Cannt strips


#1

what are cant strips? :?:


#2

jm.com/roofing_systems/built … RS5049.pdf

A beveled support used at the junction of a flat surface and a vertical surface to prevent bends and/or cracking of the roofing membrane at the intersection of the roof deck and wall.


#3

Yes, as Tar Monkey said, they are meant to eliminate cracking due to bridgeing of the roofing membrane over the transition area.

I do not usually use them, but only because we know how to install tight. If we are doing a spec job, we use them.

I warrant my roofs for ten years, and have never once had a problem due to lack of cant. IMO, it is a remedial practice due to the apathy of most installers.


#4

cant strips are required by most mfgrs as part of their warranty.unless you are using a 1.5" roller to install your modified at penetrations a good seal is not guaranteed.also with granulated modifieds cracking will occur with a 90 degree bend. its not made to take the stess well anymore.


#5

If you install 90 degree change of planes with modified bitumen that utilizes a fiberglass scrim, you will break the scrim and the change of plane becomes the weak point in your membrane. In addition, years-and-years ago, composition base flashings on built-up roofs were generally adhered to the vertical and horizontal substrates, but were not adhered to the cant strip. This allowed for movement to occur along the entire +/- four-inch face of the cant strip; nobody does this anymore, but that used to be a common practice. As previously stated, cant strips are not required with most non-bituminous single-ply membranes.


#6

Are you saying that you cannot go past 90 degrees? Its pretty darned flexible, even floppy when its hot.


#7

BTW, how you doing, Cerb?


#8

I’m doing pretty good Aaron, thanks for asking.

As for the clarification on the 90 degrees, you obviously can bend mod. bits. when hot with generally little damage. Of course, most of your mod. bits. are going to be polyester reinforced as opposed to fiberglass reinforced. There are still several membranes that are only fiberglass reinforced and even some that have both types of reinforcement. But dealing with just the fiberglass reinforced mod. bits., I would not recommend making 90 degree bends, and suggest you use a cant strip to create two 45 degree bends instead.

A good example of what I’m talking about is the old Derbigum once Owens Corning got their hands on the product. The Derbigum utilized a fiberglass scrim, and if you bent it at 90 degrees you typically broke the fiberglass scrim that is meant to reinforce the membrane.

Now if you are asking “can it be done.” Well, of course you can install mod. bit. without cant strips. I will caution those that do it, however, that you are most likely to experience movement along the 90 degree break and the flashing membrane could become disbonded and bridged.


#9

[quote=“Cerberus”]

I’m doing pretty good Aaron, thanks for asking.

A good example of what I’m talking about is the old Derbigum once Owens Corning got their hands on the product. The Derbigum utilized a fiberglass scrim, and if you bent it at 90 degrees you typically broke the fiberglass scrim that is meant to reinforce the membrane.

Now if you are asking “can it be done.” Well, of course you can install mod. bit. without cant strips. I will caution those that do it, however, that you are most likely to experience movement along the 90 degree break and the flashing membrane could become disbonded and bridged.[/quote]

Brai SP4 used to crack badly in colder temps, Am I correct to assume also a fiberglass scrim?

As far as the disbonding at the crotch, this is EXACTLY why I require full welding/adhesion at all two-ply laps. I agree with you that if you do not maintain strict adherance (sp?) to this, you will end up precisely as described.


#10

Hey,just switch to rubber roofs guys and you wont have to worry about the crap cracking or putting in a cant. Modified is a dinosaur.

RooferJim


#11

Actually, EPDM is older.