Attic Insulation Retrofit: Spray Foam Insulation (Chicago, Troy: fit in, rental, new house)

[djw228]

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.

Dan

[MSchemist80]

I have a similar vintage house. It had a few inches of fiberglass. I bought 20 bags of Green Fiber Cellulose at Home Depot for $120 they threw in the blower rental for free and I rented a truck for $20 to get it home. I blew it all over the attic while my helper fed the machine. It was simple, and only cost <$150. I decided I liked cellulose better as it is flame retardant, vermin resistant, blocks air better and has better cold insulating properties compared to fiberglass while being cheaper and more environmentally friendly to boot.

[chet everett]

I tend to agree with MSchemist -- blown cellulose is far and away the MOST COST EFFECTIVE way to insulate a space like the OP has described. The climate in our region, as we recently experienced, can be both brutally cold for extended periods AS WELL AS hot and humid for extended periods -- these extremes are very hard to plan for!
IF your house is currently in good shape as far the attic / underside of the roof deck is concerned (free from mold / no signs of ice dams / no heat damaged swelled rafters...) that means the relative "leakiness" of the whole system is working the way it was supposed to...

The basic problem with foam is unless you have a home that is already DESIGNED to be very weathertight it can be a NIGHTMARE to overinsulate the attic and the reason is simple -- trapped moisture will DESTROY the home in short order! It really does not matter if you try to use "open cell" foam (which is often recommended because it is allegedly more "permeable" but I have seen it trap moisture too...) or "closed cell" foam (which is recommend because it is a better "air barrier" but I have seen it pull away from the rafter and expose the home to extreme shifts in temperature...).

Cellulose is great material for adding insulation to homes where you really don't have to worry about changing the permeability -- it breathes. So long as you DO NOT BLOCK any vents in the soffitts / gable ends / roof deck cellulose is not going to cause any problems as long as you don't so massively overload the space or step through the ceiling and bust through!

Honestly I watch the TV shows where they get the stuff donated and the "pay back" period is therefore irrelevant but in the REAL WORLD the fact is that spending thousands of dollars for something that when you get right down to it DOES NOT WORK ANY BETTER than something that costs a couple of hundred bucks is NOT a wise use of one's money.

Don't get me work -- if you are doing some LEED certified gut remodel or building a new house and can factor in every source of air infiltration an incorporate computerized heat-recovery-ventilators that monitor the humidty and other air quality factors then by all means use spray foam but for a house that is was built when cars still ran on leaded gas and nobody wore seatbelts you are asking for trouble...

[Hunter2013]

You should check with your utility to see if they offer any incentives for adding insulation. Also, with ducts in an unconditioned attic, duct sealing may be an option.

[demouser]

Huge blog here on attic insulation:
http://www.greenbuildingadvisor.com/blogs/dept/musings/prevent-ice-dams-air-sealing-and-insulation

[zray]

Two years ago I had my attic insulated with blow-in type. Before it had 40 yr. old rock wool, original to the house and minimal, started to see condensation on a ceiling in a bedroom and decided time to upgrade.

Took advantage of an offer from Lowes. Their contractor came out in a large box truck with a built-in blower. and filled with bails of the snow white stuff.

Since he was alone I offered to keep the hopper in the truck filled.

In the attic he stapled the formed Styrofoam roof venting for the air circulation from the eaves venting. Did all of them, then proceeded to blow in R59 worth of insulation.

I couldn't be happier, did not expect such a difference, but did get a very noticable one. Never have the thermostat higher than 64 degrees in the Winter, and 74 degrees in the Summer.

Bills dropped a noticeable amount.

No matter which system you use it will pay. The less you pay up front the sooner your pay-back is in gas and electricity costs

Another thing I did was to put in a large, sized to the attic sqr. footage, thermostatically controlled roof fan. I really do get a lot cooling effect from it due to the usage of the attic access in the back bedroom closet.

I made a window screen frame to fit in the opening. when used it does a great job.
I close it off during the Winter.

Far better that the ridge vents they push so much these days during a re-roofing job. Roofers did all the cutting and installation for 20$. I just ran a new power line, set the thermostat for 100 deg. and that's it.

Now you can buy them with solar power, eliminating the power line.