Attic and Soffit Ventilation
My wife has been researching
attic ventilation needed for our house for cooling efficiency, prevention of ice dams on the roof, and for moisture prevention. According to her calculations, the vinyl soffits that all the vinyl subs normally use would not provide adequate ventilation. If that is the case, then almost no house being built in our area meets the ventilation requirements based on the fact that our soffits are 2 feet wide which is at least double the width (and therefore potentially double the ventilation) than most of the houses that are being built. We needed double the ventilation than what the vinyl installers would provide by default.
The vinyl subs who gave us estimates were recommending that 1 out of every 3 vinyl soffits be a vented soffit (i.e. has holes in it for air movement). However, we need at least 2 soffits out of every 3 to be vented to meet the ventilation requirements put out by
The Home Ventilation Institute. However, if 2 out of every 3 vinyl soffits is vented, we may have issues with sagging since our soffit area is 2 feet wide. The vented soffits are not as stiff as the non-vented soffits and are thus more prone to sagging. One of the vinyl subs is getting us a quote on how much he will charge to add 1x3 blocking along our eaves in order to support the soffits and prevent sagging.
There is a part of me that wonders how important it is that we meet the attic ventilation requirements put out by HVI since most of the homes in our area only have 1/4 of the ventilation that HVI recommends.