Maximum allowable bend in modified bituminous membranes

[Michael Thomas]

Does anyone have a link to a standard for the minimum allowable bend radius for mod-bit at an outside corner (for example, over the top of a parapet wall)?

[Jerry Peck]

I'll see what I can find, but at inside corners they limit the bend to two-45 degree bends by installing cant strips along the bottom of the parapet wall.

[Michael Thomas]

I can make a few calls Monday morning, just though someone might have the info on hand.

[Jerry Peck]

Based on skimming through this ( http://www.gaf.com/Roofing/Commercial/Products/Modified-Bitumen-Roofing/Ruberoid-Modified-Bitumen-APP-Membranes/Documents/GAF_GAFGLAS_RUBEROID_Application_and_Specification _Manual__w-12-2525-v3.pdf ) and some other ones I found - I'm not sure that extending the modified over that type of outside corner is even allowed (for the reasons your photo shows).

The outside corners described in the installation instructions is referring to, as an example, going around the end of a parapet wall, not going over top of the parapet wall. At least that is the way I read it.

[Michael Thomas]

Thanks for looking.

[Rich Goeken]

Does anyone have a link to a standard for the minimum allowable bend radius for mod-bit at an outside corner (for example, over the top of a parapet wall)?

I have always seen metal flashing at the edges. Have not seen the roofing material bent over the side as in your photo. Maybe a manufactor/supplier site might include some installation detai.

Did find this cut that may help. Private Label Accounts - Metal-Era (http://www.metalera.com/PrivateLabel/JohnsManville.aspx)

[Michael Thomas]

Talked to GAF and Johns Manville, there is no minimum radius specified for outside corners because such bends (if present) must always be protected by an appropriate flashing.