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Old 08-01-2010, 03:53 PM   #1
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Blind/False valley vs. True valley for dormer


Hello everyone,

I'm trying to work out all the details on a dormer project, and I keep coming up with different thoughts and obstacles. (Now I'm wondering if I'll lose the bid to a professional....)

Anyway, what do you guys prefer, or think is better, false valleys or true valleys? Any difference in strength? To me, the ridge deading into the sheathing on a false valley seems strange, but then again I'm not a professional.

What do you guys think?

Joe

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Old 08-02-2010, 04:00 PM   #2
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Blind/False valley vs. True valley for dormer


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Hello everyone,

I'm trying to work out all the details on a dormer project, and I keep coming up with different thoughts and obstacles. (Now I'm wondering if I'll lose the bid to a professional....)
What doers that mean? I thought this was your own house.

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Anyway, what do you guys prefer, or think is better, false valleys or true valleys? Any difference in strength?
If you are going to have a cathedral ceiling you need true valleys. If not you frame a false valley. Strength is not the issue for the width your talking about for your dormer.


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To me, the ridge deading into the sheathing on a false valley seems strange, but then again I'm not a professional.

What do you guys think?
False valley are framed every day. You put a block underneath where the ridge sits.

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Old 08-02-2010, 04:34 PM   #3
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Blind/False valley vs. True valley for dormer


Hey Joe,

Thanks for the reply. I was just joking about 'losing the bid'. It's our house, but my father would like to have these dormers finished soon so he can have a new roof done. If I don't seem certain about everything, he may not let me take a shot at doing it.

Anyway, I'm trying to decide between the cathedral or flat ceiling inside. The room already has a high cathedral ceiling, with a 4' knee wall where the dormers will go. So I'm not sure if there will be too many angles inside the room with cathedral dormers or not. What's your experience? Do more people make flat ceilings for their finished rooms?

With flat ceilings I guess that simplifies things a lot. In that case, for the ridge, I could also just make a little narrow header between the existing rafters(in addition to the main header below) , for the ridge to dead into, with the valley boards running into either side--I think I've seen a diagram out there framed like that.

We'll see. My father may want cathedral ceilings anyway, so I'll have to figure out the regular valleys still.

Joe
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Old 08-02-2010, 05:14 PM   #4
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Blind/False valley vs. True valley for dormer


Joe1, you seem to be asking the right types of questions and seeing possible issues before hand and working them out is a good thing. But have you gave any thought to how long you’ll have the roof opened up and how "fast" you can put this together and get "dried in"?

You said in your other thread you have 3 of these to do. If I was doing these the house would be getting roofed in concert with the dormers being built. As soon as the last nail in the sheathing was thumped on dormer #1, here comes the roof.

Something to think about.
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Old 08-02-2010, 05:50 PM   #5
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Blind/False valley vs. True valley for dormer


Hi Kwikfishron,

Yeah, time is something I've been considering. Not being a professional, but still wanting everything to always come out just right, I am not the fastest worker. I'm going to do one at a time, completely, until dried-in, then move on to the next one.

There's not a huge rush for the roof, but we do want to get it done. Like you're saying, we can start the dormers, and then let the roofers start before we're finished, to coordinate things. In fact, doing one dormer completely first should give use a good time frame to do the rest.

Joe

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Old 08-02-2010, 07:06 PM   #6
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Blind/False valley vs. True valley for dormer


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Anyway, I'm trying to decide between the cathedral or flat ceiling inside. The room already has a high cathedral ceiling, with a 4' knee wall where the dormers will go. So I'm not sure if there will be too many angles inside the room with cathedral dormers or not. What's your experience? Do more people make flat ceilings for their finished rooms?
I've done them both ways a million times. It's what you want and what you think looks better.


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With flat ceilings I guess that simplifies things a lot.
It simplifies framing the valleys especially since you will have two different pitches. Also, with a true valley you have to cut your existing rafters back perfect for the valleys. That right there is way more work and way more calculating especially for someone who's never done it before. It's even challenging for experienced guys.

You better get an experienced guy to help you cut that roof if you go cathedral.
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Old 08-02-2010, 08:07 PM   #7
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Blind/False valley vs. True valley for dormer


Might be thinking about venting the dormers, also. With cathedral, you would use insulation-required sized rafters; with over-framed, just 2x4 or span rated. This would vent the over-framed part of the dormer roof efficiently. Install the header carrying the top framing low enough for the dormer rafters to vent, allowing an exhaust for the dormer soffit intakes.


pp.#250, Fig. 17-6, add the dormer ceiling joists and frame the doubled top header in the picture closer (lower) to the plane of the ceiling, so the top of the main roof has a bay width vent hole of sheathing cut-out just below your valley boards peak. http://books.google.com/books?id=KKe...20roof&f=false


Be safe, Gary
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Last edited by Gary in WA; 08-02-2010 at 08:22 PM.
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Old 08-02-2010, 09:15 PM   #8
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Blind/False valley vs. True valley for dormer


With the sheathing intact under the ridge and valley area (on the existing roof), would it still be able to vent enough? Or should you trim back the sheathing somewhat inside the dormer?
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Old 08-02-2010, 11:08 PM   #9
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Blind/False valley vs. True valley for dormer


"Or should you trim back the sheathing somewhat inside the dormer?" ---- bingo! You want an air route as high as possible to vent the top area of the dormer with the lower soffit incoming air. I try to cut the sheathing just below the valley intersection at the peak. At least a 12 x 12" hole. Some Inspectors require a 1x4 rafter tie even on the valley jacks, they can be picky.... Unbelievable but true! Be sure to shear nail your dormer sheathing into the valley boards, 3"o.c. and the roof (main) connection of the over-frame sheathing. Remember to hold your dormer fascia boards up, 1-1/2", above the main roof's rake. I cut back the dormer's soffit over-hang sheathing to allow installing the main roof continuous near the dormer side wall. I tack that valley piece of sheathing in place (at an angle to show installer to put in on afterward) with two nails. OR just cut a compound miter cut on a block to close off the very top space under the dormer valley at the over-hang soffit. It has to follow the valley and start down the fascia equal to the other rafters.


Blind valley, page # 229: http://books.google.com/books?id=KKe...20roof&f=false
And in Fig. 15-11, have your ridge board sit on the valley boards for bearing, not as shown.

Be safe, Gary
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Last edited by Gary in WA; 08-02-2010 at 11:24 PM.
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Old 08-03-2010, 12:35 PM   #10
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Blind/False valley vs. True valley for dormer


Hey Gary,

Thanks for the tips. I'm curious, do you still need a ridge vent type shingle ontop, if the dormer can vent out the back? The inspector wrote ridge vent, I believe on the plans, but I'm wondering if that's necessary here.

Anyway, back to the valley board/sleeper, is there any usual method of measuring that? Or is it just a matter of using a string and measuring? The board starts with the ridge outside (top), and it extends all the way down to the outside edge of the top plate, right? Now do you bevel the board at this point in?
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Old 08-03-2010, 03:59 PM   #11
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Blind/False valley vs. True valley for dormer


If a ridge vent is on the plans, install one.

I string or level the ridge, sometimes figuring it off the Construction Calculator. Set your trusses, level over to make an intersecting ridge mark on the main roof sheathing. OR, figure the total rafter height (height above plate at ext. wall above seat cut + rise per foot x 1/2 total span) lay a 2x4 on the dormer plates near the intersecting main roof, mark center of dormer width on front wall, and 2x4 temp. plate. String-line to find center line on main roof, tack a 2x4 vertical (plumb) with a nail at total rafter rise (deduct for temp. 2x plate thickness), use level/straightedge extension to mark valley/ridge on main roof. Snap chalk lines from center dormer ridge mark to top of truss just touching main roof sheathing (slide taut line down truss towards the tail overhang).
To find valley setback from rafter and jacks top edge (existing caulk line): Tack a truss centered on dormer walls next to sloping main roof sheathing. OR, tack a rafter (or partial but with seat cut) next to main roof. Lay a scrap 2x on main roof sheathing, slide it alongside dormer truss toward dormer center. Stop and mark when top outside edge just meets top plane of truss.(or mark 1-1/2” up if sheathing is there.) Mark plumb there as this is valley board (if 2x) setting position. Measure distance of setback from existing line, mark same at valley/ridge peak. Snap another line (2-4” in) for valley outside edge. Install valley boards, double (side by side not on top) if needed to gain full support under rake/level cut of jacks. Hook tape on rafter or truss (on layout already) to mark jack layout on valley boards. Install ridge, layout similar. Measure one side of jacks, other side measurements should be same. The inside line is for outside edge of valley board, the outside line for dormer sheathing end cuts in valley.

Be safe, Gary
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Old 08-03-2010, 05:35 PM   #12
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Blind/False valley vs. True valley for dormer


Joe,

Your using trusses for these dormers?
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Old 08-07-2010, 12:02 AM   #13
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Blind/False valley vs. True valley for dormer


Hi guys,

Sorry for the delayed responses. Construction on the dormers has begun, but at the moment been stopped. We had a guy helping us, but it seems we may have to let him go after some issues arose. Anyway, we may have our roofer finish the dormers (not really my idea...).

Anyway, Joe, no we're not using trusses, just regular framing.

Joe
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Old 08-07-2010, 05:31 AM   #14
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Blind/False valley vs. True valley for dormer


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Originally Posted by Joe1. View Post
Hi guys,

Sorry for the delayed responses. Construction on the dormers has begun, but at the moment been stopped. We had a guy helping us, but it seems we may have to let him go after some issues arose. Anyway, we may have our roofer finish the dormers (not really my idea...).

Anyway, Joe, no we're not using trusses, just regular framing.

Joe
Gary mentioned trusses in his last post. I didn't think you were.. Are you going cathedral? How much framing experience does your roofer have?
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Old 08-07-2010, 09:22 AM   #15
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Blind/False valley vs. True valley for dormer


Hi Joe,

I should say, the roofer is a framer, but he is doing the roof. So the framing part, I'm not concerned about really, I was just looking forward to doing this myself. At the same time, I hope, as mainly a framer, he's good enough for the roof. He says he does them, but his business is framing.

No, we're going flat ceiling. I think it will look better than having all those angles inside.

Joe


Last edited by Joe1.; 08-07-2010 at 09:27 AM.
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