How to Prepare an Interim Valuation: A QS Step-by-Step Guide

The interim valuation construction contracts rarely get the credit it deserves. It isn't glamorous work - a few hours on site with a hard hat and a tape measure, followed by an afternoon reconciling numbers against a bill of quantities - but it's the mechanism that keeps contractors solvent and clients confident they're paying for work that has actually been done.

Get it wrong, and the consequences show up fast. Undervalue the works and the contractor's cash flow tightens, disputes creep in, and site relationships sour. Overvalue them and the employer is exposed if the contractor runs into financial trouble before completion. For a quantity surveyor, whether working on the contractor side or the client side, the monthly valuation is one of the most consistently repeated - and most consistently scrutinised - deliverables in the job. That pressure runs both ways: a QS who consistently under-prepares valuations erodes trust with the site team just as quickly as one who pads figures erodes trust with the client.

This guide is a procedural walkthrough: seven steps, in order, from the paperwork you gather before you leave the office to the certificate that lands in the contractor's inbox. If you want the underlying theory - what counts as a fair valuation, how assessment principles differ between contracts, and how QSs justify the figures they arrive at - that's covered in our companion piece, Construction Valuation Guide: How QSs Assess Interim Payments. This article picks up where that one leaves off and focuses purely on the workflow.

Follow the steps below in sequence on your next valuation, and you'll come away with a defensible, well-documented figure ready for certification - with a checklist and a step-flow graphic you can keep open on a second screen while you work.

Step 1: Prepare Before You Go to Site

The Paperwork to Gather First

A valuation prepared without proper groundwork takes twice as long and invites more queries later. Before you leave the office - or before the site meeting, if you're working from a regional base - pull together everything you'll need to compare against what you find on site.

• The previous interim valuation and payment certificate, so you know exactly what's already been paid
• The current construction programme, to check what should be complete by the valuation date
• The latest issued drawings and specification, including any revisions since the last valuation
• The bill of quantities or schedule of rates/activity schedule, whichever the contract uses
• Subcontractor valuations and applications, if you're consolidating a package contractor's figures
• Any instructed variations, compensation events or change orders not yet valued
• Confirmed day work sheets, if the contract allows for time and materials
• Material invoices, delivery notes and, where relevant, vesting certificates for off-site items
• The contract's payment terms - due date, retention percentage, and any retention-free threshold

Ten minutes with this list before you travel saves an afternoon of chasing information later - and it means you walk onto site with a clear idea of what you're expecting to see, rather than starting from scratch once you're there.

It's also worth checking whether any instructions, early warnings or notices are still outstanding from the previous period - unresolved items have a habit of resurfacing as disputes at exactly the point you're trying to close out a valuation.

Step 2: Carry Out the Site Walk

Walking the Works With the Contractor's QS

Most valuations, particularly on larger or more complex projects, involve a joint site walk - the employer's QS or contract administrator alongside the contractor's QS or site manager. Even where the assessment is being done unilaterally, as can happen under some NEC arrangements, a physical inspection of the works remains the only reliable way to verify progress.

Who attends varies by project size. On smaller jobs, the site walk might just be the contractor's QS and the contract administrator; on larger schemes it often includes the client's cost manager, the package subcontractors whose work is being measured, and sometimes the architect or engineer for technical sign-off on specific elements.

• Compare physical progress against the programme percentage the contractor is claiming
• Check workmanship and note any obviously defective work that shouldn't be valued at full rate
• Identify work that's complete but wasn't included in the previous valuation
• Record materials stored on site, including quantities and condition
• Photograph anything contentious, and anything that will be covered up before the next visit - foundations, first-fix services, waterproofing
• Note any access, sequencing or health and safety issues affecting programme

Keep a simple site diary as you go rather than relying on memory. A note of area, level and percentage complete for each element, plus a handful of photographs, is usually enough to support the valuation and answer any queries later.

Step 3: Measure Progress Against the Programme and Drawings

Turning What You Saw Into Quantities

Back at the desk - or increasingly, on a tablet on site - the next job is converting what you observed into measured quantities against the bill of quantities, activity schedule or cost plan. This is where the site walk notes earn their keep.

Work through each element methodically: substructure, frame, envelope, internal finishes, services, external works. For each line item, record the percentage or quantity complete this period, distinguishing it clearly from the cumulative total to date. Cross-check against the contractor's own payment application, where one has been submitted, and flag any items where your assessment differs so they can be discussed before the figure is finalised.

Precision matters more on some elements than others. Groundworks and structural items are usually straightforward to measure once, since they're rarely revisited. Finishes and services, by contrast, tend to be valued incrementally over several months as first fix, second fix and commissioning progress - so keep a running record of what's been claimed for each element in previous periods to avoid double-counting.

Use a checklist like the one above to track where each valuation stands - a useful discipline whether you're two years into a large scheme or running your first valuation solo.

A common pitfall at this stage is measuring against the wrong revision of a drawing, particularly on fast-moving projects where design information changes between valuations. Always check the drawing register before finalising quantities, and note the revision used against each measured item so it can be traced later if the design changes again.

Step 4: Apply Rates and Calculate the Gross Valuation

From Quantities to Pounds and Pence

With quantities confirmed, apply the contract rates - from the priced bill of quantities, schedule of rates, or activity schedule - to arrive at a gross valuation for the works executed to date. This is the calculation stage where accuracy and a clear audit trail matter most.

Preliminaries deserve particular care. Rather than releasing the full preliminaries allowance evenly across the programme, many QSs weight it toward the activities that actually drive site overheads - management time, welfare, and plant hire - so the profile better reflects real cost incurred rather than a straight-line percentage.

• Apply the priced rate for each measured item, not a re-estimated or market rate
• Value approved variations and compensation events separately, using agreed or estimated rates as appropriate
• Include preliminaries, usually valued in proportion to programme progress or time elapsed
• Apply any agreed fluctuations or index-linked adjustments where the contract provides for them
• Deduct the value of any previous valuations to isolate this period's payment, if working on a period rather than cumulative basis

Keep a clear audit trail. Every figure in the gross valuation should be traceable back to a measured quantity and a specific contract rate - that's what turns a valuation into a defensible calculation rather than an estimate, and it's what will save you time if the figure is ever queried months later.

Step 5: Value Materials On Site and Off Site

Materials Delivered but Not Yet Built In

Materials represent real cost to the contractor before they're incorporated into the works, so most standard contracts allow them to be included in the valuation - provided they meet certain conditions.

• Materials on site: confirm they're intended for this contract, adequately protected and stored, and reasonably close to being fixed
• Materials off site: check the contract permits it at all - many standard forms restrict off-site materials unless specifically listed
• For off-site materials, obtain evidence of ownership passing to the contractor: a vesting certificate, invoice, and proof of insurance while stored
• Confirm the goods are uniquely identified and set aside for this project, not general stock that could be diverted elsewhere
• Apply the same scrutiny to subcontractor and supplier materials as to the main contractor's own

Materials valuations are a common source of dispute, so err on the side of caution: value what you can evidence, and hold back items where documentation is missing until it's provided in a later period.

Where off-site materials are being valued for the first time, it's worth agreeing the evidence requirements with the other side before the valuation date rather than after - a short conversation up front avoids a much longer one when a six-figure materials claim is queried at certification stage.

Step 6: Calculate and Apply Retention

Holding Back a Percentage Against Defects

Most JCT contracts, and NEC contracts where Option X16 is incorporated, allow the employer to retain a percentage of the certified value as security against defects. Retention is usually 3% or 5% of the gross valuation, though the exact figure and any retention-free threshold are set out in the contract particulars.

Deduct retention from the gross valuation before arriving at the net sum due. Where the contract splits retention release into two moieties, keep a running note of how much has been held and released to date - it makes the final account reconciliation far simpler when practical completion arrives.

• Confirm the retention percentage and any retention-free threshold in the contract particulars
• Apply retention to the gross valuation, not to fluctuations if the contract excludes them
• Track cumulative retention held separately from the period figure
• Note the trigger points for release - practical completion and making good defects under JCT, or as set out in Option X16 under NEC

It's good practice to show retention as a running cumulative figure on every valuation summary, not just the amount held this period. That way, both sides can see at a glance how much security remains outstanding as the project approaches practical completion.

Step 7: Reconcile, Agree and Issue for Certification

Closing Out the Month

The final step is to reconcile your figure against the contractor's own application, where one exists, resolve any differences, and pass the agreed valuation to the contract administrator or project manager for certification.

• Compare your gross and net figures against the contractor's payment application line by line
• Document the reason for any adjustment - this becomes the basis of the payment notice or pay-less notice if disputed
• Issue your valuation summary to the certifying party in good time to meet the certificate deadline set out in the contract
• Keep a signed or dated record of the agreed valuation for the project file and future final account reconciliation
• Diarise the certificate and final payment dates so you can chase if either slips

Once the certificate is issued and the payment notice or pay-less notice period has run its course, the cycle resets - the next valuation date is usually only a few weeks away.

Under the Construction Act, the payment notice and any pay-less notice must be issued within strict deadlines set by the contract - missing them can mean the contractor's own application becomes the notified sum by default, regardless of whether your assessment agrees. Diarising these dates is as important as getting the valuation figure right.

Frequently Asked Questions

What is an interim valuation in construction?

An interim valuation is a periodic assessment of the value of work completed on a construction project, usually carried out monthly. It forms the basis for the interim payment certificate that determines how much the contractor is paid for that period.

How often are interim valuations carried out?

Most UK construction contracts, including JCT and NEC forms, provide for valuations at monthly intervals, though the exact frequency - described as the valuation date or assessment interval - is set out in the contract particulars and can occasionally be set at four-weekly or other intervals.

Who prepares the interim valuation, the QS or the contractor?

It depends on the contract and the party. Under JCT contracts, the contractor typically submits a payment application, and the employer's quantity surveyor or contract administrator assesses and certifies the value. Under NEC contracts, the project manager assesses the amount due at each assessment date, though contractors usually submit their own supporting application in practice.

What's the difference between an interim valuation and an interim payment certificate?

The valuation is the underlying calculation - the measured quantities, rates, materials and retention that produce a figure. The certificate is the formal document, issued by the contract administrator or project manager, that confirms that figure and triggers the employer's obligation to pay.

What happens if the contractor and consultant QS disagree on the valuation?

Differences are normal and are usually resolved through discussion at or shortly after the site walk, with each side explaining its measurement or rate. Where agreement can't be reached, the certifying party issues its own assessment, and the contractor can challenge it through a payment notice, pay-less notice or, ultimately, adjudication. Keeping detailed site notes and photographs from the walk makes these conversations far shorter, since both sides can refer to the same evidence rather than arguing from memory.

Can materials off site be included in an interim valuation?

Only where the contract specifically allows it, and even then only with satisfactory evidence - typically a vesting certificate, invoice, and proof that the goods are uniquely identified, insured and set aside for the project. Many standard contracts restrict off-site materials to items listed in advance.

How is retention calculated in an interim valuation?

Retention is calculated as a fixed percentage - commonly 3% or 5% - of the gross valuation, deducted before arriving at the net sum due. Under JCT contracts it's typically released in two halves, at practical completion and at the end of the rectification period; under NEC4, retention only applies if Option X16 is incorporated. Some contracts also include a retention-free threshold, below which no retention is deducted at all, so always check the contract particulars rather than assuming a default percentage applies.

Final Thoughts

The interim valuation process rewards consistency more than cleverness. A QS who prepares properly, walks the site methodically, and keeps a clear audit trail from measurement through to certificate will produce defensible figures month after month - and spend far less time firefighting queries than one who treats each valuation as a fresh exercise.

Bookmark the checklist above and run through it on your next valuation. Once the seven steps become habit, a process that can eat a full day shrinks to a few focused hours - leaving more time for the parts of the job that actually need judgement, like assessing variations or negotiating a contentious materials claim.

None of these seven steps is complicated in isolation. What makes interim valuations demanding is doing all of them, accurately, to a fixed monthly deadline, on multiple live projects at once - which is exactly why a repeatable process, rather than a fresh approach each time, is what separates QSs who stay on top of their valuations from those who are permanently catching up.

Want the full picture? Want the Bigger Picture on Valuations?

This guide covers the workflow - for the assessment principles behind the numbers, read our companion piece, Construction Valuation Guide: How QSs Assess Interim Payments. If cost reporting and cash flow are next on your list, see How to Prepare a CVR: Step-by-Step Guide for Quantity Surveyors and How to Build a Construction Cash Flow Forecast (With Template).