Valley flashing

Yesterday I was out in a new subdivision under construction and thought that the valley flashing was not wide enough. Of course, rarely is the full flashing visible once the roof covering has been installed, but I was wondering what the minimum width is for that valley flashing. The subdivision in question had four inches on each side of a two-inch upside-down V. Granted, we don’t have too much wind-driven rain here in San Diego, but I was wondering what the minimum is in California, and then whether or not it is different from hurricane states like Louisiana and Florida.

It depends on several factors - roof pitch, roofing material, etc. - but 4" is generally too narrow, unless the roofing material has been sealed (not nailed) to the flashing.

Hey, Jeff.

The ones in the subdivision are going to be our standard Southern California whatever-pitched roof with flat concrete tiles. Is there an absolute minimum expressed by the various codes? I’ve been looking for something but can find nothing.

I called a CREIA inspector whom I know does draw inspections, and he said 24" flashing is the standard. I never installed 24" flashing when I was working along the Texas Gulf Coast, but that was 20 years ago. We used 18" flashing. He could not cite any code either, though, simply saying that “it’s the standard.”

National Roofing Contractors Association suggests using the guidelines of the FRSA Roof Tile Institute.

FRSA (Florida based) requires a minimum of 16" wide flashing in the valleys of concrete tile roof systems.

I can send you the PDF if you’d like. . . (2.5mb)

Hey, Jeff.

Yes, I’d like to have that in my library. Thanks.

Russel Ray

I just found the one I was looking for, I’ll send you both.

ICBO and the Western States Roofing Association (WSRA) call for minimum of 22" wide valley flashing on concrete tile systems (11" from center each way).

It may be useful to others to post the link on this forum please.


The IRC also requires waterproofing shingle underlayment in valleys. Check your area’s version of the code for the width required.

Well, the only thing I can contribute here is the fact that most materials available is 36" wide, so the minimum would be 18" for valley flashings.

Before the standard of using this product

We would use the typical aluminum flashings 24" wide and that would also give us 12" in the valleys, and then the double or single coverage which also came in 36" wide rolls.

I am curious on something here;

Has the Code become the Standard or has the Standard become the Code?:-k

As a Builder, it seems that I have never been faced with issues that pertained to a Code minimum. :slight_smile:
But as an HI, I sure see a lot of it. ha.ha.

Marcel :slight_smile:


This forum won’t allow me to upload files of that size, so they’ll remain on my computer. However, I’d be happy to email you the file so long as your settings will allow you to accept large files such as this.

Send your request to

Indicate whether you want the WSRA or FRSA version, or both. The actual size is closer to 5mb each, not the 2.5 that I posted earlier.

Otherwise, maybe Russel will post a link to his library once he has included them. . .

Yes. But I think you already knew that :wink:

It was on my mind.

Here they are:



Thanks, Jeff. They made very interesting reading.

Valley Flashing - Short for streaking thru a low lying area.