If you have ever looked at an operable wall specification, you will have seen a number followed by the letters STC. It is the single most important figure on the data sheet, and also one of the most misunderstood. Pick a rating that is too low and conversations carry through the wall. Pick one that is much higher than you need and you may spend more than necessary.
This guide explains what an STC rating is, how to read one, and which rating suits different kinds of rooms. It is written for architects, builders, facility managers and business owners across New Zealand who want to make a confident decision.
What Does STC Mean?
STC stands for Sound Transmission Class. It is a single-number rating that describes how well a wall, door or other building element blocks airborne sound, such as voices, music and television. The higher the number, the better the wall is at stopping sound travelling through it.
The rating is based on laboratory testing. A sample wall is installed between two chambers, a noise is played on one side, and the amount that reaches the other side is measured across a range of frequencies. The results are then compared against a standard curve to produce one STC number.
You may also see the term Rw in New Zealand specifications. This is the equivalent rating under the international ISO system. The two numbers are usually close, but they are not identical, so always check which one a supplier is quoting when you compare products.
How Does the Rating Feel in Real Life?
Numbers on paper are hard to picture, so here is a general guide to what different STC ranges mean in a typical room. These are approximate and depend on background noise levels, but they give a useful starting point.
- STC 35 to 40: loud speech can be heard and often understood through the wall. This is not adequate for most meeting rooms.
- STC 40 to 45: loud speech is audible but usually not understandable. Quiet conversation is mostly masked.
- STC 45 to 50: loud speech is faint or barely audible. This is a good range for meeting rooms, classrooms and offices.
- STC 50 to 55: most loud sounds are very faint. Suitable for training rooms, boardrooms, and function spaces with moderate noise.
- STC 55 and above: loud sounds, including amplified speech and some music, are significantly reduced. Aimed at venues with high noise levels, or very sensitive spaces.
Doormax operable walls cover this range. The 85 Series offers STC 45 to 52, the 100 Series offers STC 45 to 56, and the 5000G double glazed glass wall reaches STC 48, with STC 50 available as an option.
Which STC Rating Do You Need?
The right rating depends on what happens on each side of the wall. Here are some common examples.
Meeting rooms and offices (STC 45 to 50)
For standard business meetings, an STC in the mid to high 40s keeps most conversations private. If the discussions are sensitive, such as HR, legal or financial matters, aim for the upper end of the range or add acoustic treatments elsewhere in the room.
Classrooms and training rooms (STC 45 to 52)
Teaching spaces need to prevent one class from disturbing the next. A mid-range rating works for general classrooms, while music rooms, drama studios and halls that host noisy activities benefit from a higher rating. For more ideas on how schools use flexible walls, see our post on creative uses for operable walls in schools.
Function rooms, hotels and conference centres (STC 50 to 56)
When one half of a ballroom is hosting a wedding with a band and the other half has a corporate seminar, you need serious isolation. The upper end of the 100 Series range is designed for this kind of demand. We look at this in more detail in our article on operable walls for hospitality venues, churches and community halls.
Medical and counselling spaces (STC 50 and above)
Privacy is a legal and ethical requirement in healthcare. Higher ratings, along with careful detailing of the surrounding construction, help protect confidentiality.
Open-plan collaborative areas (STC 40 to 48)
If your goal is to reduce distraction rather than create full isolation, a lower rating or a glass system may be enough. This is where glass operable walls shine. See our comparison of glass and solid operable walls for guidance.
Why the Lab Rating Is Not the Whole Story
This is the part many buyers miss. An STC rating comes from a lab, where the wall is installed perfectly and sound can only travel through the wall itself. In a real building, there are other paths. Acousticians call this flanking.
Sound can leak or travel around a wall through:
- Gaps at the floor, ceiling or sides of the opening
- Shared ceiling voids above the wall
- Ducting, cable penetrations and light fittings
- Floors and side walls that carry vibration
- Poorly fitted or worn seals
That is why a wall rated STC 52 in the lab may perform closer to the mid 40s once it is installed in a building with poor detailing. It is also why good installation matters as much as the rating itself.
To get the best result:
- Make sure the ceiling above the wall is sealed up to the structural slab or has an acoustic barrier
- Use manufacturer-specified seals at the head, floor and jambs
- Have the system installed by trained specialists
- Maintain the seals and tracks over time, since worn parts reduce performance
Our post on the ultimate guide to soundproof operable walls has additional detail on how seals and construction affect real-world performance.
Does the Building Code Set an STC Requirement?
Requirements depend on the building type and the use of the space. New Zealand Building Code clauses cover sound insulation between certain types of spaces, for example between household units. Operable walls used inside a single tenancy are often governed by the project brief rather than a fixed code number, but this is not always the case.
Because the rules differ by project, your architect or acoustic consultant should confirm the target rating before you specify a system. Doormax can supply test data and technical information to support that process.
Common Mistakes to Avoid
Choosing on price alone. A cheaper wall with a lower rating can cost far more if you have to add acoustic treatments later.
Over-specifying. A rating of STC 56 in a space that needs STC 45 adds cost and may not be noticeable in daily use.
Ignoring background noise. In a quiet office, even a faint sound can be distracting. In a busy restaurant, background noise helps mask leakage.
Forgetting the rest of the building. The wall is only one part of the acoustic system. Ceilings, floors and adjacent walls matter too.
Not considering how the wall is used. If an operable wall is moved often, the seals will need to be maintained so that performance does not slip.
Questions to Ask Your Supplier About STC
When you compare operable walls, it is easy to be swayed by a high number on a brochure. These questions help you look past the headline figure and understand what you are really buying.
- Is the rating from an independent laboratory test? Reputable suppliers can provide test reports that show the exact configuration that was tested.
- Does the rating apply to the exact panel and seal configuration I am buying? A rating achieved with one set of options may not apply if you choose a different finish or thickness. The Doormax 85 Series and 100 Series, for example, offer different baseboard options, which can influence the result.
- Is the figure an STC or an Rw? As mentioned above, the two are close but not the same, so make sure you are comparing like with like.
- What assumptions are made about the surrounding construction? Lab results assume ideal conditions. Ask what ceiling, floor and side wall details are required to approach the rated figure.
- How is the rating maintained over time? Seals wear and tracks settle. Ask about recommended inspection and servicing intervals.
- Who installs the system? Installation by trained specialists is one of the biggest factors in whether the installed wall comes close to the lab number.
A supplier who answers these questions clearly and in detail is a good sign. Doormax manages consultation, design, manufacturing, delivery and installation as one process, which keeps accountability for the final result in one place.
A Practical Example
Imagine a training provider in Auckland that wants to split a large room into two classrooms. One half will run presentations with a projector and a speaker, the other will host quiet exam preparation. A wall rated STC 45 might technically meet the brief on paper, but speech from the presentation room would still be faintly audible during quiet study. Stepping up to a mid-range rating of around STC 50, and making sure the ceiling void above the wall is sealed, gives the exam room the quiet it needs without moving to the most expensive option.
The lesson is that a few points on the scale can make a real difference in perceived quietness, but only when the details around the wall are right.
Frequently Asked Questions
What is a good STC rating for an operable wall?
For most offices and meeting rooms, an STC of 45 to 50 is a good target. For event spaces and venues with amplified sound, aim for 50 to 56.
Is a higher STC always better?
Higher ratings block more sound, but they also cost more and often involve thicker, heavier panels. The best choice is the rating that matches your real needs.
What is the difference between STC and Rw?
Both measure airborne sound insulation. STC is used mainly in North America and Australasian product literature, while Rw follows the ISO standard. The values are close but not identical.
Can an operable wall achieve the same STC as a fixed wall?
The best operable walls come close to the performance of many standard partition walls, but very high ratings are harder to achieve because the panels must move and seal repeatedly. Detailing and installation are critical.
Do glass operable walls have an STC rating?
Yes. The Doormax 5000G double glazed system reaches STC 48, with STC 50 available as an option.
Get Expert Advice on the Right Acoustic Rating
Selecting the right STC is easier when you have a specialist to talk it through. Share your floor plans and the way you plan to use each space, and the Doormax team will recommend a system that meets your acoustic needs without over-specifying. Contact us for a no-obligation consultation anywhere in New Zealand.
