Valley Flashing for Roofs:

This article discusses details and specifications for roof valley flashing for best construction & roof leak resistance.

We describe how to construct three common styles of roof valley: open valley, closed-cut valley, and woven roof valley, and we include roof valley underlayment and nailing specifications.

Page top photo: that Vee-shaped metal roof section drains a large volume of water into the end of intersecting roof valleys where unless a large capacity gutter is installed, the valley drain will over-shoot and may risk building water entry.

Asphalt Shingle Roof Valley Flashing FAQs

On 2022-01-04 by Maria Alvarez - What is the best metal and thickness to use for valleys in South Louisiana?

What is the best metal and thickness to use for valleys in South Louisiana? And how much of it should be exposed and how much should be covered with the shingles? Thank you

On 2022-01-04 by Inspectapedia Com Moderator (mod) - choice of valley flashingmaterial

@Maria Alvarez,

Currently you can buy standard roof valley flashing in aluminum, copper, lead-coated copper, galvalume, and 12-gauge steel.

I like copper as most durable. But aluminum, properly installed will outlast your asphalt shingles.

An example, Amerimax Home Products Aluminum Flashing .0078 4X10 66304, reminds us that thicker may be more durable, but you'll end up choosing from what's available.

On 2021-09-28 by Dan Anderson - building code on roof valley dimensions?

Is there building codes that specify dimensions of valleys? I have a tile roof and it was recently inspected and the comment was flashing valleys are too narrow, typically 3".

In some places roof tiles are almost touching. What can I do to fix this or do I need too?
Dan

On 2021-09-28 by inspectapedia.com.moderator (mod) - open valley has a 6-inch wide clear space

@Dan Anderson,

Not code but in various roofing recommendations, texts, and installation instructions for roof valley construction, you will see, as you can in illustrations on this very page, that an open valley has about a 6-inch width of clear space.

Valleys can be open, closed, or woven;

Your roof valley sounds inconsistent, and may be prone to clogging if it's on a roof in an area where leaves or foliage debris are likey to be blown onto the roof surface.

Before "fixing" the valley by trimming it to a more-consistent width, read the article above describing proper valley installation, then inspect your roof in detail to find out exactly how your roof valley in constructed: materials, underlayment, ice and water shield, nailing locations, etc.

You want to know that the metal or other valley liner is of sufficient width before cutting the valley open; if it's not you'll need to add roofing material and/or sealant to move to a more-closed valley design.

Use the Add Image button.

On 2020-06-10 by Scott

Should there be a straight line of shingles on both sides of the valley flashing?

On 2020-06-22 by danjoefriedman (mod) - Should there be a straight line of shingles on both sides of the valley flashing?

Scott

I would want to see a photo of your situation to be sure we're talking about the same condition.

In general we need to distinguish between a little bit of sloppy work in trimming shingles near a roof valley, which would be a cosmetic item, and more serious trimming errors that could result in leaks.

On 2019-08-25 by Steve

New shingle roof installed yesterday. Last 20 minutes there came a light drizzle rain.

The roofing felt was already in place and shingles were installed on damp surface. I live in Texas where it will be quite hot for the next month.

Do I need to ask the installer to remove the shingles installed in the rain and re-do them. Or is it safe as it is?

On 2019-08-26 by danjoefriedman (mod) - do not install shingles on a wet surface

roof shingle manufacturers instructions for asphalt shingles virtually always state that the shingles should be installed over a clean, dry surface. Installing over wet material may result in a shorter roof life.

However I doubt that the roof contractor is going to be willing to remove and reinstall your shingles.

Cost to them is so great that more likely the contractor would walk from the job. It's unfortunate but that's been my experience.

On 2019-04-30 by Anon - Where do I find the clips or Cleats used to fasten a metal open valley?

Anonymous asked by private email:

Your photo on your website shows an open metal valley fastened with clips or cleats.
Where do I find the clips or Cleats used to fasten a metal open valley?

My roof is off and the roofer can't find the supplies locally.

Moderator reply: we make roof valley flashing clips or cleats - it's very easy and inexpensive

Anon:

For asphalt shingle, clay tile, slate and similar roofs, it is easiest is to fabricate the clips from the same flashing metal as is being used in the valley.

Here's how I (DF) do it: A pair of tin snips is used to cut metal strips about 6" long. The clip is folded over long enough to slide under the folded over edge of the valley flashing, clip to it, and the flashing clip tail is nailed to the roof deck before shingles are installed atop those clips and over the valley edge. .

For metal roofing the roofing clips are sold by the same manufacturer who supplied the metal roofing - an important detail since those clips will match the exact bends or seams on the metal roof sections being nailed to the roof deck.

 

On 2017-09-18 by brax

Is there a minimum distance for roof plumbing vents in placing near/in/on ridge & valleys? I have seen both placements in a valley and near a ridge but cannot find any hard rules.

On 2017-09-18 by (mod) - minimum distance for roof plumbing vents in placing near/in/on ridge & valleys?

Brax

Thanks for an interesting question.

I have not found a code rule on distance from a ridge or valley, but there are both some practical limits imposed by the physical dimensions of framing (don't cut through the ridge board, avoid the ridge vent, keep room for the flashing boot) and also a common sense limit imposed around valleys: cutting right through a valley to route a plumbing vent would be, frankly, stupid, as it invites a lifetime of troublesome roof leaks in a notorious area.

Here are some dimensions that are my opinion based on having built and inspected and torn apart buildings:

The vent stack needs to be far enough away from a valley in horizontal distance that the closest-edge of the integral flashing that forms the boot used to flash the roof around the vent pipe (avoiding leaks) does not enter over or under the closest edge of the valley flashing.

With 16" o.c. rafter spacing, and a typical valley flashing and underlayment that currently, popularly installs 36" wide peel-and-stick ice and water shield under the valley regardless of roof pitch, and a typical roof vent pipe flashing boot dimension (11 x 15" Oatey example)

and taking 1/2 of each of these widths, then the center of the hole cut for a plumbing vent is likely to be no less than (36"/2 + 11"/2) about 24" away from the center of the closest roof valley measured by drawing a horizontal line between those two points. In my opinion a horizontal distance of =>36" is safer and probably makes it easier to avoid roof framing.

The minimum horizontal distance from vent to valley respected by most plumbers and roofers is 18" but I think that's too small if we want to be sure there is no overlap between the valley flashing and the plumbing vent boot flashing. That's how I got to 24"

The absolute worst installation places the vent stack actually intruding into the metal of a valley flashing - a sin regardless of whether it's an open or closed style roof valley.

ROOF FLASHING, ASPHALT SHINGLE VALLEYS https://inspectapedia.com/BestPractices/Roof_Valley_Flashing.php describes valley flashing

FLASHING on BUILDINGS https://inspectapedia.com/exterior/Flashing.php shows an example or two

On 2017-03-12 by Anonymous - OK to use ice and water shield underlayment instead of valley flashing?

can an open valley have a water and ice underlayment instead of flashing.

On 2017-03-12 by (mod) - yes if not left exposed to the weather: use a closed or woven valley design.

Anon:

There are some ice and water shield products that are covered with mineral granules but those I've seen included the granulated surface not as a long-term weather exposure protection but to keep the roofer from sliding off of the roof.

Only if you can find an underlayment product that specifies that it is designed to be left to weather would it be feasible to do as you ask.

Otherwise, put down the underlayment where the valley is - before installing shingles, then add a layer or roll roofing or other membrane for weather durability.

On 2015-12-09 by julia - water backing up in box valley on my roof

box valley .water backing up what can i do

On 2015-12-09 by (mod) -

Emergency response:

If water is leaking in to the house right now, a roofer might use a hot water hose (or salt or heat tapes) to melt channels to let water off the roof. DO NOT CHOP or you may damage the roof. And don't climb up where you can fall and be hurt or killed.

Install heat tapes to keep the roof draining until you can in better weather fix the flashing and roof venting properly.

 

Question: which metals are used for metal roof flashing?

Is the material used for most of these valleys a g60 hot dipped galvanized or galvalume? (Oct 30, 2012) mike shield said:

Reply:

Currently most roofers are using ice and water shield in closed valleys and hot dipped galvanized or copper in open metal valleys with ice and water shield below the metal.

 

Question: local roofing suppliers don't have "V" or "W" valley flashing: where do I get it

All the prior distributors don't have the v or w valley flashing I need. What can I do? (Nov 11, 2012) Rebecca said:

Reply: you make it, don't buy it

These V or W valley flashings are easy to make using a metal flashing or siding brake

 

Question:Do building codes require metal flashing?

Do building codes require metal flashing? 8 Aug 2014 Barbara said:

Reply:

No Barbara. Building codes do not specify the material to be used in valley flashings. There are various approaches some of which are perfectly acceptable and that use no metal whatsoever, such as an under layed closed or woven valley.

I would agree that some valley flashing approaches are more durable than others however, and I'd point out that while metal flashings are quite durable, improperly installed that may not be the case.

 

Question: do we cut and trim T-111 siding away from the wall to install flashing of roof to side wall?

Is it an appropriate practice to cut trim and T-1-11 siding away from the side wall to install flashing and counter flashing where the roof line meets a head wall of side wall? The aesthetics are not desirable.

Where there once was siding close to the flashed roof join there is now counter flashing and cut siding on the side wall. If it is a superior way of installing it can be justified, but it appears the contract is taking short cut of cutting trim and siding rather than remove and replace around new flashing. I have a picture if it will help explain. (Sept 2, 2014) Anonymous said:

Reply:

Where siding is installed on a wall abutting a lower roof we can run the lower roof head flashing or if along a roof side, its step flashing up under the siding provided the upper bend of the flashing is tall enough to extend an inch or more up under the siding and still leave a couple of inches or more of clearance between the siding bottom edge and the roof surface.

That approach permits omtting a cut-in counter flashing and avoids the trouble of trying to seal that well at the vertical decorative grooves cut in the T-111.

If we bring siding lower edge close down to roof surface you can bet that it will deteriorate, delaminate, rot. That's the reason for the clearance.

You posted this question in an article on roof valley flashing. You will want to read these two articles linked-to in the ARTICLE INDEX

FLASHING WALL DETAILS

FLASHING ROOF-WALL SNAFU

found in the ARTICLE INDEX

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Continue reading at ROOF FLASHING, ASPHALT SHINGLE VALLEYS - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• FLASHING, ASPHALT SHINGLE VALLEYS
  • ROOF VALLEY UNDERLAYMENT REQUIREMENTS
  • OPEN ROOF VALLEY DESIGN SPECIFICATIONS
  • METAL VALLEY FLASHING EDGE FASTENING METHODS - clips, cleats, nails at open valleys
  • METAL VALLEY LENGTH WARNING
  • CLOSED CUT ROOF VALLEY DESIGN SPECIFICATIONS
  • WOVEN ROOF VALLEY DESIGNS
  • DEAD END ROOF VALLEYS - mean leaks, possible fixes
  • ROOF VALLEY SLOPE WARNINGS - too much or too little?
  • ROOF VALLEY FLASHING MANUALS, RESEARCH & STANDARDS
• FLASHING ROOF DEFECTS LIST

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