My location is South Central Pennsylvania (17241)
I will soon be insulating the attic area of my one story with full basement 3300 square foot ICF residence and was looking for some guidance or advice. I have been researching which spray foam product (open or closed cell) would best serve my needs and of course going vented or unvented for the attic area. I checked out building science.com but they only seem to discuss encapsulating the entire attic creating a ventless/semi-conditioned attic space. Upon submitting my plans for analysis to Energy Wise Structures- McKinney, TX I outlined that I planned to place one inch of closed cell spray foam on the attic floor to complete the envelope and then add R-50 blown cellulose over top to increase the R-value, while letting the attic breathe from soffitt to ridge vent. Energy Wise Structures provided no negative feedback on this approach so I assumed this to be acceptable for my application and geographic location.
I plan to use a closed cell product and apply it directly to the attic floor on the back side of the drywall and between the bottom truss cord.
My reasoning for this is as follows: I have very steep pitched roofs that would be difficult to access. My total square foot area under the shingles equals 6400 square feet. The “floor area” of the attic equals 4550 square feet. This is almost a 2000 square foot difference (Less square footage = less product and time which = less money.) There is no HVAC, Plumbing or other equipment in the attic area. It is for this reason that I have chosen not to encapsulate the entire attic area (under the shingle area) and only spray the attic floor area. The soffitt and ridge vents are in place and so the attic area will “breathe”. I have radiant barrier on the backside of the plywood sheathing covering the roof. I have a Heat Recovery Ventilator planned for installation.
My question(s) are:
1. If using only closed cell (CC) spray foam in the attic floor area how many inches of product is required to provide me with a complete seal (no air infiltration) and at the same time guard against conduction, convection, radiation, moisture permeation and provide an acceptable R-value?
2. Is it good practice to combine the (CC) spray foam along with blown cellulose or should I stick solely with CC spray foam? With the attic being vented and exposed to moisture, dust and other factors, I am concerned with the long term effect that these elements will have on the blown-in-cellulose.
Thank you for time and assistance,
Newville, PA 17241 |