We are in the midst of a severe housing shortage. The U.S. housing market is 3.8 million single-family homes short of what is needed to meet the country’s demand, according to a recent analysis by mortgage-finance company Freddie Mac. As the vaccinations and stimulus support an economic recovery, household formations are expected to surge, according to Marcus & Millichap, who is predicting 2.5 million more households being formed each year in 2021 and 2022. 

Drive around any large city and you see cranes. Cranes, often a welcome sight—at least for those in the construction industry—represent increases in apartment or condo-style living resulting from lack of affordable single-family home supply, desire to age in place and in migration of young, highly educated people. Hot spots include Vancouver, Chicago, Seattle and South Florida, to name a few. Due to single-family home supply being insufficient to meet demand, buyers in Palm Beach migrated towards condos where sales were up triple digits in 2020. When people own or rent contiguous properties and share common spaces, they have the ability to negatively affect each other’s property value and quality of life.  

The housing shortage is also a potential indicator of enduring housing demand to come. Architects and designers seek products that enhance quality of life for the building occupants. Spec’ing the right membrane for the installation can be challenging and often requires the aid of an acoustical professional who relies on IIC (“impact insulation class”) ratings, among other ratings, to compare and contrast the various types of underlayments on the market in order to select the most appropriate product for a select project. Membranes that can do double-duty, providing crack-isolation and sound reduction, score extra points.  

The underlayment product offering ranges from very basic polyethylene foam (packaging material) to engineered rubber/cork composites. Each one has a use, but they are very different from each other in terms of performance and cost. The polyethylene foam is great for laminate floors because they offer the basic moisture control necessary to protect the flooring and a small amount of cushion to reduce the crunching sound you might hear under the flooring from sand and other granular materials.  

Cork underlayments have been around for a very long time and are used in a wide variety of applications from under ceramic tile to wood floor installations. Cork has a nice environmental story in that if comes from a sustainable source (cork trees) but the problem with cork is it only comes from a few areas geographically. Cork is therefore a victim of freight costs and pricing seems to be increasing due to demand and the increases in freight. Reground rubber seems to be the fair child these days of the underlayment domain and it works well for ceramic, wood and resilient flooring. These types of underlayments are found in pure reground rubber versions as well as blended types which include reground cork and other materials. Reground rubber also has a great story to tell from an environmental standpoint in that it uses spent tires and diverts from being dumped in a landfill. Other underlayments are also used for acoustic in the form of cellulosic fiber mats as well as thick plastic woven fabrics. All have their own unique properties and functionalities useful for acoustic dampening and providing a suitable base for many floating floor systems. 

Membranes, specifically crack isolation membranes, have gained a lot more attention these days with their use for large format tile. Tile seems to be getting larger in size every day and we have seen tile that is more appropriately called a panel due to its size. When you install large-format tile, you need to be aware that the tile is very expensive compared to traditional materials. The last thing you want to have happen to these large tiles is for them to crack due to substrate issues. There are quite a few solutions for crack isolation, but the bulk of the business is handled by two product variants; one is a roll-on crack isolation membrane which is typically an acrylic polymer based material but has good elongation properties. The other product of choice is asphaltic or bituminous extruded membranes which also act like a shock absorber and crack isolator. These membranes adhere to a primed substrate with a sticky layer that flows / moves under stress; if the substrate cracks, this viscoelastic layer effectively isolates the tile installation on the surface. Viscoelasticity enables bitumen to maintain bond to a cracking concrete subfloor without transfer of stress to mortar and tile. They also offer a bit of sound attenuation.  

With the proliferation of condo living and the need for a quiet home office, or two, sound reduction has become even more important. Some of the most annoying sources of impact sounds are hard-heeled shoes, dragging of furniture, dog toenails and dropping objects on hard-surfaced flooring. These types of sounds are considered high frequency. However, IIC often doesn’t tell the whole story since the IIC incorporates both low and high frequencies. Acoustical consultants unsatisfied with the limitations of IIC developed the high frequency IIC testing, that eventually evolved into the new ASTM E3222 standard, which defines criteria for the high frequency IIC testing.  

The new HIIC (“high frequency impact insulation class”) rating provided a single-number rating for describing these sounds. The popularly used IIC ratings are often controlled by frequency bands below 400 Hz and therefore the IIC rating may not be representative of impact insulation at high frequencies. HIIC ratings exclude impact sounds below 400 Hz. By focusing on the third-octave bands from 400 to 3150 Hz, the HIIC can aid the acoustical profession in evaluating the high-frequency insulation of an assembly, and in rank-ordering and specifying floor topping products that will affect the level of high-frequency impact sound. An HIIC of 52 may be considered average, a 58 above average and anything over 65 representing outstanding performance, for example.  

Sound ratings are controlled by municipal building codes, and until they submit for a code change, IIC will likely continue to be the prevailing rating used. Companies that employ acoustical experts are able to convert IIC ratings to HIIC without having to retest flooring assemblies in a lab. 

Learn more about the latest subfloor prep products and best practices

The standard IIC will always be around, but architects are now adding HIIC to their specifications. Eventually, you may see flooring and underlayment manufacturing companies begin publishing HIIC in their specifications.