Specified, Substituted, Signed Off: A Commercial Test for ‘Or Equal’ Proposals

The clause is a permission, not a presumption

In UK commercial specifications, the phrase ‘or equal’ is often treated as a convenient release valve. It appears to keep competition alive, avoid over-prescription and allow contractors to propose products that are available, affordable or simply quicker to obtain. In practice, however, the clause does not approve anything. It creates a route by which an alternative may be considered, subject to evidence.

The commercial risk lies in the gap between that permission and the decision that follows. If a proposed equivalent is accepted informally — through a marked-up submittal, a verbal assurance or a line in a progress meeting — the original specification can be displaced without a proper record of what has been gained, what has been lost and who carries the consequences. The purpose of this article is to set out a practical test that buyers and project teams can apply before an ‘or equal’ proposal becomes an order, a variation or an installed item.

Why equivalence is rarely a like-for-like question

A proposed equivalent is seldom identical to the specified item. It may match the headline performance figure while differing in dimensions, control interfaces, maintenance intervals, spare parts availability or warranty terms. Those differences may be commercially acceptable, but they should be identified and priced rather than assumed away.

The difficulty is that specifications often describe outcomes rather than the full operating context. A pump might meet the required flow rate but require a different pipe connection. A luminaire might achieve the specified lux level but draw a different driver, affecting spares and dimming compatibility. A cladding panel might satisfy the fire performance requirement but alter the fixing details and the programme sequence. None of these differences is necessarily fatal. Each is a question that the evaluation should answer.

For commercial clients, the relevant question is not simply whether the alternative is ‘as good’. It is whether the alternative delivers the same outcome over the same period, under the same conditions, with the same support arrangements, at a defensible whole-life cost.

A seven-part test for proposed equivalents

The following test is deliberately practical. It can be applied to a single product or a package of substitutions, and it should be recorded in writing before acceptance.

1. Specification compliance and certification

Confirm that the proposal meets every mandatory requirement, not only the most visible one. Check declared performance values, test standards, certification marks and any project-specific requirements. In the UK, this may include UKCA or CE marking considerations, Building Regulations compliance, fire performance classifications and sector-specific approvals. Where a declaration relies on a test report, confirm that the report applies to the proposed product and not to a related variant.

2. Whole-life cost, not just purchase price

Compare the capital cost with the cost of ownership. Consider energy use, maintenance frequency, consumables, access requirements and expected service life. A cheaper item that requires more frequent replacement or additional access equipment may be more expensive over the life of the building. Where the client will operate and maintain the asset, those costs should be assessed from the client’s perspective, not only the contractor’s.

3. Warranty, liability and support

Examine the warranty period, what it covers, who provides it and how claims are handled. Check whether the proposed equivalent carries the same back-to-back obligations as the specified item and whether any manufacturer support is available in the UK. A longer warranty is not automatically better if the provider is remote, the exclusions are broad or the remedy is limited to replacement of a component rather than the cost of access.

4. Spares and serviceability

Confirm that spare parts, consumables and specialist support will remain available for the expected service life. Consider whether the alternative introduces proprietary components that can only be sourced from one supplier, and whether the client’s maintenance team has the training and tools to service it. A product that performs well but cannot be maintained without a single specialist contractor has transferred a commercial risk to the client.

5. Interfaces and physical fit

Check dimensions, connections, loadings, clearances and control interfaces. An equivalent that fits the specification but not the surrounding construction is not equivalent in practice. This is particularly important where the item connects to existing services, sits within a constrained ceiling void or forms part of a fire-rated assembly. Interface changes may require consequential design work, builder’s work or trade coordination that was not included in the original price.

6. Programme and lead-time impact

Establish the lead time of the proposed item and compare it with the specified product and the construction sequence. A substitution that saves money but arrives two weeks later may cost more in delay than it saves in procurement. Confirm that any long-lead components, testing regimes or commissioning requirements have been included in the programme.

7. Documentation and traceability

Require a clear submittal that identifies the specified item, the proposed equivalent, the differences between them and the evidence relied upon. The record should state who approved the substitution, on what basis and with what conditions. If the acceptance depends on a manufacturer’s warranty, a test certificate or a client instruction, those documents should be attached or referenced.

Who carries the burden of proof?

The burden of proof should sit with the party proposing the equivalent. That is not a adversarial position; it is a straightforward allocation of responsibility. The proposer is best placed to explain what the alternative is, how it differs and why it should be accepted. The buyer’s role is to test that evidence against the project’s requirements and the client’s long-term interests.

Where the evidence is incomplete, the appropriate response is usually to request further information rather than to reject the proposal outright. A clear request for missing test data, warranty terms or interface details keeps the process moving and creates a useful record if the matter later becomes a commercial issue.

Record the decision, not just the outcome

An accepted equivalent should leave a trace. A short evaluation note can record the specified item, the proposed alternative, the evidence reviewed, the differences accepted and any conditions attached. This need not be elaborate, but it should be sufficient for someone outside the immediate project team to understand why the substitution was approved.

That record has value beyond the current project. It supports asset information, maintenance planning and future procurement. It also protects the client if performance, availability or warranty issues emerge later. The commercial discipline is not to resist every equivalent proposal; it is to ensure that acceptance is an informed decision rather than an accidental one.

Conclusion

‘Or equal’ is a useful clause when it is supported by a proper evaluation. It becomes a source of risk when it is treated as a synonym for ‘acceptable’. The test set out above is not intended to make substitution difficult. It is intended to make the decision visible, evidence-based and defensible. For UK commercial clients, that is the difference between a specification that retains its intent and one that quietly loses it.