Stair Towers — Frame & Brace
A freestanding or scaffold-integrated vertical access structure built from prefabricated steel frame and brace scaffold components, providing a code-compliant stair system for workers to travel safely between ground level and elevated scaffold platforms or building floors on construction sites where ladder access is insufficient or prohibited. Find frame and brace stair tower vendors near you through Scaffold Exchange.
What Is a Frame & Brace Stair Tower?
Definition: A frame and brace stair tower is a vertical access structure assembled from the same welded steel end frames, cross braces, coupling pins, and base jacks used in standard panel frame scaffolding, but configured specifically to house a continuous stair run — rather than open work platforms — within the frame bays as the tower rises. Stair units are inserted into each bay of the frame structure as it is stacked, creating a self-contained stair system that climbs inside the scaffold tower from ground level to the required access height. The completed tower provides a guarded, OSHA-compliant means of vertical travel for construction workers between the ground and scaffold platforms, building floors, or elevated work areas, eliminating the fatigue, injury risk, and productivity loss associated with repeated ladder climbing on multi-story projects.
Frame and brace stair towers are the most widely available and most commonly rented stair tower system in the United States because they are built from the same frame scaffold inventory that most rental houses and contractors already stock. The frames, cross braces, coupling pins, and base jacks are interchangeable with a standard frame scaffold system, meaning that a single inventory can serve both purposes — a significant cost and logistics advantage over proprietary modular stair tower systems that require dedicated non-interchangeable components. On a typical construction site, frame and brace stair towers are erected alongside the primary scaffold structure, tied to the building or the adjacent scaffold at regular intervals, and advanced upward as the primary scaffold grows.
The stair units themselves — the prefabricated steel stair sections inserted into each frame bay — are available in configurations that fit the standard 5-foot and 6-foot bay widths most common in U.S. frame scaffold inventories, with handrails on both sides and non-slip treads meeting OSHA stair geometry requirements. Platform landings at each frame lift level provide a rest point and a transition between stair runs, and the tower's guardrail system provides fall protection on all open sides of the landing platforms. Through Scaffold Exchange, you can find vendors across the U.S. who carry frame and brace stair tower systems and compare their configurations, heights, and availability in your area.
How a Frame & Brace Stair Tower Works
A frame and brace stair tower is erected using the same stacking sequence as standard panel frame scaffold, with stair units inserted into each bay as the tower rises rather than open deck platforms.
Set the Foundation & First Frames
Mudsills and adjustable base jacks are positioned on firm, level ground at the tower footprint. The first pair of end frames — selected to match the stair unit width — are stood on the base jacks and connected by cross braces, forming the ground-level bay of the tower. The tower footprint must be large enough to accommodate the stair unit width plus the frame leg clearance on both sides.
Insert Stair Units & Install Landing Platforms
A stair unit is inserted into the first bay, with its stringers resting on the frame's horizontal bearer rails. A landing platform is installed at the top of the stair unit — at the frame's upper bearer rail level — providing the transition point between the stair run below and the next stair run above, and a rest platform for workers traveling between floors.
Stack Additional Frames & Continue the Stair
Coupling pins are inserted into the top of the standing frames, and the next tier of end frames is set directly on top. Cross braces are installed, the next stair unit is inserted into the new bay in the opposite travel direction to the stair below — creating the switchback configuration that allows the stair to gain height within the tower's footprint — and a landing platform is installed at the new level. This sequence repeats for each additional lift.
Install Guardrails, Tie the Tower & Open for Use
Guardrail frames or individual post-and-rail assemblies are installed on all open sides of each landing platform. The tower is tied to the building structure or adjacent scaffold at the required intervals to resist lateral wind and live loads. Access gates at the tower's entry and at each landing level are installed and the completed tower is inspected by a competent person before it is opened for worker use.
Key Components of a Frame & Brace Stair Tower
A frame and brace stair tower combines standard frame scaffold components with purpose-built stair units and landing platforms to create a complete vertical access structure from a single interchangeable component inventory.
End Frames
Standard welded steel panel frames forming the vertical structural bays of the tower, selected in the width required to accept the stair unit — typically 5-foot or 6-foot wide frames in U.S. inventories. Walk-through frame variants provide ground-level entry into the tower without a separate access opening cut into the hoarding or frame.
Stair Units
Prefabricated steel stair sections sized to fit within the frame bay, with stringers that bear on the frame's horizontal rails, non-slip treads meeting OSHA riser and tread depth requirements, and integrated handrail attachment points. Stair units are inserted alternately in opposing directions at each bay to create the switchback travel pattern within the tower.
Landing Platforms
Level platform decks installed at the top of each stair unit at the frame's upper bearer rail level, providing a rest point and direction change between stair runs. Landing platforms must meet OSHA minimum width requirements and be fully decked with no gaps exceeding 1 inch between deck boards or panels.
Cross Braces
Diagonal steel braces connecting paired frames across the tower bay, providing lateral rigidity to the tower structure. Cross braces in a stair tower are installed on the sides of the bay not occupied by the stair run, accommodating the stair unit geometry while maintaining the structural integrity of the frame bay.
Guardrail Frames & Handrails
Guardrail assemblies on all open sides of each landing platform, combined with continuous handrails on both sides of every stair run. Handrails must be graspable along their full length and extend to the required height above the stair nosing — between 36 and 37 inches measured vertically from the stair tread nosing per OSHA 1926.451(e)(4).
Tower Ties & Base Jacks
Adjustable screw base jacks leveling the tower on uneven ground, and engineered tie assemblies connecting the tower to the building structure or adjacent scaffold at the intervals required to resist the lateral loads imposed by wind and worker traffic within the tower without the tower exceeding its height-to-base ratio stability limit.
Common Applications & Job Site Uses
Frame and brace stair towers are used wherever construction workers must travel repeatedly between ground level and elevated scaffold platforms or building floors, and where ladder access is inadequate for the volume of workers, the height of travel, or the materials being carried.
Primary worker vertical access on multi-story scaffold systems where repeated ladder climbing is impractical or prohibited
Masonry, brickwork, and exterior cladding projects where workers carry heavy materials between levels throughout the shift
Facade renovation on occupied mid-to-high-rise buildings where worker access must be fast, safe, and separate from the occupied building's internal circulation
New construction sites where the building's permanent stair is not yet installed or not yet open for construction use
Industrial plant turnarounds and maintenance shutdowns requiring rapid multi-level worker access alongside process equipment
Bridge and infrastructure rehabilitation where a stair tower provides access between the bridge deck and the scaffold or work platform below
Emergency egress provision on construction sites where OSHA requires a stair as the means of egress from scaffold at heights where ladder egress is insufficient
Event and temporary structure installations requiring compliant public stair access between grade and an elevated platform
Frame & Brace Stair Towers vs. Other Vertical Access Systems
Frame and brace stair towers are the most widely available stair tower format in the U.S. market — here is how they compare to the primary alternatives contractors evaluate for vertical worker access.
Panel frame scaffold configured as a stair tower
- Built from the same frame scaffold components already in most rental inventories
- Widest availability and lowest rental cost of any stair tower format
- Switchback stair configuration within a compact tower footprint
- Fully interchangeable components — no dedicated proprietary inventory required
Rosette or ringlock scaffold stair towers
- Built from modular scaffold systems such as Layher Allround or ringlock
- Greater geometric flexibility for complex or non-standard tower configurations
- Requires the matching modular system inventory — not interchangeable with frame scaffold
- Higher component cost; preferred on projects already using modular scaffold
Motorized vertical transport
- Motorized — carries workers and materials without physical climbing
- Higher throughput capacity on large multi-story sites
- Significantly higher cost and longer installation time than a stair tower
- Governed by OSHA 1926.552; requires PE design and anti-fall device testing
Single-person vertical climbing access
- Lowest cost and simplest installation — no tower structure required
- OSHA limits ladder access on scaffolds to heights where stair is not required
- Cannot carry materials simultaneously with a worker
- Fatigue and injury risk increase significantly with height and frequency of use
Find Frame & Brace Stair Tower Vendors Near You
Use the Scaffold Exchange map to search by location, filter by equipment type, and connect directly with local suppliers who carry frame and brace stair tower systems for construction and industrial projects.
Compliance & Site Safety Considerations
Frame and brace stair towers used in construction are governed by OSHA 29 CFR 1926.451(e), which establishes access requirements for scaffolds, including the requirement that a stair or ladder be provided for scaffold platforms more than 2 feet above or below the access point, and that workers not be required to climb cross braces to access scaffold platforms. OSHA 1926.451(e)(4) specifically governs stairway-type ladders and stair towers used as scaffold access, requiring that stair stringers be a minimum of 18 inches wide, that stair treads and landings be slip-resistant, that handrails be provided on both sides of the stair run, and that handrail height be between 36 and 37 inches measured vertically from the stair tread nosing. Stair towers must be designed to support at least four times the maximum intended load per the general scaffold requirements of 1926.451(a), and all open sides of landing platforms must be protected by guardrail systems. The tower must be tied to the building or adjacent scaffold at intervals that prevent the tower from exceeding a height-to-least-base-dimension ratio of 4:1 without ties, and the tie pattern must be verified by a competent person before the tower is opened for use. All workers who use the stair tower must be trained in accordance with OSHA 1926.454.
- Stair stringers minimum 18 inches wide per OSHA 1926.451(e)(4)
- Stair treads and landing surfaces slip-resistant throughout the tower height
- Continuous handrails on both sides of every stair run at 36–37 inches above tread nosing
- Guardrails installed on all open sides of every landing platform before the tower is opened for use
- Landing platforms fully decked with no gaps exceeding 1 inch between deck boards or panels
- Tower tied to the building or adjacent scaffold at required intervals — 4:1 height-to-base ratio not exceeded without ties
- Tower inspected by a competent person before each work shift and after any event affecting structural integrity
- All workers trained per OSHA 1926.454 before using the stair tower