The following questions, though not inclusive, are representative of the most commonly addressed inquiries. For further information regarding topics not covered below, please contact one of our FSP representatives.

How is the wall constructed?
The UL-U370 assembly has two standard 2x4 16”o.c. stud walls separated by a minimum 1” clear space with the studs staggered 8”. Each wall is faced with a single sheet of 5/8” Type C gypsum board for two hours, and a double layer for three hours. No gypsum board or shaftwall is required inside the double wall assembly. The entire 8” cavity is filled with spray-applied Fire Rated Material (FRM) for fire safety and improved sound control.

What is the STC for the assembly?
The laboratory STC is up to 63. However, the key to any sound assembly is a function of good in-field installation. FRM, unlike preformed fiberglass or mineral wool batts, naturally fills cracks, crevices, voids and any openings around outlets or electrical conduit in the cavity. The inherent advantage of FRM is that it provides for a very small difference between the laboratory STC and real world applications.

Can I make any penetrations in the assembly?
When the UL-U370 is used as a fire separation wall between dwelling units, allowable penetrations vary by code. Penetrations are allowed when constructing under the International Building Code (IBC) but requires a UL approved system for through wall penetrations. The International Residential Code (IRC) does not allow through penetrations of any kind except floor/ceiling assemblies and UL-listed electrical outlet boxes and wiring. Plumbing, vents, ducts or mechanical equipment are not permitted within this assembly under either IRC or IBC. The horizontal spacing of electrical outlets on opposite sides of the wall may be reduced to 8” instead of the typical code-prescribed 24” because the cavity is completely filled with FRM, which is a natural fireblock.

What are the key advantages of this assembly?
The UL-U370 fire separation wall provides several significant advantages over conventional assemblies using shaftwalls:

• The firewall must be constructed after the exterior envelope is built, which means the assembly is protected from the elements, minimizing water or wind damage and the potential for mold growth.
• Since there are no inner gypsum layers in the fire separation wall, workers during construction can pass from townhome to townhome through the studs before FRM is applied without having to exit the structure, increasing working efficiency.
• Typically, both cost of materials and construction man-hours expended are less for this assembly than for conventional assemblies using shaftwalls.
• It has superior sound abatement due to FRM’s inherent sound-absorption qualities and the lack of gaps or seams in its in-field installation.
• Highly flexible assembly to accommodate the builders’ need for high sound performance, fire rating and with little impact to the overall cost of the assembly.

In summary, this is a cost effective assembly with up to three hours of fire protection.

What are the installation requirements?
GreenFiber will provide its FRM product only to GreenFiber-trained FRM Specialist contractors. The material must be spray-applied with a limited amount of moisture which activates the adhesive that stabilizes the cellulose. One layer of the gypsum board can be installed before FRM is sprayed, or a netting material can be attached to one side to retain the material. FRM must contain 25% or less moisture at the time the cavity is closed up with additional layers of gypsum board, which means this assembly may require 72 hours or more before FRM can be enclosed. The assembly will normally continue to dry to both sides even after the gypsum board has been applied until it attains a stable moisture content equal to the rest of the building envelope.

Is this a load-bearing wall?
UL-U370 is a load-bearing assembly. It receives a two-hour and three-hour rating with a 75% maximum load capacity per stud and a 1 1/2-hr rating with a 100% maximum load capacity per stud of the design capacity for the species used in the construction. Since the standard fire rating test for walls, ASTM E-119, determines a full load-bearing classification at 78% of maximum design load, this is virtually the same as the UL-U370 two-hour maximum load capacity of 75%. Please remember that structural design should be addressed by a structural engineer in accordance with your local code requirements.

Is there a risk of mold because water is used to install the FRM?
The added moisture used in the installation process is limited and considered to be a catalyst to activate the stabilizing adhesive in FRM. Provided the FRM product is spray-applied according to the manufacturer’s specifications, there are no product concerns. GreenFiber uses boric acid, an E. P. A. registered fungicide, to pass the ASTM C 739 test for fungal resistance.

Does the FRM settle in the cavity?
Spray-applied FRM has moisture activated adhesive. The moisture added during installation as a catalyst dampens the fiber and activates the adhesive. Spray-applied FRM properly installed creates a fiber matrix inside the cavity. The fibers bond to each other and to the side and back of the cavity. This fiber matrix maintains its form and does not settle in the cavity over time.

What are the specific requirements for the wall to floor connections?
The UL-U370 fire separation wall works with both balloon and platform construction. It can be used as a continuous multiple floor slab-to-roof deck construction if floor joists for intermediate floors are parallel to the wall assembly. For joists perpendicular to the wall assembly, it is recommended that platform construction, with the joists resting on top plates and upper floor firewall assemblies resting on the floor decks, be used to create a series of stacked firewalls forming a continuous slab-to-deck fire separation wall. When this is used, the concealed space between top plate and floor sheathing must be filled with FRM and enclosed by 5/8” Type C gypsum board secured to the floor joists and top plate, with seams fire-caulked. Connections can be designed for either perpendicular or parallel joist details and for connections designed where the floor joists rest either on the top plate or are supported by joist hangers. Floor penetration and connection designs need to be addressed by your architect or engineer in accordance with your local code requirements. Please refer to the Design Professional Support tab for architectural and engineering support for this assembly.

How do I handle repairs to the FRM if damaged before the gypsum has been installed?
On-site damage to the wall can occur. If only a small amount of material is pulled or knocked from the wall before the gypsum has been installed, GreenFiber recommends cutting a small portion of netting and face stapling it to the studs over the spot where the insulation needs repair. You can replace the FRM behind the netting for a clean repair. If there has been a large portion of the FRM material pulled from the cavity, the FRM Specialist must install FRM to complete the repair. If the material cannot be encased in gypsum board in a timely manner, install netting on both sides to prevent fallout.

Can I extend the assembly to the roof deck?
Yes. In fact, it is recommended. In addition, a layer of 1/2” fire-rated gypsum board must be attached to the underside of the roof decking extending a minimum of four feet from each face of the firewall assembly. An acceptable alternative to the gypsum board underlayer is to substitute fire-rated APA plywood for the conventional roof decking for the same four foot extension.

What do I do about an outside wall offset?
Where the separation wall connects to an exterior wall, fire-rated gypsum board must extend a minimum of four feet on both sides of the interior wall surface. A typical design is to continue one side of the double-stud wall UL-U370 to form a UL-U305 1-hr assembly which can use FRM as an approved component. Please consult with your architect for specific conditions.

How do I use the UL-U370 wall with an open web floor system?
For platform construction, this is treated the same as a wood joist floor system if resting on the top plate of the wall.

Can I put plumbing or ductwork in this wall?
Not when using the UL-U370, but it is allowed when using GreenFiber’s proprietary firewall assembly and incorporating a chase into the existing UL-U370 design, thus eliminating the need for an external chase. The assembly is constructed nearly identical to the UL-U370 design except in those areas where the plumbing or HVAC is running vertical in the fire wall. Type C gypsum is used to “box out” a cavity in one half of the fire wall. The plumbing or HVAC would be closed off with type C gypsum as with the UL-U370 design. Please contact your local Market Development Manager for specific design information in order to be in compliance with Underwriters Laboratories construction specifications.

How do I handle roof trusses? What considerations need to be made based on run direction?
Whenever possible, the UL-U370 should run to the underside of the roof deck and roof joists should run parallel to the assembly. One common construction mistake is to stop the UL-U370 at the top plate of the top floor, rest the roof joists on the top plates parallel to them and then construct the roof assembly. US GreenFiber developed and Underwriters Laboratories successfully tested a two-hour “patch” (basically a modified UL-U339 assembly) with two layers of fire-rated 5/8” gypsum board on the outer face of two trusses and the interior filled with FRM. Details of this test can be provided to code authorities upon request.

How does the floor rating affect the use of the wall? Does it need to be a rated floor?
The floors within each town home do not have to be rated.

Once I build the wall, are all cellulose insulation materials approved for use?
No. The UL-U370 fire separation wall is a proprietary assembly that has been tested and approved by Underwriters Laboratories, Inc. Only Fire Rated Material (FRM) manufactured by US GreenFiber and installed by an FRM Specialist is allowed in this assembly.

How do I determine if there is an FRM Specialist that services my market?
The team of FRM Specialists is growing. Please contact one of our FSP representatives to find the FRM Specialist serving your market.