Shop drawings translate the design intent into material planning and coordination. They also indicate the size, material, connections, and sequence of assembly for the pieces. All trades are based on the same proven information.
Specialist drafting firms create these drawings and offer Shop Drawing Services to the contractor and fabricator in line with the architect and engineer's design set. This article explains what “shop drawing” means and how it supports planning and collaboration. Includes research information, construction photos, and records. Designed for Architects, Engineers, and Contractors.
Shop Drawings Matter in Construction
Shop drawings become important because it is possible that, due to improper drawings, rework will be required in the shop. The Construction Industry Institute has a 144-project dataset estimating that direct field rework costs about 5% of total project cost. Many of these losses can be blamed on information failures; Autodesk and FMI surveyed over 3900 industry professionals and found that the industry loses $1.8 trillion in 2020 from poor data, of which $88.69 billion is rework. A complete shop drawing that includes dimensions, tolerances, material grades, connections, revision numbers, and specification references on a single sheet helps eliminate these losses.
Shop Drawings Connect Design Intent with Construction Work
Shop drawings translate design information into component-level instructions for production. Design drawings indicate what is in the building. Shop drawings are a description of how the fabricator and installer repair every component.
Structural steel illustrates this conversion. A beam, a W12x26, weighs 26 pounds per foot, and a shear connection. The detailer displays the number of bolts, the thickness of the plates, and the diameter of the holes. They also measure the size of the weld and verify the length against the grid.
The concrete work is based on ACI 315, Details and Detailing of Concrete Reinforcement. Detailers give bar marks, bend sizes, lap sizes, and covers to each reinforcing bar. MEP shop drawings, duct routes, equipment clearances, and ceiling heights are included.
Facade and millwork drawings are used to solve movement and fit. A curtain wall drawing notes each mullion, anchor, and expansion joint, and notes thermal movement at the slab edge. The shop drawings are not contract documents; therefore they do not refine the design but never override the design, according to AIA A201.
Shop Drawing Approval Process Control Project Risk
Risk is controlled in the approval process by reviewing work between fabrication and drawing. The submittal process is normally described in project specifications under CSI MasterFormat Section 01 33 00.
The four-step process:
- In addition to communicating with other trades regarding submittals, the contractor verifies field measurements.
- Verified by the architect or engineer against the design concept and the contract documents.
- The reviewer's statuses will be either refused, changed and resubmitted, approved as stated, or approved.
- Fabrication starts after approval.
How Does Drawing Coordination Reduce Errors and Rework?
By recognizing trade disputes prior to manufacturing, drawing coordination minimizes rework. The ceiling zone is also shared by sprinklers, cable trays, pipes, ducts, and structures. There is a clash between demolition, new materials, and reinspection, which is fixed after the installation.
Clashes Occur Most Often
A 24-inch duct that passes through an 18-inch beam is one example of a dispute. Additional components include door frames and wall openings, slab edge reinforcement, sprinkler mains and cable trays, and curtain wall anchors. Remodelling initiatives pose a concern as well because the condition on the ground differs from what is documented.
How Do Teams Resolve Clashes?
Teams carry out collision detection, prioritise disputes, and map every trade onto a single grid and datum. Space is first used for gravity-drain piping, then ductwork, pressure plumbing, and conduit. Reviewers can observe the precise movement since changes in amended drawings are veiled.
How Does BIM Improve Shop Drawing Accuracy?
BIM enhances the accuracy of shop drawings through the creation of drawings, clash reports, and quantities using a single coordinated model. The models are built in Revit and Tekla. Clash detection is run in Navisworks. The BIM Forum's Level of Development specification defines LOD 350 elements as having interfaces to other building systems, such as supports and connections.
In 2007, Stanford University Center of Integrated Facilities Engineering (CIFE) conducted a study of 32 large BIM projects. It reported the detection of up to 40 percent fewer unbudgeted changes and up to 10 percent savings of the contract value by clash detection. It also indicated a maximum reduction in project duration and cost estimations of under 3% and 7%, respectively.
Revit schedules retrieve the number of elements and lengths from the model. Quantities and drawings consequently update simultaneously.
How Do Material Takeoffs Support Accurate Project Planning?
By converting drawing data into quantities for orders, timelines, and budgets, material takeoffs aid in planning. Estimators tally, gauge, and sum all the elements of the approved drawings. In estimating firms that provide Construction Takeoff Services, quantities are extracted from approved shop drawings. These are associated with counts, lengths, and areas tied to the existing revision.
Unit weights indicate the scaling of drawing errors. A reinforcing bar of 5 weights of 1.043 pounds per foot and a 20-foot bar has a weight of about 21 pounds. A one-foot deviation on 100 of the same beams, W12x26, changes the order of the steel by 2,600 pounds.
The quantities input three decisions: unit-cost budgets, supplier order dates using lead times, and fabrication sequencing. Estimators use waste factors when the base count has been used since factors are not the same across materials. An attempt to revise but not to take off would result in over-ordering, which is a tie-up of cash, or under-ordering, which would stop installation.
How Can Architects, Engineers, and Contractors Improve Documentation?
These roles enhance documentation by regulating another aspect of the information chain.
Architects and Engineers
Label all openings, specify tolerances, and cross-reference to specification parts. Issue connection requirements and loads as soon as possible to prevent guesswork on the part of detailers. Respond to information (RFIs) during the contract period. The question, drawing reference, date, and answer are recorded in an RFI log.
Contractors, Detailers, and Fabricators
Create build drawings from the issued set being used and coordinate trades. Label all the revisions, mark all the changes, and record the cause in a revision table. Store all approved sets in one place to prevent crews operating with a superseded sheet.
What Best Practices Coordinate Drawings and Material Quantities?
Consider the drawing set with the takeoff as a single package since a modification in any alters the other. These customs hold both in step:
- Send an RFI on each gap in the design set before detailing.
- Latest issue version and specification.
- Survey current site conditions before describing renovation or custom millwork.
- Carry out internal verification of dimensions, labels, and cross-references.
- Submit early, since late submittal slows orders and fabrication.
- Modify the takeoff with each revision of the drawing, and record the alteration.
- Manually count each floor or bay.
- Approve sets and quantity schedules using a single cloud platform.
- Stamp supersede sheets and store them separately from the active set.
Conclusion
Proper shop drawings connect design intent, coordination, and material planning. They translate design knowledge into tested detail, detect conflicts before production, and provide estimators with precise numbers. Teams in charge of revisions and approvals steer clear of rework, which typically accounts for 5% of project expenses.
FAQs
What is the difference between shop drawings and design drawings?
The building layout and performance requirements are indicated in design drawings. Shop drawings indicate the way fabricators make and install every part.
Who makes and verifies shop drawings?
These are contracting fabrication, supply, and drafting companies. They are reviewed by the architect or engineer of record, and a determination is made if they comply with the design concept and contract documents.
Why then are takeoffs based on shop drawings?
Takeoffs are a measure of what is represented in drawings. The accurate length and size in the drawings will produce accurate order quantities, and any drawing errors will be directly transferred to the order.
What are some ways in which BIM minimizes shop drawing errors?
BIM produces drawings, clash reports, and quantities using one model. Stanford CIFE recorded up to 40% of the unbudgeted changes in 32 BIM projects.
When are shop drawings to be submitted by teams?
Teams are expected to deliver before the procurement date, as fabrication lead times begin only after approval. Early submission also allows time for resubmittals.
What is the consequence of an error in a shop drawing?
Fabricators are able to slice, weld, or request the wrong parts. The crews will then demolish or substitute the work, which will push back other trades and add to the labor and material expenditure.
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