Everything You Need to Know About STC Ratings (& Why It’s Important for Homebuyers)

What is STC?

a woman hugging her partner holding keys to their new home with moving boxes in the back

Sound transmission class, or STC, is the rating system used to measure a partition wall’s ability to reduce the effect of airborne sound. A higher STC rating means less sound will make its way through the partition wall, sometimes called a party wall, common wall, or shared wall, and create a quieter living space.

One of the most significant issues in any space is sound transmission. If you’ve ever lived in an apartment or condo where you can hear your neighbours every move, you’re probably no stranger to acoustic problems! However, many new homebuyers don’t know about STC ratings or think to ask about them before purchasing a place they hope to be their place of comfort. Many buyers don’t put a value on a common wall with a higher STC rating, but it’s time we do.

Sound can travel through the air and vibration. Airborne sound can pass through ventilation, under doorways, and over, under, around, and through obstructions. Like that coming from talking, TV, music, footsteps, or even vacuuming, vibrational sound can travel through floors and walls. When sound makes its way to a space where it is not wanted, it becomes noise.

Your home should be a place where you can live as you so please. If you’re interested in living in an attached or multifamily home, the STC rating in your home should be top of mind during your house-hunt.

What Are STC Ratings?

STC was introduced in 1961 to compare various wall, ceiling, floor, door, and window assemblies. The rating is calculated by taking the Transmission Loss values tested at 16 standard frequencies over the range of 125Hz to 4000Hz and plotting it on a graph. The various plots on the graph will form a curve, which is then compared to standard STC reference curves. For example, if the values detected in a room in your home create a curve that best matches a standard STC 35 curve, the common wall within that room is thought to have an STC rating of 35.

Sound Transmission 101

There are several defining factors of STC ratings that affect how the ratings are achieved. Garnering a basic knowledge of these factors will give you a better understanding of what makes your home quieter and protects you from hearing your neighbours and vice versa.

At Millenium Plus Homes, we put a lot of thought and consideration into STC ratings and how we can create homes that are safe and comfortable for buyers. I believe that not enough people know about STC ratings and how much it can affect their lives. For example, if you have a noisy furnace that wakes you up every hour on the hour, you’d replace it, right? Well, unfortunately, it’s not as easy or cost-effective to replace a wall (as much as we’d like to). 

Unless you have the express interest and permission of the neighbouring party to replace a common wall, plus don’t mind intense construction and limited privacy between suites, it’s pretty much impossible. The cost of fixing a common wall can be over 10 times the cost of doing it right in the first place, plus even then you may never achieve the STC rating you desire.


Decibels (dB) are the unit used to describe the intensity of sound. The scale is logarithmic due to the exceptional sensitivity of our ears. For example:

  • A whisper is 15db
  • General conversation is 60dB
  • A lawnmower is 90dB
  • A live concert is 120dB
  • Fireworks are 140dB


Frequency is a measurement of musical sounds and is measured in Hertz (Hz). Sound waves and the speed at which they vibrate determine the overall pitch of a sound. The number of waves that occur in 1 second denotes the frequency. 

Transmission Loss

Transmission Loss (TL) measures the number of decibels lost when noise travels through a wall. For example, someone playing the drums may record 90dB and only 65dB in the neighbouring room. This means there is a 25dB TL. 

The frequency of the sound can affect Transmission Loss significantly. Some very high and very low frequencies will have little to no TL.

What is a “Good” STC Rating?

custom graphic depicting discomfort with a poor STC rating and comfort with a high STC rating, with a chart showing what levels correspond to how much noise you can hear

Typically, the higher the STC rating, the better. Higher STC ratings mean the shared wall between your unit and your neighbours has a greater ability to reduce sound transmission. However, most home builders may not always put a real effort into building proper “party walls” for the mere fact that in today’s real estate market, very little value is put on the STC rating of common walls that will keep you from hearing your neighbour’s most intimate conversations. 

In Canada, the minimum requirement for walls and floors between dwelling units is 50 STC. Some rooms or dwellings may require higher STC ratings, such as Government offices or boardrooms. If you’re home-shopping, here’s a rough guide to go off when inquiring about STC ratings:

  • Poor: 30-39 STC
  • Good: 40-49 STC
  • Great: 50-59 STC
  • Excellent: 60-67 STC

The “Party Wall”

bearded man in a plaid shirt listening to music with headphones

If you’re building a new home, you have full control over the STC rating. Suppose your building is designed to be a multifamily or attached home. In that case, you can choose a builder to properly engineer the walls in between units to ensure each is quiet and comfortable for tenants and homeowners. 

At MPH, we engineer proper “party walls,” or the walls that separate units that produce an STC rating between 59 and 67. It’s extremely important to us that anybody who lives in the homes we build get to enjoy their own home’s freedom and privacy. 

A “party wall” includes proper insulation, stud arrangement, stabilization, and how the units are attached to each other. They also need to be up to fire code. Discussing these things with your home builder, realtor, or landlord is important if you’re looking to purchase or rent a new home.

I value the integrity of builders that build homes fit for their own family, or better. For many, the exterior, cabinets, tile, hardwood, and other finishings are what create value when purchasing or building a home. But not many are concerned about how well your unit will protect you from unwanted noise! At Millenium Plus Homes, we put significant emphasis on building quality homes that you can enjoy for years to come. However, whatever your situation, be sure to ask about STC ratings; they can affect your life more than you might expect.

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