At what point is extra additional attic intake air detrimental? Please judge my attic venting strategy
Here's the scenario:
48' x 104' building in climate zone 5. 48' x 64' of that area will be unheated garage space. I'm still debating the merits of insulating this area. The other park of the building, 40' x 48' will be heated only (no a/c). The area above that is a room in attic area that will be conditioned year round. The room in attic area is 20' x 40', with two 10'x11' spur areas that were allowed by implementing a gable dormer on the main dormer roof line.
My proposed attic ventilation is as follows:
Main roof line consists of continuous Rollex vented soffit, with a free area of 9.72 sq inches per linear foot, which will provide 2021 square inches of net free area (9.72 x 104' x 2 sides). The ridge vent provided by the builder and preferred by the roofer is Lo-Omni, with specified net free area of 11 square inches per foot, which will provide 1,872 square inches of net free area. I have two questions. Is this enough total exhaust ventliation? If so, am I better off with a more balance overall ventilation, or is the extra intake okay?
My second concern is venting the gable "eyebrows". At the gable I have three ganged trusses on each side of this opening to give me the ten foot opening. The gable eye brow was then stick framed from there, and has rafters for the roof system. The building was sheeted up to the 10' opening, and the widest part of the gable is 24', which means the rafter tails extend beyond the knee walls onto the previously sheathed roof. The net result is that I have a 10'x11' conventional attic above this room that will be insulated with blown cellulose, and I have the triangular attic areas created by the extended rafter tails. I apologize if there is a proper name for this type of construction, but I don't know what it is. My ventilation strategy for this area was to install continuous ridge vent in conjunction with gable end vents. With two gable end vents I can easily match of exceed the capacity of the ridge vent. I will mount the gable end vents as low as possible to maximize air flow, but I would like to keep them a minimum of 20" above the roof deck to keep snow from coming in. The roof to wall junction is also wrapped with ice&water to the bottom of the window rough opening.
Comments or concerns?
Posted Mon, 08/11/2014 - 12:16
Edited Mon, 08/18/2014 - 06:05
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