Class 5 And 6 Buildings Are Assessed Against Section J
When people ask about 6 star energy rating insulation in modular buildings, they are usually picturing a house. A transportable office, classroom or retail unit is assessed down a different path, and knowing which path applies changes the specification you should be asking for. A star rating is a measure of a building shell as a whole, its roof, walls, windows and floor, not the batts sitting inside one wall.
Thermal performance belongs to the envelope as a system, which is why it cannot simply be read off an insulation product. Most of what we hire and sell is not residential at all: portable sales offices, site offices, classrooms and training rooms, medical and first aid stations, and retail and pop-up shops.
Under the building classifications set by the Australian Building Codes Board, an office is a Class 5 building and a retail space is Class 6, and those must meet the energy efficiency Performance Requirements of NCC Volume One Section J. For a site office, Section J is the honest thing to be asking about. We work the entire eastern seaboard, from Cairns in the north to the south coast of Victoria, out of manufacturing facilities in Brisbane and Melbourne, so the climate question further down is live on almost every job we quote.
Key Features Of A Modular Thermal Envelope
Insulation is only one part of the thermal envelope. Ceiling, walls, floor, glazing and the junctions between them all work together, which is why a high performing wall batt can be cancelled out by cheap glazing or an uninsulated floor. The envelope performs as a system, never element by element.
These are the parts of a modular building that decide its thermal result.
- Roof and ceiling: Reflective foil sarking or an insulation blanket under the roof sheeting works together with ceiling batts, and in a hot climate the roof carries much of the heat load.
- External walls: Bulk batts in the cavity are the common approach, and our wall system pairs high strength steel frameworks with insulated composite panels behind Colorbond steel cladding.
- Floor: A transportable sits on stumps rather than a slab, so underfloor insulation carries far more weight than it does in a site built office.
- Glazing: Double glazing, low emissivity coatings and thermally broken frames control heat flow and solar heat gain, while eaves and awnings do part of the same job for less money.
- Thermal breaks: Steel conducts heat straight through the frame and the chassis, so the break strips at those junctions decide how much of a batt’s nominal R value the assembly actually delivers.
That last point is the one worth pressing any supplier on, because it is the defining thermal characteristic of a transportable building. A steel framed unit loses a real share of its nominal wall R value to thermal bridging, since heat travels through the framing members rather than through the insulation. Ask for the total R-value of the finished assembly with thermal bridging accounted for, not the number printed on the batt packaging.
Factory manufacture helps in a way that is easy to overlook. Every SPM building is constructed in a specialised manufacturing facility in Brisbane or Melbourne, where insulation is fitted to a consistent standard without the compression, gaps and rushed penetrations that appear when batts go in outdoors in the weather. Units come out of that controlled environment ready for installation on site within days of delivery, and our buildings carry insulation up to 6 star energy ratings, along with energy efficient LED lighting and sustainable, locally sourced materials.
Queensland And Victoria Need Different Specifications
Any conversation about 6 star energy rating insulation in modular buildings has to begin with where the building is going, because an identical wall build up performs very differently in Brisbane than it does in Ballarat. A building headed for a hot, humid northern site is not solving the same problem as one headed for a cool Victorian one, and the two specifications should not look alike. The conditions at the site, not the state on the invoice, are what drive the answer.
Queensland Sites: Heat, Humidity And Exposure
In Queensland that pushes spend toward the roof, toward shading and toward lighter roof colours, and it makes moisture a live issue, because sealing an insulated box tightly in humid conditions puts vapour management into the wall build up alongside the R value. Site exposure changes the answer again: a unit on an open school oval or an exposed construction site has no shade trees and no neighbouring buildings, so orientation and eaves do work that no amount of extra batt can replace. Wind exposure runs on the same site logic, which we cover in our Queensland wind ratings guide.
Victorian Sites: Glazing, Airtightness And Underfloor
In Victoria the money moves to glazing, airtightness and the underfloor, because a building raised on stumps loses heat downward all winter. Getting the modular building foundations right is part of the thermal answer there, not just the structural one. We manufacture in Melbourne as well as Brisbane, and there is more on cool climate specification in our Melbourne modular offices guide.
Because the specification follows the site, the fastest way to get a real answer is to give us the address and what the building is for. Contact Brisbane Office on (07) 3260 2929 or Contact Melbourne Office on (03) 8763 3995, and either office will give you a free quote.
Certification, Hire Terms And Relocation
The certification that comes with the building is not a house star certificate. What you receive from us is Engineer’s Certificates to ensure compliance with Australian Standards, and our steel framed modular buildings carry an Engineers’ Structural Certification for class 5 or 6 buildings. Classification decides which requirements apply, so it is settled first, not last.
The order runs like this. The building’s classification and the conditions at the site are confirmed first. The design is then settled through detailed consultation and collaborative design and drafting by our in house team, with high quality 3D visualisations for your approval, which is where glazing and insulation choices are locked in. Compliance with the Building Code of Australia, including its section J energy efficiency ratings, is built into that design. Then the building is manufactured, delivered, stumped and tied down, and connections to existing services for power, water and sewage are arranged.
The statutory approvals sit outside that sequence. In Queensland, a building development approval from a private building certifier or local government is required under the Building Act 1975 before a transportable building is sited. In Victoria, the Building Act 1993 requires a building permit from a registered building surveyor before building work, and where the permit requires it the building must not be occupied until an occupancy permit is issued under Part 5 of that Act.
Relocation is part of the service rather than something you are left to solve on your own. We deliver the building on site and on time, and when it is no longer required you call with the required notice and we recover or relocate it, no fuss.
Hire, Purchase And What It Costs
We don’t publish a price for an insulated modular building, because the specification shifts with classification, site conditions, size and term. Standard sizes range from 40 sq. metres to 300 sq. metres, and there is no limit to the building’s size or scope. On hire, installation, maintenance and removal are hassle free, and rental payments are tax deductible. SPM Group was established in 1996, holds Builder’s Registration QBCC 77786 in Queensland and CB-L45357 in Victoria, and currently has in excess of 150 land sales suites throughout Australia. Our portable modular offices in QLD page sets out the range, or call 1300 888 009, or Contact Us at the Brisbane head office, 8 Orsova Street, Pinkenba, or the Melbourne office at 1/24 Columbia Ct, Dandenong South.
Six Star Ratings On A Class 5 Site Office
A Class 5 office and a Class 6 retail unit are measured against the energy efficiency Performance Requirements of Section J of NCC Volume One, which is the benchmark that applies to a site office rather than a residential star rating. Our buildings feature insulation up to 6 star energy ratings, and our steel framed modular buildings comply with the Building Code of Australia, including its PWD toilet and access ramp requirements and its structural frame and bracing requirements.
R Values Before The Design Is Settled
We won’t quote an R value before we know the classification, the site and the glazing, because a number quoted in isolation is close to meaningless. The figure that matters is the total R-value of the completed assembly once thermal bridging through the steel is accounted for, and that can only be worked out after the build up is fixed.