Chimney base flashing anchor points


Good morning!

I am in the process of finishing last detail on the roof and don’t quite have a good guidance on roof base flashing. Basically, it is very clear how regular chimney is base flashed that has roofing on both sides of chimney - since when I bend the flashing on both sides, the flashing is nailed into roof deck through the triangular tongue of flashing that will be covered with shingle above and step flashing. In our case, the chimney is on the gable edge of roof, therefore only one side will have this “tongue”. The other side will terminate flush at a stop where shingles/roof decking ends on the gable. I refuse to nail through the visible flashing part as it will be a potential leaking spot. I was thinking about nailing into the “tongue” on one side and then using mortar screw, to screw it into the mortar joint on the other side, so that the flashing is fully adhered. Then I am thinking I am attaching one metal to 2 dissimilar substrates which will have differential movement. Should I forego tongue-nailing and instead screw both sides into chimney mortar? These screws will be covered by counter-flashing, so leaking here won’t be an issue and they will be attached only to the similar substrate. Or do as I planned and nail to decking on one side and mortar joint on other? There will be some ability to differentially move, but not as well as if I only nailed to roof decking alone. Below is the photo of my soldered base flashing (once again, not the prettiest of jobs, but will do the job okay). There is no “tongue” on there as I soldered another piece of copper to eliminate potential leak spot, but the area on the top right on the roof plane is what I consider “tongue nailing spot.” The other side terminates without it, so you can see there is nothing to adhere it to besides the chimney itself.


We normally just put 1 1/2" flat clips on the roof before putting the base in, nailed 1" above where the base flashing ends once installed. Bend the clips up and and over the exposed flashing. You can rivit or solder if you like. Sometimes when necessary I will zamak the copper into the masonry where the counter flashing will cover it.


Thank you, MPA! You ALWAYS give such a great advice. I went to Lowe’s but wasn’t sure where to look for the clips, even involved a staff member to no avail. Also kind of worried of galvanic corrosion but not sure if using pliable copper in place of these clips would be much help. Don’t have copper riveting tool either and worried about setting house on fire to solder in place (I use open flame soldering gun). So I got frustrated and with 1 hour of daylight left, just jammed the blue Tapcon screw. Made a larger hole in copper so it will have some space to expand and contract and used two nails on the other end to attach to the roof decking below step flashing. Seems fairly sturdy, only hurricane is likely to bend the flashing, but time will tell. It is very sturdy on the side with the “tongue” but more pliable, albeit still hard to lift, on the other side. Worst case, I can always drive a couple of nails on the roof surface and Geocel the penetrations, although hope to never have to do this. Seems like this would increase the chance of leaking in the future. Despite have this piece soldered, I also placed a bead of Geocel at the corner just be extra sure no leaks form in that place. Until I get this counter flashed into the mortar joint, I went ahead and placed a good bead of Geocel around the top of flashing and step flashing as a temporary resistance to rain, like you suggested, since I don’t have Zamak.

I need to make another custom solder flashing for the top part of the roof to ensure it never leaks. I seem to like using solder instead of relying on permanency of Geocel. Although all my soldering jobs look like crap.


Looks great, once the counter is in you will never see the tapcon, just don’t drive the counter in super tight. All we use for clips are scraps of copper 1 1/2 x 4.

Trick I show new guys soldering with an open flame is solder from the back side first, sweat it in good, then flip it over and pretty up the front. When you hear the reverse side it will pull the solder in even better.


I should’ve gone with the first instinct after reading your advice to use the scrap pieces of copper and you’re right, it would have provided an above average uplift resistance. For some reason I thought copper is too malleable to function as sturdy clip. Oh, man! I always rush with these things and then regret rushing instead of thinking it through. But I reckon if wind is so strong to bend this copper flashing, a few shingles will also likely go missing… MPA, how far from the bottom should the counter flashing terminate? I know I shouldn’t make it flush with the roof surface, but what’s the industry average to look good while being sufficiently protective?


I like 1/2-1". I have worked with guys for years who make them flush with the shingles and when they Install the counter if it is a little tight it pushes the bend up so if the caulk fails the water runs into the masonry. 99% of the time it won’t ever leak, but it Just erks me a little because there is a better way.