Gypsum Board Assemblies
Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
Showing changes from Rev 6
to Rev 7
in Gypsum Board Assemblies.
---
title: Gypsum Board Assemblies
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### It is the most economical board type and is appropriate for the majority of interior office, retail, and light commercial applications. {note}
+### The thickness of regular gypsum board shall be specified for each application.
+
```datasheet
label: Regular Gypsum Board Thickness
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```
+### The edge profile of regular gypsum board shall be specified to suit the intended finishing method.
+
```datasheet
label: Regular Gypsum Board Edge Profile
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### The 5/8-inch Type X board is the standard board for fire-resistance-rated gypsum board assemblies in commercial construction and is the most common board type required by fire-resistance design numbers. {note}
+### Type X achieves its fire resistance through special core additives — typically glass fibers — that maintain core integrity and slow heat transmission, and the fire-resistance rating of an assembly using Type X board is a property of the entire assembly because the board alone does not carry a rating. {note}
+
+### The Contractor shall verify that the board, framing, fastener pattern, and all other assembly variables match the cited fire-resistance design number precisely.
+
```datasheet
label: Type X Gypsum Board Thickness
…7 unchanged lines
```
−### Type X achieves its fire resistance through special core additives — typically glass fibers — that maintain core integrity and slow heat transmission, and the fire-resistance rating of an assembly using Type X board is a property of the entire assembly because the board alone does not carry a rating. {note}
−
−### The Contractor shall verify that the board, framing, fastener pattern, and all other assembly variables match the cited fire-resistance design number precisely.
−
## Type C Gypsum Board {toc}
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### All Type C products also qualify as Type X, but Type X products do not qualify as Type C. Type C is required by certain GA-600 and UL fire-resistance design numbers that demand longer fire ratings (commonly two hours) at thinner board profiles than Type X can achieve. {note}
+### The Contractor shall not substitute Type X for Type C in assemblies where the design number specifically calls for Type C, because the expansion behavior that maintains joint integrity under prolonged fire exposure is specific to the Type C formulation.
+
```datasheet
label: Type C Board Required
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```
−### The Contractor shall not substitute Type X for Type C in assemblies where the design number specifically calls for Type C, because the expansion behavior that maintains joint integrity under prolonged fire exposure is specific to the Type C formulation.
−
## Moisture- and Mold-Resistant Gypsum Board {toc}
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### Mold-resistant products additionally contain biocidal additives in the core and face paper to resist mold and mildew growth under elevated humidity conditions. {note}
+### The core designation of moisture- and mold-resistant gypsum board shall be specified based on the humidity and mold-exposure conditions of the space.
+
```datasheet
label: Moisture/Mold-Resistant Board — Core Designation
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### Glass-mat boards are appropriate for high-humidity environments, behind tile in wet areas above grade, and for exterior-facing applications such as gypsum sheathing that will be exposed during construction. {note}
+### Glass-mat boards designated for interior use differ from glass-mat sheathing in their surface texture, coating, and edge treatment, and the two product types are not interchangeable. {note}
+
+### In high-humidity interior locations, glass-mat board provides a more robust moisture-resistance performance than paper-faced moisture-resistant board and should be specified wherever the consequences of mold contamination are serious — healthcare, hospitality, and occupied multi-family.
+
```datasheet
label: Glass-Mat Gypsum Board
…6 unchanged lines
```
−### Glass-mat boards designated for interior use differ from glass-mat sheathing in their surface texture, coating, and edge treatment, and the two product types are not interchangeable. {note}
−
−### In high-humidity interior locations, glass-mat board provides a more robust moisture-resistance performance than paper-faced moisture-resistant board and should be specified wherever the consequences of mold contamination are serious — healthcare, hospitality, and occupied multi-family.
−
## Impact- and Abuse-Resistant Gypsum Board {toc}
### Abuse-resistant and impact-resistant gypsum board products have reinforced cores — typically higher-density gypsum with glass fiber and polymer additives — and reinforced face papers that resist dents, scuffs, and penetration better than standard board. {note}
### They are appropriate in corridors, stairwells, gymnasiums, activity rooms, healthcare support spaces, and other areas where the wall surface will be subject to carts, equipment, rolling loads, and physical contact. {note}
+### Abuse- or impact-resistant gypsum board and its required performance level shall be specified where the wall surface will be subject to carts, equipment, or physical contact.
+
```datasheet
label: Abuse/Impact-Resistant Board
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### Coreboard is a related product in 1-inch thickness used in solid or laminated solid-core partition systems; its application is limited to specific design configurations. {note}
+### Whether shaftliner board is required for an H-stud shaft wall assembly shall be specified for each applicable partition configuration.
+
```datasheet
label: Shaftliner Board Required
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### For typical commercial partitions up to 10 feet in height under normal lateral loading, 25-gauge studs at 16 inches on center are often acceptable; partitions over 12 feet in height, or partitions subject to elevated lateral loads such as those adjacent to exterior walls in high-wind zones, require heavier gauge. {note}
+### The steel stud gauge shall be specified based on the partition height and the lateral loading it will be subject to.
+
```datasheet
label: Steel Stud Gauge
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### Furring channels — hat-shaped channels and resilient channels — are used to attach gypsum board to masonry or concrete substrates, to provide a cavity for mechanical and electrical runs, and, in the case of resilient channels, to acoustically decouple the gypsum board from the framing to improve sound isolation. {note}
+### The furring channel type shall be specified based on the substrate attachment and acoustic decoupling requirements of the assembly.
+
```datasheet
label: Furring Channel Type
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### Area separation walls and shaft walls use 1-inch shaftliner panels captured in H- or I-studs combined with Type X face layers. {note}
+### The number of gypsum board layers on the fire-exposed side of the assembly shall be specified per the governing fire-resistance design number.
+
```datasheet
label: Number of Board Layers — Fire-Exposed Side
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```
+### The number of gypsum board layers on the non-fire-exposed side of the assembly shall be specified per the governing fire-resistance design number.
+
```datasheet
label: Number of Board Layers — Non-Fire-Exposed Side
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### A gap or an improperly filled joint at the top of a rated partition creates a direct air path that negates the fire rating. {note}
+### The head-of-wall condition — whether the partition runs to a fixed deck or to a deflection head — shall be detailed on the drawings and shall be executed as shown.
+
```datasheet
label: Head-of-Wall Fire-Rating Detail
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```
−### The head-of-wall condition — whether the partition runs to a fixed deck or to a deflection head — shall be detailed on the drawings and shall be executed as shown.
−
### Where a deflection head detail is used, the joint between the top of the gypsum board and the underside of the deck or ceiling above shall be filled with a listed intumescent sealant or equivalent fire-rated flexible joint system that accommodates the design deflection movement while maintaining the fire rating throughout the life of the building.
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### Shaft walls enclose elevator shafts, stair shafts, mechanical chases, and other vertical openings that penetrate multiple floors. {note}
### They must provide both the required fire resistance — typically two hours for commercial buildings per IBC requirements for elevator and stair shafts — and the structural capacity to span floor-to-floor without framing on both sides of the panel, because the inside of the shaft is not accessible for framing after construction.
−### Shaft walls use 1-inch shaftliner panels installed horizontally between I-shaped or C-H steel studs anchored to the floor and ceiling runners, with Type X face layers applied to the stud faces on the accessible side. {note}
```datasheet
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default: "Not applicable"
```
+### Shaft walls use 1-inch shaftliner panels installed horizontally between I-shaped or C-H steel studs anchored to the floor and ceiling runners, with Type X face layers applied to the stud faces on the accessible side. {note}
### Any damage to shaftliner panels during installation — cracking, crushing of the edge, or improper fit in the stud channel — shall cause rejection and replacement of the affected panel, because damaged panels may not carry the design lateral load or maintain the fire-resistance rating.
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### Field performance measured per ASTM E336 (Field Sound Transmission Class, FSTC) typically runs 3 to 5 STC points below laboratory performance due to flanking paths, construction variations, and penetrations. {note}
+### The Architect shall specify the required STC for each partition type, taking into account the design goal (occupant privacy, program adjacency, HIPAA or similar requirements), the available wall cavity depth, and the acceptable construction cost.
+
```datasheet
label: Required STC Rating
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```
−### The Architect shall specify the required STC for each partition type, taking into account the design goal (occupant privacy, program adjacency, HIPAA or similar requirements), the available wall cavity depth, and the acceptable construction cost.
−
### Specifying STC without specifying the assembly design number or without coordinating framing, insulation, and perimeter sealing leaves the performance undefined, because the Contractor may build a compliant-looking assembly that does not achieve the rated STC when one or more critical details is missing. {note}
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### Back-to-back electrical boxes installed in the same stud bay provide a direct acoustic path through the partition because only the thin panel of gypsum board and the box depth separate the two cavities. {note}
+### Back-to-back boxes shall not be installed in the same stud bay in any acoustically rated partition.
+
+### Boxes shall be offset a minimum of 24 inches horizontally in the partition.
+
+### In high-STC applications, all boxes shall be provided with pre-formed acoustic putty pads or listed acoustic box covers that seal the box perimeter and the knockout openings.
+
```datasheet
label: Electrical Box Treatment in Acoustic Partitions
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```
−### Back-to-back boxes shall not be installed in the same stud bay in any acoustically rated partition.
−
−### Boxes shall be offset a minimum of 24 inches horizontally in the partition.
−
−### In high-STC applications, all boxes shall be provided with pre-formed acoustic putty pads or listed acoustic box covers that seal the box perimeter and the knockout openings.
−
# Accessories and Trim {toc}
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### Reveal and shadow-line beads shall be installed plumb and level, attached per the manufacturer's instructions, and finished to the same level as the adjacent gypsum board.
−## Control Joints {toc}
+## Control Joint Beads {toc}
```datasheet
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### Drying-type compound is used for finish coats because it is lighter, sands more easily, and produces a smoother surface; it cannot be applied in thick coats without shrinkage cracking and is not suitable for embedding tape in high-humidity conditions. {note}
+### The joint compound type used for the tape embedding coat shall be specified, and drying-type compound shall not be used to embed tape in high-humidity conditions.
+
```datasheet
label: Tape Embedding Coat Compound Type
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```
+### The joint compound type used for the finish coat shall be specified.
+
```datasheet
label: Finish Coat Compound Type
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### Paper tape embedded in setting-type compound at the first coat with finish coats of drying-type topping compound is the standard sequence for commercial construction. {note}
+### Joint tape shall conform to ASTM C475/C475M.
+
```datasheet
label: Joint Tape Type
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```
−### Joint tape shall conform to ASTM C475/C475M.
−
## Levels of Finish {toc}
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### **Level 0:** No finishing required. {note}
−### Typically reserved for temporary construction or spaces where the final decoration has not been determined. {note}
−### No tape, compound, or accessories required. {note}
+- Typically reserved for temporary construction or spaces where the final decoration has not been determined.
+- No tape, compound, or accessories required.
### **Level 1:** Tape embedded in joint compound at all joints and interior angles. {note}
−### Excess compound and tool marks acceptable. {note}
−### For plenum areas above ceilings, attics, and areas concealed from normal view. {note}
−### Fire-resistance-rated assemblies in concealed locations frequently require Level 1 to confirm that joints are taped. {note}
+- Excess compound and tool marks acceptable.
+- For plenum areas above ceilings, attics, and areas concealed from normal view.
+- Fire-resistance-rated assemblies in concealed locations frequently require Level 1 to confirm that joints are taped.
### **Level 2:** Tape embedded and covered with a skim coat of compound, fastener heads covered once. {note}
−### Used under tile and where surface appearance is not a consideration — garages, mechanical rooms, warehouse space. {note}
−### Not suitable for paint. {note}
+- Used under tile and where surface appearance is not a consideration — garages, mechanical rooms, warehouse space.
+- Not suitable for paint.
### **Level 3:** Tape embedded, two coats of compound on joints and angles, one coat on fastener heads, accessories coated. {note}
−### Sanded smooth. {note}
−### Suitable for heavy or medium-texture spray finishes. {note}
−### Not suitable for flat paint or light texture. {note}
+- Sanded smooth.
+- Suitable for heavy or medium-texture spray finishes.
+- Not suitable for flat paint or light texture.
### **Level 4:** Tape embedded, three coats on joints and angles, two coats on fasteners, accessories coated. {note}
−### Sanded smooth. {note}
−### Suitable for flat or low-sheen paints, light textures, and most commercial finishes. {note}
−### This is the standard finish level for commercial office, retail, and institutional applications. {note}
+- Sanded smooth.
+- Suitable for flat or low-sheen paints, light textures, and most commercial finishes.
+- This is the standard finish level for commercial office, retail, and institutional applications.
### **Level 5:** All surfaces receive a skim coat of joint compound or a proprietary compound over the entire board face after Level 4 preparation. {note}
−### The skim coat fills surface texture differences between the compound-covered areas and the raw board face, producing a uniform surface. {note}
−### Required for gloss or semi-gloss paints, critical lighting environments, and high-end residential or hospitality applications. {note}
−### Level 5 is also the correct specification for any application where the lighting angle is severe enough that board-face texture differences will be visible — sidelighting from clerestories, large windows at low angles, or track lighting. {note}
+- The skim coat fills surface texture differences between the compound-covered areas and the raw board face, producing a uniform surface.
+- Required for gloss or semi-gloss paints, critical lighting environments, and high-end residential or hospitality applications.
+- Level 5 is also the correct specification for any application where the lighting angle is severe enough that board-face texture differences will be visible — sidelighting from clerestories, large windows at low angles, or track lighting.
+### The finish level shall be selected based on the final paint sheen.
+
```datasheet
label: Finish Level
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```
−### The finish level shall be selected based on the final paint sheen.
−
### When in doubt, the Architect should specify Level 5 for any space where gloss or semi-gloss paint is indicated.
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### When perimeter relief is provided, the gypsum board at the ceiling perimeter is not fastened to the wall framing, a control joint bead or casing bead terminates the ceiling board edge, and the joint at the wall is left as a reveal or sealed with a flexible sealant. {note}
+### Whether perimeter relief is provided at the ceiling perimeter shall be specified for each gypsum board assembly.
+
```datasheet
label: Perimeter Relief Provided at Ceiling
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### The Contractor shall document any conditions observed during installation that may affect the performance or durability of the gypsum board system — such as evidence of water infiltration, inadequate climate control during installation, or structural irregularities — and shall bring them to the Architect's attention before completing the work.