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Cricket Slope

P

Phil B

SAWHORSE
Joined
Sep 15, 2018
Messages
199
Location
Florida
We all 'know' that crickets should be 1/2" in 12 minimum on a low slope roof, but where does it say that in the code. I think I've seen it but can't find it.
 
Phil B said:
Google's dangerous. Minimum slope on low-slope roofs is 1/4" / ft. That is in the code.
Click to expand...
That is correct unless it is a reroof:
R908.1 General. Materials and methods of application used for re-covering or replacing an existing roof covering shall comply with the requirements of Chapter 9.

Exceptions:
  1. Reroofing shall not be required to meet the minimum design slope requirement of one-quarter unit vertical in 12 units horizontal (2-percent slope) in Section R905 for roofs that provide positive roof drainage.
 
The prescriptive requirement for main slope aka “design slope” is found in IBC 1507 for the listed types of roof.
For example, 1507.10 says 1/4:12 for design slope.

I don’t believe there is a mention regarding crickets. However, 1507.1 says roofing should be installed per manufacturer’s instructions. Many manufacturers either state, or refer to NRCA which states, a performance requirement that any standing water should evaporate within 48 hours after rainfall under conditions conducive to drying. This is to prevent membrane tearing due to differential expansion/contraction related to dry membrane being hotter that wet membrane on a sunny day.

If you think about it, a 45 degree (in plan view) cricket will have a little over 1/8”:12” slope on the valley, and minimum 1/4”:12” on the slope of the cricket.
 
1503.5 Crickets and saddles. A cricket or saddle shall be installed on the ridge side of any chimney or penetration greater than 30 inches (762 mm) wide as measured perpendicular to the slope. Cricket or saddle coverings shall be sheet metal or of the same material as the roof covering.

It's a tangential relationship. If you're using asphalt shingles for the roof and choose to use them for your cricket, you have to follow the minimum slope requirements for that product.
 
Joe.B said:
1503.5 Crickets and saddles. A cricket or saddle shall be installed on the ridge side of any chimney or penetration greater than 30 inches (762 mm) wide as measured perpendicular to the slope. Cricket or saddle coverings shall be sheet metal or of the same material as the roof covering.

It's a tangential relationship. If you're using asphalt shingles for the roof and choose to use them for your cricket, you have to follow the minimum slope requirements for that product.
Click to expand...
Good point.
And when the original post mentioned crickets, I was envisioning huge swaths of slow-slope roof.
But of course a cricket is really any additional slope (usually triangular in plan) that redirects the gravity flow of stormwater with a lateral vector.
1718302344327.png
 
I’ve typically drawn low slope crickets at a 1:2 angle in plan. Cricket material tapered at 1/2 inch per foot sits on the base layer sloped at 1/4 inch per foot and causes a resulting surface slope of about 1/4 inch per foot toward the valley. NRCA recommends slope of at least 1/8 inch per foot in the valley, but this method is slightly lower than that. On my projects the roofing material is usually TPO.
 
The 2000 IBC required a 2% (1/4" per foot) slope. My 1970 AIA Manual of Built-up Roof Systems book recommends 1/4" per foot, although 1/8" was more common and many architects were still specifying dead-level roofs.
 
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