Valley flashing details

  1. The installer of these flashings beat the upper portion down with a hammer to level things out. It looks pretty crude but evidently it worked. Is this accepted practice?

  2. Nailing: Nail through the flashing or nail right along side, trapping the edges with the head of roofing nails to allow for expansion and contraction? These valleys are only 5 ft long so perhaps it isn’t a big deal. Incidentally, the inside flanges (garage peak sides) were nailed down; the outside flanges flapped in the wind when I removed the shingles.

  3. There was no sealant where the shingle edges rested on the flashing. Should there be?

  4. When I apply shingles to the house deck do I need to plan my first several courses so that the exposure of the first continuous course does not need to be notched at the valley peak? In other words, that course would just bypass the peak. There must be a clearer way for me to say that, I’m just not finding it.



  1. Yeah it may not look the cleanest but doing that does work if you are going to run your caps over where the two pieces meet and under the shingles of the main slope. Not exactly how I would do it but I see it done all the time with no issue if capped properly.

  2. Some will probably disagree with me on this but if you are just doing a shingle roof with aluminum valley metal I see no issue with nailing through the metal. Yeah I know about expansion and contraction and all but never really saw any real world scenario where this caused a problem. I don’t think a shingle roof will last long enough (20 years is what they should last) to create any expansion/contraction related problem. I’d be more worried about all your nails too far away and possibly have a shingle blow off issue. Now however if we are ever talking about better quality longer lasting roof such as slate, copper standing seam, ect then no you not nail through your valley, it should be fastened with cleats.

  3. No you should not use sealant under your shingles in the valley. In the unlikely case of water getting under those shingles that could cause it to get trapped. I will add one thing that is important though. Make sure you clip your top corners of your valley shingles. It prevents water from running down the valley, hitting that corner and being directed under the valley. I’ll try to find a pic of what I mean by that.

  4. I assume you are talking about making sure all your rows and key ways match up after you shingle around the valleys since it looks like you are using 3 tabs. You will want to mark out your roof with chalk lines before you start that section to insure everything comes together. I saw a video on youtube that explained how to do that nicely and I’ll see if I can find it.

This isn’t exactly how I make it out but honestly it seems easier for a diyer to do it this way than the way I do it lol.

:slight_smile: This should cover all your questions. The featured valley is on the water on Hatteras Island. No caulk, no storm shield. It’s been through many named storms including Isabelle, Sandy, and a few others.

Valley How-To

Here’s how to do the top. Well, so much for that!
Send me an e-mail at my alternate addy, ‘my handle’ at and I’ll send the three pix you need.

Thanks for the replies… now I have even more questions than in the beginning. Argh!

I’m squeamish about nailing shingles through the flashing. Also, it is not advised to seal the edges for fear of trapping water there.

What if one applied roofing cement under the shingles in segments? That way they would resist uplift and any water could escape through the gaps and the nearest nail hole would be at a safe distance.

My 2 courses of I/W will provide complete coverage under the metal. Should I lay an additional layer lenghtwise under the flashings?

What about the eaves shingle starter; over or under the flashing? I’ve seen videos depicting the use of starters up both sides of the flashing as well… is this generally recommended?

Something that appeared so simple at first is now causing me some head-spin. Internet research reveals much disagreement on proper procedure. I’ll bet DIYs get valleys wrong more than anyone knows.



I personally think you are overthinking things about being afraid to nail into the metal. But if you are really hard set against and using roofing cement here is what I recommend. Nail each shingle with 3 nails but leave the 4th out in the valley side. Then about 2" from the valley side put down a dime size glob of roofing cement in the nail line. That will be enough to keep your shingles sealed down but won’t be enough to cause any type of dam to trap water.

Personally I would run my eve starter shingle under the metal but if done properly over or under will work fine. Just if you run it over the metal you just need to make sure you trim the corner like you will every other shingle.

While you can run starters up both sides of the valley metal I don’t recommend it. I feel one of the biggest benefits of open metal valleys is the shingles lay flatter and adding extra unnecessary shingles will cause a slight hump (although very minor).

Valleys aren’t complicated.

The 2 Cardinal rules are imo:

  1. Don’t nail through them, ever.
  2. Crop cut your corners. … R_1389.pdf

Look at the diagrams on the provided pdf. file and try not to over think it.

Thanks guys for taking the time to provide these great tips. I think I’m well armed now to do this.



Yup, this is where I expected things to go wrong.

It sheds water but invites insects to reside and wind to lift things up. Besides, the inspector may have serious doubts regarding my shingling prowess.

What do I need to do to make this look prettier? That piece of the puzzle where the garage caps intersect the house shingles is just not coming to me.

Winter is now firmly ensconced here so this and the garage will wait 'til spring.

Regards… Mike

Cut that last gray shingle even with your valley line.

Cut it like Tar suggested, provided you ran your caps high enough. Things are looking good, one of the better diy shingle jobs I have seen. However, I need to ask, why were you ok with mixing shingle types but so worried about things you would never see lol?

I believe the 3tabs are the old shingles, he just did the upper section for now.
With W valley, we hammer the top 6" or so flat so you don’t get that big gap. Gently, with a rubber mallet so it doesnt get to dinged up.

Trim the last gray shingle and flatten the upper portion of the valley ridge… got it. Thanks!

Yes, the 3-tabs are the old shingles; winter was bearing down on me quickly so I had to button things up in a hurry. I’ll correct the mistake and tackle the garage next spring.

You guys are so patient with me and I appreciate that.

Regards… Mike