A tender that only names R-values will come back with prices you cannot compare, because every bidder will have assumed something different about fire, acoustics, thickness and who does the take off. Naming the properties properly costs an hour at tender stage and saves the argument at delivery. This is the checklist we wish every insulation package arrived with.
In short
- Specify element by element, not one number for the building.
- Name every property, not just R-value: fire, acoustic, vapour, duty, thickness limit.
- Say who calculates the Total R-value and who owns the thermal bridging allowance.
- State the cavity depth, because it caps what can physically fit.
- Say what documentation you want and when, or you will get it at handover.
This is written from the supply side, which is a useful vantage point: we see what happens when a package is ambiguous, and it is always the same handful of things.
Why an R-value alone is not a specification
An R-value tells a supplier one thing about the product. It says nothing about four others that the job may depend on.
| If the tender only says | Bidders will differ on |
|---|---|
| "R2.5 wall insulation" | Glasswool or polyester, standard or high density, and whether it fits the stud |
| "Acoustic insulation to separating walls" | Which density, and therefore which tested system |
| "Fire rated insulation" | Non-combustible, a Group number, an index set, or a system FRL |
| "Sarking to walls" | Barrier or breather, which vapour class, reflective or not |
| "Roof insulation" | Blanket under the sheet or batts at ceiling level, with or without spacers |
Each of those differences is a real price difference. A tender that leaves them open is not comparing like with like, and the cheapest number usually belongs to whoever assumed the least.
The checklist
If your insulation package answers these, it will price cleanly.
- Building class and climate zone. They set which code volume and which provisions apply.
- Element by element targets, with who is calculating Total R-value.
- Framing type and depth for every element.
- Fire requirements per element, named by test and number.
- Acoustic requirements per element, named by tested system.
- Vapour and membrane requirements, including class and duty.
- Quantities by element and by wall type, not one total.
- Documentation required, and when.
- Substitution rule.
- Program and delivery constraints, especially the roof package.
Element by element
NCC 2022 sets thermal requirements element by element, so a specification should too. One number for the building is not translatable into an order.
For each element, the package should say what it is, what it has to achieve, and what it is made of:
| Element | What to state |
|---|---|
| Roof or ceiling | Whether insulation is at ceiling level or under the sheeting, the target, and whether spacers and mesh are in scope |
| External wall | Target, stud depth and material, cladding type, and the membrane |
| Separating wall | The tested fire and acoustic system, not an R-value |
| Internal wall | Whether it is acoustic or thermal, and which system if acoustic |
| Floor | Suspended or slab, and the fixing method if suspended |
| Junctions | Thermal break requirements where metal framing is involved |
Our guide to what R-value goes where covers why the answer differs so much between elements.
Every property, named
This is the section that saves the most grief. For each element, state every property the product has to satisfy, with the test it comes from.
- Thermal. Material R-value, declared to AS/NZS 4859.1, and the Total R-value target calculated to AS/NZS 4859.2. Say which one you are naming.
- Fire. Non-combustible, a Group number to AS 5637.1, an AS 1530.3 index set, or a system FRL. These are not interchangeable, so name the one you mean.
- Acoustic. The tested system, including lining and framing, rather than a density on its own.
- Bushfire. The BAL from the bushfire assessment, and the detail it applies to.
- Vapour. The membrane class under AS/NZS 4200.1:2017 and whether a water barrier to AS/NZS 4201.4 is required.
- Duty. The membrane duty rating, which decides whether it survives being exposed during construction.
Our guide to fire performance sets out which of those belong to the product and which to the system, and it is the distinction that causes the most rework.
State the depth available
This is the most commonly omitted item and the most physically binding one.
A wall cavity is the stud depth. In Australian housing that is usually 90 mm or 70 mm, and no product will exceed what fits. A 90 mm cavity is roughly an R1.5 to R2.7 proposition depending on the product chosen. Specify R4 into a 90 mm stud and either the specification changes or the wall does.
The same applies at the roof. A blanket only delivers its rated R-value at full recovered thickness, so if the build up does not include a spacer to keep it off the purlin, the specified number is not what the roof gets. If spacers are intended, name them, because they are an item with a height, a wind region version and a purlin requirement.
Documentation, and when you want it
Say what you want and at what stage, or it arrives at handover when the certifier asks and everyone is busy.
The usual set:
- Product data sheet with the R-value and the test standard it was measured to
- Evidence of compliance with AS/NZS 4859.1
- Fire classification where the specification calls for one, including Group number or BAL suitability
- Acoustic test reports where the product forms part of a rated system
- The manufacturer's installation instructions
Ask for it at order confirmation rather than at practical completion. A supplier who cannot produce it then will not be able to produce it later either, and that is exactly what you want to find out before delivery.
Write the substitution rule in advance
Substitutions are normal. Ambiguity about them is what turns them into disputes.
A clear rule looks like this: alternatives will be considered where the request shows, property by property, that the alternative meets everything the specification named, with the documentation attached and the effect on the Total R-value calculation stated.
Writing that into the tender does two things. It tells honest bidders exactly what to submit, and it removes the argument where someone has priced a cheaper product on R-value alone and wants to argue about it later.
Program and delivery
The insulation scope has one item with a hard deadline and several that are flexible, and a tender that says so gets better prices.
| Stage | What has to be settled |
|---|---|
| Design development | Total R-value targets, build ups drawn, fire and acoustic requirements identified |
| Tender | Schedule of products with R-values and classifications, quantities from the drawings |
| Before the roof is sheeted | Roof package on site: blanket, mesh, spacers, thermal break. This one does not move |
| Lock up | Wall and acoustic insulation delivered and installed |
| Handover | Product data and installation records to the certifier |
Two practical notes worth putting in the package. Insulation is light and very bulky, so state the storage available and whether staged delivery is expected. And say who is responsible for keeping it dry, because wet glasswool is replaced rather than dried and somebody is going to pay for it.
We supply it, and we install batts, wall wrap and sarking
AWBM prices commercial insulation packages across Victoria and New South Wales, and we install batts, wall wrap and sarking. Roof blanket, mesh and spacers we supply for your roofing crew to lay. Send the specification and the drawings and you will get a schedule against your elements, the documentation for every product, and a delivery plan staged to your program.
Or browse commercial insulation, acoustic insulation and building membrane.
Frequently asked questions
What should an insulation specification include?
Building class and climate zone, element by element targets with who calculates Total R-value, framing type and depth, fire and acoustic requirements named by test and system, membrane class and duty, quantities by element, the documentation required, a substitution rule and the program constraints.
Why is naming an R-value not enough?
Because it says nothing about material, density, fire classification, vapour class or whether the product fits the cavity. Bidders fill those gaps differently, so the prices are not comparable.
Who calculates the Total R-value?
Say so in the specification. It is usually the ESD or services consultant, calculated to AS/NZS 4859.2, and the supplier works to the product R-value that calculation assumed.
Should I specify a product or a performance?
Either works if it is complete. Naming a product is simplest where a tested fire or acoustic system is involved. Naming performance works for thermal, provided every other property is stated as well.
How do I stop cheap substitutions?
Write the substitution rule into the tender: alternatives considered only where the request shows property by property compliance with documentation attached and the effect on the Total R-value stated.
What documentation should I ask for?
Product data sheets with the R-value and test standard, evidence of compliance with AS/NZS 4859.1, fire classifications where required, acoustic test reports for rated systems, and the manufacturer's installation instructions.
When should the roof insulation be priced and ordered?
Early. Blanket, mesh, spacers and thermal break all sit under the roof sheeting, so the whole package has to be on site before the roof is closed and that date does not move.
Do I need to state the stud depth?
Yes. The cavity depth caps the R-value that physically fits, so specifying a target the wall cannot accommodate leads to either a variation or a compressed batt that does not deliver the number.
Can AWBM price against a tender package?
Yes. Send the specification and drawings and we will return a schedule against your elements with the documentation for each product, and tell you plainly where something we carry does not meet a named requirement.
Sources
- NCC 2022 Volume One, Part J4 Building fabric
- NCC 2022 Housing Provisions, Part 13.2 Building fabric, and clause 13.2.3(7) thermal break
- AS/NZS 4859.1 and AS/NZS 4859.2, Thermal insulation materials for buildings
- AS 5637.1, Determination of fire hazard properties
- AS 1530.3, and AS 3959-2018 for bushfire attack levels
- AS/NZS 4200.1:2017 and AS/NZS 4201.4, Pliable building membranes and underlays
General information for preparing a package, not a substitute for the project's own specification. Compliance pathways, fire engineering and acoustic requirements are project specific, so confirm the requirements with the designer, the relevant consultants and the certifier.