There is an old adage – ‘A pencil costs 10 cents, but an eraser can cost a million dollars’ – meant to drive home the importance of quality workmanship. This saying applies all too well to the detailing of reinforced concrete structures. If completed by a quality detailer, concrete and rebar detailing benefits any project – it can help improve project margins, boost efficiency and productivity, minimize waste, and sure up scheduling certainty. Conversely, detailing errors can be extraordinarily expensive.
While quantifying the cost of detailing errors is difficult—there are several factors that influence the calculations—it is evident that these expenses impact the entire construction sequence, from fabricators and contractors, right through to the end client. Let us take a closer look.
The Cost to Rebar Fabricators
Often the fabricator includes detailing as part of their contract. If a detailing error becomes apparent once rebar is delivered to site, the fabricator will be lugged with the material and fabrication costs associated with resupplying, which includes shearing, bending and transporting the new material. The fabricator may be required to not only to cover the cost of transporting the resupplied material to site, but also the removal of the incorrect rebar from the construction site.
There is also the opportunity cost associated with disruptions to the detailing and shop fabrication schedule arising from manpower re-deployment to correct the mistake and avoid site delays. This could require overtime payments to employees. Re-work usually entails extra paperwork for the sales, engineering, and shop teams.
While dependent on the size and criticality of the error, a rule of thumb often cited in the industry in the US is that each detailing error can cost a fabricator approximately a thousand dollars in overhead costs. This does not include material costs, which have also been rising recently. Overhead costs in places like Australia, with much higher hourly wages, can be in the thousands.
If the detailing error leads to construction delays and schedule slips, the general contractor may apply back charges which could significantly cut profit margins for the fabricator.
The Cost to General Contractors
Re-work caused by rebar clashes and detailing errors can impinge on the entire construction schedule and cause site-wide delays. Construction workers can be left standing around on-site, waiting for the error to be rectified. Mechanical and electrical trades will have to wait for concrete to be poured before they can complete their works. Cranes and their operators may be idled or have their schedules re-worked.
According to Alex Bonfil (Vice President – Preconstruction at McHugh Concrete Construction, located in Chicago, IL, USA), “If rebar is detailed incorrectly, and we are already in the field with guys on the ground, it can cost us a lot of money. We take just-in-time deliveries of rebar so if there is an error, we don’t have additional rebar on-site. This means we have to scramble to maintain the pour sequence and construction cycle. If we have to delay the construction schedule, this costs in the order of magnitude of US$30,000 per day.”
“That US$30,000 accounts only for our overheads, without accounting for the cost of manpower—we can’t send our guys home in the middle of the day. So, we try to do everything in our power to prevent losing days. We might steal some rebar from pour B, so that pour A can continue. If that isn’t possible, we’ll check our yard or call local fabrication shops to make it work. In this instance, we might not be able to source rebar in the exact size or shape we need, which means that we’ll have to get the engineer involved to continue with the pour.”
“Even when we won’t lose a day, it could mean that several ironworkers may have to work late. For every ironworker that works late, it costs about US$200 per hour with overtime. And nothing gets fixed in an hour—it’s two to three hours on average,” said Bonfil.
“If we have to source rebar and have it delivered the same day, we’re probably paying three or four times as much as usual for the fabrication, plus the additional transport costs, just to get the rebar to site when we need it,” Bonfil added.
In many cases, the project completion date dictates the amount of funding an owner can secure for building construction. Not surprisingly then, the client usually imposes severe penalties and liquidated damages if the project is not completed on time, underscoring the importance of avoiding errors and delays for the general contractor.
Other Intangible Costs
Over and above financial expenses, detailing errors give rise to a range of intangible costs. Repeated detailing errors can lead to loss of ‘goodwill’ with the customer. If a customer is tempted to seek services elsewhere due to inordinate number of errors, the marketing cost of searching and securing a new or replacement customer cannot be overlooked.
There are also environmental and sustainability repercussions. With rebar being resupplied, twice as much material is manufactured, used, and transported. The environmental costs of load re-runs and material wastage could warrant further scrutiny given some public agencies are now starting to mandate facility-specific Environmental Product Declarations (EPDs).
There can also be impacts on the health and safety of construction workers. When working in tight and difficult conditions, wrong bar dimensions due to detailing errors can expose ironworkers to higher levels of risk. For example, on a recent project, ironworkers had to be lowered down a long vertical shaft to install rebar on a low-level pump station at a dam. There was no room for errors as mis-fitting bars identified at the worksite would have posed large safety risk to the construction crew.
As Bonfil describes, there are also other opportunity costs. “Our first line of defence against detailing errors is our project management team. Our project managers review all the shop drawings. While the cost associated with the project manager’s time is accounted for within our budget, if the project manager is spending too much time reviewing shop drawings, then they cannot focus on elements such as the production schedule and costs.”
The Solution: Quality Detailing
Quality detailing is paramount. Most contractors agree that poor detailing is the nemesis of a project.
It is very important to retain experienced and knowledgeable detailers. Their services should be contracted based on the quality
of their output, rather than their up-front price. Retaining services purely based on initial detailing price could cost the customer, as listed above, a lot more at the back end if there are many detailing errors.
The accuracy of detailing can be enhanced by involving the detailer in the project as early as possible. This ensures that any engineering conflicts, miscommunications, and other clashes are mitigated early in the construction lifecycle thus preventing unnecessary re-work, extended timeframes, and additional labor. Detailers also help confirm the constructability of engineering and architectural designs.
The adoption of BIM and 3D modeling for concrete and rebar can also help streamline the construction process by identifying conflicts, fit-ups, and clashes with other trades. Additionally, it facilitates the resolution of design discrepancies, geometry, and intent early in the process. Mistakes are mitigated before fabrication and installation, reducing unnecessary labor and material costs. 3D models also aid the ironworkers in visualizing the finished product before it is built.
Errors in detailing of reinforced concrete members can lead to large financial ramifications. This makes retaining the services of a detailing firm with skilled detailers and stringent Quality Control and Quality Assurance processes vital.
Article by Sandeep Mathur, Global General Manager – Concrete & Rebar