How to read construction drawings

The order of a drawing set

The drawing sheet index order from the US National CAD Standard (v6). Most sets use only some of these disciplines.

How to read a drawing set, start to finish

1. 1

   Start with the general sheets

   Find the sheet index, general notes, abbreviations and legends on the G sheets.

2. 2

   Read the title block

   Check the project, sheet title and number, scale, and the latest revision on each sheet.

3. 3

   Work through the disciplines in order

   Civil and landscape, structural, architectural, then fire protection, plumbing, mechanical and electrical.

4. 4

   Follow the callouts

   Use section and detail callouts on the plans to jump to the sheets that show more.

5. 5

   Check the revisions

   Look for revision clouds and compare them with the revision list before you price.

Reading a sheet number

A National CAD Standard sheet number is the discipline letter, then a sheet type digit, then a sequence number. The sheet types are: 0 general, 1 plans, 2 elevations, 3 sections, 4 large-scale views, 5 details, 6 schedules and diagrams, 7 and 8 user defined, and 9 three-dimensional drawings. So A2.00 is an architectural elevation sheet, and P2.01 is a plumbing sheet. A second letter can narrow the discipline: QF is food service equipment, EL is electrical lighting.

Plans, elevations, sections and details

A plan looks down on the building, cut horizontally, usually a few feet above the floor. An elevation looks straight at a face of the building or a wall. A section is a vertical cut through the building that shows how it's put together. A detail is a close-up, at a larger scale, of one junction or assembly. Callout symbols on plans point you to the section or detail sheet that shows more.

Check the scale on every sheet

Every sheet, and often every view on a sheet, states its scale. A set mixes scales, from small-scale site plans to large-scale details, so never assume one scale for the whole set. If you measure from a PDF, calibrate each sheet against a printed dimension rather than trusting the stated scale, because PDFs are often rescaled when they're printed or exported.

Symbols: the legend is the authority

There is no single symbol set every firm uses. The ASME standard for plumbing fixture symbols, Y32.4, is listed as historical, and electrical and mechanical symbols vary between engineers too. Each set defines its symbols in a legend, usually on the general sheets or on the first sheet of each discipline. Read the legend before you count anything.

Revisions and clouds

Changes are shown with a revision cloud, a scalloped outline around the changed area, usually with a revision number or delta symbol that matches the revision list in the title block. When a new issue arrives, look for the clouds first: they show what changed since the last set you priced. The same conventions mark field changes on as-built drawings.

Taking off from the drawings in ContractorCounter

Once you can read the set, ContractorCounter turns it into quantities. Open the PDFs in the browser, calibrate each sheet, then measure and count the symbols from the legend; the AI can take the first pass with a marker on every symbol for you to review. Everything feeds a Bill of Quantities you can price. See the takeoff workflow; plans start at US$1 a week, billed US$4 every 4 weeks.

Questions about How-to guide