What's the proper detail to apply membrane or tar paper to an inside roofing corner, where a sloped roof meets a higher wall at a corner? Of course a metal flashing goes on top of of the membrane, and the wall's WRB must lap into the metal flashing. But here I'm asking about how to lay out the details of the bottom-most redundant water shedding layer.

  • It may not make too much of a difference, but is the water running out of the corner, as in the corner is on he high side of the roof, or does it run into the corner, as if it was on the lower edge or in the middle? My gut feeling is using metal in either case, and how that is installed depends on the position on the roof. The peel and stick would be for redundancy only...
    – Jack
    Jan 1, 2016 at 15:47
  • Here I'm asking about the top of where a sloped roof meets the corner of a yet higher wall. The WRB is for redundancy (here it's a tile roof).
    – Bryce
    Jan 4, 2016 at 9:12

1 Answer 1


Tar Paper or Membrane underneath, I've never found a single drop make it through metal flashing...that was replaced or re-faced with every new roof. If we're not talking about the slope being parallel with the wall & the slope is perpendicular throwing water at the wall, then definitely membrane as far & wide as you can under very tall & wide metal flashing.

  • How is the tar paper or membrane folded and detailed? That layer does have a purpose related to condensation on the underside metal surface of the flashing.
    – Bryce
    Jan 4, 2016 at 16:00
  • Caulk the seam first or fill it & then caulk. Material length doesn't matter, but work up so each section lays on top of the prior lower piece & overlaps it by 6-inches. Fold the material right along with the Base Flashing into the wall to roof seam (press-in by hand or crease on the ground) & DO NOT nail or screw anywhere within 6-inches of the seam (nail/screw sparingly). Then, once the roof is on you'll either flash again OVER the roofing OR step-flash WITHIN the roofing over each individual row, step isn't visible & doesn't collect debris. Flashing only keeps water on the slope.
    – Iggy
    Jan 4, 2016 at 18:48
  • Sorry, um. Are you talking about a dormer type of setup & just want to know about the front? You would just lay your front membrane/tar paper & flashing first & your side membrane/tar paper & flashing would be separate. If you desire any kind of over lapping, then 45 or less the front beyond the corner & 45 or less the wall beyond the corner to lay that over your front. Wrapping around the corner to the wall side isn't too difficult but you might end up leaving a tiny open hole, unintentionally. The roofing & siding will do their majority part, flashing is just a safeguard.
    – Iggy
    Jan 4, 2016 at 19:06
  • Tile roof actually.
    – Bryce
    Jan 11, 2016 at 8:48
  • Sorry, I was suspended for a week. Flat tile would be the same as what I said above. Spanish, Wavy or Barrel tile I'm only slightly familiar with, but I believe that's all mega cemented even as the top flashing...under the face or top tiles.
    – Iggy
    Jan 16, 2016 at 1:38

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.