11

WCP Roof DrainageWCP Roof Drainage

Harry NelsonHarry Nelson

2/4/20082/4/2008

22

WCP blueprints called for roof drains with strainers

However, the space allocated for the strainer diameter (≈2”)

was much smaller than the ANSI standard (3.75”)

ANSI Standard A112.21.2M (1983)

DANSI Standard A112.21.2M

specifies the area covered by the diameter D above

Area = 11 inches2 → D=3.75”

33

Living

Dining

CourtyardStorage/Utility

Patio #2FamilyKitchen

Patio #1

StudyAtrium

2 Bedroom UnitInternal DrainLocations⊗= top of drain∇= bottom

Some units mirror-imaged.

Drain from garage deck omitted.

Drains #4 and #5 are on `flat roof’ portion and have `badmitton birdie’drain strainers

Other drains have `box mesh’ strainers of questionable effectiveness.

Adjoined units share drains #7 and #8 - #8 exits under the garage deck of one of the two adjoined units, and empties into that unit’s carport

Solitary units have #8 bottom below its top, on the wall away from the carport

⊗

∇

#1

#2

∇

∇

∇

∇∇

∇

∇

⊗

⊗

⊗⊗

⊗

#3

⊗

⊗

#4#5

#6

#7

#8(∇)

44

Living

Dining

CourtyardStorage/Utility

Patio #2FamilyKitchen

Patio #1

StudyAtrium

⊗

∇

#1

#2

∇

∇

∇

∇∇

∇

∇

⊗

⊗

⊗

⊗

⊗

#3

⊗

⊗

#4#5

#6

#7

#8(∇)

3 Bedroom UnitInternal DrainLocations⊗= top of drain∇= bottom

Some units mirror-imaged.

Drain from garage deck omitted.

Drains #4 and #5 are on `flat roof’ portion and have `badmitton birdie’drain strainers

Other drains have `box mesh’ strainers of questionable effectiveness.

Adjoined units share drains #7 and #8 - #8 exits under the garage deck of one of the two adjoined units, and empties into that unit’s carport.

Solitary units have #8 bottom below its top, on the wall away from the carport.

55

Strainers omitted when WCP built! – no roomMerely small area holes in roof surface

Strainers omitted when WCP built! – no roomMerely small area holes in roof surface

#1 D=1 1/2”Area = 1.8 in2

#2 D=1 3/8”Area = 1.5 in2

#3 D=1 3/8”Area = 1.5 in2

#6 D=1-1.5”Area = 1.2 in2

#7 D=1 3/8”Area = 1.5 in2

#8 D=1 1/2”Area = 1.8 in2

#4 D=4 1/2”Area = 16 in2 #5 D=4 1/2”

Area = 16 in2

66

• 2 out of 8 of the drains have strainers and meet ANSI standards on area

• 6 out of 8 of the drains are merely roof holes without strainers, and the holes are only 14% (on average) of the ANSI standard area

• The point of the area requirement is to suppress drain clogs

• WCP roof drains are notoriously prone to clogging, causing overflows through the scuppers, which in some cases flood home interiors

•The WCP clogging problem is likely due to the small area of the roof drains

• 2 out of 8 of the drains have strainers and meet ANSI standards on area

• 6 out of 8 of the drains are merely roof holes without strainers, and the holes are only 14% (on average) of the ANSI standard area

• The point of the area requirement is to suppress drain clogs

• WCP roof drains are notoriously prone to clogging, causing overflows through the scuppers, which in some cases flood home interiors

•The WCP clogging problem is likely due to the small area of the roof drains

77

The bottom of drain #6 is visible from the attic above the master bedroom.

This proves that a drain, and not some sort of extension of the drainage pipe, was used in the roof gutters.

The upward portion of the drain appears to have been covered with bitumen and the strainer omitted.

The fate of the 6” diameter flashing ring/flange on this drain is unclear.

The bottom of drain #6 is visible from the attic above the master bedroom.

This proves that a drain, and not some sort of extension of the drainage pipe, was used in the roof gutters.

The upward portion of the drain appears to have been covered with bitumen and the strainer omitted.

The fate of the 6” diameter flashing ring/flange on this drain is unclear.

88

Mesh strainers have been fabricated to try to prevent drain clogs. These are better than nothing, but not particularly effective.

Mesh strainers have been fabricated to try to prevent drain clogs. These are better than nothing, but not particularly effective.

99

The inner diameter of the pipes in the internal drain system is 2”, area 3.1 inches2.

1979 SMACNA ASMM (3rd ed.) specifies minimum area of 7 inches2 (D=3”), and specifies constant area over the length of the downspout.

The inner diameter of the pipes in the internal drain system is 2”, area 3.1 inches2.

1979 SMACNA ASMM (3rd ed.) specifies minimum area of 7 inches2 (D=3”), and specifies constant area over the length of the downspout.

The inner diameter of tops of the downspout pipes is at most 1 5/8”, area 2.1 inches2.

The inner diameter of tops of the downspout pipes is at most 1 5/8”, area 2.1 inches2.