MBA contracts: Master Builders residential contract suite explained

TL;DR

Master Builders associations publish state-specific residential contract suites. The BC4 is the dominant lump-sum form for new homes and major renovations in NSW and ACT; equivalent lump-sum contracts exist in every other state under different codes. Cost Plus contracts (residential) are available where scope cannot be fixed at the start. The ABIC suite (jointly published by Master Builders Australia and the Australian Institute of Architects) covers architect-administered work: SW-2018 for simpler jobs, MW-2018 for major works. MBA contracts are considered builder-leaning but more balanced in some respects than HIA equivalents. Read payment, variations, and EOT clauses carefully before signing.

What the MBA contract suite is

Master Builders Australia (MBA) is the national industry association for the building and construction sector, operating through state and territory member associations: Master Builders NSW, Master Builders Victoria (MBV), Master Builders Queensland (MBQ), Master Builders WA, Master Builders SA, and Master Builders ACT.

Each state association publishes its own contract suite, tailored to local legislation. There is no single national “MBA contract” that works across every jurisdiction. The suite covers:

Residential lump sum (fixed-price new homes and major renovations)
Residential cost plus (fixed fee or percentage margin on actuals)
Renovation and minor works (smaller renovation and additions work)
Subcontracts (between the head contractor and subbies)
ABIC contracts (architect-administered; joint publication with the Australian Institute of Architects)

MBA contracts are available to members via eContracts (digital) and as hard-copy packs from each state association store. Non-members can purchase hard copies at a higher rate.

The BC4 (NSW/ACT residential lump sum)

In NSW and ACT, the BC4 is the standard residential lump sum contract for:

New houses
Major residential renovations
Small multi-unit developments (without architect supervision)

The BC4 is a fixed-price head contract between the builder and the owner. The builder agrees to complete the work for a set price; cost overruns are the builder’s risk unless authorised as variations.

Key clauses in the BC4:

Clause	What to know
Contract sum	Fixed lump sum. PC sums and provisional sums may be included and reconciled separately.
Progress payments	Tied to construction milestones (e.g. foundation, frame, lock-up, fixing, completion). Retention typically 5% withheld until practical completion.
Variations	Must be requested and approved in writing before work commences. Both parties must agree in writing; verbal variations create risk.
Extension of Time	Builders must submit EOT claims within 5 business days of the delay event or risk losing the right. Grounds include rain, latent conditions, and owner-caused delays.
Practical completion	Triggers retention release and starts the defects liability period. Builder issues a formal notice; owner must inspect and respond within the contract period.
Termination	Builder typically has 25 days to remedy a default before the owner can terminate; the asymmetry gives builders more time than clients get under some HIA forms.
Dispute resolution	Mandatory pre-tribunal meeting required before formal proceedings.

The BC4 is considered builder-leaning in structure: variation clauses, asymmetric default periods, and payment milestone timing generally favour the contractor over the owner. This is common to all industry-association contracts (HIA included); the Fair Trading standard contract is more balanced but less commonly used in the market (verified 2026-05-09, Master Builders NSW store).

State-by-state: equivalent lump sum contracts

The BC4 is NSW/ACT specific. Other states publish equivalent contracts under different codes:

State	Association	Residential lump sum contract	Notes
NSW	Master Builders NSW	BC4 Residential Building	Also Minor Works contract for jobs under $20k HBCF threshold
ACT	Master Builders ACT	ACT Lump Sum Residential Building Contract	Plus BC4 (NSW) also available for ACT members
VIC	Master Builders Victoria (MBV)	Domestic lump sum (DECON-series)	HIC-6 Home Improvement Contract for renovations/extensions
QLD	Master Builders Queensland	Residential New Home Contract (lump sum), Residential Renovation Contract ($20k+), Basic Works Contract (up to $80k), Minor Works Level 1 (under $20k)	Multiple threshold-tiered forms
WA	Master Builders WA	Residential lump sum contract	Available in hard copy and eDocs
SA	Master Builders SA	Domestic Building Contract for New Homes, Domestic Building Contract for Alterations/Additions/Renovations	Available via Master Suite platform
TAS / NT	State MBA affiliates	Jurisdiction-specific forms	Contact local association for current suite

State contract forms incorporate local legislative requirements automatically: cooling-off periods (QLD mandates five days), home warranty insurance thresholds, SoP Act compliance, and state-specific schedule formats.

Cost Plus residential contract

The MBA Cost Plus (Residential) is a head contract for work where the full scope cannot be fixed at the time of signing. The owner pays all actual costs (labour, materials, subcontractors) plus an agreed margin: either a fixed fee or a percentage on actuals.

Who bears cost risk: The owner. Under cost plus, cost overruns flow through to the client. The builder’s exposure is limited to the agreed fee or margin.

When to use it:

Custom builds where design is still evolving
Major renovations where unknown conditions (asbestos, structural surprises, hidden services) make a fixed price unrealistic
Projects where the client and builder want full cost transparency

Key contractual points:

The margin percentage or fixed fee must be explicitly agreed in the contract schedule
The owner is entitled to copies of all invoices and subcontractor quotes
Variations under cost plus still require written approval (scope additions change the cost baseline)
Regular cost reporting to the owner is standard practice and should be built into the contract schedule

Industry guidance suggests builder margins on residential cost plus typically run 10% to 20% depending on project complexity (verified 2026-05-09, Master Builders NSW Cost Plus Residential store page). Legal advice before signing any cost plus contract is recommended given the open-ended cost exposure.

Renovation and minor works contracts

For smaller residential work, most state MBA associations publish tiered contracts:

Work type	Typical form	Threshold guidance
Small renovations, additions	Minor Works / Small Renovations and Additions contract	Often under $20,000 where home warranty insurance doesn’t apply
Medium renovation	Standard renovation contract	Varies by state
Home improvement (VIC)	HIC-6 Home Improvement Contract	Renovations and extensions without architect supervision
Queensland Basic Works	Basic Works Contract	Up to $80,000 (inc. GST), detached dwellings

Check the current threshold in your state before choosing the form. In NSW, the HBCF trigger (home warranty insurance mandatory above $20,000) is the common dividing line between minor works and full residential contracts (verified 2026-05-09, icare HBCF).

ABIC contracts (architect-administered)

The Australian Building Industry Contracts (ABIC) are a separate suite, jointly published by Master Builders Australia and the Australian Institute of Architects (verified 2026-05-09, ABIC Acumen page). They are designed for projects where an architect administers the contract.

Two main ABIC forms for residential and commercial work:

Form	Full name	Use when
SW-2018	Simple Works 2018	Simpler building projects, shorter duration, less complex scope. Typical for residential work where an architect is engaged.
MW-2018	Major Works 2018	More comprehensive, larger or more complex projects.

Both have commercial and domestic (housing) variants. State-specific housing variants exist: for example, ABIC SW-2018 H (housing) and ABIC MW-2018 H for residential use in states that require them (e.g. Victoria and South Australia).

ABIC contracts are notably more complex than the BC4 or HIA residential forms. They are contractor-oriented and written on the assumption that an architect is acting as the contract superintendent. Do not use them on jobs without an architect administering the contract.

Available from the Australian Institute of Architects Acumen platform and state Master Builders association stores (verified 2026-05-09, MBV ABIC store).

MBA vs HIA: key differences

Feature	MBA (e.g. BC4)	HIA (e.g. HIA New Home contract)
Builder/owner balance	Builder-leaning; somewhat more balanced than HIA	Builder-leaning
Default notice to builder	25 days to remedy before owner can act	Typically shorter
Dispute resolution	Mandatory pre-tribunal meeting required	Parties may proceed directly to tribunal
Payment milestones	Milestone-based; slightly more defined	Stage-based; larger upfront deposits common
EOT claim window	5 business days (NSW BC4)	Varies by contract edition
Architect-administered	ABIC suite (joint with AIA)	No equivalent architect-administered form
State coverage	Jurisdiction-specific editions per state association	National forms with state-specific schedules
Availability	Members: eContracts (digital); non-members: hard copy	Members: HIA portal; non-members: HIA store

Both MBA and HIA contracts are accepted by lenders for construction finance. The NSW Fair Trading standard contract is more balanced toward homeowners but is less commonly used in the industry.

Security of Payment coverage

State SoP Acts apply regardless of which contract form you use. MBA contract payment clauses must comply. The Acts give builders and subbies a fast adjudication pathway for unpaid progress claims. Don’t use a contract that tries to contract out of SoP rights.

State	Act
NSW	Building and Construction Industry Security of Payment Act 1999
VIC	Building and Construction Industry Security of Payment Act 2002
QLD	Building Industry Fairness (Security of Payment) Act 2017
WA	Building and Construction Industry (Security of Payment) Act 2021
SA	Building and Construction Industry Security of Payment Act 2009
TAS	Building and Construction Industry Security of Payment Act 2009
NT	Construction Contracts (Security of Payments) Act 2004
ACT	Building and Construction Industry (Security of Payment) Act 2009

What can go wrong

Wrong form for the jurisdiction. Using a NSW BC4 in Victoria without checking local requirements creates gaps in legislative compliance. Always use the state-specific edition.
Signing before home warranty insurance is in place. In most states, builder must hold home warranty insurance before signing a residential contract above the threshold. Signing without it is a breach of the state building Act.
EOT claim missed. The BC4 5-business-day window for EOT claims is strict. One wet week not notified in writing = no time extension = potential liquidated damages exposure.
Cost plus without invoice discipline. Owners often don’t understand their cost exposure until midway through. Builders using cost plus without clear cost reporting end up in disputes regardless of what the contract says.
ABIC without an architect. ABIC contracts assume architect administration. Used on a project without one, the superintendent role is vacant and dispute triggers misfire.
PC sums and provisional sums unreconciled. The reconciliation method (what happens when actual cost differs from the allowance) must be explicit in the contract schedule. “Allow $X” with no reconciliation method is the single biggest variation flashpoint on residential jobs.

References

Master Builders NSW: BC4 Residential Building contract (verified 2026-05-09)
Master Builders NSW: Cost Plus Residential contract (verified 2026-05-09)
Master Builders NSW: eContracts (verified 2026-05-09)
Master Builders ACT: Contracts (verified 2026-05-09)
Master Builders Victoria: HIC-6 Home Improvement Contract (verified 2026-05-09)
Master Builders Victoria: DCP-2 Cost Plus Contract (verified 2026-05-09)
Master Builders Australia: Master Builders Contracts (verified 2026-05-09)
ABIC contracts: Acumen (Australian Institute of Architects) (verified 2026-05-09)
Master Builders SA: Construction Contracts (verified 2026-05-09)
icare HBCF (NSW home warranty insurance) (verified 2026-05-09)