Industrialised construction against conventional building: what changes in quantities, cost and programme
Industrialised construction is building in which part of the work moves from the site to a factory or to reusable formwork: precast elements, prestressed hollow-core slabs, system formwork for casting on site, and up to modular concrete units that arrive almost finished. For the bill of quantities (BOQ) this is a real change: instead of m³ of concrete, m² of formwork and tonnes of rebar, the BOQ shows components by number or by m², transport, lifting and connections. I have experience in quantity takeoff for industrialised construction and precast elements, and in comparing them with casting on site.
Three levels of industrialised construction
Not all industrialisation looks the same. The more work moves to the factory, the shorter the site part of the BOQ becomes and the longer the component items get.
| Level | What moves to the factory | How it looks in the BOQ |
|---|---|---|
| System formwork, cast on site | The formwork only | m³ of concrete and m² of formwork as usual; the reusable formwork affects the price and the pace |
| Precast elements | Making the component: walls, beams, stairs, hollow-core slabs | Number or m² by type, thickness and length; beams in m³ by cross-section |
| Modular concrete units | Also building services, windows and part of the finishes | A complete unit, transport, lifting, connections and completion work on site |
A modular concrete unit is structural reinforced concrete, not light steel framing. The difference is explained on the light steel framing versus blockwork page.
What changes in the BOQ: chapter 02 against chapter 03
Casting on site is measured under chapter 02 of the General Specification for building works, Israel's inter-ministerial specification: concrete, formwork and reinforcement. Precast components are measured under chapter 03, where the rules are different:
- A component is measured by number, stating the type and dimensions, or by m², stating the type, the thickness and the maximum length. Unless stated otherwise, it is measured by number.
- Precast beams are measured in m³, stating the cross-section dimensions.
- Prestressed hollow-core slabs are measured in m², stating the type, the concrete grade, the thickness and the type of prestressing. The bedding layer is included in the price.
- The topping, the infill pours and their reinforcement are measured separately, under chapter 02.
- The price can be all-inclusive, with transport, storage, erection and connections, or split: manufacture, transport, storage and erection, each in its own item.
The particular specification of my graduation project also stated that concrete that runs into the cores of the slabs at their ends is not measured, and that a strip wider than 50 cm between slabs is measured as a full-thickness slab. Details like these move quantities, so I read them before pricing.
Worked example: one m² of cast slab against one m² of hollow-core slab
For illustration, a 20 cm cast slab against a 20 cm hollow-core slab with a 5 cm topping, per m² and for a floor of 400 m²:
| Component | Cast slab, per m² | Hollow-core slab, per m² | Cast floor | Hollow-core floor |
|---|---|---|---|---|
| Concrete on site, with 4% waste | 0.208 m³ | 0.052 m³ | 83.2 m³ | 20.8 m³ |
| Formwork | 1 m² | Per the propping detail | 400 m² | Minimal |
| Rebar | About 20 kg | About 2.5 kg of mesh | 8,000 kg | 1,000 kg |
| Precast component | – | 1 m² | – | 400 m² |
| Lifting | A pump on the day of the pour | A crane for all the slabs | A pour day | Crane days |
The rebar in the cast slab is calculated at 100 kg per m³ times 0.2 m³. The mesh in the topping is 6 mm bars at 20 cm centres in both directions: 10 m of bar per m², times 0.222 kg per metre, and with laps about 2.5 kg. Concrete on site drops by about 75%, and the formwork almost disappears. But the cost does not disappear: it moves from the site to the component item, to transport and to the crane.
How to compare costs fairly
Compare a finished floor with a finished floor: components, transport, lifting, connections, topping and infill pours, against concrete, formwork, rebar and labour. Then add time. According to a 2018 business article that reviewed studies in Israel, partial industrialisation shortened construction by about 32%, and full industrialisation shortened the structural frame time by about 44%. The same article stated that in a nine-storey building the structural frame is about 16% of the construction cost and about 35% of the construction time, about seven months.
For illustration only: if seven months of frame work are shortened by 44%, that is about three months. With site overheads (preliminaries) of 60,000 shekels a month, the difference is about 180,000 shekels, and it has to go into the comparison next to the price of the components. The full calculation of overheads is on the site overheads page.
What to check in a quote: whether the price per component includes transport, lifting, connections, topping and infill pours. Under chapter 03 each of these can appear as a separate item, and comparing an all-inclusive price with a manufacture-only price is comparing apples with oranges.
When industrialised construction pays off
In short: a design frozen early, repetition and good crane access → precast. Late changes, an unusual shape and a cramped site → casting on site.
- Repetition: many identical components, such as typical floors or several buildings in the same project.
- A decision at the design stage: the details, openings and connections are fixed before manufacture. A change after manufacture is expensive.
- Logistics: distance from the factory, access for lorries, storage space and a crane that suits the weight of the heaviest component.
- Size: on a small one-off project, the preparation and the early design cost relatively a lot.
For a price comparison per m³ between casting on site and precast, see concrete frame cost. And for the method in which the formwork stays in the wall as insulation, see insulated concrete forms.
In industrialised construction, the quantity takeoff moves from the site to the factory: you count components, not m³ of pour. A quantity surveyor who knows both methods can compare them on the same basis.
Frequently asked questions
Is industrialised construction cheaper?
Not always. The price of a component is higher than the price of the concrete alone, and the difference can be offset by time, overheads and less work on site. Only a full comparison, like the example above, gives an answer for a given project.
What is the difference between precast and a modular unit?
A precast component is a part: a wall, a beam or a slab. A modular unit is a room or a part of a building, including services and finishes, that arrives ready to be lifted and connected.
How is a hollow-core slab measured in the BOQ?
In m², stating the type, the concrete grade, the thickness and the type of prestressing. The topping and its reinforcement are measured separately. Contractors' units of measurement are covered on the pricing units page.
Who does the quantity takeoff for this kind of construction?
A quantity surveyor for construction projects who knows both chapters and can compare a finished floor with a finished floor.
Have a project? Tell me briefly what the project is and what already exists. When the project is a good fit, I usually reply with focused questions and a written quote.
Contact me for a quote* Created with AI for marketing, for illustration only. Not reviewed by Yaakov Avital and not professional advice. Every project must be checked on its own by a professional quantity surveyor and an engineer.