Acoustic doors for apartments and home offices

Sound treats a door as a hole with opinions. A handsome leaf that does not seal is a hole. A hollow-core bedroom door on a shared apartment corridor is a hole with paint on it. Australia has spent the last twenty years putting home offices into spare rooms and pianos into terraces, then wondering why the hallway still participates.

The useful number, when someone finally offers one, is Rw — a weighted sound reduction index. The National Construction Code uses related measures for walls and floors in Class 2 to 9 buildings, and it cares about doors because they punch through those walls. Houses are less formally policed and just as full of arguments. This is a specification note for both.

If you are still choosing sizes and styles, internal doors, sizes, styles and costs is the shopping companion. Here the subject is quiet.

What Rw is, and what it is not

Rw is measured in a laboratory on a specific door, frame and seal combination. It is a single-number rating derived from a frequency curve. It is useful for comparing products. It is not a promise about your terrace in Marrickville with a timber floor and a neighbour who owns a saxophone.

A few cautions that save disappointment:

• The lab door has seals. Your door will need those seals, installed, and still in contact after the first summer.
• The lab wall is not your plasterboard on hat-channel, or your weatherboard on studs. Flanking paths around the frame matter.
• A letter slot, a cat flap, a huge undercut for ventilation, or a glass panel can erase a surprising amount of Rw.
• Fire-rated apartment doors often carry an acoustic rating as a pair. Swapping the seals or the closer because they felt stiff can undo both.

Some specifications use Rw + Ctr, which adjusts for low-frequency noise — traffic, bass, the man downstairs with a subwoofer. If the brief is a busy road or a nightclub of one, ask for that number too.

Houses do not usually need a lab report on a study door. They need a leaf with mass, a frame that can take a seal, and an honest gap. Apartments and studios often do need the report, because the NCC and the strata by-laws will eventually ask who approved the hollow-core substitution.

Mass, cores and the myth of the egg-carton

Sound reduction at a door starts with mass and tightness. A solid-timber or solid-core engineered leaf outperforms a hollow-core honeycomb for the boring reason that there is more stuff in the way. Acoustic doors go further: designed cores, heavy skins, sometimes a steel sheet, always a seal set that includes the threshold.

Egg cartons, foam tiles and a towel under the door are household folklore. The towel is the only one that does temporary work, and it is a trip. If the room needs make-up air, use a transfer grille that is actually rated, or take air from a quieter path. Do not confuse a bathroom undercut with an acoustic specification; the wet-area essay is where that undercut belongs.

Glass is heavy and still leaks at the edge. A glazed office door can be decent if the pane is laminated (a little kinder to mid frequencies) and the frame seals. Two leaves of glass with a sealed gap are an acoustic product. A single thin pane in a rattly aluminium frame is a window you have to walk through. AS 1288 still applies; quiet glass is not exempt from Grade A in a door.

Seals, thresholds and the last 10 millimetres

Most “my new solid door did nothing” stories are seal stories. Air is sound. A 5 millimetre gap around a leaf is a loud, linear speaker.

A working acoustic set usually includes:

• Compression seals at the stiles and head, in a frame that was designed for them, not a sticky-backed foam on a painted rebate.
• An automatic drop seal at the threshold, or a raised threshold with a compressible gasket, detailed so it does not fight the access rules.
• A latch that pulls the leaf in. Magnetic seals on some studio doors do this with less slam.
• Meeting stiles on pairs that actually meet. Double doors are an acoustic hobby.

Drop seals need a flat strike surface and a leaf that has not warped. They also need to be adjusted after the floor finish goes down. A seal that kisses a thick rug will not kiss a hard floor, and the reverse.

Closers on apartment entries are there for fire and for the leaf returning to its seals. A closer that slams is not more acoustic. It is a neighbour complaint. Adjust it.

Apartment entries, fire and the corridor

Class 2 entry doors are often fire doors first — AS 1905.1 and the NCC fire-resisting construction — with an acoustic performance riding along. The corridor is a drum. Voices, trolley wheels, late keys and the lift lobby all arrive at your latch.

Do not replace a rated apartment door with a prettier unrated slab. Do not cut a cat door into it. Do not swap the seals for a cheaper pile because the official ones squeaked. If the door is tired, replace it with a tested assembly that carries the fire and acoustic numbers the building’s approval assumed, or have a competent contractor recertify the work.

The frame is part of the wall. A fire-and-acoustic door in a light decorative jamb is a costume. So is a beautiful leaf undercut for a new carpet.

Studios and warehouse conversions add a second problem: the front door is also the only door, and the bed is in the same volume as the kitchen. An acoustic entry still helps against the corridor. It will not invent a second room. A heavy curtain track inside the entry can take the last edge off a lobby, as long as it does not interfere with egress.

In bushfire-mapped apartment edges — they exist on the urban fringe — the entry may also be a BAL opening. Write fire, acoustic and BAL on the same line. Products exist. Catalogues that only mention one of the three do not.

Home offices, pianos and the spare room

The pandemic filled spare rooms with microphones. The door that used to hide a guest bed is now a broadcast envelope. A solid-core leaf, perimeter seals, a drop seal, and a soft closer will do more than a ring-light. So will a rug, a bookcase on the shared wall, and not placing the desk against the door.

Pianos and drums are a different brief. Low-frequency energy goes through floors and flanking paths that no door will stop. You can keep the scale out of the hallway with a sealed, heavy leaf. You cannot make a terrace party-proof with hardware. Be honest with the household before you buy a studio door the width of a cupboard.

Practical home-office specification, without a lab:

• Solid-core or acoustic-rated leaf, not hollow-core, even if the paint match is tempting.
• Frame packed and sealed to the wall, not sitting in a draught.
• Drop seal or threshold gasket, compatible with the way the household moves.
• Soft-close or a closer that does not announce every cup of tea.
• No decorative glass if the hallway is the noisy side, unless the glass is part of the rating.
• A second thought about the window, which is often louder than the door.

Acoustic foam on the door face is a visual shout and a modest gain. Spend the money on the seals.

Sound is just air with a grievance. If you can feel a draught at the rebate, you already know what the door is doing after 9 p.m.

Studios, lessons and the neighbour test

A music teacher at home or a podcast in a weatherboard is a small architecture project. A single acoustic door is one layer. Shed studios pick up heat as well as sound; composite and uPVC cores can help thermally and still need seals. Do the neighbour test at the actual hour of use. A door that feels quiet at noon on a Tuesday can fail at 7 a.m. on a Sunday.

Write the system: required Rw or NCC performance; leaf mass; frame packed to the wall; seal set and threshold; laminated glass to AS 1288 if glazed; a ventilation path that does not undo the seals. Then close the door and talk at ordinary volume. If you can follow the conversation on the other side, you have a leaf, not an acoustic door. Quiet is won in the boring millimetres at the edge.