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Buying a house and want to make it super efficient. I have some concerns about the attic. Can you help?

Sam_V | Posted in Energy Efficiency and Durability on

I am about to close on a house that was built in 1972. It is in Longview, Texas. It is 2100 sq. ft. The garage was made into living space at an unknown date. Has a 3.5 ton central air unit and electric furnace for heat (inspector said that is too small and likely was in place before the garage was converted). Flex type ducting in the attic. My goal is to eventually do the entire place from top to bottom, as I can afford it, and make it cheap to heat and cool. I have several plans in mind. Insulation of the attic I think will be my first step. I know I also need to find and stop air leaks. I want to remove the fire place and put in a wood stove (heat for the cost of chainsaw gas and transport cost). But before I get way out ahead of myself, I need help deciding what to do with the attic.

I have read so many articles about spray foam. I don’t the extra cost if it truly insulates better and stops air leaks. My concern is using open vs. closed cell, DIY or hiring it out (I have read that it is DIY friendly if you use it at the right temp), vented vs. unvented attic, etc.

I simply want to know the right combination of things to achieve optimum insulating capabilities. What do I need to buy tool wise to check the quality of the job? Air loss measuring devices or laser thermometers? Thermal imaging devices? I want to gather all the information so I can make the most informed decision possible. I am sure there are a thousand things I haven’t even thought of yet, but the idea of insulating the place where the ducts are just seems like common sense. How thick should I spray it? At R-7 or so per inch…I have read different recommendations on different sites. Shoot for R-30? So 5 inches to be safe? I have priced it at that thickness and the cost is astronomical. Like $21k astronomical.

Should I pay for an energy audit? How do I know if I hire a contractor if he did a quality job?

So many questions I know, but honestly I am not sure where to start. Any help is greatly appreciated.


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  1. GBA Editor
    Martin Holladay | | #1

    As far as I can determine, your house is in Climate Zone 3. Building codes require that your roof insulation have a minimum R-value of R-38. So that's what you should aim for. You can achieve that with about 6 inches of closed-cell spray foam or with 10.5 inches of open-cell spray foam.

    You can also achieve it by a combination of R-5 rigid foam insulation above your roof sheathing, and R-33 of fluffy insulation (fiberglass or cellulose) directly under (and in contact with) your roof sheathing. For more details on insulating this type of roof, see:

    Creating a Conditioned Attic

    How to Build an Insulated Cathedral Ceiling

    Installing spray polyurethane foam to create a conditioned attic is not a do-it-yourself job. It will be cheaper to hire a spray foam contractor than it would be to do this work yourself with a zillion spray foam kits.

  2. Expert Member
    Dana Dorsett | | #2

    The notion that it takes spray foam to air-seal, or that any assembly insulated with spray foam will automatically be air tight is mistaken.

    But if you're going that road, 10" of open cell foam (sprayed in 2 5" lifts, not all at once) does a slightly better job of air sealing than 6" of closed cell foam (that needs to be sprayed in lifts no thicker than 2").

    Martin's solution is cheaper though. Using 1.5-2 inches of foil faced EPS (with the foil facing up) above the roof deck & felt, held down with 2x furring through-screwed to the rafters 24" o.c. with pancake head timber screws, and putting a nailer deck of foil-faced OSB/plywood (with the foil facing down at the facer on the EPS), would give you a cool enough nailer deck and sufficient R-value to add up to R35-R40 in fluffy stuff below the roof deck. Before insulating the interior, run a blower door or large window fan to find and fix ALL of the air leaks, using caulk, can-foam, hunks of cardboard, duct mastic, whatever it takes to get the air leakage down as close to zero as possible. (Theatrical smoke machines can be rented, and will show the leakage in VERY obvious ways.)

    While damp-sprayed cellulose or dense-packed blown fiberglass would have the best performance due to the perfect fit if the batt installer is obsessive enough for near-perfect fit you can still get good performance out of high density "cathedral ceiling" batts, or any rock wool batts.

    With 2" exterior EPS (R8-ish) you can go with R30 high density batts, which are designed to fit into 2x10 bays to hit R38. If your roof is trussed or you have only 2x8 or 2x6 rafters you may want to bump up the exterior R to avoid the gaps at the rafters, or cut some 1.5" foam rafter-extenders to fill those gaps, making it co-planar with the surface of the batts, and long-screw some 1x4 furring through the extenders to the rafters onto which the interior side gypsum would be installed.

  3. Sam_V | | #3

    Thanks so much. I believe y'all just saved me thousands in wasted dollars.

    I will look into the two articles mentioned to further my education on the subject. I am relieved to see that nobody yet has said not to seal up the attic and make it a non vented space. I was concerned I would hear that due to people having the moisture issues on the sheathing OSB. My plan is to semi-condition that air anyway, removing any humidity I can.

    Thanks again for giving me solid information against going with the foam.

  4. Sam_V | | #4

    Ok guys, what if I don't want to remove the current steel roofing to install anything under it? Is there an approved method to build an unvented sealed conditioned attic doing all the work from INSIDE the attic space that still will not pose a moisture issue? All the reading I have done suggests insulating before the steel roof goes on which would obviously involve removing it first. I won't have the time or the money for that before we move in.

    Can I just use the foam board type on the rafter side and go from there or would that inevitably lead to condensation and then wet wood under the steel roof?

  5. GBA Editor
    Martin Holladay | | #5

    The answer to your question can be found in the two articles which I suggested you read in my first answer. Here are the links again:

    Creating a Conditioned Attic

    How to Build an Insulated Cathedral Ceiling

    Just because you want your attic to be unvented, doesn't mean that your roof assembly needs to be unvented.

    Either an unvented roof assembly or a vented roof assembly can be created from the interior.

    An example of an unvented roof assembly would be one that is insulated with closed-cell spray foam installed against the underside of the roof sheathing. (If your metal roofing was installed without roof sheathing, this option won't work.)

    An example of a vented roof assembly would be (from the top down): steel roofing, roofing underlayment, roof sheathing, a ventilation cavity, a ventilation baffle, and R-38 cellulose or fiberglass, held in place with some type of netting or membrane. All of the necessary components can be installed from the interior.

  6. Sam_V | | #6

    Thanks Martin. I read those two articles, but must be so ignorant to the subject that I misinterpreted the information. I thought the way the were saying to do it involved putting the rigid foam under the steel, between it and the framing. I had no idea you could do it all from the interior. Solid help, and I really do appreciate it. Sorry if I seem like I need to be told too many times, I'm just really not educated on construction. I do intend to learn however. Still trying to get a grasp on the terminology I guess is why I am not thoroughly understanding what I am reading.

  7. GBA Editor
    Martin Holladay | | #7

    I wish you the best of luck. If you take your time, and research words that you don't know the meaning of, you will gradually get a better handle on these issues.

    That said, if you are not sure that you understand the concepts or vocabulary of these articles, it may be time to call a contractor instead of trying to figure these details out for yourself.

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