​Ceiling Performance FAQs

​Answers to your most common questions about ceiling performance & maintenance

 

Performance    |    Product Selection    |    Installation and Field Painting    |    Continuous Ceilings vs. Exposed Structure

Acoustics

  1. Which Armstrong ceilings provide good acoustic performance?
  2. I see a reference to NRC in Armstrong literature; what does this stand for?
  3. So what then is Alpha w (αw) as I thought this does the same thing as NRC?
  4. Is there a direct correlation between NRC & Alpha w?
  5. For ceiling tiles, how is Sound Absorption used?
  6. How can I stop a room being "echoey" ?
  7. What is reverberation time and how do Armstrong ceilings influence it?
  8. What is the effect of sound absorption on noise levels?
  9. How can I calculate the reverberation time of space?
  10. What is a sabine and why would you use it?
  11. What is the speech frequency range and is it defined in any official standard?
  12. What is the difference between sound absorption and sound attenuation?
  13. Will materials that provide high sound absorption also provide high sound reduction?
  14. I thought decibels were for measuring noise levels so why do you use them for ceilings?
  15. Is there a difference between sound reduction and sound attenuation?

 

Performance

  1. Why RH99 and why 49 degree Celsius?
  2. Which Armstrong ceilings are suitable for use in wet or high humidity areas?
  3. Can Armstrong ceilings be used externally?
  4. What is the "U" value of your ceiling tiles?
  5. What is the advantage of air movement through a ceiling void?
  6. What is Relative Humidity and why is it important?
  7. What is a vapour control layer?
  8. Can I use the ceiling void as a return air plenum? What's the best tile to use?
  9. What do the clean room class ratings mean?

 

Maintenance

  1. Why do acoustic ceilings stain easily in the event of HVAC leaks?
  2. What causes "pattern staining" on a ceiling tile?
  3. I've got to do some touching up on a few of Armstrong mineral fibre tiles which the electrician has slightly damaged. What paint do you recommend?
  4. My ceiling has become slightly soiled, how can I clean it?

 


Acoustics

  • 1. Q:  Which Armstrong ceilings provide good acoustic performance?

A: This depends upon your definition of 'good' and whether it is sound absorption or sound attenuation that is your main application objective. Most Armstrong ceilings can provide acoustic control with balanced sound absorption and antenuation value.

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  • 2. Q:   I see a reference to NRC in Armstrong literature; what does this stand for?

A: Noise Reduction Coefficient is a method for providing a single number rating of sound absorption. It is defined in ASTM C423 as the arithmetical average of the measured sound absorption coefficients for the four one-third octave band frequencies centred at 250, 500, 1000 & 2000 Hz, rounded to the nearest 0.05.

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  • 3. Q:  So what then is Alpha w (αw) as I thought this does the same thing as NRC?

A: Alpha w (weighted sound absorption coefficient) is also a method for converting a wide frequency based range of sound absorption coefficient values into a single number but this is done using a curve fitting process. Although more complex to derive, Alpha w is considered to be more representative of how the human ear interprets sound. The method is fully described in EN ISO 11654 and has now become the preferred European unit for making a simple and rapid comparison of sound.

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  • 4. Q:   Is there a direct correlation between NRC & Alpha w?

A: No. Although they are both single number descriptors of sound absorption neither one can be deduced from the other as there is no direct relationship between them.

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  • 5. Q:   For ceiling tiles, how is Sound Absorption used?

A: When applied to room surfaces or objects, sound absorptive materials reduce the reflection of sound that strikes them which helps to make a space seem less “echoey” or “lively” or, more technically, less reverberant. The ceiling plane is often the only one of substantial size, and relatively unobstructed, where sound absorption can be introduced. However sound absorptive materials are most effective at controlling reverberant sound when distributed between several room surfaces or objects rather than just being applied to one.

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  • 6. Q: How can I stop a room being "echoey" ?

A: Echoes are discrete sound reflections from a distant surface which, if they are of sufficient intensity and time delay, can be heard distinctly from the direct sound, i.e. you hear the same sound twice in quick succession. The expression “echoey” is often used to describe the sound heard in an enclosed space which is particularly reverberant or 'lively'. This is actually the wrong use of the term as, perhaps surprisingly, echoes are a rare phenomenon in most normal sized and occupied enclosed spaces. However, excessive reverberation and noise can be controlled by the introduction of sound absorptive treatments, such as suspended acoustic ceilings.

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  • 7. Q: What is reverberation time and how do Armstrong ceilings influence it?

A:This is the time, in seconds, required for reflecting or reverberant sound in an enclosed space to decay to one-millionth (equivalent to a drop of 60 dB) of its original energy level after the cessation of the sound source. It is the most common, and easily obtained, measurement or predictor of a room’s potential sound quality. The reverberation time (RT) for any enclosed space will be influenced by the room's volume and how much sound absorption (which controls the reflection of sound) is present. Increasing the volume will increase the RT while increasing the amount of sound absorption will lower the RT. Because Armstrong suspended ceilings can provide a substantial surface area and can provide more or less sound absorption depending upon the product chosen, they can significantly influence the RT of a space. However any room will have an optimum reverberation time (RT) requirement depending upon its use and size and whether the main activity is speech or music based. Providing too much sound absorption, and hence having a very low reverberation time (RT), can be just as acoustically damaging and undesirable as having insufficient sound absorption when an excessively long reverberation time (RT) will result.

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  • 8. Q: What is the effect of sound absorption on noise levels?

A: Rooms with reasonable amounts of sound absorptive finishes appear quieter and less frenetic than those with little or no sound absorptive treatment. If the amount of effective sound absorption in a room is doubled (or halved), the noise level will be reduced (or increased) by 3dB (Decibels). However, it should be considered that a change of 3dB will only just be detected by the human ear, while a difference of 5dB is necessary to be really noticeable. In addition, sound absorptive treatments that are applied to the boundary elements (walls, ceilings, floors etc.) of a room, do not have any significant effect at enhancing the element’s sound reduction properties, ie when sound transmits through it from one adjacent room to another.

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  • 9. Q: How can I calculate the reverberation time of space?

A: By using a mathematical model based upon the 'Sabine' formula which takes into account the significant surfaces of a room, their respective sound absorption coefficients and the room dimensions. The acoustic module in "Estimate", provided by
Armstrong to registered users, will enable a simple indicative calculation to be made. Alternatively, Armstrong website is also able to do a more detailed calculation which also considers specific user criteria.

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  • 10. Q: What is a sabine and why would you use it?

A: A sabine (also known as the equivalent absorption area) is measure of sound absorption afforded by a material which is defined as the product of its exposed surface area S (m2), multiplied by its random incident sound absorption coefficient alpha s. However the sabine is also specifically used to describe the total absorption provided by individual discrete objects, such as an acoustic canopy, cloud or baffle, where all of its surfaces may be influentially providing sound absorption and the use of as would not be sensible or realistic.
Once the total sound absorption present in a room (from both planar surfaces and objects) has been calculated, an estimate can be made of the room's probable reverberation time. The installation of clouds and canopies in a reverberant space can significantly reduce the reverberation time and contribute to the reduction in background noise.

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  • 11. Q: What is the speech frequency range and is it defined in any official standard?

A: The speech frequency range is generally described as being between about 500Hz and 4000Hz. However it is not defined in any known national or international standard.

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  • 12. Q: What is the difference between sound absorption and sound attenuation?

A: Sound absorption relates to the control of sound reflections(Absorb) within a room while sound attenuation (Blocking) is associated with the control of sound transmission between adjacent rooms via a continuous suspended ceiling.

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  • 13. Q: Will materials that provide high sound absorption also provide high sound reduction?

A: Probably not. Materials that provide high levels of sound absorption are generally lightweight and porous which is the direct opposite of the qualities required for sound reduction ie massive and impervious.

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  • 14. Q: I thought decibels were for measuring noise levels so why do you use them for ceilings?

A: The decibel is a unit used in acoustics to describe the magnitude of sound levels. These levels can either describe how loud something is (e.g. 85 dB due to a passing bus), or they can describe the ability of a product or system to reduce sound, e.g a 35 dB suspended ceiling will reduce a sound level of 75 dB in one room down to 40 dB in an adjacent room. The bigger the number the greater is the sound energy level or sound difference involved.

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  • 15. Q: Is there a difference between sound reduction and sound attenuation?

A: Insofar that the terms 'reduction' and 'attenuation' both mean a decrease or lessening of something, then these expressions describe the same process and are usually interchangeable. In relation to the acoustics of suspended ceilings, 'sound
reduction' is generally used to describe the 'single or vertical pass' decrease (typically from a ceiling cavity to a room below) while 'sound attenuation' is reserved for the 'double or horizontal pass' lessening in transmitted sound energy where the ceiling is continuous above two adjacent rooms.

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Performance

  • 1. Q:  Why RH99 and why 49 degree Celsius?

A: Pre-construction; Temperature contrast when building envelop are up and HVAC is not running. RH99 up to 49 degree celsius is a warranting condition which was pinoneered by Armstrong to define the environmental conditions which the product is suitable to be used.

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  • 2. Q:   Which Armstrong ceilings are suitable for use in wet or high humidity areas?

A: Armstrong Ceramaguard Tiles and Metalworks tiles painted on both face and reverse surfaces, are suitable for use in conditions of up to 100% RH, which can occur internally in spaces such as swimming pools, showers, laundries and some manufacturing processes, although none of these tiles should be subjected to continuous direct water exposure.

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  • 3. Q:  Can Armstrong ceilings be used externally?

A: The two main considerations relating to the use of suspended ceilings for external locations are humidity and wind loading. Two of Armstrong ceiling products, Ceramaguard and Metalworks (Exterior range) painted on both face and reverse surfaces, are suitable for use in conditions of up to 100% RH, which can occur externally, although none of these tiles should ever be subjected to direct precipitation. However, wind loading can potentially be equally as serious by exerting either a positive or a negative pressure on ceilings that could dislodge and damage both tiles and grid. Therefore, because wind forces can vary considerably depending upon both topographical and geographical locations, a thorough analysis should be undertaken by a structural/environmental engineer before an external installation is considered.

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  • 4. Q:   What is the "U" value of your ceiling tiles?

A: There is no such thing as the "U" value of an individual element, such as a suspended ceiling tile. The "U" value is a measure of the thermal transmittance of a complete element of structure (such as a roof construction) consisting of all its component parts. Our mainline brochure contains information on the thermal conductivity (λ) of our ceiling tiles and this can be used in the calculation of the "U" value of a structure by others (e.g. a M&E engineer).

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  • 5. Q:   What is the advantage of air movement through a ceiling void?

A: It can remove moisture laden air that otherwise could condense out on cold surfaces and possible cause damage to the structure and suspended ceiling.

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  • 6. Q: What is Relative Humidity and why is it important?

A: This is a measure of the relative level of water saturation of the air (expressed on a 0-100 % scale) and is the ratio of the actual amount of water vapour in air compared with the saturation water vapour for a given temperature. Therefore %RH should always be quoted with a specific temperature. Within buildings humidity needs to be controlled in order to provide optimum conditions for:

  • Human comfort and well-being
  • Specific manufacturing/servicing processes
  • Electronic equipment reliability
  • Maintaining building fabric and materials in good condition
  • Conserving energy

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  • 7. Q: What is a vapour control layer?

A: This is a construction material (usually a thin plastic membrane or similar) that substantially reduces the water vapour transfer through any building component in which it is incorporated. They may be found (or required) in ceiling voids that have little or no thermal insulation and where there is a danger of condensation falling onto the back of the ceiling and causing pattern staining or damage.

 

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  • 8. Q: Can I use the ceiling void as a return air plenum? What's the best tile to use?

A: In principle the ceiling void can be used as a return air plenum provided this is acceptable to the architect and/or M&E engineer. There is no "best" tile for this as it will depend upon the permitted air leakage through the ceiling. We have air leakage data for some of our ceilings. Our low density (soft fibre, eg: Optra range) ceilings are unlikely to be suitable because of their porosity.

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  • 9. Q: What do the clean room class ratings mean?

A: The classes, according to ISO/TC209 14644-1, are a level of airborne particulate cleanliness. A Class 5 means that less than 3,520 particles (0.5 microns in size) are present per cubic meter, which equals 100 particles per cubic foot. A Class 6 indicates less than 35,200 particles per cubic meter. The higher the class number, the more particles present.The lower the class, the more stringent it is.

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Maintenance

  •  
  • 1. Q:  Why do acoustic ceilings stain easily in the event of HVAC leaks?

A: The insulation of HVAC might be worn or ducting integrity has degraded over time which results in leaks. Visible surface stains usually occurs after [a significant of leakage] x [ time ], and the symptom would suggest abnormal functionality above which leads to poor indoor air quality, possibly encouraging the growth of mold & mildew above plenum..

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  • 2. Q:   What causes "pattern staining" on a ceiling tile?

A: Pattern staining on the face of a ceiling tile may be due to three adverse causes:

1) Dirty water may have dripped onto the back of the tile and soaked through to the face causing discoloured stains. These will normally be yellow or brown in colour and probably due to ferric oxide (rust) contamination.
2) Tiles in the immediate vicinity of air grilles or diffusers sometimes display black marks or streaks. This is due to dirt in the air being deposited on the tile's surface as the air emanates from or returns to the distribution system. Smooth tiles such as Plain or Orcal plain etc are less likely to be affected.
3) Heat from a room will rise (due to convection) and migrate through a suspended ceiling towards the (normally) cooler ceiling void. Minute particles of dirt in the atmosphere will also rise and be deposited on the ceiling tile's surface. However,
if the thermal insulation of the tile is not consistent (as often occurs with metal tiles with mineral wool pads in the back, that are not carefully laid flat particularly at the corners) then the dirt will be deposited unevenly with a build-up at the "cold
spots" and appear as straw, brown or grey coloured marks.

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  • 3. Q:  I've got to do some touching up on a few of Armstrong mineral fibre tiles which the electrician has slightly damaged. What paint do you recommend?

A: Any formaldehyde-free emulsion paint available from paint store may be suitable subject to colour matching.

 

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  • 4. Q:   My ceiling has become slightly soiled, how can I clean it?

A: Armstrong recommended cleaning methods depend upon the type of tiles used and the degree of soiling encountered. Armstrong has a maintenance brochure which gives appropriate advice so please request a copy from your technical representative.

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