The GA's Technical Services Department provides answers to frequently asked questions about the installation, finishing, storage and handling of gypsum panel products.
How do I prevent mold growth on gypsum board?
Gypsum panels, particularly paper-faced gypsum wallboard, must be kept dry at all times to prevent the growth of mold. Review publication GA-238-2016 Guidelines For Prevention of Mold Growth on Gypsum Board. This quick reference publication will note transportation, storage, handling, application, and maintenance guidelines.
How do I know whether or not to replace gypsum board after it has been submerged in a flood?
You will want to reference GA-231-15 Assessing Water Damage To Gypsum Board. Most notably, gypsum board that has been exposed to sewage or flood waters must be replaced. Levels of bacteria, such as E. coli, can be hundreds of times above safe levels in flood water. Also, hydrocarbons from underground gas storage tanks and fuel leaks from submerged vehicles can be present. Often, the gypsum board will need to be removed anyway to assess the underlying substructure.
Is there a way to ensure that the gypsum board selected for my home restoration is code compliant?
Reference GA-1000-2017 Identification of Gypsum Board. This two-page publication will help you identify the criteria that are enforced in the U.S. and Canada for the sale and installation of gypsum board. Ensuring you are using gypsum board that meets the ASTM C1396 standard will help avoid specific local code violations. Never use board that is not labeled appropriately. Building codes throughout the United States require each individual sheet of gypsum board have the following information legibly printed on the back surface of each board, parallel to the bound edge of the board:
- The name of the manufacturing company or a unique alpha code identifying the name of the manufacturing company. The decision to print the name of the company or to create and use a unique code is at the discretion of the company.
- A code identifying the manufacturing facility and, where applicable in a multi‐line facility, the production line.
- A code identifying the date and time of manufacture.
- The country of manufacture as designated by the three letter code in ISO 3166‐1. The code for United States is USA. The code for Canada is CAN.
What is the proper way to store gypsum board on a project site to prevent moisture damage?
Pages 8 and 9 of GA-801-2017 Handling and Storage of Gypsum Panel Products: A Guide for Distributors, Retailers, and Contractors describes guidelines for stocking gypsum panel products on job sites. GA-801-2017 notes that gypsum panel products must be delivered just prior to installation time. This practice helps minimize damage to the material and reduces the risk of mold growth in surrounding areas of elevated moisture. GA-801 also states that panels must be kept in an enclosed covered, dry area, such as a garage, to minimize exposure to rain, etc.
After a fire event, does the gypsum board need to be replaced in rooms where fire occurred? What about rooms without fire exposure?
This is a very complex question. First, let’s look at just the fire/heat exposure aspect of a fire. For fire rated assemblies, the GA-600, Fire Resistance and Sound Control Design Manual states, “It is the intent that classifications shall register performance during the period of exposure and shall not be construed as having determined suitability for use after fire exposure.” Therefore, any assembly directly exposed to the fire should be rebuilt. For rated-assemblies not exposed directly to the fire, it is always best to have a certified/licensed fire protection engineer or inspector assess them and determine if they are still capable of performing as designed in a future fire. For non-fire rated assemblies exposed directly to the fire, replacement is also suggested as the exposed gypsum board would have experienced adequate heat to begin calcination. The board may be brittle, the paper face burned off, etc. Again, for gypsum board in non-exposed rooms, a judgment call by a specialist should determine the extent, if any, of replacement. However, fires also result in exposure to smoke and water. Water is the easiest to assess. First, it is critical to determine if the studs and other materials in the wall cavity are dry and undamaged. It is likely that at least some gypsum board will be removed to inspect the cavity and require replacement. If it can be verified that the contents of the wall cavity are dry and undamaged, a thorough examination of the board itself is necessary: The panels must be dry and free of mold with the paper facing completely intact. If in doubt, play it safe and replace the board. Smoke damage is very subjective. Some individuals claim to smell smoke in sealed and repainted rooms years after a fire. Some people never catch a hint of the odor. Restoration services exist that are licensed and bonded, and these specialists should be consulted to determine if restoration without replacement is possible.
Is it necessary to tape the joints in the base layers of fire-resistance rated multi-layer gypsum board systems to maintain the fire resistance rating?
No. In multi-layer systems, the joints and fasteners in the base layers are covered and protected by the overlying layers of gypsum board.
The system I am installing calls for "cooler" nails. I am having trouble locating a supply of these nails in my area. What kind of nail can I substitute for the cooler nail?
Any nail having a length, shank diameter, and head diameter equal to or greater than the dimensions specified for the cooler nail in the system description can be substituted for the cooler nail.
In a tested/listed fire assembly, what is the tolerance on the spacing of the fasteners described in the system?
Working with UL, the GA and its members have determined that approximately ± 1” (± 25.4 mm) is an acceptable tolerance in the spacing defined in a fire-rated assembly.
Must gypsum board be finished and painted?
According to ASTM C1396/C1396M Standard Specification for Gypsum Board, Section 13.1, “Gypsum board, except for pre-decorated gypsum board, is intended to be a substrate. The surfaces of gypsum board shall be true and free from imperfections that would render it unfit for finishing and final decoration. Gypsum board shall be installed and finished to the specified level in accordance with Specification C840.” All gypsum board used in interior wall and ceiling applications should be finished with tape and joint compound embedded in joints and interior angles, as well as an appropriate primer and paint. The application of these materials protects the integrity of gypsum board. Note, in a fire-rated system that includes multiple layers of wallboard, only the visible, board surface needs to be finished with tape, joint compound, primer, and paint. Paint and primer are unnecessary only in concealed areas that receive little or no active use, examples include attics and plenum areas above ceilings. Paint and primer are not necessary for these areas but tape and joint compound are required to provide fire resistance. To determine the level of finish appropriate to a specific situation, including gypsum panel products used as a substrate for tile, as a base for textured finishes, wallcoverings, and paints of various sheens, and lighter and darker tones, consult GA-214-2015, Recommended Levels of Finish for Gypsum Board, Glass Mat and Fiber Reinforced Board, available in the GA Bookstore.
What considerations should we bear in mind when designing and building fire-resistive gypsum board enclosures for duct assemblies?
Fire-resistive duct enclosures provide for some unique and challenging design and construction scenarios. In most cases, the code specifies that fire-resistive enclosures around duct assemblies be symmetrical (i.e. the inside of any one plane must be identical to the exterior). The intent is that regardless of whether the fire is on the inside or outside of the enclosure, it has the same degree of restriction. If a system is asymmetric but tested and certified both ways and passes the required fire-resistance criteria, it is acceptable. When designing the enclosure, remember that systems designed/tested for vertical surfaces cannot be arbitrarily used on the horizontal (i.e. underneath side) of the enclosure. This is the case for full wall systems, which cannot be used arbitrarily in floor-ceiling applications. Finally, the system must be built as tested. In a duct-specific system, the supports must be tied in, etc. per the drawings for that system. Also, system designs adapted from tested wall or floor-ceiling assemblies must be supported/built as in the drawings for the full system, including right-sized structural members, spacings, fasteners, and, etc. In the end, consulting with a fire design engineer is usually a very good idea when dealing with fire-resistive duct enclosures.
What is a thermal barrier? What gypsum panel product(s) can be used as thermal barriers?
A thermal barrier is a material that provides some protection from heat for substances that can melt or burn. National Fire Protection Association (NFPA) standard NFPA 275 provides a method for qualifying the fire performance of a thermal barrier. The Temperature Transmission Fire Test and the Integrity Fire Test are used to evaluate a material’s capacity to prevent ignition from a standard fire exposure or to delay its occurrence. The code reference often reads as follows, “[Material in question] shall be separated from the interior of a building by an approved thermal barrier consisting of 1/2 -inch (12.7 mm) gypsum wallboard or a material that is tested in accordance with and meets the acceptance criteria of both the Temperature Transmission Fire Test and the Integrity Fire Test of NFPA 275.” As indicated in the text above, a ½” gypsum board is a thermal barrier as would be gypsum panels of greater thickness when applied as part of a fire-resistant system. Want to learn more? Read Thermal Barriers and Ignition Barriers for the Spray Polyurethane Foam Industry.
What are the acceptable joint tolerances in gypsum construction?
Joints between boards in fire-rated assemblies must be in “moderate contact,” meaning that the gypsum boards should be touching and gaps minimal. All gaps and joints in such assemblies must be properly taped and filled with compound. Around electrical boxes, the UL Fire Resistance Directory references no more than a 1/8” (3.2 mm) gap/joint, though in the field this can be difficult to attain and measure. All gaps must be filled with joint compound, fire-rated caulking or other materials/means suitable, per the local code authority. In non-rated construction, joints up to ¼” (6.4 mm) tolerances are acceptable when filled with setting type, all-purpose joint compound. Note that the type of compound used to prefill gaps in the joints must be compatible with the compounds used to tape and finished the walls and/or ceiling. More information on joint tolerance is contained in the Northwest Wall and Ceiling Bureau Document #500-103 Gaps at Gypsum Board Joints available here.
The standard practice is to mount gypsum panel products such that a ¼” gap at exists between the board and the floor. Does this mean a fire-rated wall assembly needs to be caulked between the board and the floor?
More often than not, the answer is yes. In addition, fire-resistant walls often serve as a smoke barrier wall, which must be caulked. And, while some may see this as a control joint, the joint itself is not normally tested in most assemblies.The International Building Code addresses this firestopping in Section 715 as directed in Section 708: 708.8 Joints. Joints made in or between fire partitions shall comply with Section 715. 715.1 General. Joints installed in or between fire-resistance rated walls, floor or floor/ceiling assemblies and roofs or roof/ceiling assemblies shall be protected by an approved fire-resistant joint system designed to resist the passage of fire for a time period not less than the required fire-resistance rating of the wall, floor or roof in or between which the system is installed. Fire-resistant joint systems shall be tested in accordance with Section 715.3. Exception: Fire-resistant joint systems shall not be required for joints in all of the following locations:
- Floors within a single dwelling unit.
- Floors where the joint is protected by a shaft enclosure in accordance with Section 713.
- Floors within atriums where the space adjacent to the atrium is included in the volume of the atrium for smoke control purposes.
- Floors within malls.
- Floors and ramps within open and enclosed parking garages or structures constructed in accordance with Sections 406.5 and 406.6, respectively.
- Mezzanine floors.
- Walls that are permitted to have unprotected openings.
- Roofs where openings are permitted.
- Control joints not exceeding a maximum width of 0.625 inch (15.9 mm) and tested in accordance with ASTM E 119 or UL 263.
What is an R-value and how can I calculate the R-value of a wall assembly shown in GA-600 Fire Resistance and Sound Control Design Manual? Finally, why am I being asked to do this?
R-value (resistance value) measures the capability of a material or assembly to resist the transmission of heat. As energy codes have strengthened over the past several code cycles, so have the R-value requirements for exterior walls and roof assemblies. As codes have become less prescriptive and more performance-based, calculating R-values is becoming a design team duty. The GA does not list R-values for wall assemblies due to the high degree of variability between what is shown in GA-600 and what is actually constructed. Common elements, such as resilient channels, thicker studs, decreased stud or joist spacing, varying amounts and types of insulation, etc., are variables that are allowed for any system, per the General Explanatory Notes in GA-600. Variables such as cladding type also play a role in total R-value. However, calculating the R-value for an assembly is not exceptionally difficult, as it is essentially the sum of the R-value of the individual layers, accounting for stud closeness. ASHRAE, ICC, DOE, and others have developed code acceptable practices and methods for calculating R-values. One online tool based on ASHRAE’s Handbook of Fundamentals is available at www.ekotrope.com/r-value-calculator/. A quick online search will provide additional online tools for performing these calculations.
I understand that even mold/moisture resistant gypsum panels should not be used in so-called “wet areas.” Can you explain where this product can and cannot be used?
Mold/moisture resistant gypsum panels are excellent for use in high humidity areas and even where an occasional splash of water is expected. Appropriate areas include powder rooms, adjacent to showers or tubs, behind counter areas/base cabinetry where plumbing fixtures are located, and in laundry rooms, mud rooms, etc. However, neither the model codes nor the Tile Council of North America’s (TCNA) Handbook allows for the use of these panels behind the tile in the shower or tub area or as a base under the pan or around a swimming pool or sauna. For acceptable materials in wet areas, consult the local code or the TCNA.
What guidance can the Gypsum Association provide on the painting and finishing of new gypsum wallboard?
Over the years, the Gypsum Association has worked with many organizations to develop recommendations on finishing. The most important recommendation is priming: Before any additional decoration, gypsum board must be primed. For a more complete guide on painting and finishing new wallboard, we suggest the Drywall Finishing Council publication entitled, “Recommended Levels of Paint Finish Over Gypsum Board.” Access this publication here. Additionally, GA-214 Recommended Levels of Finish for Gypsum Board, Glass Mat and Fiber-Reinforced Gypsum Panels, provides guidance for surface preparation. GA-214 is available in hardcopy or PDF in the Gypsum Association Bookstore.
Is there specific guidance from the Gypsum Association on when gypsum board needs to be replaced after a fire?
The short answer is no. Any gypsum board that has been damaged by fire or as a result of the firefighting process must be replaced; however, a board that was simply exposed to smoke has no definitive replacement criteria. In this case, the replacement will be determined on a case-by-case basis by the owner, contractor, and the insurance company.
I have a renovation project where I am required to install a 1-hour fire-resistant floor/ceiling assembly that is also sound rated. I have found an assembly in the Fire Resistance and Sound Control Design Manual that is comparable, but uses I-joists of the same dimension of the lumber joists I have on this project. Can I use that assembly?
This question, like many received by the Gypsum Association’s Technical Services Department, is answered by referencing the Manual’s General Explanatory Notes. Note 19, page 20, in the 22nd edition of the Manual, GA-600-2018, provides the answer: "Specified floor-ceiling and roof-ceiling framing sizes or truss dimensions are minimums. Greater joist or truss sizes (depths) shall be permitted to be used in metal- or wood-framed systems . . . [emphasis added]." As a sawn lumber joist is of greater dimension and mass than the same sized I-joist (you can see this by looking at the cross-section), as long as the structural criteria are met, you may make the substitution.