Interim Payment Certificates in Domestic Building Contracts: A Homeowner's Guide

Introduction

Interim payment certificates are the mechanism through which a contractor is paid progress payments during a building project. Understanding how the certificate process works, what the Contract Administrator is certifying, and how retention is applied helps homeowners manage their cash commitments during construction and protects them from over-paying a contractor who then fails to complete the works. This guide explains interim payment certificates in domestic building contracts and their practical implications for homeowners.

Why Progress Payments Are Made

A building contractor cannot reasonably be expected to fund all the materials, labour and subcontractor costs for a major project over many months and invoice only at the end. Standard building contracts therefore provide for progress payments at regular intervals — typically monthly — as the works proceed. The contractor submits an application for payment, the Contract Administrator assesses it and certifies an appropriate amount, and the employer pays the certified sum within the specified period.

The Payment Cycle

Under JCT Minor Works and similar domestic contracts, the payment process typically works as follows:

1. At the agreed payment interval (typically monthly), the contractor submits an Application for Payment — a written statement of the value of works completed to date, materials on site, and any other sums claimed
2. The Contract Administrator (architect or other named person) assesses the application, visits the site, and checks that the value claimed reflects actual progress
3. The CA issues an Interim Payment Certificate specifying the certified amount — typically the value of work properly executed and materials properly on site, less any retention, less sums previously paid
4. The employer pays the certified amount to the contractor within the payment period specified in the contract (typically 14 days from the certificate date)
5. The process repeats at the next payment interval

What the Contract Administrator Certifies

The CA's assessment of the value of works completed is a professional judgement. The CA is not certifying that the works are complete or defect-free — they are certifying the fair commercial value of what has been properly executed to the point of assessment. Key principles:

• Work that has been executed but not to the required standard should not be included in the certified value — the CA should deduct the value of work requiring replacement or significant remediation
• Materials on site are included in the certified value only where they are properly stored, protected, and irreversibly dedicated to the project — not materials that could be taken away and used elsewhere
• Variations (changes to the contract works) are included in the certified value at the agreed or assessed value, whether or not final agreement on their value has been reached

Retention

Retention is an amount withheld from each interim payment as security for the contractor's performance. Under JCT Minor Works, a standard retention of 5% of the certified value is applied to each interim payment, reducing to 2.5% from the point at which the works reach a value of 50% of the contract sum in some contract forms. Retention is released in two stages:

• Half the retention (typically 2.5% of the final contract value) is released when the Practical Completion Certificate is issued
• The remaining half is released when the Making Good Certificate (Defects Liability Certificate) is issued at the end of the Defects Liability Period

Retention is designed to create an incentive for the contractor to return and rectify defects during the DLP — if the contractor simply disappears after practical completion, the unreleased retention provides a financial disincentive.

Payment Notices and Late Payment

The construction industry legislation (Housing Grants, Construction and Regeneration Act 1996 as amended) requires that interim payments are processed in a defined way, with Payment Notices and Pay Less Notices used where the employer intends to pay less than the certified amount. For domestic clients (homeowners), the full statutory scheme applies in a modified form — the CA's certificate functions as the Payment Notice.

Paying less than the certified amount without issuing a valid Pay Less Notice within the required timeframe is a breach of contract and of the Act. Homeowners should not withhold payment from a certified amount without taking specific legal advice first — even where they believe the contractor has done defective work, the correct process is to raise the issue through the contract administrator rather than simply deducting from certified amounts.

Disputed Certificates

Where the contractor disputes the CA's certified amount — claiming they have been under-certified — the contract typically provides a mechanism for the contractor to seek adjudication or arbitration. Adjudication under the Scheme for Construction Contracts is a fast, mandatory dispute resolution process that applies even to domestic building contracts.

Where the employer believes the CA has over-certified — certifying more than the true value of work done — the employer can raise this with the CA and, if necessary, challenge it through the contract's dispute resolution mechanism.

Practical Advice for Homeowners

• Ensure the building contract specifies the payment interval, the retention percentage, and the payment period clearly — ambiguity about these terms creates disputes
• Ask the CA to attend site before issuing each interim certificate and to provide you with a brief summary of the progress assessment
• Pay certified amounts promptly within the contract period — late payment is a breach of contract and creates unnecessary tension with the contractor
• If you have concerns about the quality of work, raise them with the CA before the next payment certificate is issued — not by withholding a certified payment unilaterally

Conclusion

Interim payment certificates are a fundamental part of the construction contract machinery that protects both contractor and employer. For homeowners, having an architect acting as Contract Administrator to assess applications, issue certificates and manage the retention mechanism is one of the most valuable aspects of the full RIBA service. It ensures that payments are made for work that has actually been completed, that retention is properly applied, and that the financial controls of the contract are in place throughout the project.