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enTue, 21 Aug 2018 02:02:32 GMTvBulletin1440http://www.inspectionnews.net/home_inspection/images/misc/rss.pngInspectionNews - Home Inspection - Roofing System: Home Inspection and Commercial Inspection
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New shingle warranty only valid if roof has proper through ventilation. Do I?
http://www.inspectionnews.net/home_inspection/showthread.php?t=51965&goto=newpost
Sun, 19 Aug 2018 17:01:50 GMT 16 * 31 = 496 squared for whole ridge vent = 496/144 = 3.444 squared for whole ridge vent.
A 12" ridge vent has 18 squared/liner foot => 18 * 31 = 558 squared for whole ridge vent = 558/144 = 3.875 squared for whole ridge vent.
Formy soffits: 2 wide * 35 long = 2 * 12/foot * 35 = 840squared/side of house = 1,680 squared for both sides of house. 1,680 / 144 = _11.67squared for the soffits_. NOTE: I don't know how to account for the actual slot area; these were installed a few decades ago. I expect the actual ventilation area is less than the 11.67' squared.
This gives me a ratio of 23 / 67 for thr 9" ridge vent, and 25 / 75 for the 12" ridge vent. Certainly not the 45 / 55 ratio noted above.
So am I at least 1/300 sq ft as per the shingle manufacturer guidelines? Is the ventillastion ratios I have better than the 45 / 55 ratio?
And if I do not meet the 1/300' squared rule, then what needs to be done?
thanks,
signed confused]]>Installing a new roof and want to assure that I have proper through ventilation for my new shingle warranty.

Attic space is 38'x30' = 1,140' sq. I rounded this to 1,200' sq for ease of math.

New ridge vent will be Certinteed (either 9" or 12", not sure which the roofer uses), 31' long.
Existing soffits are 2" wide x 35' long * 2 sides of the house.
I think the slot in my ridge sheathing is 3/4" on either side for a total of 1.5" along the 31'.

The shingle manufacturer states: Forconventional roofs, the ratio of unobstructed vents to the totalinsulated ceiling area must be atleast1/300 sq. ft. Vents should be distributed as follows: 55% at thebase of the roof (soffits) for air inflow and 45% at the ridge forair outflow.

Doing the math:

A 9" ridge vent has 16 squared/liner foot => 16 * 31 = 496 squared for whole ridge vent = 496/144 = 3.444 squared for whole ridge vent.

A 12" ridge vent has 18 squared/liner foot => 18 * 31 = 558 squared for whole ridge vent = 558/144 = 3.875 squared for whole ridge vent.

Formy soffits: 2 wide * 35 long = 2 * 12/foot * 35 = 840squared/side of house = 1,680 squared for both sides of house. 1,680 / 144 = 11.67squared for the soffits. NOTE: I don't know how to account for the actual slot area; these were installed a few decades ago. I expect the actual ventilation area is less than the 11.67' squared.

This gives me a ratio of 23 / 67 for thr 9" ridge vent, and 25 / 75 for the 12" ridge vent. Certainly not the 45 / 55 ratio noted above.

So am I at least 1/300 sq ft as per the shingle manufacturer guidelines? Is the ventillastion ratios I have better than the 45 / 55 ratio?

And if I do not meet the 1/300' squared rule, then what needs to be done?

thanks,
signed confused

]]>Roofing System: Home Inspection and Commercial InspectionJDBS32http://www.inspectionnews.net/home_inspection/showthread.php?t=51965