How Do You Read Construction Drawings Before You Bid?

Before you count anything, check what you are holding. The cover sheet's index lists every sheet with its number, title and revision; compare it page by page with the files you downloaded. Then list the addenda issued so far and check that each revised sheet is in your set. A bid priced on last week's sheets is a common reason a sub's number is wrong on bid day. The general approach to the bid itself is in how to bid a GC's job as a subcontractor; this guide is the reading.

Sheet numbers usually follow a pattern: a discipline letter, a sheet type and a sequence, so A-101 is an architectural floor plan and E-501 an electrical detail sheet. Many U.S. firms base the pattern on the U.S. National CAD Standard, which includes a Uniform Drawing System module, but each firm's index and legend are the authority for its own set.

1. General notes and legends. They apply to every sheet and often carry scope: "all conduit concealed in finished areas" changes a price.
2. Your trade's plans, one floor at a time, then your schedules and details.
3. Every callout. A bubble reading 5 over A-501 means detail 5 on sheet A-501; a cut line with an arrow points to a section. Follow each one that touches your work.
4. The other trades' sheets. Ceiling plans locate your fixtures; equipment schedules size your circuits; structural sheets limit your routes.
5. The specifications for your sections and Division 01. Materials, testing, submittals, closeout documents and warranties are priced from the specs, not the drawings.
6. Your scope of work in the GC's invitation, line by line against what you found. Anything the drawings show that the scope leaves unclear is a question.

A fictional retail shell and tenant space, Mesa Commons Building C. An electrical subcontractor reads the set and keeps a list as it goes.

Question 1 is a conflict between two sheets; question 2 is a scope gap between two trades. Both change the price, and both are the GC's to answer for every bidder at once. Where the federal clause applies, FAR 52.236-21(a) says that "in case of discrepancy in the figures, in the drawings, or in the specifications, the matter shall be promptly submitted to the Contracting Officer", and that "any adjustment by the Contractor without such a determination shall be at its own risk and expense." Asking is how you move that risk.

Federal prime contracts spell out what bidders are expected to know, and many subcontracts pass the same language down. FAR 52.236-21(a) says that "anything mentioned in the specifications and not shown on the drawings, or shown on the drawings and not mentioned in the specifications, shall be of like effect as if shown or mentioned in both", and "in case of difference between drawings and specifications, the specifications shall govern." The site investigation clause, FAR 52.236-3(a), has the contractor acknowledge it has "investigated and satisfied itself as to the general and local conditions which can affect the work or its cost", and says a failure to do so "will not relieve the Contractor from responsibility for estimating properly the difficulty and cost of successfully performing the work."

So "it wasn't on my sheets" rarely works after award. Read the whole set, walk the site if you can, and put real exclusions in your proposal in plain words. If you also measure quantities from the set, the next step is a quantity takeoff. More for subs is in the subcontractor's guide and the project lifecycle.

When a GC invites you to bid through Conflo's trade bids, the invitation shows the bid documents the GC attached (drawings, specs and the rest of the set), the trade addenda issued so far, the scope of work with its scope items and the alternates to price, and the questions and answers shared with every bidder. Ask your question on the invitation; the GC's answer goes to all bidders, so the job is bid on the same information.

Reading a set for a bid is a method: confirm the set, read the notes, then your sheets, then everyone else's, with the specs open and a running list of questions.

Ask before the deadline, in writing, and price what the answers say. The sub who asks the right question on Tuesday doesn't carry the conflict on Friday.

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1. FAR 52.236-21, Specifications and Drawings for Construction, paragraph (a) — Acquisition.gov (General Services Administration). Read October 22, 2026.
2. FAR 52.236-3, Site Investigation and Conditions Affecting the Work, paragraph (a) — Acquisition.gov (General Services Administration). Read October 22, 2026.
3. United States National CAD Standard, Version 7 — National Institute of Building Sciences. Read October 22, 2026.