Key takeaways
- The Question: How do you plan and control repetitive construction work, such as floors, units or road sections, so trades flow through without clashing or waiting?
- The Answer: Line of balance plots locations against time and draws each trade as a line whose slope is its production rate. Matching those rates, separating trades with deliberate buffers and fixing the slowest trade first gives a shorter, steadier programme than a bar chart can show.
- The YelloSKYE Angle: A line of balance chart is only useful if actual progress is plotted on it. Construct IQ records which locations each trade has really finished, from drone, 360° and fixed-camera capture, so actual flowlines can be drawn from evidence.
Line of balance (LOB) is a scheduling method for projects where the same work repeats across many similar locations: floors in a tower, units in a housing scheme, rooms in a hotel, or sections of a road, pipeline or tunnel. Instead of a list of bars, it draws a chart with locations on the vertical axis and time on the horizontal axis. Each trade becomes a line, and the steepness of that line is its production rate. When the lines are parallel and spaced apart, work flows; when they converge, a clash is coming. Construct IQ supports the method by showing where each trade has actually reached.
This guide explains how to draw and read a line of balance chart, how production rates and crew numbers set the slopes, where buffers go, how to find the bottleneck trade, and how LOB compares with a Gantt chart, with a worked example for a twelve-storey fit-out.
Where line of balance comes from and where it fits
The method grew out of manufacturing. It was developed at the Goodyear company in the early 1940s to control production of repeated items, and the US Navy later adopted it for its programmes. Construction researchers took it up because so much building work is repetitive, and it now underpins location-based planning and takt planning in lean construction.
It is the right tool when three conditions hold:
- Repetition. The same sequence of activities happens in many locations of broadly similar size.
- Continuity matters. Trades are more efficient when they can move from one location to the next without stopping.
- Speed differences are the main risk. The question is less "what depends on what" and more "who is going faster than whom".
It is a poor fit for one-off, highly interdependent work such as a plant room, a complex facade junction or a bridge abutment. For those, the logic network in a conventional programme does the job better.
Reading a line of balance chart
Picture a chart with floors one to twelve running up the side and weeks running along the bottom. Each trade is drawn as a band or line that climbs from the lowest location to the highest. A few patterns tell you most of what you need.
| What you see | What it means | What to do |
|---|---|---|
| Steep line | High production rate: many locations finished quickly | Check the trade behind it can keep up |
| Shallow line | Slow production rate | Likely bottleneck; consider more crews or smaller scope per location |
| Parallel lines with a steady gap | Matched rates with a constant buffer | The target pattern |
| Lines converging | A faster trade catching a slower one | Start the faster trade later or slow it down |
| Lines crossing | Two trades planned in the same place at once | A clash; the plan is not buildable as drawn |
| Gaps within a line | The trade stops and restarts | Wasted mobilisation; aim for continuous work |
| Wide gap between lines | Excess buffer, work-in-progress sitting idle | Tighten the gap if risk allows |
Because time runs left to right and locations bottom to top, the horizontal distance between two lines at any floor is the time gap between those trades on that floor. The vertical distance at any date is how many floors apart they are.
Production rates and crew numbers
The slope of each line comes from a simple calculation:
Production rate = number of crews ÷ time for one crew to complete one location
A drylining crew that needs three working days per floor has a rate of one floor every three days. Two crews double it, provided there is room on the floor for both. The time for a trade to cover all locations is then the number of locations divided by the rate.
This makes LOB a tool for crew sizing as much as for dates. Planners can choose a target rate for the whole sequence, often set by the trade that is hardest to speed up, and work out how many crews every other trade needs to match it. When a trade cannot physically match the rate, perhaps because the floor only has room for one crew, that trade sets the pace for everyone.
A worked example: twelve floors of fit-out
Take a twelve-storey residential block where five fit-out trades work floor by floor. Each trade must finish a floor before the next trade starts it, with a two-day buffer between them. Durations are in working days.
The first plan
| Trade | Days per floor (one crew) | Crews | Rate | Days for 12 floors | Start floor 1 | Finish floor 12 |
|---|---|---|---|---|---|---|
| Partition framing | 4 | 1 | 1 floor / 4 days | 48 | Day 0 | Day 48 |
| Services rough-in | 6 | 1 | 1 floor / 6 days | 72 | Day 6 | Day 78 |
| Boarding | 3 | 1 | 1 floor / 3 days | 36 | Day 47 | Day 83 |
| Taping and painting | 5 | 1 | 1 floor / 5 days | 60 | Day 52 | Day 112 |
| Floor finishes and fixtures | 4 | 1 | 1 floor / 4 days | 48 | Day 70 | Day 118 |
Notice how the start dates are set. When a slower trade follows a faster one, such as services after framing, the tightest point is floor 1, so it starts two days after framing finishes the first floor. When a faster trade follows a slower one, such as boarding after services, the tightest point is the top floor: boarding has to start late enough that it does not catch services on floor 12. That is why boarding cannot begin until day 47, even though floor 1 has been ready for it since day 12. The fit-out takes 118 working days.
Finding the bottleneck
On the chart, services rough-in is the shallowest line. Every trade after it either waits for it or is forced to start late so it does not overtake. Painting is the second slowest and creates the same effect for floor finishes. These two trades, not the total amount of work, set the length of the programme.
The rebalanced plan
Suppose the site can hold two services crews and two painting crews per floor without them getting in each other's way.
| Trade | Crews | Effective days per floor | Start floor 1 | Finish floor 12 |
|---|---|---|---|---|
| Partition framing | 1 | 4 | Day 0 | Day 48 |
| Services rough-in | 2 | 3 | Day 17 | Day 53 |
| Boarding | 1 | 3 | Day 22 | Day 58 |
| Taping and painting | 2 | 2.5 | Day 32.5 | Day 62.5 |
| Floor finishes and fixtures | 1 | 4 | Day 37 | Day 85 |
The same scope now finishes on day 85, 33 working days sooner, with two extra crews. Services and boarding run parallel, three days per floor each. The new limits are framing at the start and floor finishes at the end, both at four days per floor. If the team wanted to go further, those are the trades to look at next.
The example is simplified: real floors differ, crews have learning curves and the first floor is often slower. But the logic is the one planners use on real projects, and the chart makes it visible in a way a bar chart does not.
Buffers: time and space
Buffers protect a following trade from small slips in the trade ahead. They come in two forms.
- Time buffers leave a set number of days between one trade finishing a location and the next starting it. They absorb variation in production.
- Location buffers leave one or more empty locations between trades. They are useful where a trade needs physical separation, for example wet trades and finished joinery.
Too little buffer and every slip passes straight down the line. Too much and the programme lengthens and work in progress sits idle, which lean practice treats as waste. Our guide to lean construction covers the wider thinking behind keeping that waste low. A sensible starting point is a buffer of a day or two between steady trades, with more after trades whose output varies widely.
Line of balance vs Gantt chart
| Question | Gantt chart | Line of balance |
|---|---|---|
| Best for | One-off work with complex logic | Repetitive work across similar locations |
| What it shows clearly | Dependencies, critical path, float | Production rates, trade spacing, continuity |
| How a speed mismatch appears | Hidden in hundreds of similar bars | Lines converging or crossing |
| Number of rows | One per activity per location | One line per trade |
| Crew sizing | Implicit in durations | Explicit in slopes |
| Tracking progress | Percent complete per bar | Actual line plotted against planned line |
The two are not rivals. A typical high-rise uses a network programme for the substructure, core and plant rooms, and line of balance for the repetitive floors above, with the two linked at the hand-over points.
Plotting actual progress
The plan is only half of LOB. Its real value comes when actual progress is drawn alongside it: for each trade, the date it actually finished each location. Where the actual line runs shallower than the planned line, the trade is underperforming its rate, and the chart shows how many floors it will take before it collides with the trade behind.
That requires reliable, location-by-location records of what has been finished. Asking each foreman which floors are done gives an optimistic answer at the moment it matters most. Construct IQ records interiors with 360° walks organised by floor and room, and the interior fit-out use case reports snags closed five times faster once teams could find each location in the record. For external and linear work, dated drone imagery gives the same location-by-location picture; our linear corridor mapping use case covers progress along corridors hundreds of kilometres long, and the construction progress capture use case shows weekly flights over building sites. DEX then holds every capture on a timeline, so the date a trade finished a floor can be read from the record rather than recalled.
A line of balance checklist
- Confirm the work really is repetitive and divide it into locations of similar size.
- Fix the trade sequence within one location before drawing anything.
- Calculate each trade's rate from crew numbers and days per location, using measured output where you have it.
- Draw the lines, then look for convergence, crossing and gaps before checking dates.
- Identify the shallowest line and decide whether more crews, smaller work packages or a different method can steepen it.
- Set time or location buffers deliberately, larger after trades with unpredictable output.
- Start faster trades late enough that they do not catch the slower trade at the last location.
- Plot actual finish dates per location every week from site evidence and compare actual slopes with planned ones.
