storage, see VLM vs Floor Storage: Footprint, Density, and Throughput Compared, and for the tray/load/ceiling tradeoffs between a small-parts VLM and a pallet VLM, see Pallet vs Small-Parts VLM: Tray, Load, and Ceiling Tradeoffs.
Outdoor Envelopes: When the Building Won't Grow Vertically
When interior clear height is fixed and slab capacity is fixed, a weatherproof, climate-controlled exterior enclosure attached to the building wall is a documented alternative. Operators still pick from interior access windows that can be cut on a single floor or on multiple floors (2025-07) [S4]. This converts the constraint from "renovate the building" to "pour a new isolated pad, run power to it, and route the access windows through the wall", and it reclaims the full interior footprint that an indoor VLM would have occupied (2025-07) [S4].
Outdoor envelopes shift the same three constraints (height, load, service) onto a new isolated foundation outside the existing slab, with added wind, snow, and thermal loads that an interior unit never sees. For a typical VLM the access bay also doubles as a goods-to-person workstation, a layout principle shared with the broader class of vertical lift module designs and with related construction machinery and equipment classifications.
Pre-Order Site Survey Checklist
Lock these answers before signing a PO: finished clear ceiling height to the underside of the lowest obstruction (sprinkler piping, HVAC ducts, lights, joists); slab thickness, compressive strength, reinforcement, and any known below-slab utilities; available three-phase power with adequate ampacity; the longest tray dimension in current and planned inventory; the heaviest single tray payload including dunnage; and the bay count and locations that match the warehouse's pick path. Modula's three bay-height options (27.36 in, 35.23 in, 50.98 in) and White Systems' 2,200 lb heavy-tray option both need to be matched to the largest item and the heaviest tray you will store, not your average SKU [S1][S2].
Two verifiable signals to track next: OEM submittals increasingly distinguish belt-driven versus rack-and-pinion extractor drives as a maintenance and stretch-cost differentiator (White Systems explicitly markets the rack-and-pinion design across its line) [S2], and outdoor-enclosure VLMs are being specified as a way to avoid interior slab and ceiling retrofits on sites where the existing building is fixed (2025-07) [S4].
For the relevant spec sheets and selection criteria, see floor grinder.