QOD for 1/28/2006

Hi to all,

Here’s todays question



IMG_0032 (Small).JPG

Hmmmm :mrgreen:

I’ve seen my share of those kinds of roofs.

Hi to all,

the correct answer to this question is:

Full counter flashings

These are critical in these installations, in most cases they are not only there to stop moisture entering into the roofing plys, but also to protect the exterior finish from water intrusion.



**The illustration below is courtesy of Inspection Depot click here for more information

ROOF (136) (Small).JPG

Actually, Gerry’s illustration is close, but there is another which probably better describes what the original installation looked like.

In the photo, there is a metal cap seen, though there is no cant strip seen. This suggests that another acceptable method of istallation was used at one time. I base this observation on the small radius curve in the membrane at the base of the parapet wall. It also suggests that the base flashing is not metallic, and may also not be felt based.

In addition to this, when you look closely, one can clearly see a line, running parallel with the parapet walls, approvimately 4" from the wall/deck intersection. This suggests that flat counter flashing may have been installed over a base flashing of modified bitumen. This base flashing sits over the roof deck’s modified bitumen membrane. The original metal counter flashing was attached at the top, and secured via metal bar attached to the parapet wall.

There is nothing wrong with this type of installation, though ongoing maintenance caulking at the attachment bar is a pain. This may explain the installation of the metal cladding onthe parapet wall, which I suspect, was installed somethime after the fact.

For those with the Carson Dunlop Illistrated Home, illustration 0111 makes some sense of what I said.

The illustration provided here also shows ballast (gravel) installed over the membrane, which is not the case in the subject photo.

To Gerry’s point, it is called counter flashing. I just wanted to point out that there is an approved method other than the illustration suggested. I would hate to see someone call out an installation defect, based on a missing cant strip.

gerry, if you have a similar illustration from ID to what I described, would you mind posting it for folks to see? Thanks!

Hi to all,

Hi Joe, actually the illustration is surprisingly close to what this installation was originally. I am not sure as to whether this actually had a can’t strip originally (the roof tends to crack less at this point if it does). The flashings had been butchered over the years but in places I could still see the original full “cap” style counter flashing. as in the photo what you are looking at is roll roofing hot-mopped down over the original flashins due to rust on the top of the parapet.

However like you say there are several ways of skinning this particular cat, where the counter flashing is screwed to the wall structure, sealing it will always be a trouble spot, unless it is embedded into the structure.



Righty- O