Why do construction bids for the same project vary so much?

Start from the assumption that the low bid excludes something#

Two builders receive the same drawings on the same day and return numbers a third apart. The instinct is to conclude that one is expensive and one is efficient. Occasionally that is true. Far more often, they priced different projects, because the drawings did not fully define the project and each bidder resolved the gaps in their own favor.

A set of drawings is never complete. There is always work that the documents imply without specifying: how the tile meets the plaster, what happens at a transition the detail sheet never drew, which trade owns backing and blocking. Every bidder decides what to do with those gaps. Some carry them. Some exclude them in a sentence on page four. The excluded version is cheaper, and it is cheaper because it is smaller.

That is the whole answer, and everything below is the anatomy of it. The question worth asking is not "why is this one higher." It is "what did each of these bidders assume, and can I see it written down."

The six places numbers actually diverge#

Scope gaps#

The largest single contributor. A drawing set that shows a wine room without specifying cooling, or a site plan showing a driveway without a section, invites two legitimate but incompatible interpretations. The bidder who carries the cooling unit looks expensive next to the bidder who did not see one specified.

Allowances set to win#

Allowances are supposed to be a placeholder for undecided selections. Used honestly they are a reasonable device. Used competitively they are a discount that expires: a tile allowance set well below what the client will actually choose produces a low contract sum and a predictable series of adjustments once selections begin.

General conditions#

Supervision, site office, temporary power and water, protection, cleanup, dumpsters, safety, and the project manager's time. This is the cost of running the job rather than building it, and it scales with duration. A bidder with a short assumed schedule carries less of it. If the schedule was optimistic, the general conditions were too.

Assumptions about the site#

Soil, groundwater, existing utilities, access, staging space and neighbor conditions. On a hillside or a tight infill lot these decide the excavation and retention scope, which is why two bidders can differ by a very large figure on site work alone. A bidder who assumed no engineered retention and one who carried it are not in the same conversation.

Contingency, escalation and risk#

Some bidders carry contingency inside the number and some do not carry any. Some price material escalation over a long build and some price today's cost. Neither approach is wrong, but the two produce different totals for identical work, and only one of them will hold.

The estimate that is calling itself a bid#

An estimate is a forecast of probable cost. A bid is an offer to perform defined work for a stated sum. They look similar on paper and behave completely differently once a contract exists. If the document does not identify the exact drawing set and revision it prices, it is an estimate regardless of what it is titled.

Normalizing bids onto one basis#

You cannot compare numbers until they describe the same work. Rebuilding them onto a common basis takes an afternoon and is the highest return work in the whole selection process.

• Identify the exact drawing set, revision and date each bid priced.
• List every exclusion from every bid, then apply all of them to all bids.
• Reset every allowance to one agreed value across all bidders, using real pricing from actual selections rather than the bidder's placeholder.
• Separate general conditions and fee from the trade costs so they can be seen as their own line.
• Confirm each bidder's assumed schedule, since duration drives general conditions.
• Confirm each bidder's site assumptions, especially excavation, retention, shoring and utility work.
• Check whether contingency and escalation are inside the number, outside it, or absent.

Once that is done, the spread usually shrinks dramatically. What remains is the real difference: fee, overhead, buying power and how the builder prices risk. That difference is worth paying attention to. The one you started with was mostly noise.

What to ask each bidder before you decide#

"What did you exclude, and why?" The answer tells you how carefully the set was read. A bidder who names three specific gaps has done the work. A bidder who says nothing was excluded has either not read the drawings or is about to write change orders.

"Show me general conditions as its own line." If it is buried in a percentage or absent, the number is incomplete. This line is also the fastest way to see whether the assumed schedule is honest.

"What are you assuming about the soil and the site?" Ask for it in writing. Site assumptions are where the largest post-contract surprises live, and a geotechnical report resolves most of them before anyone signs.

"Which numbers are allowances, and what do they buy?" Then go price two or three of them yourself. It takes an hour and it recalibrates the entire bid.

"What is your fee, and what does it cover?" A builder who will state fee plainly is a builder who expects the relationship to survive scrutiny. That posture matters more over an eighteen month build than any single line item, and it is worth weighing alongside how the firm actually works, which is what an about page and a reference call are for.

What the comparison is really measuring#

By the time bids are normalized, price differences have usually collapsed into three real variables: what the builder pays for labor and material, what the builder charges to manage the work, and how much risk the builder priced rather than deferred.

The third one is the one that decides how the project feels. A bid that priced risk shows up as a slightly higher number and a stable contract. A bid that deferred risk shows up as an attractive number and a stream of adjustments that arrive when you have the least leverage, because the walls are open and the crew is on site.

The most useful protection is to involve a builder during design rather than at the end of it. A constructability review and a real budget before the drawings are final removes most of the ambiguity that produces bid spread in the first place. That preconstruction sequence is a core part of how residential development work should be run, and it converts bidding from a guessing exercise into a comparison of firms.