Sound Attenuating Fire Blankets for Acoustic and Fire-Resistive Protection

Sound Attenuating Fire Blankets (SAFB) are a type of wall insulation developed to help solve two different problems in wall construction.

Sound Attenuating Fire Blankets

This type of insulation provides benefits for acoustic separation, as well as benefits for fire-rated separation. This type of product can be useful for those types of walls where both fire and acoustic ratings are required by code. The most common type of walls where this is a factor are interior partitions in multi-family construction, which per code, are required to provide 1-hour of fire-resistant construction, and a Sound Transmission Class (STC) rating of 50 minimum for air-borne sound transmission. Of course, there are exceptions and other relevant information related to both of these requirements.

Walls separating dwellings in Group R occupancies are required to be constructed as Fire Partitions per section 420.2 of the International Building Code (we’ll be referencing the 2021 edition of the IBC in this article). As to the required 1-hour rating, this is the standard requirement, however, some of these types of walls (for example, dwelling-to-corridor walls) can have this requirement reduced to only 1/2-hour when allowed by Table 1020.2. As well, in construction types II-B, III-B, and V-B, such walls can also be reduced down to 1/2-hour, when the building is equipped throughout with an automatic fire sprinkler system in accordance with section 903.3.1.1 (that’s an NFPA-13 system – not 13-R or 13-D). SAFBs can contribute to a strong and robust fire-resistive partition when required by these sections of code, and they have specifically been included in multiple fire tests establishing their use as effective components of a fire-resistance-rated wall system.

Per Section 1206 of the IBC, walls separating dwellings from each other, and from adjacent public areas (most commonly corridors, but also including meeting rooms and other public areas), are required to provide a minimum 50 STC rating to help reduce the amount of air-borne sound that can transmit through the walls from one side to the other. If you’ve ever stayed in a hotel or lived in an apartment where the neighbors are loud and the walls aren’t rated against sound transmission, you know just how bothersome unwanted sound can be. To this point, it is important to understand that the code minimum STC rating of 50 is exactly that: a minimum. The ICC’s own Guideline for Acoustics explains that this code minimum many times is not enough to satisfy most building occupants, and therefore two higher standards are established in this document. Above the code minimum STC is an “acceptable” level of STC 55 (or “Grade B”), with a “preferred” level of 60 (or “Grade A”). Depending on the expectations of the tenants, it may be prudent to design walls with higher levels of air-borne sound transmission than code minimum. This is also where an SAFB may be a prudent insulation choice, as the addition of an SAFB into a wall assembly can increase the STC level of the wall by as much as 11 points.

SAFB Materials and Benefits

As to what makes up an SAFB and why it provides benefits for acoustic and fire performance, typical SAFBs are composed of mineral wool or rock wool, in 3-inch thick blankets. This thickness allows the SAFB to fit snugly in a standard 2×4 wood or 3 5/8″ metal stud cavity. Because the insulation is a mineral wool, it meets the noncombustibility tests established by the code (based on ASTM E136), and is expected to remain in place during a fire event (it will not melt, nor will it be consumed by fire). The nature of the mineral wool SAFB makes it a great choice for fire-rated assemblies. As to acoustics, there are special types of SAFBs intended for “creased” installation, whereby the blanket is manufactured in widths 1-inch wider than the cavity in which it is intended to be installed. For example, for non-load-bearing partitions with metal studs spaced at 24-inches on center, a 25-inch wide SAFB can be used in a “creased” installation. For such installations, the SAFB is cut vertically down the face of the blanket, to score the SAFB and allow it to be bent like a book. The SAFB is pressed into the 24-inch cavity, and the pressure on the studs can help dampen sound vibrations from traveling through the studs. These types of installation allow the SAFB to provide a higher degree of sound isolation to the assembly in which it’s installed.

While the benefits of an SAFB can help you solve two problems at once, keep in mind that many of the fire tests which establish the basis for their recognized fire ratings are proprietary systems, which means that the fire tests were specifically created to test a specific product from a specific manufacturer, and they may not be substituted for generic or alternative materials. If a proprietary system is designed and/or specified, care must be taken to ensure the specific product is installed, otherwise, the fire and acoustic benefits may not be achieved. As well, keep in mind that in wall types such as these, joints at the edges of the walls and penetrations through the walls are areas where attention needs to be kept in order to ensure both the acoustic and fire properties of the wall are maintained