Considering gable vents only for attic ventilation.
New construction in climate zone 6A, northern NH, r40+ walls, r70 attic.
Current stage is that exterior walls and roof are framed and sheathed. Unconditioned attic will be totally sealed off from living space by the drywall, no can lights or other penetrations besides minimal plumbing vents. Attic will have cellulose blown in and covering 24″ deep on attic floor. Metal roof, raised heel trusses, with 9/12 pitch. The house is simple rectangle, 24’x32′. The long axis of the house is parallel to prevailing wind (westerly) in the area, although winds can come from all directions.
It seems that venting from soffit vents to a ridge vent is considered best practice for ventilating an unconditioned attic. However, we’re considering just gable vents because they would be simpler/cheaper/quicker to install versus setting up soffit vents leading into rafter vents (blocking is already in place and would have to be removed or cut for rafter vents).
We know that gable vents might not be ideal, but would gable vents (sized to code) at least be “adequate” for ventilation of a tight/well-insulated house given the size, shape, and orientation of the attic? Would gable vents and a ridge vent be a better approach?
Does anyone have experience venting the attic of a similar house with only gable vents or a gable/ridge venting combination?
Thanks for any help.
Brian
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Brian,
The need for attic ventilation is wildly overrated. If you have an airtight ceiling and deep cellulose, there really is no point to installing ventilation -- except to keep your building inspector happy.
Still, you should have thought about vent channels before you installed the blocking -- eh?
Gable vents may let in snow. You can install them or not -- your choice.
Thanks for the input. The house was framed to this point with no attic ventilation in mind, the change to some ventilation is mostly to keep the inspector happy.
I assume on a conditioned attic utilizing SIPS one does NOT have to install attic vents as that would defeat the purpose of a SIP. Does code require attic venting on all attic types?
Peter,
The code distinguishes between unconditioned attics (which need to be vented) and conditioned attics (which are not vented). For more information on how building codes handle attic venting, see Creating a Conditioned Attic.