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Community and Q&A

How to best control mix of unheated attached garage temperature and heated house temp affecting overall climate in entire attic?

jimcava55 | Posted in Energy Efficiency and Durability on

Just to give you a mental visual, the house is 1460 sq.ft. single story truss roof and vented crawlspace. Front half of roof has two dormers.

Could you elaborate on air sealing the attached garage.
Seal gaps only or seal gaps and insulate attic floor over garage?
Would vapor barrier be beneficial since rest of attic has none?

Garage roof has front dormer with no eave vents.
The rest of attic is insulated and vented (bird block eave and ridge vent).
How would this affect the balance of intake & exhaust for entire attic pertaining to moisture control?
Would partitioning off garage attic space from rest of attic be beneficial and if so with what materials?

I would like to make garage passively warmer to work in during winter. Two inside walls are insulated. I plan to insulate 16′ garage door. I should mention also, that the propane furnace and hot water heater are located in the garage. The D box and cold air return duct are located above in attic and I have air sealed around them, as well as the exhaust.

Your feedback would be greatly appreciated…

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  1. GBA Editor
    Martin Holladay | | #1

    There are many issues here. A few comments:

    1. It's not a good idea to locate a furnace in a garage, since the garage is outside of the thermal envelope of your house. If the furnace supply plenum has any leaks -- most do -- the furnace can distribute carbon monoxide from your car exhaust through your heating system ducts.

    2. Your house needs an air barrier. In general, the air barrier follows the insulation layer. If you know how to perform air sealing work, that's where you need to concentrate your efforts. If you don't know how to perform air sealing work, you can hire a home performance contractor or start studying the topic on this website.

    3. Before you start heating your garage, I think it would be a good idea to see if you can bring your furnace inside your home's thermal envelope.

    4. If you want to keep your garage warm during the winter, you can install insulation in your garage walls and ceiling.

  2. jimcava55 | | #2

    Martin, thanks for your response but I need more detailed answers to my questions in order to address the issues effectively and not waste time and money.

    I have tried researching for any known issues with garage attic space/partitioning, with no true results. A house inspector said it might be a good idea and a tech college instructor for house construction said he had seen it done in the past and that some municipal codes required it but he doesn't know how effective it is.

    In answer to your comments:
    1. That's the way the house was built.

    2. I have done some air sealing and thanks to this site I am learning more about air sealing. There seems to be many gaps to fill and finances are slim to hire out a contractor especially since I'm in need of a new roof. It's hard enough to find a competent roofer at any price.

    3. I don't plan on heating my garage mechanically, just make it more comforting and energy efficient without breaking the bank, while addressing the moisture issues, which is my main concern.

    4. As I stated previously, the two innermost garage walls are insulated.
    I'm asking about the ceiling and partitioning off the garage attic because I need to replace the roof decking on the back half of the house especially, due to moisture damage. (Not a fan of OSB sheathing either). Even after air sealing gaps, if it is beneficial to partition off the garage attic space, the most opportune time would be while the decking is being replaced, in order to bring in materials needed. Not able to fit to much through the hatchway in garage ceiling.

    My neighbors house which is similar was built by the same builder, about same time (20yrs ago) and their garage is partitioned off. They have some moisture problems too, also on back half of roof and are planning to replace roof also but only what osb sheathing needed. Their windows sweat where mine don't. Of course they do keep heat set higher for two infants. No air sealing has been done to their house.

  3. wjrobinson | | #3

    James, your home situation most likely can't be solved via the net asking for help. You need someone there to look at things directly.

    Homes should not have moisture issues and failing sheathing and more.

    Call contractors, ask for solutions and estimates. Save money by doing some or all the work yourself. Another option might be to sell and rent so as to have maintenance be the landlords responsibility.

  4. GBA Editor
    Martin Holladay | | #4

    In my first response, I wrote that "the air barrier follows the insulation layer." What I meant was this: your attic and garage are currently outside your insulation layer. That's why you don't need to partition your attic.

    All of this assumes that you have an effective air barrier, and that you aren't leaking indoor air into your attic.

  5. jimcava55 | | #5

    Reply to AJ Builder:

    I have had an inspector, a general contractor, an insulation contractor and several roofing contractors come and assess the situation and all have different points of view and no solid answers.
    If sealing as many gaps as I can find in the attic and adding insulation is what I can do on my own then that will have to suffice.
    Unfortunately, not all so called profe$$ionals are very proficient.

    I never did like stick built housing really. Straw Bale or Earth Ship design would be my preference now.

  6. wjrobinson | | #6

    James, I agree about contractors. In my area I only know 3 contractors that somewhat understand the state of the art of what we did thirty years ago.

    I.E.- I have yet to find one shingle laying roofer that understands the need to overhang shingles past the drip edge enough to break the dripping water loose to drip so it does not curl back onto the facia leading to green mold stains and more. And that concept is not in the thousand books written on homebuilding.

    We do need a very well written complete guide on the hows and whys of building a home. I once added up the weight and the tasks and the shear number of items that make a home. 100,000 or more of each.... of pounds, of tasks, of details that work, of weight and and items! That's a lot, it's complicated, and we need ALL the details. One misstep to do with moisture can destroy an entire home.

    GBA is working on this situation it seems and certainly we in the business and our customers sorely need it, especially now as energy codes are changing rapidly.

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