With the more stringent 2014 Florida Building Codes now in effect, the questions that often arise from my homeowner and builder clients are “How much benefit in the Energy Forms do you get by using spray foam versus batt or blow-in insulation?”, and “how much insulation do I need to get Florida Energy Form compliance?” Most of the time my clients are looking for the most cost effective way to meet Florida Energy compliance without having to put in an expensive, high efficiency A/C unit in order to get there. So here’s the best advice I can give to these questions:
As revisions to the Florida building codes press on, vented roofs (insulating the attic floor with batts or blow-in and venting the attic to outside) are becoming problematic toward meeting energy compliance. Up to 40% of a home or commercial building’s energy loss is due to outdoor air leaking into the conditioned space (know as air infiltration), and the Florida Energy Compliance software is well aware of it. Gaps and holes in a structure help promote air leaks into the space and this in turn causes the A/C to work overtime. The Energy Compliance software considers this fact to be aggravated in attic systems that are vented. So and ‘unvented’ attic design (spray foam insulation on underside of roof with no venting of the attic – completely sealed up) will always out perform a ‘vented’ attic in quest for energy compliance. Unfortunately the cost of spray foam insulation can be 4 to 5 times the cost of traditional batts or blow-in. Currently batts and blow-in are not allowed on the underside of the roof deck as a direct replacement for spray foam in order to form an ‘unvented’ attic design (although some insulation manufacturers such as Owens Corning are currently trying to develop an alternate approach to spray foam insulation for unvented roof insulation systems using more traditional insulation types).
So what else can we do? Some homeowners and builders find it cheaper to just stay with the ‘unvented’ attic system and apply additional batt or blow-in insulation in the attic (beyond R-30) until Florida Energy Compliance is reached for the building or home. This approach can be less expensive than staying with R-30 in the vented attic and then being forced to compensate with an expensive, high efficiency A/C unit in order to achieve overall energy compliance.
Construction cost is still king with my clientele and the less expensive, traditional ‘vented’ attic design approach still seems to be more popular in comparison to the more expensive, and more energy efficient ‘unvented’ attic design – at least for this latest round of Florida Building Code changes.