The upstairs neighbor with the hard surface floor

The Noise

This story has to do with condominium floor/ceiling separation assemblies between upstairs and downstairs units. A woman purchased a very expensive downstairs unit only to discover that it was barely habitable due to noise from the people upstairs.

Another story comes  from a homeowners’ association board (HOA). They were trying to respond to complaints from condominium owners whose upstairs neighbors had removed the carpeting and pad from their floors, and had installed hardwood flooring in its place.

Another two stories came in regarding complaints involving conversions of existing buildings into condominiums. In one situation, the problem had already erupted into a full-blown lawsuit.  

The Problem 

What did all these calls have in common? In layman’s term’s, footfall noise. In acoustical terms, this is known as impact noise.In each case, a hard surface flooring material such as wood, tile, slate or marble had been installed on a floor/ ceiling separation assembly that wasn’t designed to accommodate such materials. This led to dramatic increases in noise levels in the downstairs units when a person upstairs walked around, or dragged an item of furniture, such as a chair, across the floor.

What Causes the Problem? Without the proper design, a floor/ceiling assembly can act like a drum skin, broadcasting the noise into the unit below. Imagine the force exerted on the floor/ceiling assembly every time a shoe heel strikes the floor, and you’ll begin to understand the nature of the problem. There are actually several sources of noise involved with a simple footfall. The first is the actual impact of the foot on the hard surface material. This creates a noise that, if not properly mitigated, travels directly through the floor structure into the unit below.

It can also radiate across the floor surface, causing the walls to vibrate, which in turn transmits the noise into the unit below. Lastly, if the floor structure is too flexible, it will bounce as a person walks across it. This can amplify the noise experienced in the unit below, particularly at low frequencies. Noise Measurements It is possible to measure the ability of the floor/ceiling assembly to reduce impact noise. For the purposes of the test, the sound of a person walking (or causing an “impact”) on the floor/ ceiling assembly, is imitated by a specialized piece of test equipment known as a “tapping machine”. This instrument has a row of small hammer-like “tappers” that knock on the floor of the upstairs unit when the machine is turned on, while an acoustics specialist in the downstairs unit uses a sound level meter to measure the level of noise transmitted through the assembly. After analysis, the measurement result can be expressed as a single number, which is the “Impact Insulation Class” or “IIC” rating for the assembly. Since the assembly is fieldtested (i.e., tested in situ as opposed to being tested under laboratory conditions) the result is referred to as an “FIIC” figure.

The State of California’s Title 24 standards require that floor/ceiling separation assemblies between units in multifamily developments achieve an IIC rating of not less than 45 when field tested. The impact testing will demonstrate whether or not the problematic assembly complies with these requirements. And that information is often very useful when dealing with upset tenants who have no other quantitative way of expressing their subjective experience of the noise.

How to improve the situation

The problem of footfall noise is very difficult to resolve in existing construction. Though the assembly can be brought up to code, it is safe to say that with typical wood frame construction, there is really nothing that can be done to make a hard-surface flooring material “sound the same” as a good quality carpet and pad to the neighbor below. As stated previously, the floor/ceiling assembly must at the outset be designed for hard-surface materials. The only way to achieve a noticeable improvement is to tackle the floor/ceiling assembly from both sides. The problem cannot be resolved by simply blowing insulation into the ceiling assembly. 

Start with the Upstairs Floor

In the upstairs unit, typically the flooring material will need to be removed as well as any concrete or gypsum underlayment. Then an acceptable vibration-break material (usually a springy or spongy material) is laid down and a concrete material is poured or placed on top. Finally, the flooring material is replaced. The correct installation of this type of assembly is crucial to its success. One of the inherent difficulties with this corrective method is that the extra layers can significantly increase the height of the floor. This can result in height inequity problems with the existing door thresholds, plumbing fixtures and cabinets. Another problem with this fix is that it can significantly increase the weight of the floor. Because of these problems, an architect and structural engineer need to be consulted to ensure that designand safety issues are appropriately addressed.

Fix the Downstairs Ceiling

The downstairs ceiling design must also be corrected. Typically, the ceiling should be removed, batt insulation should be added to the joist bays, and the drywall should be remounted on resilient channels with sound clips. For an increase in sound isolation you can use Green Glue with drywall and attach it to the underside of the floor between the joist bays. Again, correct installation of each element is crucial to the overall effectiveness.

Is It Worth All The Trouble? As you can see, it takes a great deal of upheaval and expense to rectify this problem in an existing building. Of course, in most of these situations, there is a simple answer. Insist that the upstairs tenants put the carpet and pad back down!