roof ventilation

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Old 11-06-15, 10:12 AM
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roof ventilation

On roofing for cathedral ceilings what type ventilation is used and does there need to be the attic vents that let air in/out even though there is no attic area to get into?
There is some buckling from plywood in a few places.
 
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Old 11-06-15, 11:20 AM
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Hi trotter,
Not sure what "There is some buckling from plywood in a few places." refers to.

There are two approaches for cathedral ceilings, vented or unvented and each has a method.

Vented is the more common, with soffit vents under the eaves and a vent space below the bottom of the roof all the way up to a small attic or ridge vent.

What do you have now?

Bud
 
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Old 11-06-15, 08:57 PM
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Looks like venting at soffett.There is no top vent at top of roof -that goes the length of roof,nor is there a vent on the top point inside the soffett area where the two top sides of roof meet.
What is odd is that i saw a wave in the wood ,after removing shingles and felt, ,as it popped up some -maybe expansion/contraction but no rot .And wood was against next panel-may not have been installed with the space between them and that caused it..
Also only the side that the sun doesnt hit as much is showing theses signs,the entire other side that gets all day sun more looks fine,but no roof vents in either side.

Also before reattaching the plywood back down is it important to trim the edge if it had been butted up close to the adjacent board? there is no water penetration.

-tried to send pic via JPEG but to no avail -again..(upload of file failed)

Any info is appreciated
 
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Old 11-06-15, 10:41 PM
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The pictures are probably too big data wise, here's a guide.
http://www.doityourself.com/forum/el...-pictures.html

If there is no high exit, that buckling you see could be due to expansion from moisture (humidity not water) being trapped in the roof assembly.

Somehow you will need to determine how that roof was built.
How old is the house?
Can you see the insulation at any point?
Is there any attic space up top, even a small space?
Is the slope of the ceiling the same as the slope of the roof, search scissor trusses to see how they can be different?

Once we know how it was build, then we can advise on how it should be ventilated.

Is the roof under construction now?

Bud
 
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Old 11-07-15, 08:34 AM
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Ok -i think i got the pic now..
Directly under it is the insulation then the ceiling -about a 8 inch area . and ceiling is same direction as roof.
Looks like it didnt have the spacers installed for expand/contract and swelled up.
Its the same slope on ceiling as roof and the top of roof has no venting ridge Now on the inside of room at top where 2 ceilings meet there is a box like row across room that may be allowing air to flow but i cant see it working well if its insulated between rafters and ceiling..This is an addition someone else did and at the end of the addition near the roof there is no opening for air flow either.
Only the shady side of roof has shown the distress the other side has no issue but it gets a lot more sun .
 
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Last edited by trotter; 11-07-15 at 08:56 AM.
  #6  
Old 11-07-15, 12:41 PM
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If they wanted to allow for expansion they would have manufactured the sheets of plywood 1/8" shorter. The primary concern for expansion is when the sheathing is exposed during construction. Once covered it should remain relatively dry with little or no expansion. What you are seeing is a lot more than a little expansion.

8" rafters do not allow enough space for the minimum required insulation in TN, and that is without the suggested 1" to 2" of space above the insulation for air flow.

Then you need to determine where that air would flow to?? A ridge vent would be a start if there is at least some space above the current insulation. To get things built the way they should have been would be a major project. But, since you are replacing the shingles, it would be a missed opportunity to not add the ridge vent.

There are other factors which we can't see, slope of the roof and how that addition fits in with what was there.

let's see if some of the active contractors can add further advice.

Bud
 
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Old 11-10-15, 09:37 AM
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Some more pictures would help. You might also want to consider getting a - usually free - roof inspection from a local roofing company.
 
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