26 October 2026 Uncategorized 0

Stair Opening Slab: How to Cut a Stairwell Void Safely

A stair opening in an existing concrete slab is cut with diamond wall saws, wire saws or ring saws, but only after an engineer has confirmed the slab can lose that section, the slab has been scanned for steel and services, and any required approvals are in place. The sawing itself is often the shortest part of the job. The planning, support and safe removal of the cut panels decide whether it goes well. This guide walks through the sequence we follow in Melbourne and across Victoria, so you know what to ask for and what to expect.

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Plan Your Concrete Stair Opening Safely

Vic Sawing & Drilling provides concrete sawing and drilling across Melbourne and Victoria, with qualified operators and a focus on safety.

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TL;DR

Never cut first. An engineer must assess the slab type, span, supports and the opening’s position before any saw touches the concrete.
Scan the slab for reinforcement, post-tensioning tendons, conduits and pipes. Drawings are a starting point, not proof of what is inside.
Check the permit pathway with your building surveyor, because approvals for work on existing buildings vary by state and territory.
Cutting a stairwell void is high-risk work in Victoria: expect a Safe Work Method Statement, wet cutting, exclusion zones and a controlled plan for lifting out the cut panels.
Cost depends on slab type, opening size, reinforcement, access, temporary support and how the panels leave the building.

What a stair opening in a slab actually involves
Step 1: Find out what the slab really is
Step 2: Scan before you mark
Step 3: Engineering, approvals and the Australian rules
Step 4: Temporary support and strengthening
Post-tensioned slabs: a separate process
Step 5: How the void is cut and the panels are removed
Safety controls that apply on the day
What affects the cost and the time
Our perspective: plan the void as an engineering task
Get your stair opening cut by a crew that scans first
Frequently asked questions
Sources

What a stair opening in a slab actually involves

When a building gains a new staircase between levels, a section of the suspended slab has to go. That sounds simple, but a floor slab is part of the structure. It carries loads sideways to beams, columns and walls. Taking out a rectangle of it changes how those loads travel.

The STRUCTURE magazine article on openings in existing floors sets out the normal sequence. You choose the location after reviewing available construction documents and inspecting and probing the floor. You assess the structural effects, obtain a construction permit where required, install shoring for interim loads, mark the corners to prevent overcutting, and then saw with diamond blades. Strengthening may be needed around the new edge.

The same article explains why this matters. An opening can remove reinforcement, reduce stiffness or flexural resistance, overload neighbouring areas, or disrupt the original load path. That is why the order of work is fixed, and why we do not start cutting on a verbal “it should be fine”.

Step 1: Find out what the slab really is

Before anything is marked on the floor, someone has to establish the slab type, its span and its support conditions. The position of the opening relative to columns and beams matters as well, because guidance on cutting stair or riser openings points to these as the first questions for the engineer.

Common slab types behave differently:

One-way slabs span in a single direction. The direction of your opening decides which reinforcement is interrupted.
Two-way and flat slabs carry load in both directions. Openings near columns raise punching-shear concerns, so the engineer will look hard at any void close to a column.
Post-tensioned slabs hold high-tension steel tendons. They need their own process, which we cover below.
Composite metal deck slabs use the deck profile as tension reinforcement, which changes the strengthening approach.

Start with the paperwork. The Australian Building Codes Board handbook on upgrading existing buildings tells you to locate documentation about the original design, approval and construction first. It also warns that existing construction should not be assumed to match those documents. Older Melbourne buildings have often been altered, and the as-built slab can differ from the drawings.

Step 2: Scan before you mark

Scanning turns an assumption into a map. Ground-penetrating radar and similar methods can identify reinforcing steel, post-tensioning tendons, electrical conduits and pipes that may not appear on structural drawings. That matters for two reasons: you do not want to hit a live conduit, and the engineer needs to know which bars the cut will interrupt.

WorkSafe Victoria’s industry standard goes further. Its Safe concrete cutting and drilling standard says planning must confirm the structural components and services in the slab, include structural-engineer advice for alterations, and use a competent person to supervise the work.

Our concrete scanning service covers this stage. If you want to understand the technology first, we explain what concrete scanning is, compare five scanning methods and list seven checks before drilling that apply equally to saw cuts.

What the scan results change

The scan can move the opening by a few hundred millimetres, or change the cutting sequence. Typical outcomes include:

A clash with a pipe or conduit that must be isolated or relocated before cutting.
A concentration of reinforcement along one edge, which affects how the engineer designs trimmer beams or plates.
Tendons in a slab that was thought to be conventionally reinforced, which stops the job until the post-tensioned process has been followed.

Mark the confirmed outline on the slab and mark the corners clearly. The STRUCTURE article notes that marking corners helps prevent overcutting, where the blade runs past the corner into slab that must stay.

Step 3: Engineering, approvals and the Australian rules

An engineer, not the cutting contractor, decides whether the opening can be made and what must be added. Their analysis should evaluate load paths, punching-shear capacity near columns and the reinforcement being interrupted, particularly in two-way flat slabs or post-tensioned construction. They will also consider the cumulative effect of other penetrations. Several small penetrations close together can have a significant combined effect on slab strength and stiffness, so tell the engineer about any core holes and service risers nearby.

Permits and the National Construction Code

The NCC does not generally apply to existing buildings unless they are altered, extended or change use, and it gets legal effect through state and territory frameworks. Adding a stair void is an alteration. The ABCB handbook adds that application and approval processes for upgrading existing buildings vary by state and territory, and recommends advice from an appropriately qualified person where assessment and analysis are needed.

In practice, confirm with your building surveyor whether the work needs a building permit before you book a crew. We do not issue permits and we do not replace your engineer, but we will work to the engineer’s drawings and sequence.

The stair itself must comply

The opening is only useful if the stair that goes in it is compliant. For housing, the NCC 2022 provisions on stairway construction cover limits on risers per flight, consistent risers and goings, the 2R + G relationship, and restrictions on openings in risers. Give your designer or stair builder the exact void size before the cut, because a void that is 100 mm short can force an awkward stair layout that cannot be fixed afterwards. Commercial buildings follow different parts of the code, so ask your designer which provisions apply.

If the new stair also leads to a landing, handrail or balustrade in an older home, plan that early too. In heritage houses, balustrade restoration for heritage homeowners is worth considering alongside the new void edge so the finished staircase suits the original character.

Step 4: Temporary support and strengthening

The slab does not stop carrying load the moment a saw cuts through it. The STRUCTURE article explains that temporary shoring can support interim design loads, and that it may be omitted if the floor is strengthened before the opening is made. After the opening exists, permanent strengthening can include transfer beams or externally bonded or bolted steel plates.

The engineer specifies which approach applies. Typical practical questions are:

Does the floor below need propping, and who is responsible for installing and removing the props?
Is the strengthening installed before or after the cut?
Can the area below stay occupied, or must it be cleared?

In Victoria, structural alterations involving temporary support to prevent collapse count as high-risk construction work under the Occupational Health and Safety Regulations 2017, so a Safe Work Method Statement (SWMS) is required.

Post-tensioned slabs: a separate process

Post-tensioned slabs are common in Melbourne apartment and commercial buildings. Cutting one without a plan can release stored energy in the tendons. The Concrete Repair Institute’s technical article says large stairwell openings in post-tensioned slabs need engineering analysis, that existing tendons must be located, and that affected strands may need to be detensioned and reanchored before concrete removal. That article is from the United States, so follow Australian standards and your engineer’s design for the actual job.

Our article on three checks engineers require before cutting post-tensioned slabs goes through this in more detail. If the scan finds tendons, stop and tell your engineer before any cutting.

Step 5: How the void is cut and the panels are removed

For a stairwell void, the main methods are wall sawing and wire sawing. WorkSafe Victoria’s standard says a stairwell opening can be cut by wall sawing or wire sawing, and that you need a controlled method for removing the concrete blocks, securing them against overturning or falling, and confirming that any crane or lifting device is designed for the load.

Method	Where it suits a stair opening	Points to plan
Wall sawing	Straight, clean cuts through slabs of most thicknesses with track-mounted blades	Track fixing, water control, panel weight
Wire sawing	Thick or heavily reinforced slabs, awkward access, cuts where a blade cannot reach	Wire routing, anchor points, slurry management
Ring sawing	Deep cuts where a standard blade runs out of depth	Flush-cut limits at the corners
Hand sawing	Corner finishing and small adjustments where access is tight	Overcut control, operator vibration
Core drilling	Corner holes so cuts do not overrun, and lifting-point holes	Hole positions agreed with the engineer

Corner core holes are a common technique. They give a clean radius or stop point, so straight saw cuts do not extend past the corner and weaken the slab. Core holes can also take lifting anchors for the cut panels.

Managing the cut panels

A 150 mm thick slab weighs a lot per square metre, so a stair void cut into sections produces heavy panels. Before cutting, decide:

How big each panel can be given the lifting equipment and the route out.
How each panel is secured before the final cut so it cannot drop onto the floor below.
Whether panels go out by crane, by hoist or are broken down in a controlled way. Our concrete removal service can handle breakdown and disposal when the job needs it.

This is also why access matters. A void in a basement carpark and a void in a fifth-floor apartment need different removal plans even when the slab is the same thickness.

Safety controls that apply on the day

WorkSafe Victoria’s standard calls for a qualified person to determine slab capacity when sawing suspended slabs, control unneeded services, secure the cut area and set up an exclusion zone. Combined with the wider standard, the controls on a typical stair void job include:

SWMS prepared for high-risk work, including tasks with a risk of falling more than 2 metres, which applies when the void opens onto a lower level.
Wet cutting and respiratory protection to control dust. Our guides on wet versus dry cutting and minimising dust when sawing concrete cover the methods, and our page on dustless concrete cutting explains capture at source.
Exclusion zones and barricades above and below the cut.
Service isolation and electrical controls, including water near powered equipment.
Manual handling and vibration controls for operators.

Silica is the reason dust control is not optional. The exposure standard for respirable crystalline silica is 0.05 mg/m3 as an 8-hour time-weighted average, and WorkSafe Victoria recommends keeping exposure below 0.02 mg/m3. WorkSafe also lists manual handling, vibration and loss of vacuum pressure in suction-held equipment among the key hazards in concrete cutting. For a wider look at site practice, see our summary of safety measures for concrete cutting.

What affects the cost and the time

Nobody can quote a stair void accurately from a photo. Time and cost depend on the same factors that shape the engineering:

Slab type and thickness, including the reinforcement or tendons the cut interrupts.
Opening size and position, which sets the length of cut and the panel sizes.
Strengthening and temporary support, which can be a bigger line item than the sawing.
Access and occupancy, including working in occupied buildings, after-hours work and lift or stair limitations.
Panel weight and removal route, which decide whether you need a crane, hoist or breakdown on site.

These factors are consistent with published guidance on slab openings. For reference, our published price range for concrete cutting jobs is $450 to $5,000 one-off, and a stair void will sit wherever your slab, access and engineering put it. Scanning, engineering fees, shoring and stair fabrication are separate from the cutting. Ask for a written scope that lists what is and is not included.

Our perspective: plan the void as an engineering task

Most problems we see on stair openings come from skipping steps, not from the cutting. A plan sketched on a floor plan looks tidy, then the scan shows a bundle of conduits exactly where the stair should start. Or an owner books a crew before the surveyor has confirmed the permit pathway. Neither is a cutting failure, but both stop a job halfway.

Our view is simple. Treat the opening as a structural alteration from the first phone call. Get the engineer involved early, scan the slab before the design is fixed, and ask your cutting contractor to work to the engineer’s sequence. Licensed and qualified operators, suitable equipment and strict OH&S practice are what we bring to that sequence. The same discipline applies whether it is a small domestic stair in a renovation or a large commercial project across several levels.

If you are unsure about a detail, ask us before you commit to a design. A short conversation about access, panel size and cutting method can save a redesign.

— MYBMC

Get your stair opening cut by a crew that scans first

We provide concrete scanning, wall sawing, wire sawing, ring sawing, core drilling and concrete removal across Melbourne and Victoria, for contractors, property managers, architects, engineers and homeowners. Send us your engineer’s drawings and site access details through our main page and we will quote the cutting, scanning and removal as one scope. For larger jobs, see concrete cutting around Melbourne.

Frequently asked questions

Can I cut a stair opening in a concrete slab without an engineer?

No. WorkSafe Victoria’s industry standard calls for structural-engineer advice for alterations to slabs and a competent person to supervise. The engineer checks load paths, supports and reinforcement, and specifies any strengthening. Cutting without that advice risks damaging the structure and the people below.

Do I need a permit to cut a stairwell void?

Often yes, because adding a stair is an alteration to an existing building. Approval processes vary by state and territory, so ask your building surveyor before work starts. Your surveyor will tell you which documents, such as engineer’s drawings, they need.

What is the best way to cut a stairwell opening?

Wall sawing and wire sawing are the methods WorkSafe Victoria names for stairwell openings. Wall sawing suits straight, accessible cuts, while wire sawing handles thick or awkward slabs. Corner core holes and hand sawing finish the corners without overcutting.

Can a post-tensioned slab have a stair opening?

Sometimes, but only with engineering analysis. Tendons must be located by scanning, and affected strands may need to be detensioned and reanchored before the concrete is removed. Never cut a slab you suspect is post-tensioned until the engineer has signed off the plan.

How long does a stair opening take to cut?

The cutting can take a day or less for a standard residential void, but scanning, engineering, approvals, propping and panel removal add time before and after. Slab thickness, reinforcement, access and the removal route set the timeline. We confirm it once we have the drawings and have seen the site.