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Insulating a Vented Attic

whnh121 | Posted in General Questions on

Hello,

I need to insulate my attic (5a climate zone) primarily to reduce heat/cooling loss as my geothermal system struggles to maintain comfortable temperatures during hot or cold periods. That is pretty much the only motivation–the attic currently is vented, I just put a new roof on, and I am not aware of any ice damming problems (it’s a steep roof too). The second floor air handler was built in the attic which is obviously not ideal but I can’t change that.

I am down to two options:
-Closed cell foam on attic ceiling: this was my initial preference and I was thinking around $14K to bring the ceiling to R49. This is the cleanest as it brings the air handler into the envelope but it’s closer to $20K for R49 according to the quote I just got. My contractor is suggesting I do R38 for $14,500 (there is existing pink insulation below the attic floor as well but it is probably 50 years old).
-Accept some less efficient solution at lower costs and accept the tradeoff of higher HVAC costs on the second floor. I think this would mean blown in insulation on the floor where it is possible and over the ductwork, which is on the floor. There are some low voltage relays on the floor as well so I’m not sure how much coverage I could get here but presumably covering the ducts and as much of the floor would help. I also may be able to get the state efficiency program to pay 75% of the cost up to a few thousand dollars so this could be a lot cheaper.

Any thoughts on the best approach here? Or a third option?

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Replies

  1. user-6623302 | | #1

    Could you build an insulated room/box around the air handler and then cover the ducts in insulation?

    1. whnh121 | | #2

      I could do that. I'm not sure how important insulation around the air handler itself is versus just getting the ducts insulated? Does the air handler need free airflow?

      If I could get the ducts at least well insulated that would help my efficiency problems but obviously not do much for heat/cooling loss through the attic floor. I'm just not sure how much of my problem is due to the lack of good insulation on the floor and how much is due to the underinsulated ducts

  2. user-6623302 | | #3

    The more area with improved insulation, the better. The rooms your best choice and least expensive. Consider air handler servicing if you build it.

    Give us some more information about how your system struggles to keep up with hot and cold periods. Are you using set backs or on and off periods during the conditioning seasons?

    1. whnh121 | | #7

      Unfortunately I don't have great data on this. I bought the house in the spring and all I know from the previous owner is that the system struggled to maintain a comfortable temperature during very hot or cold weather. I'm trying to deal with it now rather than wait until the middle of the summer as I have a young toddler and I don't want to deal with an emergency situation

      1. user-6623302 | | #10

        If you don't know how it works first hand, any changes you may make may be money not well spent. Run the system constantly, either heat or cool as appropriate. Use no set backs and no off periods. If it has an automatic setback check that it works and is reasonable. Ask you question next year when you have experience with the system. The system and insulation could be fine. Sometimes the problem is operator error.

  3. user-2310254 | | #4

    I'd be inclined to do the spray foam. If you have a good installer, it's a lot quicker and easier to accomplish and brings your HVAC inside the conditioned envelope.

    But...

    You could hire a weatherization contractor to run a blower door test in combination with air sealing. With the air sealing out of the way, you could install blown in cellulose (maybe even DIY) over the existing batts. Check again to see if there are any programs to offset these costs.

  4. walta100 | | #5

    If what you are proposing is to “condition the attic” understand it will be a marginal improvement over the silly equipment in your vented attic. Mostly because the move almost requires the use of expensive spray foam and almost scrimps on R value installed and people end up with R24 ceiling with 50-100% more surface area losing heat.

    If what you proposing is something like an “encapsulated attic” I say you would be playing Russian roulette with mold and rot.

    My first question is how leaky are your ducts?

    Have you had the house blower door tested and air sealing work done?

    Ground source HPs are rarely undersized I would suspect it may not be operating correctly.

    Walta

    1. whnh121 | | #6

      I'm not sure the difference between "conditioning the attic" and "encapsulating" it. The floor of the attic is insulated with the original 1960s insulation which I assume is not very effective. The foam option would be (allegedly) R38 worth of closed cell on the gables and attic ceiling and removing the ridge vent.

      I am working on servicing the HP as well. I bought the house recently and I don't have good data on how it performed in hot/cold weather but the previous owner passed along that it did struggle during extremes

      1. user-2310254 | | #8

        Flash and batt is another option. In your climate, that would be R-20 of close cell applied to the underside of the sheathing. You would then install R-29 (approximately) of air permeable insulation (batts or netted cellulose, for example) against the closed cell layer.

  5. walta100 | | #9

    In my mind the difference between “encapsulated attic” and a “condition attic” is the attitude of the owner.

    Seems to me the owner of the “encapsulated attic” is looking for a free lunch in that they are unwilling to spend the money needed to condition the air in the attic and keep it at more or less the same temp and humidity as the rest of the house and are willing to risk mold and rot with a backup plan to sell without disclosing before it gets too bad.

    The insulation on the attic floor works against keeping the attic more or less the same as the rest of the house. Letting the dew point of the air in the attic get above the temp of the surface of the enclosure allowing water to condense.

    Walta

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