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Interior finishes in modular homes
| Default plasterboard finish (QLD) | Level 4[1] |
|---|---|
| Visible crack in first 12 months (QLD) | A defect, judged from 1.5 m in diffused light[1] |
| Wall flatness limit (QLD) | 4 mm within any 2 m length[1] |
| Usual cause of lining cracks | Movement in the building or frame, not the board[2] |
| Exposed CLT surface | Appearance grade by arrangement with the manufacturer[3] |
| *Queensland figures are given as one published example; other states publish their own standards and tolerances. | |
The interior walls of a factory-built home are judged by the same finish standards as any other new house: Queensland's published guide, for example, takes Level 4 plasterboard as the default and treats a crack visible from 1.5 m within the first 12 months as a defect.[1] Plasterboard itself barely moves with heat or humidity, so cracks usually point to movement in the frame or building — which in a modular home means the joins between modules and the stresses of transport and lifting.[2]
A common assumption is that a home built in a factory will look and feel different inside. In most cases the more accurate statement is that the materials are familiar and the conditions are different. This page sets out what is known about the difference, what is only claimed, and how a finish is judged once you are living with it.
Same materials, different conditions §
None of the sources compiled here identifies an interior wall lining that is used only in factory-built homes. Walls and ceilings in modular and prefab homes are finished with the same kinds of products found in site-built houses, and the same finish and tolerance standards are applied to them.[1]
What changes is where the work happens. Linings in a volumetric module are fixed, jointed and often painted inside a factory, before the module travels by road and is lifted by crane. That reverses the usual order: in a site-built house the frame has settled and the roof is on before the plasterer arrives; in a modular house the finished lining goes on the journey.
Whether factory conditions produce a better or worse finish than site conditions is a common marketing claim in both directions. No independent Australian comparison is covered here.
Where a modular home moves differently §
Plasterboard is dimensionally stable and changes little with temperature or humidity. A plasterboard manufacturer's guidance is that cracks therefore usually reflect movement somewhere else — in the frame, the footings or the building as a whole — and that a small amount of superficial cracking is normal because all buildings move.[2]
The same guidance lists the places cracks tend to start. Two of them describe a modular home closely: plasterboard fixed rigidly to two different substrates without a control joint, and ceiling junctions between a large room and a corridor.[2] A module junction is exactly a line where two separately built frames meet, and in an open-plan modular layout it often runs through the middle of the largest room. How the lining is detailed across that line — a deliberate control joint, a cover strip, a cornice, or a plastered joint made on site after installation — decides whether movement shows up as a neat line or a crack.
Transport and craneage add a second source of movement before anyone lives in the house. Who carries responsibility for damage at that stage is covered in handover on a factory-built home and delivery, transport and craneage.
How finish quality is judged §
Each state applies its own published standards and tolerances. Queensland's guide is used here as one worked example; it collates requirements from the NCC, Australian Standards and manufacturers, and those sources prevail if they conflict with it.[1]
Level of finish describes how much jointing and sanding plasterboard receives. In Queensland, Level 4 is the default unless the contract says otherwise, and Level 3 is acceptable in places that are not readily visible, such as inside cupboards.[1]
Finish is judged from a normal viewing position: 1.5 m or more from the surface, in diffused rather than glancing light.[1] A flaw that only appears when a torch is held along the wall is generally not a defect under this test.
| Item (Queensland guide) | When it is a defect | Source |
|---|---|---|
| Cracks in walls, ceilings, bulkheads, joints | Visible from normal viewing position within 12 months | QBCC[1] |
| Cracks after 12 months | Category 3 or 4 only; categories 0 to 2 (up to about 5 mm) are not defects | QBCC[1] |
| Wall flatness | Bowing more than 4 mm within any 2 m length | QBCC[1] |
| Cornice alignment | More than 4 mm off a straight line over up to 2 m | QBCC[1] |
| Nail popping, visible jointing | Within 12 months | QBCC[1] |
The 12-month line is the practical point for an owner. Because the test changes after the first year, noting and photographing any cracking — at module junctions or anywhere else — within that year keeps it inside the period in which visible cracking counts as a defect in Queensland.[1] The Queensland guide has no section specific to prefabricated or modular buildings.[1]
Exposed timber walls §
The one finish that does feel different is exposed engineered timber. Cross-laminated timber (CLT) is made as large wall, floor and roof panels suited to factory manufacture, and it can be left visible inside instead of being lined.[3] Timber framing and engineered wood more generally are covered in timber framing and engineered wood in prefab homes.
The national timber industry's design guide makes several points relevant to anyone choosing an exposed finish:[3]
- A visible surface has to be ordered as an appearance grade, at extra cost and by arrangement with the manufacturer; appearance specifications vary between manufacturers.
- Panels are not always planed or sanded, and some are supplied with a textured, wire-brushed surface.
- Internal exposed walls can be sealed with a clear coat.
- Solid timber absorbs moisture from humid air and releases it into dry air, which helps keep indoor humidity within a comfortable range.
- Sound insulation depends on the whole assembly, not on the CLT panel alone.
The same guide describes the NCC housing provisions as placing no limits on CLT use, but it was revised in 2018 and predates NCC 2022.[3] Fire and acoustic requirements for a specific design should be confirmed against the current code.
What you cannot see §
Some of the most important interior work is behind the lining. Reinforcement for future grab rails in bathrooms, required in some states under the Livable Housing Design Standard, is invisible once the board is fixed — see the Livable Housing Design Standard and factory-built homes. Waterproofing membranes in wet areas are in the same position; see bathroom pods and factory-built bathrooms.
The ABCB's handbook on prefabricated and modular construction says evidence for off-site work, and for elements concealed once modules are joined, has to be planned into the process rather than reconstructed afterwards.[4] For a buyer, that means asking before signing for photographs or inspection records of concealed work to be handed over with the house.
Common questions §
Do modular homes crack at the joins between modules?
Plasterboard itself is dimensionally stable, so cracks usually reflect movement in the frame or building; plasterboard fixed across two different substrates without a control joint is a known cause.[2] A module junction is that kind of line. How often junction cracks occur is not covered by the sources compiled here.
Is a crack in a new modular home a defect?
Under Queensland's published guide, a crack visible from 1.5 m in diffused light within the first 12 months is a defect; after 12 months only larger cracks count.[1] Other states publish their own guides.
Do modular homes have different walls from normal houses?
None of the sources compiled here identifies a wall lining used only in factory-built homes, and the same finish and tolerance standards apply to both.[1] What differs is that linings are fixed in a factory before the module is transported.
Can a prefab home have exposed timber walls?
Yes, where it is built from cross-laminated timber. A visible surface is ordered as an appearance grade from the manufacturer and can be sealed with a clear coat.[3]
What is not covered here §
No independent Australian study comparing the interior finish quality of factory-built and site-built homes is covered by the sources compiled here. How often cracks appear at module junctions, how large they typically are, and how long they take to stabilise are also not covered; statements on those points come from builders and inspectors describing their own experience.
The finish and tolerance figures on this page are Queensland's. Other states publish their own guides, and their content is not set out here.
Paints, wallpapers, wet-area wall finishes and hard flooring are not covered.
Questions worth asking §
- What level of finish is specified for walls and ceilings, and is it written into the contract?
- Where do the module junctions fall, and how is the lining detailed across each one?
- Which junction joints are finished in the factory, and which are made on site after installation?
- Who rectifies junction cracking that appears after handover, and within what period?
- If any timber is left exposed, what appearance grade and surface coating are specified?
- Will photographs or inspection records of concealed work be handed over?
Related: living in a modular home · warranties, defects and maintenance for modular homes
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References §
- Queensland Building and Construction Commission — Standards and Tolerances Guide, December 2023, based on NCC 2022 and valid from 1 May 2023. States Level 4 plasterboard finish is the default unless otherwise specified, with Level 3 acceptable in areas not readily visible; that within 12 months cracking in walls, ceilings, bulkheads and joints, and cornice joint cracking, is a defect if visible from a normal viewing position of 1.5 m or more in non-critical light; that after 12 months cracks are assessed by category, with categories 0 to 2 (up to about 5 mm) not defects and categories 3 and 4 defects; that walls bowing more than 4 mm within any 2 m length are defective; that a cornice deviating more than 4 mm from a straight line over up to 2 m is defective; and that nail popping and visible plaster jointing are defects within 12 months. The guide has no section on prefabricated or modular buildings. qbcc.qld.gov.au/sites/default/files/documents/guide-standards-tolerances.pdf
- Siniat (Etex Australia) — Plasterboard manufacturer's technical article. States plasterboard is dimensionally stable and changes little with temperature or humidity, so cracks usually reflect movement elsewhere in the building or its frame, and that some superficial cracking is normal because all buildings move. Lists contributing factors including joints near window and door corners, plasterboard bridging a movement joint, plasterboard fixed rigidly to two different substrates without a control joint, and ceiling junctions between a large room and a corridor. Advises finding the cause of movement before repairing a crack. siniat.com.au/en-au/resources-link-page/blog/2074257
- WoodSolutions (Forest & Wood Products Australia) — Technical Design Guide 16, Massive Timber Construction Systems — Cross-laminated Timber, revised October 2018. States the outer layer can be specified to an appearance grade at extra cost by arrangement with the manufacturer, that panels are not always planed or sanded and some are offered wire-brushed, gives an example of an internal CLT wall sealed with a clear coat, states massive timber absorbs and releases moisture to help keep indoor humidity in a comfortable range, and states acoustic performance depends on the whole assembly rather than CLT alone. Describes the NCC housing deemed-to-satisfy provisions as placing no limits on CLT use; the guide predates NCC 2022. woodsolutions.com.au/sites/default/files/2025-10/WS%20TDG%2016%20-%20Massive%20Timber%20Construction%20Systems%20CLT.pdf
- Australian Building Codes Board — Prefabricated, modular and offsite construction handbook, NCC 2022, published November 2024. Sets out why evidence of suitability for off-site work and for elements concealed once modules are joined has to be planned into the process rather than reconstructed at handover. abcb.gov.au/resource/handbook/prefabricated-modular-and-offsite-construction-handbook
Figures are as published by the sources above at their respective dates and are paraphrased summaries, not verbatim reproductions. Verify current pricing and rules directly with builders, lenders and planning authorities.