How do I evaluate a bid that is dramatically lower than the others?

Direct Answer

A commercial roofing bid that is dramatically lower than the others should be evaluated by comparing its scope of work, materials, exclusions, allowances, warranties, and contractor qualifications before making an award decision. A significantly lower price may reflect genuine cost efficiencies, but it can also indicate omitted work, different material specifications, unrealistic assumptions, or costs that may appear later as change orders.

The best approach is to level all bids against the same written project requirements. Confirm that each contractor has priced the same roof area, removal requirements, roofing assembly, insulation, flashing, drainage work, deck repairs, permits, testing, and warranty obligations. Ask the lowest bidder to explain significant price differences in writing and compare the adjusted project costs rather than relying on the initial totals alone.

1. Compare the Scope of Work Line by Line

The first step is to determine whether all contractors are pricing the same project. Two proposals may use the same description, such as commercial roof replacement, while including very different work.

Compare the following items across every proposal:

• Roof area, measurements, and the sections of the building included.
• Removal of existing roofing materials and the number of layers to be removed.
• Insulation type, thickness, thermal performance, and installation method.
• Roof membrane type, thickness, manufacturer, and attachment method.
• Cover boards, separator layers, fasteners, adhesives, and accessories.
• Flashing at walls, curbs, penetrations, edges, and transitions.
• Roof drains, drainage improvements, and related sheet-metal work.
• Debris removal, disposal, cleanup, and protection of building operations.
• Testing, inspections, closeout documents, and warranty requirements.

A lower bid that excludes wet insulation removal or proposes a different roofing assembly is not directly comparable with a higher bid that includes those items. Resolve these differences before deciding which contractor offers the better value.

2. Examine Exclusions Carefully

The exclusions section can reveal why a bid is substantially cheaper. An exclusion transfers responsibility for a particular item outside the quoted price, potentially leaving the owner to pay for it separately.

Look for exclusions involving:

• Roof deck repair or replacement.
• Removal of wet or damaged insulation.
• Replacement of deteriorated flashing or sheet metal.
• Drain repairs and drainage corrections.
• Structural repairs or damaged rooftop curbs.
• Equipment relocation and coordination with other trades.
• Permits, testing, inspections, and required documentation.
• Temporary weather protection and emergency leak repairs.
• Interior protection, debris disposal, and cleanup.

Not every exclusion is unreasonable. Existing roofs can contain concealed conditions that cannot be fully assessed before demolition. The important question is whether the exclusion is clearly disclosed and whether the contract explains how the work will be priced, approved, and completed if it becomes necessary.

3. Verify That the Roofing Materials Are Comparable

Material substitutions can create substantial differences between bids. Confirm that each proposal specifies the intended roofing system and equivalent components rather than comparing only the total price.

Item to compare	What to verify
Roof membrane	Material type, specified thickness, manufacturer, and product designation.
Insulation	Type, thickness, thermal performance, number of layers, and attachment.
Cover board	Material, thickness, compressive characteristics where specified, and installation method.
Attachment system	Fasteners, plates, adhesives, spacing, and compatibility with the deck.
Flashing and accessories	Materials, installation details, and whether existing components will be reused or replaced.
Roof-system approval	Compliance with project specifications, applicable code requirements, and the specified system approval.

A proposal using a different membrane thickness, a less expensive assembly, or fewer specified components may be cheaper for a legitimate reason, but the substitution should be identified and evaluated before acceptance.

4. Review Allowances and Unit Prices

Commercial reroofing often involves uncertain quantities of concealed damage. Contractors may handle these conditions through allowances, unit prices, or separately authorized work.

Compare the following:

• Deck replacement: Is an allowance included, and what is the price per square foot or other specified unit?
• Wet insulation: Is removal and replacement included, limited by an allowance, or excluded?
• Additional tear-off: What happens if more existing roof layers are found than anticipated?
• Sheet metal and flashing: Are quantities defined, and are additional repairs priced?
• Change orders: How are quantities measured, prices established, and additional work approved?

Do not treat a small allowance as proof that the contractor will complete all necessary work at the quoted total. Ask how the allowance was calculated, what it covers, and how unused amounts or cost overruns will be handled.

5. Compare Warranties and Their Actual Coverage

Warranty differences can explain part of the price gap. A proposal offering a longer or more comprehensive manufacturer warranty may require specific materials, a qualified installer, prescribed installation details, and inspections.

Compare:

• Manufacturer warranty type and duration.
• Contractor workmanship warranty and duration.
• Coverage limitations, exclusions, and maintenance obligations.
• Whether the proposed roofing assembly qualifies for the specified warranty.
• Required inspections, documentation, and registration.
• Who is responsible for warranty-related service and repairs.

A longer warranty is not automatically better. Review what it covers, which conditions can void or limit coverage, and whether the proposed assembly satisfies the manufacturer’s requirements. Confirm that the contractor can provide the warranty described in the proposal.

6. Investigate Contractor Qualifications and Project Execution

Price should be evaluated alongside the contractor’s ability to deliver the specified work. A low bid is not evidence of poor workmanship, just as a high bid does not guarantee superior performance.

Before making an award, verify:

• Appropriate licensing and insurance for the project and jurisdiction.
• Relevant experience with comparable commercial roofing systems.
• References for similar completed projects.
• Manufacturer qualifications where required by the proposed warranty.
• The planned project supervisor and installation team.
• Safety procedures, quality-control practices, and inspection arrangements.
• Project schedule, material availability, and plans for protecting building operations.

Ask the contractor to identify who will perform the work, whether subcontractors will be used, and who will be accountable for quality and closeout. Evaluate these details against the project requirements rather than making assumptions based on price alone.

7. Ask the Lowest Bidder to Explain the Price Difference

Before accepting or rejecting the lowest proposal, send the contractor a written request for clarification. The purpose is to identify the reason for the difference, not simply to demand a price increase or a match to another contractor’s bid.

Useful questions include:

• Did you price the complete scope and all issued addenda?
• Does your proposal include every required roofing layer, flashing detail, and accessory?
• Which items are excluded or subject to additional charges?
• Are your proposed materials and installation methods identical to the specified system?
• What allowances and unit prices apply to concealed deck or insulation damage?
• Does the price include permits, disposal, testing, inspections, and closeout?
• Can you provide the specified warranty under the proposed assembly?
• What assumptions or cost efficiencies account for the lower total?

Request written answers and incorporate any agreed changes into a revised proposal. Verbal assurances should not replace a clear contractual scope.

8. Use Bid Leveling to Compare the Real Cost

Bid leveling is the process of adjusting competing proposals to a common scope and set of assumptions. It allows the owner to see whether a lower base price remains lower after missing items and differing allowances are accounted for.

Cost component	Bid A	Bid B	Low bid after adjustments
Base bid	Enter amount	Enter amount	Enter amount
Missing required scope	Adjustment	Adjustment	Add verified cost
Allowance differences	Adjustment	Adjustment	Normalize allowances
Required material or system changes	Adjustment	Adjustment	Add verified cost
Other contractual differences	Adjustment	Adjustment	Document and evaluate
Comparable evaluated cost	Calculate	Calculate	Calculate

Only add costs supported by written clarifications, comparable pricing, or clearly stated project assumptions. Avoid inventing estimates to make one proposal appear more expensive. Keep a record of each adjustment and its basis.

For complex projects, a roofing consultant or qualified project professional can help assess technical compliance, normalize competing proposals, and identify risks that cannot be resolved through price comparisons alone.

9. Recognize Warning Signs Without Rejecting a Low Bid Automatically

A dramatically lower bid deserves closer review, but it should not be rejected solely because it is inexpensive. Contractors may have different overheads, supplier arrangements, scheduling efficiencies, or installation approaches.

Warning signs include:

• A vague description of the roof system or installation scope.
• Numerous exclusions involving essential project work.
• Unusually low allowances for foreseeable repairs.
• Unspecified or unapproved material substitutions.
• No clear unit prices or change-order procedure.
• Unclear warranty terms or unsupported warranty claims.
• Missing permit, testing, safety, or closeout responsibilities.
• Unrealistic scheduling or inadequate evidence of relevant experience.
• Pressure to sign before reasonable questions are answered.

One warning sign does not necessarily disqualify a contractor. The decision should be based on documented findings, the contractor’s explanations, the completeness of the proposal, and the risks remaining after clarification.

10. When Should You Reject or Reconsider a Low Bid?

Consider excluding or reconsidering a proposal if the contractor cannot demonstrate compliance with mandatory project requirements, refuses to clarify material exclusions, cannot substantiate required qualifications or insurance, or will not confirm the scope and contractual terms in writing.

For a public or formally procured project, follow the applicable solicitation rules and evaluation criteria. Do not change the criteria after bids are received or treat a proposal as nonresponsive without following the governing process.

For a private commercial project, the owner should document the reasons for the decision and compare the remaining proposals using consistent criteria. The objective is to select a qualified contractor offering an acceptable combination of scope completeness, technical compliance, price, schedule, warranty, and risk.

Bottom Line

A dramatically low commercial roofing bid should be treated as a question to investigate, not an automatic bargain or an automatic rejection. Compare the scope, materials, exclusions, allowances, warranties, qualifications, and contractual terms line by line. Ask the contractor to explain significant differences in writing, then level all proposals to a common basis.

The most useful comparison is the evaluated cost of delivering the required roofing system, including clearly identified additional work and contractual risks. Once the proposals are comparable, price can be considered alongside quality, experience, warranty protection, and the ability to complete the project as specified.

Related Questions

• How should owners evaluate competing commercial roofing proposals?
• Which unit prices should be requested in every roofing bid?
• What allowances are typical for deck replacement in a bid?
• How many bidders should be invited to a commercial roof project?
• What is a pre-bid site walk, and should attendance be mandatory?

Sources

• ShieldLine Roofing — How to Evaluate Competing Commercial Roofing Proposals
• National Roofing Contractors Association (NRCA) — Roofing Industry Resources
• International Institute of Building Enclosure Consultants (IIBEC) — Building Enclosure Resources
• Commercial Roofing Advisors — How to Read a Roof Bid

Last reviewed: October 2026

Explore Commercial Skylights & Roof Access