Stair type guide
Custom spiral staircases in steel and aluminum
Spiral staircases solve a specific problem: vertical access in a footprint where a conventional stair won't fit. Loft access, secondary stairs, exterior deck access, mezzanines, and rooftop access are all common applications. They are also a strong architectural choice when the design calls for a sculptural element. We build custom welded spiral stairs from steel, aluminum, and stainless — designed to the project, not pulled from a catalog.
Geometry and code
Every spiral stair starts with three numbers: total rise (floor to floor), diameter, and number of treads. The BC Building Code sets the minimum tread run at 190 mm measured 300 mm from the narrow end of the tread, and the minimum stair width at 660 mm. In practice, for comfortable residential use we recommend at least a 5 ft (1500 mm) outside diameter — anything smaller feels tight and is hard to use when carrying anything.
The total rise determines the number of treads. For a typical 9 ft floor-to-floor residential rise, expect 12–13 treads at 175–185 mm rise per step. Headroom on a spiral has to be checked carefully — the BC Building Code minimum 1950 mm headroom applies to spirals just like straight stairs, and it is measured vertically from any tread nosing to the lowest obstruction above.
Construction
A welded spiral stair is built around a central column — typically 5–8 inch diameter steel pipe, sized for the structural load and the stair height. Each tread welds directly to the column, forming a structural assembly that doesn't need additional support along its run. The top and bottom platforms anchor to the floor structure above and below.
- Central column: 5–8 in OD steel or stainless pipe, plate base for floor bolt-down
- Treads: Wedge-shaped, fabricated from steel plate, checker plate, perforated steel, or with hardwood inserts
- Handrail: Continuous bent steel rod or tube, mounted on balusters spaced per code (100 mm sphere rule applies)
- Top platform: Quarter-landing welded to the column, bolted to the floor diaphragm above
Materials and finish
For interior residential spirals, we usually fabricate in mild steel and finish with powder coat. Common finishes are matte black, charcoal grey, and custom RAL colors for design-driven projects. Hardwood treads (oak or walnut) are added on top of the steel for warmth.
For exterior and industrial spirals, hot-dip galvanizing is the right answer. Galvanized treads with checker plate or perforated pattern handle the Pacific Northwest climate without coating maintenance. For high-end exterior applications where the look matters, stainless steel 316 is an option.
What drives spiral stair pricing
The main cost drivers for custom spiral stairs are:
- Diameter: Larger spirals require more material and more complex geometry. A 6 ft diameter spiral costs meaningfully more than a 4 ft diameter spiral.
- Height: More treads mean more welding time. Each tread is individually fitted and welded to the central column.
- Tread material: Steel-only treads are the most cost-effective. Hardwood treads (oak, walnut) add material and fitting cost. Stone treads are the most expensive option.
- Finish: Powder coat is the standard for interior spirals. Hot-dip galvanizing is standard for exterior. Stainless steel construction is the premium option.
- Handrail design: A simple bent steel rod is less expensive than a custom flat bar or stainless handrail with decorative balusters.
For a project-specific price, request a quote with your floor-to-floor height, preferred diameter, and finish preference.
Lead time
8–12 weeks from approved drawings to installation for most spiral projects. Galvanized exterior spirals add 1 week for the galvanizing trip. Stainless and aluminum spirals require specific welding procedures and finishing that adds 1–2 weeks.
Common applications for custom spiral stairs
- Loft access: Studio apartments, garage conversions, and home offices with mezzanine levels. A 4–5 ft diameter spiral fits into corners that conventional stairs can\'t serve.
- Secondary stairs: Homes with a primary staircase but needing secondary access between levels — basement walk-outs, upper-floor private office access, children\'s play spaces.
- Rooftop and deck access: Exterior spirals for private rooftop patios, upper-level decks, and green roof access. Galvanized finish for durability.
- Commercial mezzanines: Retail, restaurant, and office mezzanine access where a full-size stair would consume too much floor area.
- Architectural centrepieces: Where the spiral is the statement piece of the room, typically with hardwood treads and a stainless or brass handrail.
- Industrial equipment access: Rooftop HVAC service, mechanical room access, warehouse mezzanine access. Usually galvanized steel with checker plate treads.
Design considerations specific to spirals
Spiral stairs have a few design quirks that come up on every project and are worth planning for:
- Upper landing geometry: The top of the spiral lands on a quarter platform welded to the central column. That platform has to align with the floor opening above and tie into the floor structure.
- Carrying things up: Narrow spirals are hard to use when carrying furniture, boxes, or laundry. If the stair is a primary access route, plan for 5 ft diameter or larger.
- Moving day: If the spiral is the only access to an upper floor, large furniture may never fit up. Plan for access to the upper floor through another route.
- Under-stair space: The centre of a spiral stair is unused. Some projects add a round closet, planter, or storage element at the base.
- Sound transmission: Steel spirals can carry footstep noise between levels. Hardwood treads reduce this. For sound-sensitive applications, a rubber isolator at the base plate helps.
Related reading
For a comparison between spiral and other stair types, see the metal stair fabrication hub. For exterior spiral applications, read our exterior galvanized stairs guide. And for what drives pricing across all stair types, see the cost guide.
FAQs about spiral staircases
Are spiral staircases code-compliant in BC?
Yes, with limits. The BC Building Code (Section 9.8.4.5) allows spiral stairs in residential applications with a minimum tread run of 190 mm at a point 300 mm from the narrow end of the tread, and a minimum stair width of 660 mm. They cannot be used as the only means of egress from a dwelling unit larger than 50 m², and they are generally not permitted as required egress in commercial occupancies. For loft access, secondary stairs, and architectural focal points, they are fully code-compliant.
What diameter spiral staircase do I need?
For comfortable residential use, a 5 ft (1500 mm) diameter is the practical minimum. 4 ft is technically code-compliant but feels tight and is hard to use when carrying anything. 6 ft (1800 mm) is comfortable and is what we recommend for primary residential use. Commercial and industrial spiral stairs run 4–7 ft depending on the application.
Can spiral staircases be used outdoors?
Yes — exterior spiral stairs are common for deck access, second-storey decks, and rooftop access. For exterior use, hot-dip galvanizing is the right finish. The treads are usually steel with a non-slip pattern (checker plate, perforated, or grating) for drainage and traction. Stainless steel is an option where the look matters, and aluminum spirals are sometimes used where weight matters.
How much does a custom spiral staircase cost?
Custom welded spiral staircase pricing depends on diameter, height, materials, and finish. Smaller-diameter steel spirals with powder coat finish cost less than larger spirals with hardwood treads and stainless handrails. Exterior galvanized spirals fall in a similar range because the galvanizing process offsets the simpler finish requirements. The best way to get an accurate number for your project is to <a href="/request-a-quote/">request a quote</a> with your dimensions and design preferences.
Prefab vs custom — what is the difference?
Prefab spiral kits come from a catalog with fixed dimensions and limited materials. They are fine for utility access and budget-driven projects. Custom spiral stairs are designed to your floor-to-floor height, your diameter, and your finish, and they are welded as one assembly so the geometry is exact. The price difference reflects the engineering, fabrication time, and the quality of the result.
How many treads does a typical spiral staircase need?
That depends on floor-to-floor height. For a standard 9 ft (2740 mm) residential rise, a comfortable spiral has 12–13 treads at 180–200 mm rise per step. For a 10 ft rise, 14 treads. The minimum rise per step is 125 mm and the maximum is 200 mm under BCBC 9.8.4.5 for residential applications. Going taller than 200 mm rise makes the stair feel steep and difficult to use.
Can I put a spiral staircase through an existing floor opening?
Yes, if the opening is large enough. A 5 ft diameter spiral needs a minimum 5'2" by 5'2" square opening (with a round opening being slightly more efficient at 5'4" diameter). The opening also has to clear headroom at the upper landing — at least 1950 mm measured from each tread nosing to any obstruction above. If the existing opening is too small, the opening has to be enlarged, which affects the floor framing.
What is the handrail style on a spiral staircase?
The outer edge of every spiral stair has a continuous handrail that follows the spiral geometry. The handrail is usually a bent steel rod or tube at 1050–1070 mm above the tread nosing for residential, with balusters spaced per the 100 mm sphere rule. For modern designs, we often use a single flat bar bent around the perimeter. For more traditional looks, round tube or solid round rod.
How is the spiral stair anchored to the floor below?
The central column is welded to a heavy steel base plate that bolts directly to the concrete slab or the structural floor below. For wood-framed floors, the base plate anchors into a blocked or reinforced area of the floor framing. The engineering sizes the base plate and anchor bolts for the vertical load, the overturning moment from lateral loads, and the torsional reaction of the stair under eccentric loads.
Can the spiral rotate clockwise or counterclockwise?
Either. The direction of rotation is specified during design and doesn't affect cost. Most spiral stairs are designed right-handed (clockwise going up) by default because it follows the natural movement of right-handed people, but left-handed spirals are common when the stair placement requires it.
Are spiral stairs slippery?
Depends on the tread surface. Smooth steel plate is slippery when wet or dusty. Checker plate and perforated plate have enough grip for normal use. Hardwood treads with a natural finish are comfortable underfoot and not slippery. For exterior spirals, we always specify a textured tread surface so drainage and grip are handled.
What is the lead time on a custom spiral staircase?
From approved shop drawings, a custom spiral spans 8–12 weeks to finished installation. Fabrication runs 4–6 weeks because each tread has to be fitted and welded individually around the central column. Finishing (powder coat or galvanizing) adds another 1 week. Installation is usually a half-day to a full day depending on access.
Can I have hardwood treads on a spiral staircase?
Yes. Solid hardwood treads (oak, walnut, maple) can be cut to the wedge shape of each spiral tread and bolted to the steel tread structure. The wood adds warmth to the stair and is a popular choice for interior residential installations where the stair is visible from a living area.
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