Hey All,
New member here. Initially a little background on myself. I have been a HVAC contractor all my life so going on 35+ years now.
I run a truthful heating and cooling computation on all my project to size my devices. Just recently I have actually been facing insulation professionals spraying about 6 ″ of open cell ( 0.5 lb/ft3) foam at the roof deck creating an encapsulated attic space. Being in climate zone 4, I believed the minimum attic insulation is R-38. Might even be more now.
Do not get me wrong I love an encapsulated attic space if I have devices and duct located there. It can easily decrease my cooling loads by 25% or two.
What I don’t comprehend is how the building code enforcement people allow a R-22 insulation worth in an attic. (r-3.8 x 6 ″)? The response the insulation individuals give me is that it is equivalent to a R-such and such of fiberglass.
Like I say I run lots of load calculations and to me an R value of X is = to an R value of X. It doesn’t matter the product you use to attain that value. Infiltration is a different calculation totally separate from the heat conduction through the product.
That being stated a foamed building envelope will have less infiltration than conventional insulation methods however once again infiltration is determined separately. To put it in math terms the equation would be– Thermal conductivity of foam x area+seepage=Thermal conductivity of fiberglass x location+seepage. deduct seepage from both sides of the equation
and it is apparent a R-22 foam assembly has more loss than a R-38 assembly. Not to discuss the total area when foaming at the roof deck is substantially more than the surface area of the ceiling of the conditioned area. What am I neglecting here? value your remarks, Axiscat