Design-bid-build

Design-bid-build is the method most people picture when they think of construction: an owner hires an architect or engineer to design the project completely, invites contractors to bid on the finished documents, and awards the contract to the lowest responsive and responsible bidder, who then builds what was drawn. It remains the most common delivery method for public work in both countries and the default for many private owners. It is also the baseline against which every other method is measured. Understanding why it works where it works, and why it fails where it fails, is the foundation for the rest of this course.

How design-bid-build is organized

In design-bid-build the owner holds two separate contracts: one with the design consultant (often an architect leading a team of engineering subconsultants) and one with the general contractor. The designer and the contractor have no contract with each other. They communicate through the owner's contract administration process, usually with the designer acting as the owner's representative during construction: reviewing shop drawings, answering requests for information, certifying payment and deciding on changes within the limits the owner sets.

The project moves through three phases in sequence. First, design: pre-design and programming, schematic design, design development and construction documents, with cost estimates by the designer or a cost consultant at each stage. Second, procurement: the owner advertises or invites bids, answers questions by addenda, receives sealed bids at a set time, opens them, checks responsiveness and awards. Third, construction: the contractor mobilizes, builds, and hands over, with the designer administering the contract.

Why owners choose it

Design-bid-build has lasted because it does several things very well.

For straightforward, well-defined projects, such as a typical school, a road resurfacing job, a fire hall or a warehouse, these strengths often outweigh everything else. There is little that construction input during design could add, the market is competitive, and the documents can be completed with confidence.

Why it fails

The weaknesses of design-bid-build come from the same sequential structure that gives it its strengths.

The most damaging of these is the combination of owner design risk and low-bid pricing. A contractor who wins on price has every reason to price only what is shown and to treat every gap, conflict or ambiguity in the documents as a change. Owners commonly budget a construction contingency of 5 to 10 % of the contract for changes on new buildings and more on renovations, and change orders on public design-bid-build projects frequently consume much of that. Whether that is a weakness of the method or of the documents is a fair question; with excellent, well-coordinated documents, design-bid-build change rates can be low.

In the United States the owner's responsibility for its design is reinforced by the Spearin doctrine, from United States v. Spearin (1918): an owner who provides plans and specifications impliedly warrants that a contractor who follows them will produce an adequate result. Disclaimers can narrow the warranty in some states, but the principle still shapes how design risk sits with the owner in design-bid-build. CON-220 covers implied warranties and differing site conditions clauses.

The bid: responsive and responsible

Public design-bid-build awards usually go to the lowest bidder who is both responsive and responsible. A responsive bid conforms to the bid documents in all material respects: it is on the required form, signed, on time, includes the bid security and any required lists, and does not qualify or change the terms. A responsible bidder is one capable of performing: it has the experience, financial capacity, bonding, safety record and integrity required. Responsiveness is judged on the face of the bid at opening; responsibility may be investigated afterwards. CON-300 lesson 10 covers bid day and bid submission from the contractor's side, including bid bonds, mistakes in bids and Canadian bid depositories.

# Bid tabulation analysis for the Alder Bay aquatic facility (illustrative)
estimate = 46_400_000
bids = {"A": (44_980_000, False), "B": (45_620_000, True), "C": (46_150_000, True),
        "D": (47_300_000, True), "E": (49_900_000, True)}   # (amount, responsive?)
ok = {k: v for k, (v, r) in bids.items() if r}
low = min(ok, key=ok.get)
vals = sorted(ok.values())
print("Lowest responsive bidder:", low, f"{ok[low]:,}")
print(f"Versus estimate: {ok[low] - estimate:+,} ({(ok[low] - estimate) / estimate:+.1%})")
print(f"Spread low to high (responsive): {(vals[-1] - vals[0]) / vals[0]:.1%}")
print(f"Gap to second responsive bid ('money left on the table'): {vals[1] - vals[0]:,}")
mean = sum(vals) / len(vals)
print(f"Mean responsive bid: {mean:,.0f}; low bid is {(mean - vals[0]) / mean:.1%} below the mean")

Lowest responsive bidder: B 45,620,000
Versus estimate: -780,000 (-1.7%)
Spread low to high (responsive): 9.4%
Gap to second responsive bid ('money left on the table'): 530,000
Mean responsive bid: 47,242,500; low bid is 3.4% below the mean

The gap between the lowest and second-lowest bids, often called "money left on the table", is watched closely by contractors. A large gap can signal that the low bidder missed something, which is exactly the situation that leads to aggressive change-order behavior later. Some owners review a bid that is far below the others with the bidder, within the limits their tendering rules allow, before awarding.

Change orders and the real final cost

The contract price in design-bid-build is not the final cost. Owner changes, design errors and omissions, unforeseen conditions and regulatory changes all add to it. A useful owner discipline is to track change orders by cause, because the causes tell you whether the problem is the method, the documents, the site or the owner's own decision-making.

# Change order growth on the Alder Bay aquatic facility at completion (illustrative)
contract = 45_620_000
changes = {   # cause: approved change order value
    "Design errors and omissions":     1_210_000,
    "Owner-requested scope changes":     860_000,
    "Unforeseen site conditions":        540_000,
    "Code or authority requirements":    180_000,
    "Value engineering credits":        -310_000,
}
total = sum(changes.values())
for cause, v in changes.items():
    print(f"{cause:32} {v:>+11,}  {v / contract:+.1%}")
print(f"Net change orders {total:+,} = {total / contract:.1%} of contract")
print(f"Final contract value {contract + total:,}")
contingency = 0.07 * contract
print(f"7 % owner contingency {contingency:,.0f}; remaining {contingency - total:,.0f}")

Design errors and omissions       +1,210,000  +2.7%
Owner-requested scope changes       +860,000  +1.9%
Unforeseen site conditions          +540,000  +1.2%
Code or authority requirements      +180,000  +0.4%
Value engineering credits           -310,000  -0.7%
Net change orders +2,480,000 = 5.4% of contract
Final contract value 48,100,000
7 % owner contingency 3,193,400; remaining 713,400

Here net changes reached about 5.5 % of the contract, inside a 7 % contingency. The largest single cause was design errors and omissions, about 2.7 %. That is the cost the owner bears because, in design-bid-build, it stands behind its designer's documents. The owner may be able to recover part of it from the designer if the errors fell below the professional standard of care, but recovery is rarely complete and always slow.

Multiple-prime contracting

A variant of design-bid-build has the owner award several separate prime contracts, for example general construction, mechanical, electrical and site work, instead of one general contract. The owner, or a construction manager acting as its agent (lesson 3), then coordinates the prime contractors. Multiple-prime contracting can widen competition and let owners buy directly from trades, but it moves the coordination risk to the owner.

In the United States, some states have required multiple prime contracts on public work. New York's Wicks Law, for example, requires separate prime contracts for plumbing, heating and ventilation, and electrical work on many public projects above set dollar thresholds, though the thresholds were raised and project labor agreements can provide exemptions. Several other states have repealed or relaxed similar rules.

Contracts used for design-bid-build

Because design-bid-build has been the default for so long, its standard forms are the most mature and the most tested in the courts. That is a real advantage: parties know what the words mean.

Making design-bid-build work better

Owners who stay with design-bid-build, often because procurement rules leave little choice, can reduce its weaknesses. They can hire an independent constructability reviewer or a cost consultant during design; run peer reviews of documents at 50 % and 95 %; prequalify bidders to keep the field capable; use early works packages, such as site preparation or demolition, bid separately to start sooner; pre-purchase long-lead equipment and assign it to the contractor; use alternate prices in the bid form to manage the budget; and set a realistic contingency. Some public owners in both countries also use a best-value design-bid-build, in which bidders submit both a price and a short technical proposal, though most still award on price alone.