Specification

Fibre Reinforced Facade Encyclopedia: Design and detailing

A facade specification is the written document stating what the external wall package must achieve and, where it matters, how it must be built. In Australia it is normally drafted in a NATSPEC worksection structure, in the United Kingdom in NBS, in New Zealand in MasterSpec. Its job is to define performance precisely enough that a compliant facade can be priced, engineered, made and verified, and loosely enough that more than one competent supplier can tender for it.

At a glance

Performance and prescriptive, and when to use each

A performance clause states the result and how it will be proven: the external wall must be non-combustible when tested to AS 1530.1; the system must withstand a stated ultimate design pressure; the panel must not deflect more than span over 240 under the serviceability pressure. It leaves the supplier free to reach that result by any compliant route, which keeps the tender competitive and puts design liability with the party that has the manufacturing knowledge.

A prescriptive clause states the means: a 12 mm sprayed GRC skin, a 25 mm clear drained cavity, an undercut anchor rather than a face fixing. It is the right instrument where the outcome cannot be reduced to a measurable test, where an interface with another trade must be fixed, or where a client maintenance policy dictates a method, such as requiring individually demountable panels.

Good facade specifications are mostly performance with a small, deliberate prescriptive core. Trouble starts when the two are mixed without intent: a performance target the supplier must meet, sitting beside a prescribed method they did not choose and cannot vary. When the facade underperforms, liability is genuinely unclear.

The clauses that carry the risk

Fire is first and must name the standard, the pathway and the evidence. The routes are different things: non-combustible when tested to AS 1530.1 is a material property; a group number to AS 5637.1 is a reaction-to-fire classification for a lining; an AS 5113 result belongs to a tested system, not to a panel; a fire resistance level from AS 1530.4 belongs to an assembly and is measured in minutes. Write which applies, whether the building takes the Deemed-to-Satisfy route or a Performance Solution, against the NCC edition adopted in the relevant state (NCC 2022 in New South Wales, Queensland and South Australia until 1 May 2027; NCC 2025 in Victoria, the ACT and Western Australia), and who authors the fire engineering if it is the latter. The phrase fire rated, used alone, means nothing.

Structure needs zoned ultimate and serviceability wind pressures issued by the project engineer, deflection limits, a stated design life, and an explicit statement that the panel, its fixings and its substructure are a contractor-designed element to be certified by a registered professional engineer. A deferred design clause with no design brief attached is not a specification, it is an unpriced risk.

Weathering is verified through AS 4284: air infiltration, static and cyclic water penetration and a structural proof test at a multiple of design pressure, on a full-size mock-up. Nominate which tests apply, at what pressures, on what specimen and at whose cost, and be clear which line in a drained rainscreen is being tested, because the outer skin is not the airtight line.

Tolerance is the clause most often left out. State the panel manufacturing tolerance, the permitted setting out tolerance, the nominal joint width with its permitted variation, the accumulated tolerance allowed along a run, and the structural tolerance the facade must absorb. Without those numbers the contractor prices no adjustment and the problem surfaces on the first elevation.

Samples, mock-ups and warranties complete the set. Approve a range of control samples rather than a single one, because variation in a cast finish is real and one perfect sample becomes an unachievable benchmark. State the mock-up size, when it must stand, what it tests and when it may be demolished. Split warranties into product, installation and system, name who carries each, and keep durations inside what the evidence and the entities can support.

Requiring evidence that means something

Ask for full test reports, not summary certificates. A report identifies the sponsor, the exact product, the thickness, the date, the standard and its edition, and the conditions of test. A certificate summarises it and often loses the detail that decides whether it applies to the product being supplied.

Require reports from a body accredited for that test, NATA accredited in Australia, and require assessments and opinions to state their basis and their limits. An assessment extending a test result to a thinner panel, a different substrate or a different fixing is a legitimate document but it is not a test, and the specification should say whether it will be accepted.

Drafting errors that make a specification unbuildable

• Copying a proprietary data sheet into a performance clause. Naming a fibre type, a skin thickness and a fixing that only one manufacturer uses single-sources the package while appearing open. Test every dimensional and material requirement by asking whether two suppliers could meet it.
• Or equivalent with no criteria. State what equivalence is measured against, which properties matter and who assesses it, or the clause just moves the argument to site.
• Requiring non-combustibility and then naming a product that cannot achieve it. Polymer composites including FRP are classified by reaction-to-fire and full-scale facade tests, not by a furnace combustibility test, and no specification language changes that.
• Requiring a test on the wrong line, such as an airtightness test at the outer skin of a drained and back-ventilated rainscreen, which asks the facade to do something it is deliberately not designed to do.
• Naming a standard with no edition, or naming a superseded edition. Both cause a tender clarification at best and a non-compliant submission at worst.
• Deferred design with no design brief: no zoned wind pressures, no movement allowances, no deflection criteria, no structural tolerances. The supplier prices an assumption, and the assumption is always the cheap one.
• Silence on tolerance, followed by a visual acceptance clause requiring uniform joints. Those two clauses cannot both be satisfied.
• Warranty durations the evidence cannot support, or a system warranty demanded from a subcontractor with no product liability behind it.
• Colour and finish described by reference to a photograph or a render rather than an approved sample range with a stated variation limit.
• A specification issued without the fire strategy, the wind report and the structural tolerance schedule attached. Those three documents are what makes the rest of it buildable.

Standards and references

• NATSPEC National Building Specification worksections (Australia); NBS (UK); MasterSpec (New Zealand)
• NCC 2022 Volume One, Part C fire resisting construction, Part B1 structural provisions, and the Performance Solution provisions of Part A2
• AS 1530.1 combustibility, AS 1530.3 early fire hazard, AS 1530.4 fire resistance, AS 5637.1 group number, AS 5113 external wall fire test
• AS 4284 Testing of building facades
• AS/NZS 1170.0 and AS/NZS 1170.2 structural design actions
• ISO/IEC 17025 and NATA accreditation requirements for testing laboratories
• CWCT Standard for Systemised Building Envelopes, used as a specification reference in the UK
• AAMA 501 series test methods, where a US specification framework applies

Related terms

• NATSPEC
• NBS
• MasterSpec
• Performance solution
• Deemed to satisfy
• Mock-up
• Tolerances
• Accredited testing body
• Wind load

Questions specifiers ask

Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.