Precast construction has become a standard option for the Australian commercial, industrial, and residential markets mainly due to its ability to shorten the construction programs and enhance quality control. Behind every precast element, there is a comprehensive set of drawings that instructs the factory on casting, reinforcing, lifting, and connecting every element. This task of detailing determines the ultimate price.
At 12 Meter Engineering, contractors and developers have similar questions: what exactly is the influence on the price of precast detailing services, and how can it be controlled? Read this guide and find out about the main aspects in simple language so that you can understand the scope of work and compare quotes effectively.
Key takeaways
- The element complexity is a key factor directly impacting total costs related to precast detailing.
- The congested reinforcement and design of the connection play an important role in causing increased detailing costs.
- Additionally, lifting needs and changes made at a later stage may lead to more costs incurred for detailing activities.
- The early standardization and precise definition of the project scope enable more streamlined budgeting.
What does precast detailing involve?
Precast detailing facilitates the transformation of a design idea into manufacturing and installation data for the casting yard and the crew at the site. A detailer makes shop drawings, reinforcement schedules, formwork drawings, and erection drawings. Each type of document contains separate information, and the total amount of work depends on the number of unique elements in the project.
Several customers decide to go for precast panel detailing services in Australia in order to get a comprehensive package, which includes only the details of the panels. Other customers opt for precast fabrication drawings services where they receive only the manufacturing drawings and no detailed drawings of connections or reinforcements. The first thing you need to do to get an approximate budget is to decide which type of package is suitable for your project.
Essential deliverables affecting the price:
- Formwork (Shop) drawings specifying the sizes and dimensions of all the openings and embedded items
- Reinforcement drawings and bar bending schedules
- Layout of lifting and handling, as well as insertion points
- Assembly and connection drawings for the construction site
How does element complexity change detailing costs?
Complexity is most often the biggest single contributor to spending. A flat panel having uniform reinforcement is far quicker to produce than a curved facade panel with many openings. Detailers need to check each dimension, compare it with the architectural and structural documentation, and settle any inconsistencies first.
- Panel size and repetition
Repetition decreases the cost. Details of numerous panels using similar formwork can be consolidated into a master drawing and a list of changes. Each unique panel will have its dedicated drawing. A project with ten standard types and a hundred duplicates is usually less costly than a project with a hundred unique types.
- Openings, penetrations, and cast-in items
The locations and surrounding reinforcement of all windows, service penetrations, electrical boxes, and cast-in plates must be exact. Every opening generally has a trimmer bar and edge distance, thus adding more detailing for every opening. Projects with dense service coordination have this category increase substantially.
| Element type | Typical detailing effort | Relative cost impact |
| Standard flat wall panel, repeated | Low, one master detail with schedule | Low |
| Panel with multiple openings | Moderate, opening-specific trimmers | Moderate |
| Curved or sculpted facade unit | High, bespoke geometry and formwork | High |
| Heavily loaded beam or column with complex connections | High, detailed reinforcement and connection checks | High |
Why do rebar detailing requirements influence pricing?
It’s in the reinforcement where precision is most important. Precast rebar detailing services in Australia will need to meet the requirements of AS/NZS 4671 for steel reinforcing materials and AS 3600 for concrete structures. The spacing between the bars must be verified, as must lap lengths, cover and anchorage, with respect to the structural design and manufacturing tolerances.
- Reinforcement density and congestion
More heavily reinforced members require longer detailing time as bars have to be arranged around each other while maintaining cover. Most of the drafting time is frequently spent at connection zones. Seismic detailing requirements and high load paths tend to increase this effort further.
- Cover, anchorage, and lap lengths
Steel is covered by a concrete structure: it must be protected at every edge and around every opening, and in this way, it is protected from corrosion and also ensures fire performance. Length of anchorage and lap must also comply with AS 3600. One of the most frequently cited causes for drawings to be returned for revision is incorrect drawings. One of the most frequent causes for drawings being returned for revision is incorrect drawings, and each return is a cost.
Which connection details add the most cost?
Connections are the links between elements and are usually the most complicated component of a precast system. They contain structural risk and often need to be carefully checked, closely coordinated with the structural engineer, and may necessitate further calculations. Detailing connections is not a budget line item to be taken lightly.
The usual order of connection detailing is:
- Discuss the design load path and connection concepts with the structural engineer.
- Describe connection hardware, such as bearing pads, sleeves, bolts, and plates.
- Look for reinforcement clashes at all connection points.
- Coordinate tolerances, grouting and fixing requirements with the installer.
- Produce connection drawings for review and approval before release.
How do lifting and handling requirements affect the budget?
All precast elements must be lifted from the casting bed, stored, transported, and erected. Lifting inserts and their positions should be planned for the real lifting angles, dynamics, and handling equipment to be used at the site. For heavier or longer units, extra checks may be required and even some temporary bracing details.
Typically, handling-related scope encompasses:
- The design and lifting capacity of the insert is verified.
- Temporary bracing for transport & erection.
- Outline storage and support point layouts.
- Capacity and site access for cranes.
Safe handling is also regulated. Safe Work Australia sets out expectations for lifting risk management on construction sites, and it is important that decisions made about the process are detailed from the outset to reflect those expectations.
How do revisions and coordination shape the final quote?
Unplanned cost is a significant part of design changes. If the opening is changed late, or the reinforcement is moved, or the finish of the building is changed, many sheets may need to be redrawn, and the reinforcement rechecked. This risk is significantly mitigated by early coordination: changes made before the beginning of the detailing will be much less costly than changes made after drawings are issued.
The choice of scope model also has an impact on the predictability of your costs:
| Scope model | What is included | Best suited for | Cost predictability |
| Fabrication drawings only | Formwork and element drawings | Projects where in-house engineers manage reinforcement | Moderate |
| Full detailing package | Formwork, reinforcement, lifting, and connection drawings | Projects needing one accountable detailing team | High |
| Design-assist detailing | Full package with early input into structural and architectural design | Complex or fast-track projects | Varies with design maturity |
Which standards shape precast detailing scope in Australia?
Much of the scope is determined by compliance requirements. The typical way that detailers work with references is:
- AS 3600: Concrete structures, covering design and detailing of reinforced and prestressed concrete
- AS/NZS 4671: Steel reinforcing materials – bar grades and properties
- AS 1170 series: Structural design actions, such as loads that control the design of elements
- The National Construction Code (NCC): Performance requirements for structure and fire resistance.
Discuss current standards with the engineer; ABCB maintains the NCC, and Standards Australia maintains AS/AS-NZS.
How can you control precast detailing costs?
The majority of the cost control occurs prior to the beginning of detailing. The most important is to have inputs clear and early standardisation, this helps to maintain comparable quotes from suppliers.
- Use standardised elements in early stages to minimise the number of different drawings
- Freeze out the open details and openings before the start of detailing.
- Share complete architectural and structural information in a single package
- Ask for itemised quotes, which break down drawing, revision, and checking allowances
- Match scope to in-house capability, to not pay twice for the same work.
If you have a standard and unique component in your project, you may want to bundle up the unique component and request a separate allowance for it. This allows more visibility of where extra expenditure is occurring.
Final word
Precast detailing costs are a matter of a couple of factors that can be controlled: complexity and repetitiveness of the elements; the congestion of the reinforcement; the design of connections and lifting; and the stability of the design during detailing. The closer a project is to being standardized and all the information is shared, the more accurate the quotes will be and the less surprise the project will bring. No matter if you require fabrication drawings or a complete detailing package, the right scope and proper inputs will help you to control precast detailing services in Australia from the beginning itself. Here at 12 Meter Engineering we are pleased to discuss your drawings and advise you upon a scope that will suit your project.
Frequently asked questions
Fabrication drawings comprise the formwork and information about an element required for the factory to make each unit. Full detailing includes reinforcement schedules, lifts, and connection drawings for installation. The full package is more expensive but gets you one team that is responsible for the entire package.
Yes. Master drawings and variation schedules can be shared between repeated panels, reducing drafting and checking time. Many one-off units will increase the cost of detailing since each unit requires a separate drawing set.
The size and placement of lifting inserts should be determined for the specific lifting angles and equipment. Greater mass and length of units need more checking and sometimes temporary bracing. These checks are considered as part of the scope from the outset, to be sure of no surprises when it comes to erection.
An opening, service penetration, or finish change might necessitate redrawing multiple sheets and a re-check of reinforcement around the affected area. Once drawings have been issued, changes are more expensive than if they had been determined while designing, so it is advisable to freeze essential elements early on.
