NZS 3910 §10.3 extensions of time — the §10.4 20-day notification clock on NZ residential (2026)

Steve Parker
May 30
7 min read

Updated: Jul 9

§10.3 of NZS 3910 governs extensions of time; §10.4 sets the 20-working-day notification clock. Miss the clock and the EOT claim becomes contestable. The cost of a missed notification on a six-week weather delay can run $25-60k in liquidated damages exposure.

By Steve Parker · Trueworks · NZ construction estimation · 6 min

§10.3 governs the extension-of-time determination; §10.4 sets the 20-working-day notification window. The clock starts the day the contractor knows or should have known the delay event will affect the programme. Most contractors don't track it. Most disputed EOT claims die on the §10.4 timing test, not on the §10.3 merits.

By Steve Parker · Trueworks · NZ construction estimation · 6 min

What you'll learn in this post

What §10.3 and §10.4 actually say
How the 20-day clock fails on NZ residential builds
The 5-item check before an EOT claim leaves the office

Quick answer: NZS 3910:2023 §10.3 is the clause that gives the Engineer authority to determine extensions of time. §10.4 sets the procedural notification: the contractor must notify the Engineer within 20 working days of the event or circumstance giving rise to the delay. Miss the 20-day window and the EOT claim becomes contestable on procedural grounds, regardless of merit. The liquidated-damages exposure on a missed-EOT six-week weather delay can run $25-60k on a residential head contract.

§10.3 and §10.4 of NZS 3910:2023 work as a pair. §10.3 names the events that can ground an EOT — weather, variations, suspension, latent conditions, principal-caused delays. §10.4 sets the procedure: written notification within 20 working days, with substantiation following. The clauses are short. The compliance failure is enormous.

This post is the working-builder / working-CA read of the two clauses — what they actually say, where the 20-day clock starts, and the five items that make an EOT claim defensible.

What §10.3 and §10.4 actually say

§10.3 — entitlement to extension of time

§10.3 of NZS 3910:2023 gives the Engineer authority to grant an EOT where the delay arises from:

A variation under §14
A suspension under §6.7
A latent or differing site condition
Inclement weather beyond what was reasonably foreseeable
A breach or act of prevention by the Principal
An event for which the contract specifically allows an EOT

The Engineer's determination is for the delay caused by the event on the critical path, not for delays caused by other factors running in parallel.

§10.4 — notification of delay

§10.4 is the procedural gate. The contractor must:

Notify the Engineer in writing of the event or circumstance giving rise to the delay
Notify within 20 working days of becoming aware of the event
Provide substantiation within a further period (often 20 working days, depending on the contract particulars)

The clock starts when the contractor knew, or ought reasonably to have known, that the event would affect the critical path. Not when the substantiation is complete. Not when the programme has been re-baselined. When the contractor first knew.

§10.3.4 — the impartial determination

The Engineer determines the EOT under §10.3.4 based on the contractor's substantiation, the programme analysis, and the actual critical-path effect. The determination must be impartial — §6.1.1 imposes that obligation on the Engineer regardless of who pays them.

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How the 20-day clock fails on NZ residential builds

1. The "we're tracking it informally" failure. The contractor and Engineer are talking weekly on site. Everyone knows the cladding has been delayed by a 10-day weather window. Nobody has put a §10.4 notification in writing. Three months later, when the contractor seeks the EOT formally, the §10.4 procedural defence kicks in. The Principal contests on grounds of late notification. The Engineer's determination is overturned in adjudication. Programme exposure: liquidated damages of $250-800/day on a residential head contract, running from the original completion date until practical completion.

2. The "wrong start date" failure. The contractor notifies at 18 working days, but the Engineer assesses the contractor knew of the delay 25 working days earlier — say, when the cladding supplier first emailed about the shipment delay. The §10.4 clock started on that date, not when the cladding failed to land on site. Defensibility lost.

3. The "bundled notification" failure. The contractor notifies a single delay event that's actually three concurrent events — a weather delay, a variation, and a supplier failure. Each has a different §10.4 clock and a different §10.3 entitlement. The bundled notification gets unbundled in adjudication, and the dates fail individually.

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The reference table

| §10.3 / §10.4 step | Timing | Who does it | What goes wrong | |---|---|---|---| | Event occurs or first becomes apparent | Day 0 | Site reality | The contractor doesn't recognise the event will affect the critical path | | Contractor's §10.4 written notification | Within 20 working days | Contractor | Notification is verbal only, or sent late | | Substantiation submitted | Per contract particulars (often a further 20 days) | Contractor | Programme analysis missing or unconvincing | | Engineer's §10.3 determination | Per contract (typically 20-30 working days from substantiation) | Engineer | Determination bundles cost and time, conflating §10.3 and §14.4 | | Notification of determination | In writing, with reasoning | Engineer | No written reasoning — vulnerable to §13 dispute | | §13 dispute window opens | On notification | Either party | Determination overturned for procedural defect under §10.4 |

Worked example

A residential build, $2.1M head contract under NZS 3910:2023. In month 7, the cladding supplier emails the contractor to confirm a 14-working-day delay on a key product line. The contractor knows on day 1 that this will affect the critical path — cladding is the second-to-last trade before lockup.

The compliant version: the contractor sends a §10.4 written notification to the Engineer within 5 working days, naming the event (supplier delay), the date first known, and a preliminary critical-path assessment. Substantiation follows in 18 working days with a re-baselined programme. The Engineer determines a 12-working-day EOT under §10.3 — the supplier delay isn't a §10.3 ground per se, but the variation that flowed from substituting an alternative cladding is. The determination is written, dated, and noted on the file.

The non-compliant version: the contractor talks about the delay informally on site for two months, then files a 35-working-day EOT claim. The §10.4 notification is 47 working days late on the original event. The Engineer's determination grants 4 days only — the procedurally compliant portion of the claim. The Principal then claims 28 days of liquidated damages at $400/day — $11,200. The contractor disputes under §13. Eight months of legal exposure on both sides.

What to check before the EOT claim leaves the office

Five items, every time:

The §10.4 written notification is on the file, dated within 20 working days of the event
The "day 0" is named and defensible — what date did the contractor first know the event would affect the critical path
The notification identifies the §10.3 ground — variation, weather, suspension, latent condition, Principal act
The substantiation includes a critical-path programme analysis — not just a list of delays
Cost and time are tracked on separate determinations — §10.3 for time, §14.4 for cost

If those five items are present, the EOT claim is defensible on procedure. If they're not, the next person to read the file is the adjudicator under the Construction Contracts Act 2002 — and the procedural defect under §10.4 is the easiest argument in the room.

FAQ — NZS 3910 §10.3 and §10.4 on NZ residential

Q1: Does §10.4 apply if the delay event is the Principal's fault? Yes. §10.4 is the procedural gate regardless of who caused the delay. A Principal-caused delay still requires §10.4 notification within 20 working days. Procedural compliance is independent of merit.

Q2: What if the contractor can't tell on day 1 whether the event will affect the critical path? The §10.4 clock starts when the contractor knew or ought reasonably to have known. A reasonable contractor with current critical-path knowledge should know within a few days of most events. Erring on the side of early notification is the lower-risk approach — there is no penalty for notifying an event that turns out to have no critical-path effect.

Q3: Can multiple concurrent delays be notified in a single §10.4 notification? Best practice is separate notifications per event, with separate substantiation. A single notification covering three concurrent events is procedurally vulnerable because each event has a different §10.4 clock.

Q4: Who pays liquidated damages while a §10.3 EOT claim is being determined? The contract sets the answer. Under most NZS 3910 head contracts, LDs accrue from the contractual completion date until the Engineer's §10.3 determination revises that date. Until determined, the contractor is exposed.

Q5: What's the relationship between §10.3 and §14 variations? A variation under §14 may include a time effect, but the §10.3 determination is separate. The §14.4 valuation handles the cost; the §10.3 determination handles the time. Two determinations, two paper trails. Bundling them is the most common conflation in residential EOT disputes.

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