Internal doors: hollow core vs solid core, door types, hardware and install sequence

TL;DR

Most internal doors on a residential build are hollow core, but three situations force a core upgrade: the door penetrating a fire-separation wall to an attached garage (self-closing solid core, min 35 mm thick, per NCC 2022 Housing Provisions Part 9.2.3(3)(b)), wet-area and laundry doors where moisture resistance matters (HMR MDF solid core), and high-traffic doors where hollow core skins delaminate inside two years. Since 1 October 2023, internal doors on the ground level of a new Class 1a dwelling that connect to habitable rooms, laundries, toilets and accessible showers must achieve a minimum 820 mm clear opening width under the NCC livable housing standard, which in practice means specifying an 870 mm door leaf. The costliest internal door mistake is framing rough openings too small before lining goes on: on a stud wall with 10 mm plasterboard each side, you lose 20 mm before a frame is even in.

When you do this

Internal doors are a second-fix item: they go in after lining is hung and set, cornice is run, and the floor substrate is in. Frames (reveals) typically go in at first-fix rough-in for cavity sliders (the pocket frame must be in before sheeting), but door leaves and hardware are second fix. Barn door tracks can go on a painted wall, making them one of the last items on site.

Who’s involved

Chippy: frames rough openings, installs cavity slider pocket frames at first fix, hangs door leaves, fits hardware at second fix.
Plasterer: sheets and sets walls around frames; finish height determines reveal rebate depth.
Painter: primes and finishes door leaves and frames before hardware fits.
Concretor / floor layer: floor substrate level determines door undercut clearance.

Door core types

All internal doors in Australia are governed by AS 2688:2017, Timber and composite doors, which classifies flush panel doors into hollow core, semi-solid core, and solid core (verified 2026-05-10 via Standards Australia).

Core type	Construction	Mass (approx.)	Typical use	When to specify
Hollow core	Cardboard honeycomb within a timber perimeter frame, faced with MDF or plywood	8 to 15 kg (leaf only)	Bedrooms, living rooms, robe doors, corridors	Standard internal rooms, light traffic
Semi-solid core	Honeycomb replaced with timber cross-members or foam-filled panels	18 to 25 kg	Higher acoustic rating needed, moderate traffic	Where STC rating matters but budget is tight
Solid core MDF	Continuous particleboard or MDF infill, timber perimeter frame	30 to 45 kg	Wet areas, laundries, high-traffic doors	Moisture exposure; fire doors; solid feel
Solid HMR MDF	High moisture-resistant MDF core	30 to 45 kg	Bathrooms, laundries, ensuites	Wet-area and humid environments
Solid timber stave	Glued timber stave infill	35 to 60 kg	Premium joinery, heritage, feature doors	Budget allows; heavy hinges required

Standard sizes (stocked internally): Heights 2040 mm and 2340 mm; widths 520 mm to 920 mm in 30 mm increments; thickness 35 mm standard. Custom sizes available to approximately 2400 x 1200 mm at a lead-time premium (verified 2026-05-10 via Hume Doors product catalogue).

Trim allowance: Most hollow core and MDF doors can be trimmed no more than 5 mm from any edge without cutting into the perimeter frame. If the floor-to-ceiling height or rough opening requires more trim, specify a door with a wider perimeter frame or order a custom-height door.

When hollow core is not appropriate

Situation	Minimum requirement	Reason
Fire-separation wall (dwelling to attached garage)	Self-closing solid core, min 35 mm thick	NCC HP Part 9.2.3(3)(b), verified 2026-05-10
Wet area or laundry (moisture exposure)	Solid HMR MDF core	Hollow core honeycomb wicks moisture, skins delaminate
High acoustic separation (home theatre, study, bedroom beside living)	Solid core or semi-solid + appropriate seal	Hollow core STC is approximately 27 dB, solid core can reach 35 to 40 dB
Door receiving a mortise lock (pocket-size cavity too small)	Solid core	Mortise cavity in hollow core only hits perimeter frame

Door types

Hinged (standard swing)

The default for most rooms. Single leaf, hinged on one jamb, swings into or out of the room. Requires clear floor area equal to the door width in the swing arc. Two or three butt hinges at 100 mm per leaf (three recommended for solid core and fire doors). Standard reveal (gap between door leaf edge and door stop) is 2 to 3 mm all round.

Rough opening: Door leaf width + 50 to 65 mm (frame each side plus clearance). Door leaf height + 80 mm (frame head plus clearance). Confirm with the specific frame manufacturer’s data sheet before framing.

Cavity slider (pocket door)

The door leaf retracts into a wall cavity. No swing arc required: the full opening is usable when the door is open. The cavity pocket frame replaces standard studs over a double-width wall section and must be installed at first fix before sheeting.

Rough opening: Door leaf width x 2 + 60 mm (stud opening for a single slider). Height: door leaf height + 75 mm (measured from subfloor to trimmer) for Phoenix-type systems (verified 2026-05-10 via Triline cavity slider sizing guide). Confirm with the specific system supplier before framing.

Wall stud thickness must accommodate the pocket frame: standard systems suit 70 mm, 75 mm, 90 mm and 100 mm stud walls.

Limitations: Cannot be used where a fire door is required (self-closing mechanism cannot work in a cavity), cannot be used as a wet area door (water ingress into cavity), and has limited acoustic performance. Maximum door weight for standard single-leaf cavity systems is typically 65 kg.

Barn door (surface-mounted slider)

The door leaf slides on a surface-mounted track fixed to the wall face. No cavity required: the track is fitted post-sheeting and painting, making barn doors one of the last items installed. Requires clear, unobstructed wall area adjacent to the opening equal to at least the door leaf width plus 50 to 100 mm.

Limitations: Does not seal the opening when closed (gap at track side); not suitable where acoustic or smoke separation is needed. Barn door track capacity must match the door leaf mass: standard residential hardware is rated to 80 to 120 kg.

Bi-fold

Two or more leaves connected by a centre hinge and suspended from a top track. Fold back to one or both sides. Common for robes and laundries where space is tight. Not typically used as a fire door or acoustic separation door.

NCC livable housing design: internal door widths

Under the NCC 2022 ABCB Standard for Livable Housing Design, mandatory for new Class 1a dwellings from 1 October 2023, the following internal doors must achieve a minimum 820 mm clear opening width (verified 2026-05-10):

All internal doors on the ground level (or entrance level) connecting to habitable rooms
The door to the laundry on the ground level
Doors to rooms containing a toilet on the ground level
Doors to accessible showers on any level required to comply with the standard
Garage-to-dwelling access doors that form part of the continuous access path

In practice: An 820 mm clear opening requires an 870 mm door leaf for a hinged door (the leaf takes approximately 25 to 30 mm of clear width at the hinge side plus the leaf thickness). Cavity sliders require a wider rough opening to achieve 820 mm clear.

Corridor width: Internal corridors and hallways connected to a door that must comply must be at least 1,000 mm clear width between finished wall faces (verified 2026-05-10 via Livable Housing design standard clause 3.1).

State adoption: VIC, NSW, QLD, SA, WA, NT, ACT from 1 October 2023. TAS from 1 October 2024 (verified 2026-05-10 via ABCB).

Fire separation: dwelling to attached garage

Where a door opening penetrates a fire-separation wall between a Class 1a dwelling and an attached Class 10a private garage, the door must comply with NCC 2022 Housing Provisions Part 9.2.3(3)(b) (verified 2026-05-10 via NCC HP Part 9.2):

Self-closing solid core door, not less than 35 mm thick, or
A non-openable fire window or other construction with an FRL of not less than -/60/-

The self-closing mechanism must return the door to the fully closed position automatically (spring hinge or door closer). A hold-open device or wedge defeats compliance.

The fire-separation wall itself must achieve FRL 60/60/60 tested from the garage side, or be at least 90 mm masonry construction (NCC HP Part 9.3, verified 2026-05-10).

A cavity slider cannot satisfy this requirement: it cannot be self-closing and cannot achieve the necessary fire rating.

Hardware grades

Internal door hardware in Australia is covered by AS 4145.2-2008, Locksets and hardware for doors and windows (verified 2026-05-10 via Standards Australia).

Function	Hardware type	Where to use
Passage	Lever latch, no lock cylinder	Hallways, living rooms, robe doors
Privacy	Lever latch + push-button or turn knob, emergency release on outside	Bathrooms, ensuites, WCs, master bedrooms
Entry	Keyed deadlatch or deadbolt	Study, home office, internal external-access doors
Fire door closer	Overhead closer or spring hinge	Self-closing fire doors to garage
Dummy	Non-latching lever (push-pull)	Where a lever is cosmetic only (bi-fold, fixed leaf)

DDA-compliant lever handles must have a return leg of minimum 20 mm (to prevent snagging clothing or medical equipment) and the handle face must be within 45 mm of the door surface (verified 2026-05-10 via Lemaar DDA hardware guidance). Specified for all 820 mm livable housing doors.

Hardware mass for solid core doors: Solid core leaves require heavier-duty hinges. Three butt hinges at 100 mm per leaf (or 75 mm x 75 mm for lighter solid core) rather than two. Cavity slider hardware must be rated to the door leaf mass: confirm with the track supplier.

Install sequence

Cavity slider (first fix, before sheeting)

Confirm rough opening dimensions from the supplier’s framing guide (door width x 2 + 60 mm for single slider; height = door height + 75 mm from subfloor).
Install the pocket frame kit in place of the standard double stud. Follow the specific kit instructions: steel and timber systems differ.
Install the head track within the pocket frame.
Sheet over the pocket frame on both sides per normal lining sequence. The frame flush-faces with the sheet face.
At second fix: hang the door leaf on the track rollers, adjust the rollers to achieve level travel, install the flush pull and privacy latch hardware.

Hinged door (second fix, after lining set)

Confirm rough opening is clear of plasterboard, cornice and floor substrate. Check the opening is square: diagonal measurement difference should not exceed 3 mm.
Install the reveal (frame). Jambs are typically primed MDF (18 mm) or finger-jointed pine (19 mm). Pack the hinge jamb plumb; shim the head level; nail through shims into the trimmer framing.
Check the reveal is square and the door stop face is co-planar before nailing off.
Hang the door leaf. Fit butt hinges to the leaf first, then locate the leaf in the opening. Mark and chop the hinge recesses in the jamb. Fix hinges and check operation: reveal should be uniform (2 to 3 mm).
Mark and fit the strike plate and latch bolt.
Install hardware: lever set, privacy lock, or closer as specified.
Cut the door bottom to achieve 10 mm clearance over finished floor level (or 25 mm over carpet if carpet is not yet laid but is specified).

Barn door (post-paint, late second fix)

Fix the header track to the wall structure (not to plasterboard alone): locate and fix into the framing members behind the wall lining.
Hang the door on the track rollers; check level travel.
Fit floor guide to prevent the leaf swinging out at the bottom.
Fit flush pull, privacy latch or barn door bolt hardware.

Tolerances and acceptance

Per the HIA Guide to Materials and Workmanship and state Guides to Standards and Tolerances, verified numerical tolerances for internal door reveal gap, door plumb, leaf-to-stop gap and undercut clearance are pending HIA member access. [HIA-108]

What the builder should check at practical completion inspection before HIA values land:

Door leaf opens and closes without binding or racking in the frame.
Reveal gap is consistent around the door stop (aim 2 to 3 mm).
Door does not drift open or shut under its own weight when positioned at 45 degrees: indicates the jamb is not plumb or the floor is out of level.
Fire door self-closes fully from any open position without assistance.
Hardware operates smoothly: lever depresses and returns, latch engages strike plate cleanly.
Undercut clearance is consistent (10 mm over hard floor, allow for carpet if specified).

What can go wrong

Defect	Cause	When it shows up
Hollow core skin delamination	Moisture exposure (bathroom, laundry); rough handling; hollow core specified in wet area	During occupation; first wet season
Door binding in frame	Rough opening out of square; jamb not plumb; excessive moisture in green timber frame; door leaf swells in humid climate	First wet season; immediately post-install
Cavity slider leaf drops off track	Rollers not matched to door leaf mass; adjustment not locked off	Early occupation
Fire door held open (non-compliant)	Owner wedging door; spring hinge worn	Inspection or fire event
Reveal gap inconsistent	Jamb shimmed off plumb; head shimmed off level; door leaf not trimmed parallel	At second fix or PCI
820 mm clear opening not achieved	870 mm leaf not specified; wrong rough opening framing; non-compliant hardware reducing clear width	At inspection; occupancy sign-off
Barn door track pulled from wall	Fixed to plasterboard only without locating wall framing	Weeks after installation
Door undercut too small	Floor substrate not considered; carpet allowance not made	When floor coverings are laid

References

AS 2688:2017, Timber and composite doors, Standards Australia (verified 2026-05-10)
AS 4145.2-2008, Locksets and hardware for doors and windows, Part 2: Mechanical locksets, Standards Australia (verified 2026-05-10)
NCC 2022 Housing Provisions Part 9.2, Fire separation of external walls (clause 9.2.3(3)(b)), ABCB (verified 2026-05-10)
NCC 2022 Housing Provisions Part 9.3, Fire protection of separating walls and floors, ABCB (verified 2026-05-10)
NCC 2022 Volume Two Part H8, Livable housing design, ABCB (verified 2026-05-10)
Triline cavity slider stud opening calculator, Triline (verified 2026-05-10)
Hume Doors internal door range, Hume Doors and Timber (verified 2026-05-10)