Waterproof roofing fasteners

Stan in Oly, WA

Well-known Member
I had to tear off and replace the siding on two very small gable ends at the top of the hips on the roof of the house I just reroofed. I put down a flashing before I installed the new siding, but when I pressed the siding into place, it made the horizontal part of the flashing stick out at a 90 degree angle instead of lying against the roofing. I don't know how to make it lie down. If I nail it, then I will have exposed nail heads to become the source of future leaks. I went to considerable lengths to make sure that no seam in the roofing was within 4" of a nail in the course below it, so I hate to have to nail down a flashing and then depend on some kind of waterproofing product to seal it. But I can't think of what else to do.

Stan
 
Hi Stan.

I have a similar detail over my front porch, where the roof meets the floor and the exterior wall of the 2nd floor. Sounds like you want it larger than a 90 degree angle to follow the roof pitch.

Exposed fasteners if not properly selected, or installed, can be problematic, as I have seen in assemblies I have built or mocked up in the various architectural and engineering testing labs I have worked at across the U.S. and were required by architects specifications for air and water infiltration testing of their designs. They can be one of the primary sources of leaks in some situations if not installed correctly. Sometimes there is no other work around, although designers will try to avoid using them if possible, they can be installed and be waterproof as I have seen.

I assume you have new 5/8" sheathing and shingles, but do you have any W R Grace Ice & water shield under the shingles or just 15/30lb felt paper ? W R Grace is an excellent product, because it is self healing around fasteners that penetrate it. Its elastomeric enough to seal.

You could install screws with gaskets under the head of the screw that adjoin or will clamp down on the metal flashing. I would select a Silicon type sealant to cover each screw head. Be sure to follow the manufacturers instructions on preparation of the metal around the screw, clean or prime if necessary. I used to prefer Dow 790, 791 or 795 series of sealants, it simply was the best material judging from pull and adhesion testing I have witnessed. I used to call in Dow reps for the mock ups at testing labs as their material was high quality and instrumental for waterproofing these assemblies, so they passed the tests.

The shingles are not one even plane, so the torque applied to the fastener as it clamps down, must be monitored closely, so as not to deform, divot or tear through the metal.

Silicon is fine on aluminum flashing and likely most other non ferrous metals that would be used here, copper, etc. It is not compatible with asphaltic or bituminous materials. Cleaning the surface is important to achieve a good bond.

I thought of using some small sections of that WR Grace Ice and water shield on the under side of the flashing at each fastener location, but the adhesion side would be up and under the metal. My reasoning is the self healing properties, as the fastener penetrates through the metal, and that the course surface of the shingles will not penetrate the ice and water shield as its clamped or compressed by the fastener penetrating the metal flashing. It is an odd suggestion, but that elastomeric property is a good one. Silicon will bond to the metal, but not to the shingles.

The roofer used nails here and its 15 years or so now, I see they are just now needing some work, clean and apply sealant or new fasteneres, they did cover each nail head and though they are not 100%, I have no leaks or have noticed any problems. They are a small maintenance item at worst, so unless you find another solution, fastening and sealing the heads should suffice.

This is one of those gray areas where some careful thought may help find an alternative, but you can still use fasteners, just be sure to be redundant on sealing them where ever possible.
 
If using shingles on the roof I step flash as the shingle courses go up then counterflash with a single piece.

The ice guard that billy suggests is good stuff too and I have used it in trouble spots.
J
 
I'm familiar with copper and soldering, but what else can you solder in regards to sheet metal, I'd love to do that on the similar condition I have here on the house. I'm just not sure what and how you solder different metals. Simple and effective, really like the idea of that. I've seen a lot of copper flashings and soldered joints, but not fasteners, there's usually a reglet involved above and its bent in a fashion that's rigid.

The below detail is more for a parapet, but with shingles you can't return up against a wall, nor with asphalt roll roofing, would be nice if you could.
Detail
 
I used to work with a state agency and the guy in materials who signed off on the submital approvals, "if an as equal" was submitted, would take a nail and hold a sample of the as equal, ( to WR Grace I&W) puncture it and observe how it heals around the shank of the nail. If it performed he'd approve it, if not, thumbs down, and it was rejected, with a notation to provide specified material.
 
(quoted from post at 08:07:14 05/11/15) I've seen a lot of copper flashings and soldered joints, but not fasteners, there's usually a reglet involved above and its bent in a fashion that's rigid.

They do solder over fasteners, I have seen it on copper so I assume they are copper rivet type nails but Im not sure (It wasnt my work, I was just up there for related work). Its old school tech, hard to find people to do the work now.

I dont have pictures on this phone, I think that group is all in my archives from when I carried a dedicated camera or I would post some pictures of them.
 
I've seen a lot of copper flashing on jobs and recall some old timers knowing that kind of work, soldering copper flashing joints and such. It's ironic Stan posted about this kind of detail, (while clearing snow off the section on mine this past winter) I have about the same kind of flashing detail. I was wondering myself what else I could do there, besides topping off the heads with silicon. If the metal is cleaned up around the fastener, it will bond and stay for quite some time. I was wondering what alternate details would work, definitely like this idea.
 

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