Parking garage construction is deceptively complex. From the outside, a parking structure looks like stacked slabs of concrete — simple, repetitive, fast. In practice, structural system selection drives every downstream schedule decision, and the wrong choice can add months and millions. A Gantt chart built around your structural system is the correct planning framework because the critical path changes completely depending on whether you're building cast-in-place post-tensioned concrete, precast concrete, or structural steel. Each has a different procurement timeline, erection sequence, and inspection cadence.
Structural System Selection and Its Schedule Implications
The single most important schedule decision for a parking garage is structural system, and it must be made during schematic design — not after permits are issued.
Cast-in-place post-tensioned (PT) concrete is the most common system for above-grade garages in the western and southern US because it handles seismic loads efficiently and the sloped slab geometry is easily formed. The schedule constraint: each floor requires a full pour-and-cure cycle before post-tensioning can occur. Standard practice is to wait until concrete reaches 3,000 psi compressive strength (typically 3–5 days with Type III cement, 7 days with Type I/II) before stressing the PT tendons, then wait until the design strength of 5,000 psi (approximately 28 days) before removing shoring and loading the slab with the next level's formwork. In practice, with flying form systems on a large floor plate, the vertical cycle time is roughly one floor every 5–7 weeks for a typical 60,000–80,000 sf level. A five-story structure takes 6–9 months of elevated concrete work alone. On your Gantt, each floor level should be its own phase with concrete pour, curing, PT stressing, and shoring removal as explicitly sequenced sub-tasks.
Precast concrete delivers the fastest erection speed: once precast members are fabricated and delivered, a single level can be erected in 1–2 weeks. The Gantt-critical constraint is fabrication lead time — precast manufacturers require 12–20 weeks minimum from design approval to first delivery, and this cannot be accelerated easily. Precast requires the structural design to be fully detailed before the fabricator can produce shop drawings; design changes after the fabrication order is placed result in costly re-fabrication. Map the precast procurement as the critical path item during design. Erection follows delivery on a just-in-time basis — your site logistics plan must include a laydown yard or just-in-time delivery coordination, as precast members cannot be stockpiled easily on urban sites.
Structural steel with concrete on metal deck offers the most design flexibility and fastest erection speed, but requires spray-applied or intumescent fire protection on all steel members (IBC requires 2-hour fire rating for parking structure framing in most occupancy configurations). The fire protection application adds a full phase after steel erection and before finish work. Steel also requires more detailed connection engineering in high seismic zones, which can extend the structural design phase.
Slab Design: Drainage Slope and Post-Tensioning Layout
A parking slab is not a flat slab. Drainage requirements — minimum 1.5% slope toward drains, with 2% preferred — must be incorporated into the PT tendon layout and forming system. This is a design coordination item that is often underestimated: the PT tendon profile must accommodate the sloped geometry while maintaining the required slab thickness at every point. Flat-slab PT design on sloped decks requires careful coordination between the structural engineer of record and the PT subcontractor.
Trench drains running perpendicular to parking stalls are more effective than point drains at collecting water across a wide parking bay. The location of trench drains must be coordinated with the structural layout — concentrated loads at drain locations affect PT design. Establish drain locations in design, not in the field.
Traffic Coatings: A Schedule-Critical Finishing Phase
Traffic coatings protect the structural slab from chloride attack — road salt carried in on vehicles degrades concrete and corrodes PT tendons catastrophically if the protective coating fails. This is not an optional finish item; in cold-weather climates, an uncoated PT parking slab will begin deteriorating within 5–10 years, leading to multi-million dollar repairs.
Common coating systems: polyurethane traffic membrane (most common, 2-layer system with aggregate broadcast in first layer), epoxy deck coating (lower cost, shorter service life, 5–8 years before recoat), and vehicular traffic membranes per ASTM C957.
The schedule constraint: coatings cannot be applied until concrete has reached full carbonation and the slab moisture content drops below the coating manufacturer's threshold — typically 75% relative humidity measured by in-situ probe per ASTM F2170. This can take 60–90 days after the final pour for a PT slab with adequate curing compound. On your Gantt, do not schedule coating application immediately after concrete work. A 60-day moisture testing window should follow the final level pour before coating work begins on lower levels. Many projects sequence coating from the bottom up as upper-level concrete work proceeds, which efficiently uses the waiting period.
Application requires dry weather (typically >40°F, <90°F, no rain within 24 hours) — weather dependency should be noted as a schedule risk on your Gantt, particularly in climates with limited coating windows in fall or spring.
Elevator and Stair Core Construction
The elevator and stair cores are typically cast-in-place concrete shear walls regardless of the primary structural system. For structural reasons, these cores provide the lateral resistance for the entire structure — especially important in seismic zones. The cores are typically poured using slip form or jump form techniques and can proceed at a faster vertical rate than the floor plates.
Elevator equipment lead times are 14–20 weeks for standard traction elevators and 20–28 weeks for hydraulic elevators in current market conditions. The elevator rough-in (pit, hoist way dimensions, machine room if required) must be completed before the elevator contractor can install equipment. Coordinate the elevator equipment submittal approval and procurement on your Gantt as a parallel track to structural work — delays in elevator procurement have delayed parking structure openings more than once.
EV Charging Infrastructure
EV charging requirements are increasingly mandated by code. California's Title 24 requires a percentage of parking spaces to be EV-ready (conduit and panel capacity) even if chargers are not installed at opening. IBC 2021 and many local amendments have adopted similar requirements.
EV infrastructure requires planning at the structural and electrical design stage. Conduit sleeves through PT slabs cannot be added after concrete is poured without core drilling through PT tendons — which is prohibited or severely restricted. Every conduit penetration through a PT slab must be designed and sleeved in before the pour. This is a coordination item between the electrical engineer and structural engineer that must happen in design, not in the field.
Electrical service sizing for EV charging can be substantial: a 100-space EV-ready installation may require 400–800A of additional electrical service capacity. If Level 2 chargers or DCFC are anticipated, the utility service entrance, transformer, and main switchgear must be sized accordingly — utility transformer lead times in most markets are 20–40 weeks. Include electrical utility coordination as a parallel-path item on your Gantt from day one of design.
Permitting and Inspections
Structural engineering stamped drawings are required for permit — for a PT structure, the PT subcontractor must provide shop drawings reviewed by the engineer of record before permit issuance in most jurisdictions. Allow 3–5 weeks for shop drawing review cycles.
Egress calculations per IBC Chapter 10 are required: parking garages require exit stair spacing within 300 feet travel distance in sprinklered structures. Sprinkler design may or may not be required depending on occupancy and jurisdiction — open parking structures with adequate natural ventilation are often exempt from sprinkler requirements under IBC Section 406, but confirm with the AHJ (Authority Having Jurisdiction) before permit submission.
Traffic control and circulation studies may be required for large structures in dense urban areas. Allow 4–8 weeks for city transportation department review if required.
Sample Gantt Timeline
| Phase | Duration | Notes |
|---|---|---|
| Schematic Design + Structural System Selection | 4–6 weeks | System selection gates all downstream procurement |
| Design Development + Construction Documents | 8–14 weeks | PT shop drawings coordinated during CD phase |
| Permitting | 6–12 weeks | Concurrent with procurement start |
| Precast Fabrication (if applicable) | 12–20 weeks | Starts at permit submission, not permit issuance |
| Site Work and Foundation | 4–8 weeks | Includes pile or spread footing depending on soils |
| Elevated Structure (per floor) | 5–9 weeks/floor | Cast-in-place PT; faster for precast/steel |
| Elevator and Stair Core | Concurrent with structure | Shear wall cores built parallel to floor plates |
| MEP Rough-in and Lighting | 4–6 weeks | LED per IES RP-20; EV conduit per electrical design |
| Moisture Testing (slab) | 6–10 weeks | Cannot compress; coating window depends on this |
| Traffic Coating Application | 3–6 weeks | Sequenced bottom-up concurrent with upper floors |
| EV Charger Installation | 2–4 weeks | After electrical service and panel energized |
| Striping, Signage, and Accessories | 1–2 weeks | Parking control equipment, gates, signage |
| Inspections and CO | 2–4 weeks | Structural, electrical, fire, building final |
Total: 18–36 months depending on size, structural system, number of levels, and jurisdiction.
The critical path for cast-in-place PT structures is almost always the structural cycle time — each floor takes time, and no amount of crew hours can compress the concrete cure. For precast structures, the critical path is precast fabrication, which begins as soon as the structural design is sufficiently complete for shop drawing production. Start procurement early, and your structure goes up fast. Start late, and you wait on a fabricator's backlog regardless of how many workers you have on site.