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Old 04-10-2008, 02:37 PM   #1
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Wavy Roof-No Ventilation


Hello. I'm glad I found this site and that there are people willing to share their knowledge.

I have a roof that was recently hail damaged. Insurance is paying for the shingle replacement. Since we bought the house 6 years ago the roof has alway bothered me. It is wavy and looks like it sags in between rafters. When I replace the shingle I want to do the entire roof correctly.

The house has 17 foot celings. There is no attic space in the house. The ceilings are built parallel with the roof line. The material from ceiling to shingle are as follows:

Shingle - 30# felt - 1/2" OSB - 2x4 spaced every 16" (filled with insulation) - 1/2" foam - 1x6 tongue and groove car siding - 4x6" beams every 36"

I have very large eaves and no ridge vents. I understand the need for good air circulation and have done the studying to find our exactly how much I need for intake and exhaust. I'm sure the reason for the warping is because of no ventilation.

BUT.....

How do you ventilate
if there is no dead air space to circulate air from the eaves to the ridge vent?
What do I do??

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Last edited by FireMan; 04-10-2008 at 02:54 PM.
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Old 04-10-2008, 03:46 PM   #2
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Wavy Roof-No Ventilation


Create a false deck on top of the existing deck, which will allow unimpeded air flow.

I have some pictures from a job I did that way, but they are not scanned into my computer yet, so it wil take 1-2 days to find them and post them.

Ed

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Old 04-10-2008, 05:44 PM   #3
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Hello Ed,

Thank you for responding.

The existing deck is already warped. By creating a second deck on top with I assume 2x4's underneath, it would not be level. Could you perhaps explain in more detail what I would need to do? Do I first need to remove the existing deck? The main support across the ridge also sags, I believe it is called the purlin.

I appreciate your time. If you could go to www.vrbo.com and enter #125508 in the search by VRBO # it will have some pictures. The first picture will show you how the inside is supported. The picture at the bottom will show you the roof.

Kind regards,

Darren
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Old 04-10-2008, 06:19 PM   #4
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Wavy Roof-No Ventilation


If the existing decking is warped already and/or the structural supporting beams or rafters ore also sagging, they would need to be repaired and replaced if required, at the same time.

The first 5 photos are showing the installation of the decking over the old, vaulted solid T & G decking and the last photo swows the Eave Drip Edge Vent, prior to the gutters being installed.

Ed
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Old 04-10-2008, 06:21 PM   #5
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Some more photos.

Now remember from the previous post, I had 100 % continuous Fresh Air Eave Intake Ventilation. On the top of the roof, I balanced that with 100 % continuous ridge exhaust venting, using the Shingle Vent II Ridge Vent.

Look at the last 3 photos in this set. 3 seperate Sunny days in a row. None of the snow has barely begun to melt, due to the air flow we created with this false deck configuration.

I usually use the Smart Vent from DCI Products, Inc., but at this time I felt the Eave Drip Edge Intake Vent was the better choice. Also, I did not have enough previous experience and real world history testing the other product, at that time, new product.

Ed
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Old 04-10-2008, 06:22 PM   #6
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Last Ones.

I am pretty much just trying to show that the Eave Drip Edge Vent is completely hidden from the ground view once properly installed. Also, I am showing a shot of the gutter, reflecting how much room is still remaining for the roof drainage to still properly enter the gutter trough.

Please not, that I always use the larger 3" x 4" downspouts on all of my gutter work. It relieves the gutters much more efficiently of any potential clogging from leaf and small twig or flowering bud debris, much more adequately than the Gold Plated and high priced Gutter Guard products in the market place.

Ed
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Old 04-13-2008, 09:50 PM   #7
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that`s called a cathedral ceiling, If you have trapped condensation due to no air space/rafter mate between the joists,the problem is if the condensation has damaged the decking which is causing the waviness,and if the condensation has soaked the insulation as well,in these cases the roofing needs to be removed including the decking,and possibly also the wet insulation,so you do not develope exyensive MOLD problems,I would try to have spray in closed cell foam insulation to seal and insulate the airspace,the foam has an R value of approximately R-7 per inch,and then leave an air space of at least 1/2" from the foam insulation to the top of thwe rafter,then install new decking ,sturdy enough according to the rafter spacing,also be sure to have proper soffit and ridge ventilation(total is code for cathedral ceilings),Then be sure to flash behind the gutter install the proper amount Ice AND WATER SHIELD,AND A BREATHABLE FELT ON THE ROOF REMAINDER,then install good shingles---it is definitely not an add it to the top,or cover it up situation,doing so will only cause more problems,including health issues if there is mold present
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Old 04-13-2008, 10:00 PM   #8
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ed`s insulation technique is valid,as you don`t have the same type as i thought from your description,after posting the reply ,I saw your link,and looked thru it,I would still look to rip out what you have resupport,and start fresh,the use the technique ed mentioned to finish up--I don`t like that set up at all !!
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Old 04-17-2008, 12:16 PM   #9
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Thankyou guys for all the advice and the time you took to respond.
I've talked to two local roofers about the job and have showed them the pictures and your advice. They both believe as you do the false deck and complete ridge vent will solve the problem of warping.

I have two additional questions or ideas about the install.

In Missouri 99% of all houses are decked with 7/16" OSB and 15# tar paper.
I like the idea of 3/4" T & G decking for the extra strength. Is this what you use on all of your installs where you are at? Is that the code there? I believe you are in the Chicago area. We may have a total of 10" of snow a year that lasts for a couple days. Basically what I'm asking is if I need to put 3/4" T & G on or if OSB will work just as good in our climate.

Second, I am concerned about the additional weight of a second deck on the house. The end result is a 1.5" space that will allow air flow from the soffit vent to the ridge vent. Can I achieve the same result by removing my existing decking, nailing 2 x 6 rafters to the 2x4 existing rafters, then installing new 3/4" T & G decking with full ridge and soffit vent? The end result would be one deck with a 1.5" space allowing air flow.

Can you tell me if there are any disadvantages to my idea, or if it would work just as good. By attaching 2 x 6's to the existing 2 x 4's I could also level out any bows that may be occuring in the 2 x 4's.

Thanks again for taking the time to share your knowledge.
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Old 04-17-2008, 02:13 PM   #10
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Quote:
Originally Posted by FireMan View Post
Thankyou guys for all the advice and the time you took to respond.
I've talked to two local roofers about the job and have showed them the pictures and your advice. They both believe as you do the false deck and complete ridge vent will solve the problem of warping.

I have two additional questions or ideas about the install.

In Missouri 99% of all houses are decked with 7/16" OSB and 15# tar paper.
I like the idea of 3/4" T & G decking for the extra strength. Is this what you use on all of your installs where you are at? Is that the code there? I believe you are in the Chicago area. We may have a total of 10" of snow a year that lasts for a couple days. Basically what I'm asking is if I need to put 3/4" T & G on or if OSB will work just as good in our climate.

Second, I am concerned about the additional weight of a second deck on the house. The end result is a 1.5" space that will allow air flow from the soffit vent to the ridge vent. Can I achieve the same result by removing my existing decking, nailing 2 x 6 rafters to the 2x4 existing rafters, then installing new 3/4" T & G decking with full ridge and soffit vent? The end result would be one deck with a 1.5" space allowing air flow.

Can you tell me if there are any disadvantages to my idea, or if it would work just as good. By attaching 2 x 6's to the existing 2 x 4's I could also level out any bows that may be occuring in the 2 x 4's.

Thanks again for taking the time to share your knowledge.

We did that on a very major structural overhaul about 1 1/2 years ago also. Many jobs we do, require the additional rafters to get sistered to the existing ones, but this particular job was a 100 % complete deck removal and reframing the rafters and applying new decking. also, the one I am speaking of, was a 12/12 pitch roof on an approximate 100 year old home.

I will get those photos loaded, but probably not until tomorrow evening, so please be patient. I need to find them in my 35 mm photo catalogue first and then scan them into my computer.

The weight of the new decking is approximately 40 pounds per sheet, which would be about 1.2 pounds per square foot. That, plus the minor insignificant weight of the 2" x 4" false rafters to create the air space are insignificant as far as the total dead load.

If you look carefully again at the photos I already submitted, you will see spots under the false 2" x 4" rafters, where we installed some shims to lift up the height so that the new decking would be completely level.

The old existing deck must have had an addition installed, because in one of the photos near the chimney, you can see the several inch variance rising higher and higher on the original section compared to the additional decking installed later on.

You also can see a masonry string line, or a chalk line, which we used to detemine the proper height requirement desired.

Personally, I would use either 4-Ply exterior grade 1/2" CDX plywood or 5/8" for new decking. It is much more dimensionally stable than the cheap OSB stuff, plus it has better nail pull out resistance for a firmer and long term seating of the fasteners, like the nails from the shingles. It is also significantly less prone to moisture absorbtion ans drastic swelling, which wind up telegraphing through the final shingle installation.

Ed
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Old 04-17-2008, 11:27 PM   #11
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Here is the link to the photos of a job that had to be entirely stripped of the skip sheathing so that we could sister in new rafters at a proper elevation to straighten out the roofs deck structure.

I was in a hurry, so a couple of photos are mislabeled or the wrong ones intended to be uploaded.

http://www.contractortalk.com/showthread.php?t=38075

Ed

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Last edited by Ed the Roofer; 04-18-2008 at 11:09 PM.
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