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Is closed cell spray worth it?

Richard Briede | Posted in Energy Efficiency and Durability on

I live in Chicago and have had a recent quote of $6,000 to insulate my attic space. It is intended to be a finished living space. I expect to live there for at least the next 12 years. I believe the quote to be fair based on the amount of board feet.

Most of the space consist of 2×6 roof while the remainder consists of 2×4 roof that I can not fur down because of height restrictions and the balance is some 2×4 vertical cavities in dormers. I suggested just spraying the 2×6 area with just 2″ and then I could complete it with fiberglass R-15 batts and was told that I would be disappointed.

Also I considered using extruded polystyrene boards cut to fit between studs and foaming them in place heard this may work but very labor intensive and I might run into a problem because of very large air gaps (3/4″ by 2″ and sometimes 3″) created from 1×6’s used as decking instead of plywood.

Originally I had intentions of making this a vented attic and had Insulated the floor up to the knee walls with R-21. The quote included the whole attic roof making insulating that floor area a waste of time and money.

Would I be able to foam just the roof area and insulate the rest of the area (Knee walls) with maybe XPS leaving that part of the roof cold behind the knee wall? I’ve lived in this house for the last 7 years without any insulation in the attic other than the R-21 in the floor up to the knee wall so I know anything would be an improvement.

I just want to do it correctly but am finding out that everyone’s definition of correct is different. Don’t want to spend $6,000 if I’m not going to see a return on it.

Thanks much I would appreciate any advice.
Rich

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Rich,
    You are only going to do this job once, so you want to do it right. Energy prices are headed up, not down.

    In Chicago, the code says that your minimum ceiling R-value should be R-38. Don't skimp. If ceiling height restricts insulation thickness, your best choices are closed-cell spray foam or rigid insulation on top of the roof sheathing (which only happens if you are also installing new roofing).

    More information here: Creating a Conditioned Attic.

  2. Richard Briede | | #2

    Thanks for fast reply Sounds as if I need to insulate whole slanted ceiling and not the knee wall at all. I would love to meet that r38 requirement but was wondering if I where to spray 2" and complete the rest with r15 fiberglass bat totaling r 29 what are my differences that I can expect. I could in fact fir out the slant section behind the knee wall and obtain the r38 there. I love the foam product but it's so darn expensive.How long would it take to justify the extra 3 1/2" of foam?

  3. Aaron Vander Meulen | | #3

    "How long would it take to justify the extra 3 1/2" of foam?"

    Who knows. You'd have to save $275/yr to make it back in 12 yrs. Who knows what Energy prices are going to be in 3 years, let alone 12. You stated its intended to be living space, I take it then that it is not currently? Meaning you will need to heat/cool it which you're not now. So your consumption is going to go up anyway. I doubt that you will see your money back, if that's your motivation, but its virtually impossible to tell definitively how long it would take. On the other hand, you'll never regret having the most insulation you can. Just my .02.

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