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Discussion Starter #1
I have a customer I am working with that did an addition to the house 15 years ago and the shingles are curled up pretty bad. It's a trophy room addition with cathedral ceiling constructed from a 2x8, roof on top side, drywall on bottom side with batts insulation between. It looks like I need to add ventilation to save the new shingles from excessive heat. I can't do that with typical attic venting because the 2x8 cavity is stuffed full of insulation. I was thinking of nailing 1/2"x 1-1/2" furring strips over the existing roof sheathing and then laying new 1/2" sheathing over that leaving a 1/2" void for ventilation. Use a smartvent at the bottom and ridge vent at the top. What do you guys think? Or other ideas?
 

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I spoke to a SIPS panel company a few days ago and had the question about venting the roof. He said no matter if its SIPS or stick framing with fiberglass he said venting attic space is a waste of time. He explained about the shingles wearing out about 10% quicker but the cost of cool air and hot air being pushed out the vents in the attic ends up costing more than the 10% loss in shingle lifespan. He was more technical in his explanation than above but what he said made sense.
 

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Sean
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The problem as others pointed out isn't the ventilation nor "excessive heat" the issue is how it was built. +1 to Scipio for adding XPS foam to the sheathing, more sheathing & reroofing. With that though you actually do need more based on your climate zone
Check out this piece (What is a hot roof) & scroll down to the section on foaming the exterior / click on the picture for how to do it - also check out the link on ice dams which has how much foam you will need to eliminate dew-point issues / required by code.
Now after you add the foam, if you still believe you need ventilation, just add some sleepers & away you go (just don't forget to tape the seams of the foam (both layers)
 

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Always Learning
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You shouldn't have fiberglass until the recommended thickness of xps or closed cell spray is reached first at the cold side of the assembly.
 

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Johnny Cash said:
How would you do closed cell spray foam on the cold(outside) side of the assembly?
I wouldn't...I would rip out the drywall and make sure there isn't more damage that you can't see. Then I would spray foam the interior and re-drywall. Prob a wash compared to furring the roof and re-roofing...plus a better highly recommended way. Even with ventilation, fiberglass is not recommended without the xps or foam in a cathedral ceiling.
 

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I think for your climate zone, 3" of foam is the minimum recommended thickness before fiberglass should be used.
 

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Johnny Cash said:
I have a customer I am working with that did an addition to the house 15 years ago and the shingles are curled up pretty bad. It's a trophy room addition with cathedral ceiling constructed from a 2x8, roof on top side, drywall on bottom side with batts insulation between. It looks like I need to add ventilation to save the new shingles from excessive heat. I can't do that with typical attic venting because the 2x8 cavity is stuffed full of insulation. I was thinking of nailing 1/2"x 1-1/2" furring strips over the existing roof sheathing and then laying new 1/2" sheathing over that leaving a 1/2" void for ventilation. Use a smartvent at the bottom and ridge vent at the top. What do you guys think? Or other ideas?
I would consider removing the shingles, roof sheathing and insulation. Add spray foam leaving an air space. New sheathing, shingles and ridge vent. Make sure you have an intake vent.
 

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Well, whatever else is decided upon, the roof needs to be replaced.

Curled shingles are likely the result of lesser quality material, whether by design or just a bad run.

Before tearing out everything it is best to make a reasonable cost/benefit assessment.

There is no mention of the use of the space or its size, so I will speculate.

Let's say the roof was 1000 sq ft. Since the roof needs to come off anyway, it would seem the best contingency would be to access from the outside.

Removing the plywood and fiberglass, adding 3" SPF and supplementing additional fiberglass might cost an additional $5K.

And that might be conservative. It's a relatively small job. It's 12:12. Logistics between tear off and insulation and getting it water tight can make for an exciting day.

Just sayin'.
 

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Discussion Starter #16
Did you try the link I shared as I am sure it is mentioned on the picture? Same way you do with SIP panels, etc... specialty screws
I did read the link and saw nothing in there about attachment. As much as you made it sound like you knew what you were talking about I would expect a more detailed answer than "specialty screws" ?
 

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There are products referred to as an 'insulated nail base' that provide both the insulation and air space. It may be cheaper to built it yourself with strapping though.

I'd have to disagree with a lot of the posters here. Ventilation is very important for all roof types (shingles especially) to prolong the lifespan.
 

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Sean
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I did read the link and saw nothing in there about attachment. As much as you made it sound like you knew what you were talking about I would expect a more detailed answer than "specialty screws" ?
Well it is on the picture like I thought & there are numerous types out there - what you pick can be dependent on what is available, local AHJ, etc... As for my preferences, I have used a few all with great results. Here's a great way to get started http://bit.ly/GLcqpU
 

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I did read the link and saw nothing in there about attachment. As much as you made it sound like you knew what you were talking about I would expect a more detailed answer than "specialty screws" ?
I am curious as to what exactly it was that you did "expect".

You expected an answer that would solve your roof issue?

Maybe you expected someone to give you a detail with all notes and specs. detailing exactly what size fasteners and foam and fiberglass insulation you need for your specific situation?

Jeez, some people.



Andy.
 

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I actually have a similar problem only the roof is 3/12 and they want to finish their attic. I can see the eaves at this point. I am unsure how to go about it...do you leave a 2 inch gap from the insulation? Or is just using spray foam allowed?
 
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