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ugabulldog 09-27-2010 04:07 PM

ridge vent
 
This is new construction and I had a standing seam metal roof installed with a ridge vent. They did not cut the titanium underlayment that laps over the ridge board. Is there a good reason why not, this should be cut to allow air to vent, correct? (plywood stops short of ridge) I can cut it out in between rafters now, only more difficult.....Also, we have two round gable vents going in, and have been told by one person not to cut sheathing out behind these (use as decorative only) because it actually interferes with the air flow from soffit up through ridge vent, and opinions on this? Thanks

Jim F 09-27-2010 08:45 PM

So there is or is not air flow to your ridge vent? Without knowing anything about metal roofs I can tell you there must be air flow to the ridge vent that equals the intake from the soffit vents. And yes, if there are gable vents added for decor, they should not be functional because they will short circuit the ridge and soffit vents. If the builders did not vent the ridge I would ask them why not rather than cutting it myself. It needs to be the proper sized vent, not just a random cut.

ugabulldog 09-27-2010 08:56 PM

Quote:

Originally Posted by Jim F (Post 508129)
So there is or is not air flow to your ridge vent? Without knowing anything about metal roofs I can tell you there must be air flow to the ridge vent that equals the intake from the soffit vents. And yes, if there are gable vents added for decor, they should not be functional because they will short circuit the ridge and soffit vents. If the builders did not vent the ridge I would ask them why not rather than cutting it myself. It needs to be the proper sized vent, not just a random cut.

Thanks Jim, I am the builder...I will ask the roofers why they did not cut the titanium....As far as size... the ridge board runs the width of house and framers left osb a few inches shy of ridge.....

Slyfox 09-28-2010 07:05 AM

The roofers goofed, they should have cut the underlayment and didn't.
Make them climb up into the rafters and cut it out with a straight blade utility knife, check and make sure they make full & clean cuts.

If you have proper intake and exhaust than it is best to use the gable vents as decoration and not cut the wall sheathing out.

MetalEra 09-28-2010 08:59 AM

I agree with Jim's comments. You have to be very careful about not short circuiting your airflow system and interrupting it with gable vents will likely do that. He is also correct in that a ridge vent that is blocked is not going to do you any good. Having the correct amount of NFA (net free area) is critical to achieving a balanced system. If you don't have any way for the air to exhaust at the ridge, you'll be preventing a balanced system and inviting ice dams, increased energy costs, moisture build-up and a host of other potential issues.

I'm guessing that you have an attic vented roof. In that case, you'll want to follow the 1/300 rule, or maybe a little more conservatively the 1/150 rule. Hopefully your roofer took this into consideration when he was designing your ventilation strategy.

To figure out the calculation with the 1/300 rule (for the 1/150 rule, just divide by 150 instead):
(af/300)*144)/LF = Square Inches of NFA/LF

AF=Attic Square Footage
LF=Lineal Foot of Vent Space

If you're using a vented nailbase, then I'd check out Metal-Era's Ventilated Roof System Calculator. Our company also has a free continuing education webinar on ventilation. So if you're interested in learning more of the technical information, I'd check it out.

Good Luck!


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