Level four wants a stair to level five
The tenant has taken two floors and wants them to feel like one, so there is a feature stair on the fit-out drawings and a slot through the slab to put it in. The architect has drawn the slot at 1.4 m by 4.2 m. Nobody on the drawing has said what the slab is, what is in it, what happens to the floor while a piece that size is missing from the middle of it, or how roughly two tonnes of reinforced concrete gets from level four down to a skip on a street with a loading bay window of ninety minutes.
Those are four questions with four owners, and on a fit-out they arrive out of order. The saw contractor prices a cut, the demolition contractor prices a removal, and the temporary works designer is appointed after both — usually once somebody asks who is signing the propping drawing. The engineer who can say whether the floor works with a hole in it is often not appointed at all, because the fit-out team has no relationship with the landlord's structural consultant and nobody budgeted for one.
So the sequence that keeps this job out of trouble runs backwards from the saw. Establish what the slab is and what it does. Get the opening approved as a permanent alteration, with its trimming designed. Get the temporary support designed and installed to hold the floor and everything standing on the piece coming out. Then, and only then, cut — in panels sized by what can leave the building rather than by what a saw can reach.
The as-built is a drawing of intent, not a record of what got poured
Every opening in existing concrete begins with two surveys that people routinely collapse into one. The first is structural: what type of floor is this, which way does it span, what is the opening about to interrupt. The second is a scan: where exactly is the steel, and are there tendons. Record drawings answer the first badly and the second not at all — bars get moved on site to clear a service box, a bay gets thickened after a late load change, and a ribbed slab picks up a topping in a refit nobody drew.
The structural answer changes what the opening costs. In a one-way slab an opening running with the span cuts distribution steel and can often be trimmed conventionally; turn it ninety degrees and it cuts the main tension reinforcement, so a load path has to be built round it. In a two-way flat slab, position relative to the columns is everything — ACI 318 sets out where openings may be placed in the column and middle strips without a special analysis, and a hole creeping toward a column head is a punching shear problem rather than a bending one. On composite metal deck the profile is the reinforcement, so a cut removes steel rather than exposing it.
The scan is a specialist visit and it is worth insisting it happens from both faces. Ground-penetrating radar and covermeter work on concrete are described in ACI 228.2R, and the practical limits matter more than the physics: a covermeter finds the top mat and gets vague about a second layer directly beneath it, radar resolves depth better but wants a clean surface, and neither is at its best through 60 mm of screed and a raised access floor. Mark the findings on the soffit as well as the top — that is where the drilling for the propping heads and the trimming steel happens, and it is the face the tenant below is looking at.
What comes back from that scan is a constraint on the opening, not a report to be filed. If the slot as drawn clips a beam, sits over a column head, or runs along the line of a banded tendon, the argument to have is about moving the stair a bay — while it is still lines on a screen and not a fabricated flight with a deposit paid on it.
| Floor type | What the cut interrupts | Settle first |
|---|---|---|
| One-way reinforced slab | Main steel if the opening runs across the span; distribution steel only if it runs with it | Span direction confirmed on site, not assumed from the drawing |
| Two-way flat slab | Column and middle strip reinforcement, and the punching shear zone if the hole is near a column | Distance from every column face, and the engineer's view on strip position |
| Ribbed or waffle slab | Whole ribs, each of which is a beam, plus the topping spanning between them | Which ribs may be cut and what picks their load up at the trim line |
| Composite metal deck | The deck profile itself, which is acting as the tension reinforcement | Whether the deck can be trimmed at all, or needs steel beneath before it is cut |
| Precast hollowcore | Pretensioned strands, with no redistribution available along the plank | The plank manufacturer's written position and the framing that replaces the plank |
| Post-tensioned flat slab | Tendons, which release their force the moment they are severed | A tendon survey, and a de-tensioning method if any tendon must go |
What a finished opening is made of
A trimmed opening is not one item on an order. It is a temporary support scheme that exists for weeks, a cut edge, a permanent steel trim that gives the edge its continuity back, a finishes detail that returns the floor build-up into the void, and guarding that has to be in place from the first cut to the day the balustrade is signed off. They are bought from four different people and each of them assumes one of the others has allowed for the interfaces.
Read as a section, they also come apart in a fixed order, which is the order they have to be built in reverse. Nothing above the slab can be finished until the trim below it is fixed; the trim cannot be fixed until the props are in and the edge is cut clean; and the props cannot come out until the trim is doing what they were doing.
A trimmed opening, taken apart
- Edge protection round the void — up before the first cut and down only when the permanent balustrade replaces it, which on a fit-out can be four months of standing guardrail Guardrail System Fall-Protection Compliance Checker
- Screed, kerb and edge return — the floor build-up stops at the opening and has to turn down into it, which is where the acoustic and fire seals at the edge get detailed or forgotten
- Existing slab, cut through — the piece removed is concrete plus the reinforcement inside it, and its mass decides the propping, the lifting gear and the number of skips Concrete Slab + Rebar Combined Mass Calculator
- Steel trimmer at the cut edge — bolted to the soffit on post-installed anchors, it is what gives the severed bars a load path once the temporary support is struck Post-Installed Concrete Anchor Drill Depth Calculator
- Backpropping to the floor below — carries the cut slab and anything standing on it, and lands its load on a floor that was never designed to receive a point load Needle and Prop Load Calculator (Temporary Masonry Support)
A tendon does not let go politely
If the scan finds post-tensioning, the job changes category. An unbonded monostrand runs greased and sheathed from one anchorage to the other, and its whole force is held by those two anchorages — cut it anywhere along its length and the entire tendon releases, at both ends, instantly. There have been fatalities. A grouted bonded tendon is less violent because the bond re-anchors the force over a transfer length either side of the cut, but the slab has still lost the prestress that tendon was providing across the whole panel, which is precisely the force the slab's deflection and crack control were relying on.
So a tendon is either avoided or it is de-tensioned deliberately, by a specialist, under a written procedure, with the slab propped and the surrounding structure checked for the redistribution before anything is released. The routes are all slow and all involve exposing an anchorage or a live length in a controlled pocket rather than meeting a strand halfway along with a saw. Where the opening can be nudged to sit between banded tendons in one direction and pass through the sparser distributed tendons in the other, the whole conversation shortens — which is another reason to survey before the architect commits to a position.
What the slab was stressed to, and how much of that force reached mid-span, is a design question rather than a demolition one — the mechanics of anchorage and seating loss are covered in the guide on sizing a suspended slab, with the Post-Tensioning Institute's Post-Tensioning Manual as the standing reference. What matters on site is narrower: no blade, no core, no anchor drilling and no fixing of any kind into a post-tensioned slab until somebody has scanned it and marked it, and that includes the holes for the propping heads and the trimming steel.
The floor below is now part of your temporary works
Propping a slab that is about to have a hole cut in it looks like standard falsework, and the arithmetic of the props themselves usually is. What is not standard is where the load goes. On a new build, falsework stands on the ground or on a slab designed for construction loading. On a fit-out, the props stand on another suspended floor, in an occupied building, and that floor was designed for an office imposed load spread across it, not for a column of load arriving through a 150 mm baseplate.
That is what backpropping is for, and it is routinely under-designed on fit-outs because the visible part of the problem is one floor deep. The load has to be traced down through however many floors it takes to reach something that can disperse it — often two levels, sometimes a transfer structure or a ground slab. Each level in the chain gets its own props, each slab is checked for what lands on it, and the props on successive floors have to line up. Props at level three sitting 600 mm off the props at level four are not a load path; they are a point load on the middle of a bay.
The procedural side is not optional either. BS 5975 sets out the temporary works procedures — a design brief, a designer, an independent check proportionate to the risk, a coordinator, and permits to load and to strike — and BS EN 12812 covers falsework performance and design. The practical test of whether that has happened is simple: ask who signed the permit to strike, and on what evidence the trimming steel was accepted as carrying what the props were carrying.
And the floor below has a tenant. Backpropping through an occupied storey means an agreed possession, protected finishes, and props standing where somebody's desk was — a negotiation that takes longer than the propping design, and the reason schemes get squeezed into fewer, more heavily loaded props than the designer wanted.
The partition standing on the strip you are taking out
Feature stairs land in the middle of floor plates, and floor plates in existing buildings have walls on them. A blockwork partition, a masonry spine wall in an older frame, or a brick chimney breast that was left in place at the last refit — any of these standing on or across the piece of slab you are removing has to be supported independently before the slab goes, because the slab it is standing on is about to stop existing.
That is a needling and propping problem, and it is the same statics as an opening formed under a wall: the height of masonry above, its thickness, its unit weight, and any floor bearing on it combine into a line load, which is shared onto needles at whatever spacing the coursing allows. The difference here is entirely in what happens underneath. The props take their load onto the same suspended floor already carrying the slab propping, so the two schemes are one scheme, and the allowable bearing figure under the sole plates comes from the temporary works designer looking at that specific floor rather than from any figure associated with a ground-bearing slab.
Take the height above the opening to whatever genuinely arrests the load — in a framed building that is usually the slab above rather than a distant gable, which makes these loads far more tractable than the domestic equivalent. But a masonry wall in a 1930s frame may be doing more than dividing space, and a wall that has carried a floor edge for ninety years does not announce it.
Build the line load from the wall standing on the slab and anything bearing on that wall, share it onto needles at the spacing available, and get the bearing area each prop needs — then hand the bearing pressure question to whoever is checking the floor the props are standing on.
From the head of the new opening up to the top of the wall, or to the next support.
The thickness of the masonry being held, excluding any leaf that is not being supported.
The bulk unit weight of the wall being held, mortar included.
The clear width of the opening being formed under the supported wall.
Centre-to-centre spacing of the needles through the wall.
The combined permanent and imposed load of any floor framing into this wall.
How much floor this wall carries — normally half the span of the floor either side of it.
What the surface the props stand on can take without settling or punching through.
Load carried by each needle
3.63 kips
Needling and propping is temporary works. This gives the loads to design to; it does not select the props, check them for buckling at their extended length, or confirm that what the props stand on can take them. All three belong to a temporary works designer.
- Load carried by each prop
- 1.81 kips
- Needles across the opening
- 4 needles
- Combined line load along the wall
- 1,208.77 lbf/ft
- Masonry share of that line load
- 707.52 lbf/ft
- Floor share of that line load
- 501.25 lbf/ft
- Sole plate bearing area required beneath each prop
- 0.87 ft²
They open the calculator with your figures already in it
Needle and Prop Load Calculator (Temporary Masonry Support): 3.63 kips — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 3.63 kips — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Takes the full rectangle of masonry above the opening. That is deliberately conservative — arching can carry some of it away, but only in sound masonry with enough height and no nearby opening.
- Does not check the prop itself. A prop's safe working load falls sharply with extension and with any eccentricity at the head, and the manufacturer's chart is the only place that answer lives.
- Does not check the needle. Bending, shear and bearing on the masonry at the needle hole all need sizing against the load this page gives.
- Assumes props each side of the wall share equally. A single-sided scheme, or props at different extensions, does not.
The piece has to be held before it is free
The moment that goes wrong here is not the cutting. It is the instant the last cut completes and a panel that has been part of the building since it was poured becomes a suspended load. Cut from above it drops; cut from below it drops onto whoever is beneath. Both are predictable, which is why the panel is rigged before the cut is finished rather than after: lifting eyes drilled and anchored into the piece, taken up on chain blocks slung from an independent frame, with the tension checked before the final pass.
So somebody has to know what the panel weighs, and volume alone stops a few per cent short — the reinforcement in a 200 mm slab adds something in the order of three to five per cent on top of the concrete, which is nothing until a panel is sitting just inside a chain block's rating, and it is the total the chain block, the temporary support point and eventually the hoist are rated against. Divide the opening into panels sized by that number rather than by convenience: one that fits the goods lift and the chain block beats one that saves a metre of cutting.
The cut geometry decides the tool. A wall saw's cut depth is roughly the blade radius less its flange, so a thick slab means a large blade, a pass from each face, or a wire saw — and a pass from each face means access to the soffit, which means a scaffold or a MEWP in the tenant's space below. Corners are the other detail worth insisting on: a circular blade overruns at the end of every cut, longer on the far face than the near one, and on a feature stair whose soffit will be on show, stitch-drilled corners are the difference between an edge worth trimming and an edge to be made good.
- Confirm the propping and any needling are installed, loaded and signed off, with the permit to load on site rather than in an inbox.
- Set the panel divisions from the weight each produces and the route it will travel, not from where the saw track is convenient to fix.
- Check the saw track fixings against the scan — the track anchors go into the same slab you are trying not to damage.
- Stitch-drill the corners so the blade never overruns past the trim line on either face.
- Rig each panel and take its weight before the final cut on that panel closes.
- Cut in an order that keeps the remaining slab supported, working away from the propping rather than isolating it.
- Lower each panel to a prepared, load-checked stack area — never onto an unprotected floor and never onto the propping below.
- Re-check every prop for plumb and tightness after the first panel comes out, and again once the opening is formed.
Concrete plus its reinforcement in one figure, which is what the chain block, the temporary support point and the hoist are all rated against — run it per panel, at the panel size you actually intend to cut.
The length of the slab.
The width of the slab.
The thickness (depth) of the slab.
Rebar grid spacing in both directions.
The rebar bar diameter used in the grid.
Total combined mass
9,960 lb
General-purpose slab reinforcement guideline, not a structural engineering design — load-bearing slabs should follow an engineer's specification.
- Concrete volume
- 2.41 yd³
- Concrete mass
- 9,738.76 lb
- Rebar linear length (incl. lap splice)
- 325.45 ft
- Rebar mass
- 217.38 lb
They open the calculator with your figures already in it
Concrete Slab + Rebar Combined Mass Calculator: 9,956 lb — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- It models one flat mat of bars at a single spacing. Top mats, chairs and bar supports, perimeter and edge bars, dowels, and trim steel around openings are not counted — a slab detailed with both a top and a bottom mat carries roughly twice the steel this returns.
- This is a quantity estimate, not a reinforcement design. Nothing here checks the bar size or spacing you chose against span, load, subgrade or crack-control requirements, and no minimum steel ratio is enforced. Load-bearing and permitted slabs need an engineer's bar schedule.
- The 15% lap allowance is a blanket figure applied to every metre of bar, not a splice schedule — it is added even on a slab whose sides are shorter than one stock bar, where no splice is physically needed. Bars are also counted running the full slab dimension edge to edge, so end cover, hooks and an actual cut list are not modelled.
- Concrete density is fixed at normal-weight and cannot be changed for lightweight, heavyweight or high-density mixes, and the concrete volume is not reduced for the space the steel occupies. Bar weights are the ASTM #3/#4/#5 figures; the metric sizes shown beside them are customary near-equivalents, and a true 12 mm bar is around a tenth lighter than the #4 weight used. The grid pitches are near-equivalents in the same way: picking "300 mm" spaces the bars at 12 in, which is 304.8 mm, so on a round metric slab the count can come out a bar short of a true 300 mm grid and the rebar rows a few per cent light.
- The result is concrete plus grid steel only. Formwork, welded mesh, macro fibre, vapour barrier, insulation, embedded conduit and pipework, and any topping or screed are excluded — so it is a floor on the mass for a lift or a load limit, not the whole make-up.
Out through a building that is still trading
A hole through a slab produces two waste streams and a liquid, and the liquid is the one nobody prices. Wall sawing and wire sawing are wet processes: the water that cools the blade comes back as an alkaline slurry carrying cement fines, it runs to the lowest point available, and on a floor plate that has been drilled for services for thirty years the lowest point available is a penetration into the tenant's ceiling below. Bunding the cut area, a vacuum on the return, and a settlement and disposal arrangement that satisfies the site's discharge consent are all cheaper than one ceiling grid and a claim.
The solid arisings are heavy in a way general strip-out debris is not. Broken reinforced concrete carries far more mass per unit of loose volume than the mixed construction and demolition waste a fit-out otherwise produces, so a container hits its weight limit long before it looks full, and the vehicle collecting it is limited by axle weight rather than by the size of the box. The same figure governs the floor you stage it on: a stack of slab panels waiting for the lift is a concentrated load on a floor that is already carrying your propping.
The vertical route then decides the method. Panels leaving through a goods lift leave at the rated capacity on the lift's own plate, in pieces that fit the car, at whatever times the building manager will give you — which frequently sets the panel size, working all the way back to how the opening is divided. Where a chute or an external hoist is available instead the arithmetic changes but the discipline does not, and the guide on running a debris chute covers what a lump of masonry is carrying by the time it reaches the bottom. NFPA 241 and OSHA's Subpart T are the standing references for safeguarding alteration work in an occupied building.
Put the loose volume of broken slab against a density that reflects reinforced concrete rather than mixed fit-out waste, and the tonnage tells you whether the container fills up or weighs out first — and what the staging floor is being asked to carry.
The estimated debris volume — switch the unit to match your skip or container ticket.
The material's density — mixed construction & demolition debris commonly runs 300-800 lb/yd³ (180-475 kg/m³).
Estimated debris weight
6 tons
Debris density varies enormously with material mix (loose wood/insulation vs. concrete/masonry can differ by 5-10x) — use a density figure specific to your actual debris composition, ideally confirmed against a recent weight ticket for similar material, rather than a generic average.
They open the calculator with your figures already in it
Demolition Debris Weight-to-Volume Conversion Calculator: 6 tons — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- A total tonnage is not a number of loads, and loads are what you pay for. A container fills by volume or by weight, whichever arrives first: concrete and rubble weigh a truck out at a fraction of the container's rated volume, while light mixed debris cubes out long before the axle limit is anywhere near. Dividing this tonnage by a container's volume rating undercounts loads on heavy material every time.
- Density is a wet-weight property. An open container of gypsum, timber and insulation standing through a wet week gains weight without gaining volume, and the scale at the gate charges whatever is on the truck that day. A density taken from a dry load, or from a summer weight ticket, runs well under a winter one for exactly the same debris.
- A figure off a weight ticket is an as-loaded density, with the way that load was placed already baked into it. The same debris tipped loose from a chute, packed down by a grab, or hand-stacked into the container differs by around a third — so a density borrowed from a job that handled the material differently carries that difference across even when the material mix matches perfectly.
The hole is set by the thing going down it
An opening for a feature stair is not a free choice of rectangle. Its length is the going of the flight plus whatever the landing arrangement needs at the top, and its width is the flight width plus the structural tolerance on each side, plus anything the balustrade fixing needs to bite into. The number that ties it together is the slope length of the stringer: with the floor-to-floor rise measured on site and the run set by the going you have chosen, the diagonal follows, and that diagonal is the piece of steel that has to arrive at level four through a lift lobby, round a corner, and up through the hole you have just cut.
This is where fit-out stairs go wrong. A single-flight stringer for a 4.2 m floor-to-floor is long, heavy and awkward, and the building it is going into has a goods lift car around 2.5 m long. Either the flight is spliced — a fabrication and finish decision, not a site one — or it comes in through the opening from above, which means that opening must exist, be unguarded for the duration of the lift, and have a crane or gantry over it. That sequence changes the order the slabs are cut in, and it is settled at the stair design meeting or it is settled badly.
Two dimensions get checked against the opening rather than against the stair: headroom from the pitch line to the underside of the trimmed edge, and the finished floor levels at both ends, which in an existing building are what they are rather than what the drawing says. Measure the rise at the position of the stair, after the screed and the raised floor are resolved — a 30 mm change in either level redistributes across every riser in the flight.
The diagonal from the measured rise and the chosen run — the length that has to be fabricated, delivered, manoeuvred through the building and lifted through the opening, which is often the number that decides whether the flight is spliced.
The total vertical height the stair climbs, floor to floor.
The total horizontal distance the stair covers.
Stringer length
16.4 ft
They open the calculator with your figures already in it
Structural Steel Stair Stringer Length Calculator: 16.4 ft — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- The figure is one stringer. A flight normally carries a stringer each side, and a wide flight adds an intermediate one, so the steel take-off is this length multiplied by the number of stringers; treads, nosings, landing framing and handrail posts are separate items this number does not include.
- It assumes a single straight flight between the two levels. Where the stair breaks at an intermediate landing or turns on winders, the total run entered must be the run of one flight alone: including the landing depth returns a diagonal longer than any member that actually gets fabricated, the real stringers stopping at the landing beam and restarting above it.
- This is geometry, not a structural check. It does not select the channel or plate, and it does not test the stringer for bending, deflection or lateral-torsional buckling as an inclined beam spanning between its end connections, even though a longer diagonal is a longer unsupported span. The stair live load, the concentrated tread load and the deflection limit that govern the section come from the code in force, not from this length.
- Total rise and total run are taken as given and never divided into risers and treads, so nothing here tests riser uniformity, tread going, headroom or pitch. A 3 m rise over a 4 m run is a 36.9 degree pitch, but the same formula returns 10.05 m just as readily for a 10 m rise over a 1 m run, an 84.3 degree pitch no occupied stair would be built to; the permitted maximum pitch is jurisdictional and is not applied to your entries.
- The length says nothing about whether that member can be rolled, coated or delivered in one piece. At the top of the accepted input range, a 10 m (33 ft) rise over a 15 m (49 ft) run, the result is 18.03 m (59 ft), which is beyond ordinary mill stock lengths, beyond most galvanising baths and beyond routine road transport, so a splice or site joint is implied that the geometry never shows. Bath capacity and available stock lengths are supplier-specific.
A retrofit lift is a stack of holes that have to agree
Putting a lift into a building that never had one is the same cutting job repeated on every floor, plus an excavation at the bottom, and the difficulty is not in any single opening. It is that the openings have to form one plumb shaft. Each slab was set out with its own tolerance and screeded to its own level, so a stack of holes cut individually to the same plan dimension can still leave a shaft out of plumb by more than a lift will accept — discovered by the lift contractor's survey after every slab is cut and every trim is fixed.
So a retrofit shaft is set out once, from a single vertical reference dropped through the whole height before anything is cut, with each floor's opening marked from that line rather than from its own grid. Size the plan generously in the axis you can afford to lose, because there is no moving a wall later. What the plan has to contain — car, rails, counterweight on whichever side the supplier puts it, door operator, running clearances — is set out in the hoistway sizing guide next door, along with the pit and overhead reservations that decide whether this building can take a lift at all.
The pit is usually where the scheme lives or dies, because it is an excavation below the lowest floor of an existing structure, often inside the footprint of foundations already there. Depth comes from the adopted lift code — ASME A17.1/CSA B44 or the EN 81 family — read with the model's data, and where the building genuinely cannot give it, EN 81-21 covers reduced pit and headroom in existing buildings at the price of additional protective devices and a specific approval.
Run the plan the supplier's layout demands before any of the stacked openings are marked out — in a retrofit the clear dimension has to be held plumb through slabs that were never set out to agree with each other.
The manufactured width of the elevator car interior.
The manufactured depth of the elevator car interior.
Extra clearance the manufacturer's shaft layout adds to the car width for guide rails and running clearance.
Extra clearance the manufacturer's shaft layout adds to the car depth for guide rails, counterweight, and running clearance.
Required hoistway plan area
35.9 ft²
Hoistway clearances are always model- and capacity-specific per the elevator manufacturer's shaft layout drawing and ASME A17.1 — this calculator applies whatever clearance values you supply, it does not determine the correct clearance for your specific elevator.
- Hoistway width
- 5.98 ft
- Hoistway depth
- 6 ft
They open the calculator with your figures already in it
Elevator Hoistway Shaft Sizing Calculator: 35.88 ft² — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
What this calculation does not cover
- The dimensions are clear inside dimensions between finished shaft faces, held plumb for the full rise. Parging, block tolerance and a shaft that drifts out of plumb over ten floors all come off the inside, and installers work to a tight plumb tolerance over the run. A shaft laid out to a rough or gridline dimension arrives undersized where it matters, and the fix is chipping concrete.
- Says nothing about whether the car itself is legal. Minimum inside car dimensions for an accessible passenger elevator come from accessibility rules, not from the shaft, so a car sized to fit the space that happened to be left can pass this arithmetic and fail plan review.
An escalator wants a bay, not an opening
Retrofitting an escalator into an existing floor plate is a different order of intervention and the reason is arithmetic rather than engineering. The opening length falls out of a rise you cannot change — the floor-to-floor is measured, not designed — divided by the tangent of an incline angle that is conventionally thirty degrees, or thirty-five where the footprint will not take the shallower run, plus the flat step allowance at each end from the manufacturer's data. A four metre rise at thirty degrees gives a shade under seven metres of horizontal run on its own, and closer to nine once a flat step allowance of around 0.9 m goes on each end, so an existing frame with a six or seven metre grid means the opening crosses at least one beam.
That is the point at which the job stops being a cut and becomes a structural alteration: a beam removed and its load transferred, or the escalator relocated to a bay where it fits. Both are engineer's decisions and both change the programme by months. Run the opening length first, against the rise you have actually measured, and put it on the grid before anyone commits to a position — the geometry costs nothing to check and it is the only part of an escalator that can be settled without the manufacturer.
Rise, angle and the flat step allowance give the opening length in one step — overlay that on the existing column grid and you find out immediately whether this is a cut or a transfer structure.
The floor-to-floor vertical height the escalator must climb.
The escalator's incline angle from horizontal — almost always 30° or 35°.
The length of flat (level) steps at the top and bottom of the escalator, before/after the incline.
Wellway floor opening length
34.6 ft
This is a GEOMETRY-ONLY calculation for preliminary floor-opening planning — it does NOT calculate truss structural capacity, support reactions, or anchor loads, which must always come from the specific escalator manufacturer's certified engineering data per ASME A17.1. Flat step allowance varies by manufacturer/model; confirm the exact value from the specific unit's shop drawings before finalizing the opening dimensions.
- Inclined truss length
- 33 ft
- Horizontal run (excluding flat steps)
- 28.58 ft
They open the calculator with your figures already in it
Escalator Wellway Floor Opening Length Calculator: 34.58 ft — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
What this calculation does not cover
- Gives the opening's length and says nothing about its width. Width comes from the nominal step width — 600, 800 or 1000 mm (39 in) — plus truss and balustrade each side, and it multiplies again where units run as a parallel pair or a criss-cross bank sharing one void. The slab penetration is set out from both dimensions, not one.
- Nothing here checks headroom over the incline. Clear height is measured vertically from the step nose the whole way up, and the floor edge, a beam or a duct crossing above the diagonal is what usually fouls it. Where it cannot be cleared, deflector guarding at the intersection stops being a detail and becomes a requirement.
- The result is a hole in a slab. The escalator also needs a recess below the lower landing for the machinery pit and prepared bearing points at both ends, and those are what turn a correct opening into a buildable one — neither follows from the rise.
Giving the cut edge its continuity back
A sawn edge is a clean line through reinforcement that has been anchored at its ends since the slab was poured. Every bar the saw meets now has no development length on the opening side, which is why an opening is trimmed rather than simply cut: the trim takes the load that used to travel through the removed slab and carries it round the hole to the supports. The usual answers are a bolted steel angle or channel frame beneath the edge, a bonded or bolted plate arrangement, or new beams spanning between existing members with the slab hung from them.
Everything fixing into the existing slab is a post-installed anchor into concrete of unknown strength, unknown cover and known congestion, so drilled depth, edge distance and spacing are established against a qualified system rather than assumed — and every hole is scanned in, since a trimmer anchor that clips the reinforcement it is compensating for is a poor trade. Where the design calls for reinforcement continuity rather than a steel frame, post-installed bars are a qualified connection with their own approval and embedment, not a matter of resin and hope. Nothing is struck until that trim is complete and accepted: the props and the trimmer carry the same load in turn, and the handover between them is the moment the design either works or does not.
The paperwork behind it belongs to two documents. ACI 562 is the code framework for assessment, repair and rehabilitation of existing concrete structures, and it is what puts an engineer's name against the alteration; in the United States the alteration provisions of the International Existing Building Code decide whether the change is permissible at all, and a new stair opening reaches that threshold without anyone intending it to.
Then there is what the hole does to the building as a building. A new opening between two storeys breaches the floor's compartmentation, and the International Building Code's vertical opening provisions allow a limited unenclosed opening connecting no more than two storeys under stated conditions — beyond that it is an enclosure or an atrium with the smoke control that implies. The same opening destroys the airborne sound separation the tenant below relied on and changes the smoke and sprinkler design of the space it connects. All of it is cheap at design stage and extremely expensive after the balustrade is glazed.
The edge is open for months
From the first panel removed to the day the permanent balustrade is signed off, there is an unprotected hole in an occupied building, and on a fit-out that period is measured in months rather than days. Guarding it is not a temporary courtesy: OSHA's fall protection requirements treat a hole in a walking or working surface as a fall hazard to be guarded or covered, and a cover has to hold at least twice the maximum intended load and be marked for what it is. A sheet of ply laid over the opening, unmarked and unfixed, is the classic version of getting this wrong, and it is worse than no cover because it invites people to stand on it.
Keep the guarding on the same drawing as the propping and the trimming, with the same permit discipline, because all three get removed by different trades on different days — and the last to leave is whoever takes the edge protection down to fix the balustrade. That handover belongs in the method statement rather than with whoever is on site that afternoon.
Settle these before the saw contractor is booked
Six things a fit-out has to have answers to before a blade turns, in the order they stop being free. Every one of them can move the stair a bay, and none of them gets cheaper after the concrete is cut.
- What the slab is, and what is inside it — Span direction, floor type and a scan from both faces, marked on the soffit as well as the top. If it is post-tensioned, the tendon survey comes before any drilling at all, including the propping fixings.
- The propping load, traced to something that can take it — Not one floor deep. Backprop until the load reaches a transfer structure or a ground slab, with props aligned floor to floor and each intervening slab checked for what lands on it.
- Anything standing on the piece being removed — Partitions, spine walls and old chimney breasts get needled and propped in their own right, onto the same floor that is already carrying the slab propping.
- The mass of each panel you intend to cut — Concrete plus reinforcement, per panel, at the panel size you will actually cut — it rates the chain block, the staging floor and the hoist, and it usually decides the panel size itself.
- The route out, and the slurry route as well — Lift capacity, car dimensions and access hours set the panel size; the wet-cutting slurry needs bunding, collection and a disposal arrangement before the first cut, not after the first ceiling.
- The trim design, and who signs the permit to strike — Steel trimmer or new framing, its post-installed anchors scanned in, and a named engineer accepting the handover of load from the props to the permanent work.
Opens the calculators above on one screen with the dimensions from this article already filled in. Quantities only — this site publishes no price list, because local prices vary too much to publish honestly.