Celotex Exposed Edge Between Vinyl Siding and Step Flashing

This is old Foil Faced “polyurethane” Celotex which is OVER the Step Flashing (and UNDER the vinyl siding.

The siding will be cut 1.75in above the tops of the roof shingles to allow drying.

The Celotex edge is about an inch higher than the siding due to original construction with a 1x3 touching the shingle tops and the Celotex. - Celotex 2.5in above shingle tops.


  1. Insects burrowing into the exposed edge foam,
  2. Hornets building nests in the “inch higher” which means cavity…


  1. Wrap Celotex bottom with 4in strip of I&WG or Window/Door Tape
  2. Same as above but hold a 1in strip of foam insulation to make even with vinyl siding.

I think I get it, but you gotta show a picture or draw it out. The Ice and Water or Window wrap aren’t compatible in the long pull with iso board but are fine with the foil.


Best way would be to encase the foam with metal such as a #66 stucco stop. If you can’t do that use the butyl tape with foil film. I hope the waterproofing paper/felt is between the foam and the wall and over the step flashing.

Stuff like #66 stucco stop and stucco weep edge is unavailable about 45 min east of Pittsburgh.

But let me give you the complete picture. The layers encountered were:

  1. Old shingles
  2. Felt
  3. Flashing (valley style - should have been step)
  4. Felt
  5. Celotex
  6. Siding

The old shingles were laid over the “valley” flashing.

I Cut the valley flashing about 1in above the shingle tops and the new step flashing will go behind that.

The Celotex, being foil faced on both sides, I don’t see any need for felt anywhere.

There were exposed Celotex edges under the vinyl and yes, they sort of darkened in color and maybe 1/16 in had turned to powder you could easily scrape away. But here’s the biggee: no insect burrowing.

As far as need foil covered tape, I believe that is for UV protection. Since bottom edge under siding, don’t need UV protection.

I also have 2 types of I&WG, one of which is like thick Door & WIndow Sealing Tape - VERY flexible and stretchy. While it may not be the best product, it is probably good enough to last 20 years which should exceed my life expectancy (I’m 65.) Yes, a ghoulish consideration, but so is aging (!)

I do like the #66. I was thinking of bending up some sheet but there are 4 dormers which is 8 pieces which is more hours. These dormers are a real PITA. 7 square job. The intersections are everywhere.

Don’t know if hornets or wasps would like building nests in the gap if the Celotex bottom is 1in higher than he siding bottom… Wonder if there is “nest building criteria” published for those buggers…

Can you bend a piece of aluminum into an “L” and use the short leg of the “L” to cover the bottom of the foam?

It would have to be abou 4in tall nailed @ top edge so nails don’t obstruct step flashing.

I think Door & Window Tap should work since behind siding is pretty much what that stuff is made for.

OR I could cut some foam strips and glue them in - I’m assuming foam edges are left exposed if over step flashing.

If you can’t get the 66 stucco stop, vinyl or galvanized 5/8 drywall j bead with a few 1/8" holes in it would cap the foam the same way. If you have access to a break could bend the same thing out of trim coil.