Choose a demountable building when you need short-term space that will be moved, hired or removed, such as a site shed or a temporary office. Choose a modular building when the building will stay in use for many years, must meet the NCC for a permanent class such as housing, accommodation, an office or childcare, and needs to look and perform like a site-built building. Both are made offsite; the difference is the use, the life and the approval behind it.
This page is for builders, councils, schools, mine operators and businesses across Australia weighing up the two. The problem is that the words are used loosely. Suppliers, hire companies and buyers all mean slightly different things by demountable, portable, transportable and modular, and the wrong choice shows up later as a failed approval or a building that wears out early.
How the two compare
Demountable buildings
- Usually single units on skids or simple footings.
- Built for repeated moves and short to medium use.
- Common as site sheds, crib rooms and temporary offices.
- Often hired rather than bought.
Modular buildings
- Volumetric modules joined on site into one building.
- Built for a long life on permanent footings, or engineered to relocate.
- Used for homes, accommodation, offices, classrooms and childcare.
- Built to the specification of a site-built building of the same class.
In industry use, a transportable building is one finished offsite and moved to site on a truck in one or more pieces. It is permanent or relocatable depending on its footings and approvals. Our guide to modular vs portable vs transportable buildings covers the terms in more detail.
Why modular fits long-term buildings
A structural steel module is engineered for the loads of a permanent building, plus the loads of the road trip and the crane lift. Linings, wet areas and services are inspected in the factory at hold points before they are closed up. That is what lets a modular building be approved as a home, motel, office or classroom and stay in service for decades.
What EcoPrestige supplies
EcoPrestige supplies engineered structural steel volumetric modules, built and inspected in an offsite factory. We do not hire demountables. Our modules are for buyers who want a building they keep: workforce rooms, site offices that stay for the life of a project, community buildings, and housing. For site sheds and project offices, see modular site offices.
What does not fit
If you need a crib room for a few weeks, a modular building is the wrong tool; hire a demountable. If the site has no crane access or the road cannot carry an oversize load, larger modules may not reach it. And a modular building is not a quick way around approvals: it needs the same permits as any building of its class.
The approval path
Permanent buildings need a building permit or approval like any other building. The NCC class comes from use: site offices and sheds typically Class 5 or 10a, offices Class 5, workforce accommodation Class 1b or 3, and homes Class 1a, each confirmed by your building surveyor. Who signs the structure and who issues the approval depends on the state, so always confirm with your building surveyor or certifier. Our building permit guide for modular buildings sets out the common steps.
The programme
A modular building follows a short stage of design, then approval, then the factory builds the modules while the builder prepares the site. Factory and site work run in parallel, so time on site is shorter. A hired demountable may arrive sooner, but it is built for a different job.
What to send us
- 1. What the building is for and how long it must stay.
- 2. Whether it will move again.
- 3. The site address and access.
- 4. The number of rooms, people or workstations.
- 5. Any drawings or a sketch.
Builders pricing a job can read our modular supplier guide for builders.
Demountable vs modular: questions buyers ask
What is the difference between a demountable and a modular building?
A demountable is usually a single unit built for short-term use and repeated moves. A modular building is made of volumetric modules joined on site into a long-term building that meets the NCC for its class.
Are demountable buildings and transportable buildings the same?
Not exactly. A transportable building is any building finished offsite and moved by truck. It can be a demountable or a permanent modular building, depending on its footings and approvals.
Does a modular building need a building permit?
Yes. A permanent building needs a building permit or approval like any other building of its class.
Can a modular building be relocated?
It can if it is engineered and approved to relocate. The footings, connections and services must be designed for removal.
Not sure if your project needs a demountable or a modular building?
Send the site, the use and any drawings to prebuilt@ecoprestige.com.au or download our technical brochures.
Related: portable buildings in Australia.