Carpark Acoustic Insulation
Concrete reflects. Polyester absorbs.
Installed to the specified NRC.
- Published NRC data
- ISO 354 tested
- Thermal in the same layer
- QA documentation
Auckland based, nationwide
We travel. Most regions have no carpark soffit crew of their own.
Programme focused
We plan and deliver around your schedule.
QA & PS3 supplied
Complete documentation at practical completion.
Commercial specialists
Carparks, basements and podiums.
Carpark acoustic insulation is a sound-absorbing lining fixed to the underside of a concrete carpark slab. A bare carpark is acoustically hard on every surface — floor, walls and ceiling are all concrete — so engine noise, door slams, alarms and voices reflect rather than decay, and reverberation times run long. A polyester soffit liner absorbs that sound energy instead of returning it. The ceiling is the largest uninterrupted surface in the space, which is why treating it does more than treating anything else.
Why carparks are so loud
A carpark is close to the worst-case room for reverberation. Every boundary is hard, the volume is large, and there is almost no soft furnishing or occupant mass to absorb anything. Sound produced anywhere in the space keeps reflecting until it runs out of energy, which takes a long time.
That matters most where people live above it. In an apartment or retirement village with parking underneath, the carpark is not a service space — it is the room directly below somebody's bedroom, operating at six in the morning. Roller door cycles, engine start-up, reversing alarms and conversation all carry, and they carry through a slab that was designed for structural performance rather than acoustic separation.
It also matters at the point of sale and at the point of complaint. Reverberation is the thing that makes a basement feel cheap when a buyer walks through it, and noise from a carpark below is one of the more common body corporate complaints in mixed-use buildings. Neither shows up on a drawing.
Absorption is not isolation — and the difference matters
A soffit liner absorbs sound within the carpark. It reduces reverberation, so the space is quieter to be in and noise generated there decays faster. That is absorption, and it is what an NRC figure measures.
It is not the same as stopping sound transmitting through the slab into the apartment above. That is isolation, it is a function of the floor assembly — mass, decoupling, floor finishes — and no ceiling lining fixed to the underside of a slab changes it much on its own. Anyone who tells you a soffit liner will solve an impact noise complaint upstairs is overselling it.
What absorption does do is reduce the sound energy in the room, which reduces what is available to transmit anywhere. On a real project the two get specified together, by an acoustic engineer, and we install to whatever they call for. We will tell you which problem the liner actually solves before you buy it.
What the products actually achieve
Both polyester systems publish absorption data. The rigid phenolic boards do not, because they are closed-cell and are not acoustic products — that is the clearest single reason to specify a liner over a board where noise is in scope.
| System | Absorption | Basis |
|---|---|---|
| Mammoth Carpark Panel | NRC 0.85 | R1.7 at 70mm, tested to ISO 354 |
| GreenStuf ASL (Autex) | NRC 0.65 – 1.05 | Varies by thickness and facing. Full octave-band absorption data published. |
| Kingspan Kooltherm K10 G2 | Not an acoustic product | Rigid closed-cell phenolic. No absorption data published. |
| GreenStuf Phenolic Foam Board | Not an acoustic product | Rigid closed-cell phenolic. No absorption data published. |
NRC is a single-number average of absorption across four frequency bands. An NRC of 0.85 means roughly 85 percent of the sound energy hitting the surface is absorbed rather than reflected. Where an acoustic engineer needs more than a single number, Autex publish the full octave-band table for ASL and we can supply it with the tender.
Read the variant, not the brand. GreenStuf ASL spans 0.65 to 1.05 across the range — the figure depends on thickness and on whether the facing is unlaminated, foil or black. A specification that names the product without naming the variant has not specified the acoustic performance.
Where it earns its place
Apartments and retirement villages over parking
The most common case, and the one where it matters most. Occupied space sits directly above a hard-surfaced room that operates around the clock. The soffit is doing thermal duty under H1 anyway — specifying a polyester liner rather than a board gets the acoustic performance in the same layer, at the same install cost.
Podium and basement carparks that read as part of the building
Where a carpark is lit, finished and used by residents or the public rather than treated as plant space, reverberation is the thing that makes it feel unfinished. A black-finish liner treats the acoustics and the appearance in one pass.
Mixed-use ground floors
Retail or commercial tenancies adjacent to parking share air paths through lobbies, lift cores and stair pressurisation. Reducing the source energy in the carpark reduces what reaches them.
Where an acoustic report already exists
If a reverberation time or absorption target has been set, it will be expressed as a coefficient or an NRC. We install to the specified variant and hand over the manufacturer's acoustic documentation with the QA pack, so the sign-off is evidenced rather than assumed.
Coverage is what makes it work
Absorption is a function of area. A liner that covers eighty percent of the soffit does not deliver eighty percent of the acoustic benefit you specified — the untreated concrete keeps reflecting, and hard patches between absorbent ones are what produce flutter.
So the acoustic result is decided by the same thing that decides the thermal result: whether the panel is cut and scribed around every duct, tray, hanger and sprinkler drop, or butted up to them and left short. Every gap of exposed concrete around a services run is a reflective surface in a ceiling that was paid for to absorb.
This is also why services sequencing matters more on an acoustic job than a purely thermal one. A soffit that is already full when we arrive gets more cuts, more short panels and more exposed concrete — and the performance loss does not show up until somebody complains about the noise, long after practical completion.
Acoustic soffit liner, installed to the specified performance
We install polyester acoustic soffit liner to carpark, podium and basement ceilings throughout New Zealand, from a base in Auckland. We install the variant the acoustic report calls for rather than an equivalent R-value, because the absorption figure changes with thickness and facing and a substitution can quietly cost you the performance the report was written around.
Installed to AS/NZS structural fixing requirements.
Get your carparkpriced
Send drawings and the acoustic report if you have one. We'll confirm the variant, price the scope and flag anything in the specification that will not achieve what the report assumes.
- Fast turnarounds — within 24–48 hours
- Acoustic documentation supplied with the QA pack
- We install the specified variant, not an equivalent
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Your project details are kept confidential.
Carpark acoustics — common questions
- Does carpark insulation reduce noise?
- Polyester systems do. A bare concrete carpark reflects sound off every surface, so engine noise, doors and voices reverberate. A polyester soffit liner absorbs that energy instead of returning it, which shortens reverberation time and makes the space measurably quieter. Mammoth publish NRC 0.85 for the R1.7 panel tested to ISO 354, and Autex publish NRC 0.65 to 1.05 across the GreenStuf ASL range. Rigid phenolic boards are closed-cell and are not acoustic products.
- What NRC do I need for a carpark ceiling?
- There is no Building Code minimum for absorption in a carpark — it is set by the project's acoustic report, if there is one, or by the developer's expectations if there is not. Where a target exists it is usually expressed as a reverberation time or an absorption coefficient, and the acoustic engineer converts that into a product and a coverage area. Where no report exists, the practical answer is that the highest NRC available in the specified R-value costs no more to install.
- Will a soffit liner stop noise coming through into the apartment above?
- Not on its own, and be careful of anyone who says otherwise. A soffit liner absorbs sound inside the carpark, which is a different thing from isolating sound transmitting through the slab. Isolation is a function of the floor assembly — mass, decoupling and the floor finish above. Absorption does reduce the total sound energy in the room, which reduces what is available to transmit, but a ceiling lining is not a fix for an impact noise complaint upstairs.
- Do rigid insulation boards provide acoustic absorption?
- No. Kingspan Kooltherm K10 G2 and GreenStuf Phenolic Foam Board are rigid closed-cell phenolic, and neither manufacturer publishes absorption data because absorption is not what the product does. If noise is in scope, that is the clearest reason to specify a polyester liner instead — and if headroom forces a rigid board, the acoustic treatment has to come from somewhere else in the design.
- Does the finish change the acoustic performance?
- Yes, and it is the detail most often missed. GreenStuf ASL publishes NRC from 0.65 to 1.05 depending on thickness and on whether the facing is unlaminated, foil or black — a foil facing reflects some of the sound a bare polyester face would absorb. A specification naming the product without naming the variant has not actually specified the acoustic performance, which is worth resolving before it is priced.