I am rehabbing a two story house built in 1967 located in the Chicago suburbs. Currently, the attic has a minimal amount of blow-in fiberglass insulation on the attic floor (top of the second floor ceiling). The HVAC system is designed with the furnace in the basement and a large interior column bringing conditioned air up into the attic. This main column then branches out into smaller ducts in the attic that are fed down into the second floor rooms. The duct work in the attic is wrapped in very thin insulation. The house is a full two stories (with partial basement) with a small footprint of about 1000 feet. The roof is low slope, so the attic is low height, but it is a full ventilated attic above the second floor.
The combination of HVAC system design (ducts up into the attic) and under-insulation has, as you can imagine, resulted in a tremendous amount of heat loss this winter. In fact, during -20F days, I've been up in the attic and it's basically room temperature up there. Since I'm located in Chicago, the attic is extremely hot in the summer, heating the duct work carrying cool air. Considering the local climate and layout of the HVAC system, I believe that spray foam insulation on the underside of the roof decking is probably the best approach, effectively turning the attic into conditioned space. I've researched spray foam insulation both here and on the web and there seems to be a large number of conflicting opinions on, e.g., whether open or closed cell spray foam is best for an attic retrofit. My questions to you all are:
1. Does anyone have experience with a similar attic spray foam retrofit that they can share?
2. Thoughts regarding open vs. closed cell spray foam for this application - which is best? And if you have an opinion, do you have a website or document that you could link that discusses your point of view?
3. If I do have spray foam installed, does outside air need to be routed into the furnace/AC?
4. Any spray foam products to avoid or other pitfalls?
Thanks in advance for any help.