Acoustic doors and how to read an Rw rating

At a glance

Descriptions come from Approved Document E, BSI scope text and free previews; the full texts of BS EN ISO 10140-2 and 717-1 were not read.

What Rw tells you, and what it leaves out

A door is tested on its own in a laboratory, in a test opening between two rooms, with other sound paths suppressed. BSI's listing for the test standard says the method covers walls, floors, doors, windows and similar elements, and that the results are not applicable directly to the field situation. For doors, Annex B of ISO 10140-1:2021 sets the rules: it applies to internal and external doors including door sets; the result is the sound reduction index, R, by frequency; the door is mounted so that it opens and closes normally; and it is opened and closed at least five times just before the test, to bed in its seals.

Rw is the single number worked out from those band results under BS EN ISO 717-1. Approved Document E defines it as a single-number quantity that characterises the airborne sound insulation of a material or building element in the laboratory. Two limits follow. The number belongs to the doorset as tested, not to a leaf alone. And one number hides the shape of the result, which is why the band-by-band table and the C and Ctr terms matter where the noise is not ordinary speech.

The sheet gives no dB requirement for any project. What a particular door must achieve depends on the acoustic consultant's brief and the operator's standards, and none of those figures was found in a source we could read.

Why a laboratory figure is not a site figure

On site the door sits in a wall, with a frame, a floor and a ceiling around it. ISO 16283-1 defines the apparent sound reduction index, R′, as the figure in which the sound radiated by flanking elements is counted as well as the sound through the test element, and says it can be used to compare field measurements with laboratory measurements of R. Flanking transmission is sound that reaches the next room by a route other than the element being tested (Approved Document E, Annex C).

Approved Document E, paragraph 6.5, says it is likely that the sound insulation of a corridor wall will be reduced by the presence of a door. Paragraph 1.8 says that pre-completion sound testing should not be carried out between living spaces and corridors, stairwells or hallways. Our reading is that in England the bedroom-to-corridor door is not tested on completion under Part E, so what the door achieves rests on the test report for the doorset and on how it is installed. A project may still ask for a site test: ISO 16283-1 gives the field method.

The weakest-link sum

Sound goes through every part of the door, and the leakiest part decides the result. A simple sum shows the order of magnitude. If a leaf has a sound reduction index R and a share f of its area is a fully open gap, the combined figure is -10 log10 [ (1 - f) x 10^-R/10 + f ]. This is our own simplified arithmetic: it takes a gap as passing all the sound that reaches it, and it treats Rw as if it were a single-band figure. An acoustic consultant works band by band.

Example leaf ratings of 35, 40 and 45 dB are variables, not claims about any product. Rounded to the nearest decibel.

Take an example leaf of 926 x 2,040 mm, an area of 1.889 m². A 10 mm gap under it is 9,260 mm², or 0.49 per cent of the leaf, and the sum gives about 23 dB for a 40 dB leaf. A 3 mm margin all round is 17,796 mm², or 0.94 per cent, and the same leaf falls to about 20 dB. A one per cent open area can never beat 20 dB, whatever the leaf. On this example leaf, Approved Document E's 25 kg/m² comes to 47.2 kg.

The lesson for a specifier is that seals and the foot of the door matter more than extra leaf mass once the leaf is reasonable, and that a tested doorset is worth more than a heavy leaf with gaps. Real gaps are partly closed by seals, so the true figures are better than this worst case: that is what the test report measures.

The parts that decide the result

These are the places a result is won or lost. Where the basis is trade practice with no source read, the table says so and the item is in the review list.

Fire, access and hotel guestroom doors

Fire. A fire doorset is tested and certified as a complete assembly. Approved Document B Volume 2, Appendix C, paragraph C4, says test evidence must be applicable to the complete installed assembly and that small differences in detail might significantly affect the rating. Our reading is that an acoustic seal, a drop seal or a threshold is such a difference, so the fire evidence has to cover the doorset with the acoustic parts fitted. Where smoke control is needed the door carries the Sa suffix (paragraph C2), evidenced to BS EN 1634-3 unless pressurisation is used (Table C1, note 3). See the fire door specification guide.

Access. Approved Document M Volume 2, paragraph 2.7(e), limits a raised threshold at an accessible building entrance to 15 mm in total height, with upstands over 5 mm chamfered or rounded. That paragraph is about entrances. We found no figure for the threshold of an internal guestroom door, so a raised acoustic threshold on an accessible bedroom door is a question for the accessibility consultant. A drop seal, which closes the foot gap without an upstand, is one way to avoid the question (our reading). See Approved Document M for furniture and joinery.

Hotel guestroom entrance doors. For a room for residential purposes, which includes a hotel room, paragraph 6.6 of Approved Document E asks for good perimeter sealing, including the threshold where practical, and a mass of at least 25 kg/m², or alternatively a doorset of at least 29 dB Rw measured in the laboratory. It names BS EN ISO 140-3:1995 and BS EN ISO 717-1:1997 for that measurement. BSI shows the first as withdrawn on 28 February 2011, and the second has been replaced by the 2020 edition; the current laboratory method is BS EN ISO 10140-2:2021. That is an example of construction in a statutory guidance document, not an operator's standard, and paragraph 0.8 adds that a higher standard may be needed next to noisy or non-domestic spaces, with specialist advice.

What to ask for

The evidence matters more than any single figure. A request that works for a doorset in a hotel corridor:

1. The requirement, in writing, from the acoustic consultant: Rw [x] dB for the doorset (with C and Ctr if they are used), and what it is for.
2. A test report for the complete doorset to BS EN ISO 10140-2, from a named laboratory: leaf size and construction, seals, threshold or drop seal, glazing and ironmongery cut-outs as tested, the band-by-band R table and the Rw with its adaptation terms.
3. A comparison of the tested configuration with the doorset to be supplied. Any difference approved in writing before manufacture.
4. Fire evidence (and the Sa classification where needed) that covers the same doorset with the acoustic parts fitted.
5. Installation instructions and who installs, including how the frame is sealed to the wall and how the foot of the door is closed.
6. A first-room check before the run: seals bed evenly, the drop seal closes, the latch pulls the leaf onto its seals and no ironmongery has opened a new gap. See prototype and mock-up approval.
7. Seal information for handover: seal type, where it is fixed and how it is replaced, because seals wear on busy corridors. See handover and O&M pack.

This sheet states no Rw for any door and makes no claim about any partner's doorset. Ask the door maker for its report.

Doorset to achieve a weighted sound reduction index of Rw [x] dB (C [ ]; Ctr [ ]), as tested in accordance with BS EN ISO 10140-2 [2021] and rated to BS EN ISO 717-1 [2020], for the complete doorset: leaf, frame, perimeter seals, [drop seal / threshold], [glazing] and ironmongery cut-outs as supplied. Test report from [a named laboratory] to be submitted before manufacture, with the tested construction drawn and the band-by-band results given. Any difference between the tested construction and the doorset supplied to be approved in writing by [acoustic consultant].

Doorset to achieve [FD30S / E30 Sa] and Rw [x] dB. The fire test or assessment evidence and the acoustic test report to describe the same doorset, including the acoustic seals and [drop seal / threshold] as fitted. Certificate, field of application and installation instructions to be submitted before manufacture.

Frame sealed to the surrounding wall on both faces with [sealant and backing as the doorset maker's instructions] before architraves are fixed. Perimeter seals to bed evenly on all four edges; foot gap closed by [drop seal / threshold] with the door latched. No cut-out or penetration other than those in the tested construction. Before the run, [one] doorset to be installed and checked by [acoustic consultant / project manager] against the test report (seal contact, drop seal, latch pull-in) and approved in writing. [Site sound test to BS EN ISO 16283-1 if required.]

Standards and sources

• Approved Document E (England), 2003 edition incorporating amendments to 2015: paras 6.5 to 6.7, 1.8, 0.8, Annex C read.
• BS EN ISO 10140-2:2021: current at BSI; scope read. Approved Document E names BS EN ISO 140-3:1995, withdrawn 2011.
• ISO 10140-1:2021, Annex B (doors): free preview read.
• BS EN ISO 717-1:2020; BS EN ISO 16283-1:2014+A1:2017: both current at BSI; 717-1 not read (ADE names the 1997 edition), 16283-1 free sample read.
• Approved Document B Vol 2 App C (C2, C4); Approved Document M Vol 2 (2.7(e)): read.

Questions we are asked

What is an Rw rating on a door?

A single number, in decibels, for the airborne sound insulation of a doorset as measured in a laboratory. It is calculated from the result in each frequency band. It describes the doorset as tested, with its seals and threshold, not the leaf alone, and it is not what the door will achieve on site.

Does a higher Rw always mean a quieter room?

Not by itself. The leakiest part of the door and wall decides the result, and the one number can hide a weakness at low frequencies. A door with a high Rw and a gap under it will do worse than its label. Ask for the test report, the band-by-band results and the installation detail.

What Rw does a hotel bedroom door need?

There is no single answer. In England, Approved Document E paragraph 6.6 gives, for a room for residential purposes, good perimeter sealing with a mass of at least 25 kg/m², or a doorset of at least 29 dB Rw. A hotel operator's standard or the acoustic consultant's brief may ask for more. We give no figure for them because none was found in a source we could read.

Why is the site result lower than the test report?

The laboratory test isolates the door; a building adds flanking paths, the frame joint, the wall around the door, the foot gap and the quality of fitting. The field figure, R′, counts all of them, so for the same door it is not expected to be higher than the laboratory R.

Can a fire door also be an acoustic door?

Yes, if the fire evidence and the acoustic report describe the same doorset. Approved Document B says test evidence must apply to the complete installed assembly, so acoustic seals, a drop seal or a threshold have to be covered by the fire evidence too. Ask for both documents to name the same construction.

Does the threshold matter?

Yes. Approved Document E asks for sealing including the threshold where practical, and the foot of a door is usually its largest opening: on our example leaf a 10 mm gap is about half of one per cent of the leaf area, enough to take a 40 dB leaf to about 23 dB in a simple sum. A raised threshold may conflict with level-access needs, so settle it with the accessibility consultant.