Minimum flashing height?

I’ve seen numerous references to a “minimum flashing height” of 8 inches for flat roofs, yet when I look at some roofs and photos of roofs I see skylights with curbs that are way less than 8 inches high. Some look like they’re maybe 4 inches or so. What’s the real story on “minimum flashing height”?

See attached pic for an example.

It can depend on the roof. Is that tape on a rock? Or the roof below the rocks? Are there parapet walls on all sides? Open on all sides?

I’ve seen ‘bowl’ roofs built to hold water and 18" high wasn’t enough when the ‘bowl’ was only 1/2 full.

Check out the equipment curb under the small unit on the left. There’s no way that is 8 inches. The counter flashing is maybe 2 or 3 inches max, so that makes that curb about 6 inches max.

2" C.F. is fine. 5-6" flashing may be fine too. What heights were spec’d for the AC, etc? How much water does the roof hold? Does it just get wet as the rain water runs off?
There is no one spec that fits every roof.

BTW, you’re complaining or pointing out potential defeciencies by the HVAC people, and others. The roofer has to work with what’s there in most cases.
I haven’t seen anything wrong so far in your pix.

The reason I’m asking is because I’d like to use an equipment curb that would be a maximum of about 6" high, with a metal cap as the counterflashing (about 2"). I keep seeing that it has to be 8" but I’m also seeing some that are less. I guess the 8" is just a standard minimun flashing height that you’d like to have, but it can be flashed if it’s less?

I can see a skylight on my neighbors roof that has a curb about 4" or 5" high, and this was on a new house built in the last few years.

Waht kind of roof will it be on? Flat? Good drainage with 1/2" to 2" slope? 6" is about par for the course.

“I guess the 8” is just a standard minimun flashing height that you’d like to have, but it can be flashed if it’s less?" Yes, depending on the roof though! See my last reply.

Velux skylights for instance are a standard 4", but higher curbs can be built if necessary.

Yes, flat roof with good drainage. I don’t know the slope exactly but I think it’s 2".

You should be good to go.

Because of snow we go for 12" above membrane preferably, 8" minimum. If the insulation is poor water will pond and freeze and could overflow come spring.

Snow, what’s that? But seriously, we get a little here, but not much. If you’re up in Nova Scotia or New Brunswick I guess you get a lot more. By the looks of my roof and some others I’ve seen, people around here don’t worry about it too much. Ive see a lot of flat roofs with skylights on curbs that are maybe 4 to 5 inches tall. The flashing on some of my vents goes up maybe 4 to 6 inches.

The aluminum pipe portal that I just installed for refrig lines is only about 4 inches tall with a EPDM cap that adds another 2 inches or so.

So, there’s no “roofing code” like for electrical? I’ve seen some written roofing guidelines and standards though.

Gary im not sure if its really in the code book or not. However if i recall Carlisle & Firestone want a minimum of 9 inches to pass their inspections. Thats 9 inches from the epdm to the top of the flashing where its lapsealed. For instance, like if you field flashed a pipe instead of using a pipeboot or pitchpocket.

Carlilse and Firestone are EPDM roofing manufacturers? What do they do if something doesn’t pass inspection, do they not warranty the roof at all, or just exclude those items that don’t meet their requirements?

From what I’ve seen in my neighborhood, there would be a lot of things that don’t meet that requirement. From my rooftop I can see a neighbors skylight that is on maybe a 5 inch curb.

Gary, the foreman, job super, & project manager on a commercial job usually know what Carlisle & Firestone want so you just automatically do these things out of habit after awhile. You learn whatll fly & what wont. If a curb needs raising you just do it. Lift it, frame it up with 2x6s on edge & wrap it with rubber, simple. Theres always plenty of lumber on a commercial job for things like nailers, building ramps, sleepers, & misc. stuff like raising curbs. Just figure it into your bids or hit them for an extra. Btw, you can field wrap a pipe & pass inspection, it just has to be 9 inches minimum.

I see. I’m not a roofer, I’m just putting in an equipment curb on my own roof, and will need to have a roofer flash it. It will be just like a skylight curb, but with a solid top and metal cap. Or think of it like a commercial RTU curb with no penetration, but a solid top with a metal cap. The whole idea of this is to avoid requiring future roofers to move the equipment for reroofing.

Just an update. The roof seems to have minimal slope, maybe 1/4" in 12". Curb is built from 2x6 lumber and could allow a maximum flashing height of 5.5" 6.5", depending on how I do the top deck and metal cover. I might as well make the top deck full size. Even if I had a 2" drop on the sides of the cover, I doubt if you could get the flashing up under there the full 2" anyway, so let’s say the maximum flashing height will be 5.5".

We could also use a metal counterflashing that is screwed in under the sides of the cover. I guess that makes removing the roof flashing easier, when time comes to do that. Otherwise I guess it’s just cemented up under the side overhang of the metal cover?

I think the key to this discussion is “if you want to get an NDL warranty” for a commerical property’s roof and you want all construction details relating to the roof to be accepted and included as part of the NDL warranty, then the answer is “yes”, you need to have the base flashing extend up any wall or equipment base “wall” to the minimum defined acceptable level (in most cases that acceptable level is 8.0" above the finished surface of the roof membrane).

You can still get the NDL warranty from the manufacturer for the roof with noted exceptions per the inspector’s report. Most inspectors understand that now and then there will be some roof top equipment or other detail that just can’t be reasonable made or readily done to get the base flashing up to the minimum 8.0" over the top of the finished surface of the roof membrane(s). The roofing manufacturer’s, when issuing their construction details, typically view the roof terminating at 8.0" (or thereabouts depending on manufacturer) up a wall. After that, the “wall” becomes a “wall” and they do not cover walls with the NDL warranty.