Calculating concrete quantities requires a solid understanding of structural drawing sheets. Unlike architectural floor plans, which focus on spatial layout and finishes, structural plans show the load-bearing elements of the building.
If you do not know how to navigate structural sheets, you will miss foundation details, slab thickness changes, and rebar requirements.
1. Start with the Structural Notes and Details
Before looking at the plan views, read the general structural notes. This sheet contains critical specifications, including:
- Required concrete compressive strengths (PSI ratings) for different elements.
- Rebar grades and lap splice lengths.
- Soil bearing capacities and compaction requirements.
- Key design assumptions.
Understanding these specifications ensures that you categorize concrete mixes correctly in your takeoff report.
2. Decode Common Plan Abbreviations and Symbols
Structural drawings use standardized abbreviations to keep layouts readable. Knowing these symbols saves time during measurements:
- SOG: Slab on Grade
- Ftg: Footing
- GB: Grade Beam
- TOC: Top of Concrete
- BOF: Bottom of Footing
- CJ: Control Joint
- EJ: Expansion Joint
These notations clarify elevation changes and joint locations that affect material ordering.
3. Reconcile Foundation Plans with Schedules
The foundation plan shows the locations of footings, piers, and grade beams. However, the dimensions of these elements are usually listed in schedules on separate sheets.
For example, the plan may label a column base as "F1." You must check the Footing Schedule to find that F1 represents a 6-foot by 6-foot by 24-inch concrete pad.
To prevent errors, verify every label against the schedules. Keep the schedule sheet open on a second monitor while performing your digital takeoff.
4. Cross-Reference Sections for Wall Heights and Thicknesses
Foundation plans show the length and location of concrete walls, but they do not show wall heights. You must locate the structural section cuts (indicated by symbols like a circle with a sheet number) to determine:
- Wall heights from footing to floor slab.
- Vertical rebar spacing.
- Keyway details at the wall-to-footing connection.
- Brick ledges and top-of-wall details.
Final Thoughts
Reading structural drawings is a skill developed through consistent practice. By starting with the notes, checking schedules, and cross-referencing section cuts, you can identify every structural concrete component and prepare highly accurate quantity takeoffs.