USG Cavity Wall Shaft Systems Page 8

USG Cavity Shaft Wall Systems

Air Handling Systems
Gypsum shaft walls have been used for many years to house all types of ducts in the shaft area. Their fire-resistant features plus economical dry construction make them ideal for this use. Today shaft walls are used successfully without a metal liner for handling return air in HVAC systems. To function properly, shaft wall systems should be designed with the following performance provisions.

1. Gypsum board surface temperature does not exceed 125°F
   
2. Air stream dew point temperatures are maintained below gypsum board surface temperature.
   
3. The assembly is constructed to withstand sustained design uniform air pressure loads not exceeding 10 psf.
   Start up surge loads should not be greater than 1 -1 /2 times the design static load. (See table below for limiting heights).
   
4. Separate approved liners should be installed in areas subject to continuous moisture overspray, condensation
   or air stream temperature over 125°F
   
5. To ensure airtight construction, select appropriate sealants and apply where required.

Limiting Heights--Unlined Return Air Shafts

Sustained pressure load-psf

2 hr Fire-rated
system

1 hr Fire-rated
system

Stud type & size

Desig-
nation

Stud
Spcg

Allow.
defl.

5

10

5

10

2-1/2" C-H
Studs

212CH25

24"

L/120

10'5"

7'5"

10'5"*

6'0"*

L/240

10'5"

7'5"

8'6"

6'0"*

L/360

9'3"

7'5"

7'5"

5'11"*

212CH22

24"

L/120

14'8"

10'5"

14'8"

10'5"

L/240

13'0"

10'4"

11'11"

9'5"

L/360

11'5"

9'0"

10'5"

8'3"

212CH20

24"

L/120

15'9"

11'2"

15'4"

11'2"*

L/240

13'4"

10'7"

12'2"

9'8"

L/360

11'7"

9'3"

10'8"

8'3"

4" C-H
Studs

400CH25

24"

L/120

13'10"

9'8"*

13'9"*

6'11"*

L/240

13'10"

9'8"*

13'4"

6'11"*

L/360

12'5"

9'8"*

11'8"

6'11"

400CH20

24"

L/120

20'0"

15'0"*

19'3"

15'0"*

L/240

15'10"

12'7"

15'3"

12'2"*

L/360

13'10"

11'0"

13'4"

10''7"*

6" C-H
Studs

600CH20

24"

L/120

27'7"

18'0"*

26'8"*

13'6"*

L/240

21'11"

17'5"*

21'2"'

13'6"*

L/360

19'2"

15'2"

18'6"

13'6"*

Double 6"
E-Studs

600ES25

24"

L/120

18'9"

9'3"

18'9"

9'3"

L/240

18'9"

9'3"

18'9"

9'3"

L/360

18'9"

9'3"

18'9"

9'3"

600ES20

24"

L/120

28'0"

20'0"*

28'0"

20'0"*

L/240

26'3"

20'0"*

24'9"

20'0"*

L/360

23'0"

18'3"*

21'9"

17'3"*