Flashing a roof valley?


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Old 01-14-06, 08:56 AM
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Flashing a roof valley?

Hello,
I live in FL and have a roof with a 2in12 pitch. When flashing a roof valley, do I first install an 18 inch mineral roll roofing strip on the bare sheathing, then cover it with felt paper, then apply the metal flashing on top of that?
Also, Ive noticed the metal flashing comes in 10, 14, and 20 inch widths. Which should I use? Do I need to bend the flashing with a metal brake, or can I just unroll it and install it flat?
Finally, Grace makes an underlayment that says you can use it instead of the mineral roll roofing underlayment. Its more expensive and not as thick as the mineral roll roofing. Which would you use?
I want to make sure its waterproofed well due to the heavy rains we have as well as the low pitch.
Thanks in advance for your help.
 
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Old 01-14-06, 08:21 PM
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Use the grace underlayment that sticks to the sheathing. Then run the rows of felt- one row on the left side of the valley, then one row on the right, weaving them (running them through the valley and up the other side 3 ft so that they overlap) as you go. Then get the widest valley tin you can find- W style is preferable, it comes in 10' lengths, not in rolls. Lay it on top of everything and shingle away. If you need to put 2 pieces together in your valley, overlap them 12" eyeball down the center of the W to ensure it's straight before nailing it off.
 
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Old 01-14-06, 09:02 PM
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Thanks XSleeper.
Can you tell me why the Grace underlayment would be better than the mineral roll roofing? I noticed the roll roofing was a lot thicker, and thought it might be better if I used that and sealed the edges with roofing cement. If you recommend Grace I'll use that instead, I was just curious as to why that would work better.
Also, can you explain what a W flashing is? Is that a flashing that is pre bent, and can I use that in a closed valley? If I use the roll flashing, do I have to bend it, or can let it curve naturally in the valley and then nail it in?
Sorry about all the questions....this is my first roofing job and I wanted to make sure I did it right. Thanks again for your help.
 
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Old 01-15-06, 12:29 AM
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Brian: You can also use ice and frost as the first layer. It is 3' wide, and put it equally on each side.. W channel is pre bent and is the choice of most roofer. You usually do not enclose your valleys using W channel. Closed valleys on a shallow roof like yours is not really the preferred method. The Grace underlayment sticks to the roof like ice and frost does and makes a tight seal. If you want to use rolled flashing you can just lay it in the valley, and let it form naturally. If this is your first roof, I would probabally use the W channel and not close your valley. W channel will get your water off your roof in a hurry. Good Luck
 
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Old 01-15-06, 06:28 AM
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The Grace membranes are clearly superior because they stick to the sheathing, protecting it completely. Also they are self healing, so the membrane will seal around every nail that penetrates it. Roll roofing will not. I agree w/ everything jack mentioned and I also would not recommend a closed valley.

Since you're roof is 2:12, you need the widest valley flashing possible, which is likely a 20" w-style, a preformed valley tin that has a little ^ down the middle. I would think that a closed valley would be problematic on such a low pitch. I've also seen roofers cut the shingle right up to the ^, to give the appearance of a closed valley, while maintaining the straight look of a cut valley. Personally, I like open valley's cut about 1" away on each side at the top and 2" away at the bottom. It allows for better drainage.
 
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Old 01-15-06, 08:12 AM
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Okay, thanks guys. I'll go with the w flashing, open valley and the grace underlayment. Appreciate the help.
 
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Old 01-16-06, 04:58 AM
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Flordia Building Code

Florida building code requires an open valley using metal to be at least 24" wide and be of corrosion reistant metal.

Otherwise you are required to use 2 plies of mineral surface rolled roofing with the bottom layer 18" wide and the top layer a minimum of 36" wide.

Roof slopes between 2:12 and 4:12 requires the installation of double layers of underlayment (felt paper) or self adhering polymer modified bitumin (ice and water shield).

Underlayment needs to be applied in overlapping 19" sheets.

Check with your local code office before proceeding because the information you have been heretofore given may not comply with Florida Code.
 

Last edited by manhattan42; 01-16-06 at 04:59 AM. Reason: a
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Old 01-16-06, 05:03 AM
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Both Sleeper and I gave correct information that meets or exceeds Florida code. I have a crew roofing there now.
 
 

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