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Will Insulating attic have a noticeable effect on lower level

shrews01 | Posted in General Questions on

I have an old 1930 2 story. The attic only has about 1 inch of insulation. We are in Michigan so are going to be adding more. Last winter we only heated the lower portion of the house and kept the upper vents all sealed off and the temps upstairs were very comfortable. I have two main questions. 

Will insulating the attic above the second floor have any significant effect on the first floor?

Is it likely that if I bring the r value up in the attic, that the second story will then be too hot? 

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  1. walta100 | | #1

    "Will insulating the attic above the second floor have any significant effect on the first floor?"

    Insulation not so much but if you did a very good job of air sealing the upstairs ceiling it will be noticeable down stairs and in your bills. All the warm air that leaks out thru the ceiling cracks is replaced thru the cracks in the lowest level with cold air from outside.

    The smart move is always to air seal before insulating.

    Try to find someone with a blower door to test before and after sealing.


  2. user-5946022 | | #2

    Do a massive air sealing effort before you even consider insulation.

    And by air sealing, that is not just the traditional air sealing you typically think about. Do some reading on this. Air seal around outlet boxes, light fixtures, window, EVERY penetration, and figure out where in your unique construction air is entering. This is really important.

  3. Expert Member
    BILL WICHERS | | #3

    1" of insulation, assuming some kind of loose fill, is probably around R3(ish). Not much. You will surely benefit from adding more. What benefits you'll see can vary a bit.

    I agree with the others who have mentioned air sealing. Air sealing is very important -- if you have a bunch of leaks, stack effect is essentially sucking heat out of your home. This won't necassarily be felt as cold spots, but it WILL be costing you money, probably a lot of money. After you've done a good job of air sealing, insulation is the next best thing to keep heating costs down. I would recommend REMOVING the 1" layer you have now, then doing a good job of airsealing (there are lots of articles here about how to do that), then put in a fresh layer of blown cellulose up to code depth (R49). Make sure to add baffles out at the eaves if you have soffit vents, and situate them so that you get as much insulation coverage over the top plates of the exterior walls as possible.

    In terms of how much you'll notice that insulating for comfort, I think you'll probably notice it more in the summer than the winter. In the summer, upper levels often get hot due to heat coming in from the attic. Extra insulation on the attic floor will make a big difference here, and will help to keep your upper level cooler in the summer. In the winter, extra insulation will help to make temperatures a little more even on the upper level, but the big benefit to the extra insulation will be seen on your heating bill.


  4. Expert Member
    Dana Dorsett | | #4

    ^^ What they said! ^^

    An upstairs that is still comfortable despite sealing off the heating supply registers with only the downstairs is heat it's likely an indication of MASSIVE air leakage between the upstairs and attic. Leaks through the upstairs ceiling to the attic depressurizes the upstairs relative toe the downstairs, drawing copious fully heated air up from the downstairs to the upstairs.

    Air sealing between the attic and conditioned space is absolutely the first step- and the second step! Be damned sure all significant air leaks have been addressed before adding insulation to the attic floor.

    With the air sealing properly addressed adding insulation at the attic floor will improve comfort to both the first and second floors. With the supply registers to the upstairs turned off the upstairs will likely run cooler in winter than it did prior to air sealing, but with the registers open it might run somewhat warmer than it did previously with registers open, and you may need to tweak (or add) balancing vanes reduce the supply flow to the second floor (TBD).

    After air sealing the attic floor plane and reducing that stack-effect driven leakage, the amount of outdoor air getting sucked into the first floor & basement or crawlspace will also drop, which has the effect of keeping the indoor humidity a bit higher. To improve upon this even further air sealing the foundation and band joists is Job 1 part B further throttling back the stack effect flows. Air leaks at the first and second floor walls, windows & doors etc only begin to matter once you've sealed off the top of the stack (leakage into the attic), and the bottom of the stack (leakage below the first floor).

    The ability to control heat and moisture movement through the house begins with air sealing. A rule of thumb used by Nate Adams is that control becomes possible or comparatively easy once the blower door cfm at 50 pascals pressure is less than or equal to the square feet floor area of fully conditioned living space. That rough target for air sealing is usually possible in a retrofit on a plank sheathed 1930s house, but it's an iterative process. Fixing all the bigger and obvious leaks comes first, after which it can pay to chase the rest with blower doors and infra-red cameras, etc.

    Other things to look at is how tight the ducts are, and where the return paths are for all doored off rooms. If there are no return ducts from the second floor or doored rooms with only supply registers there can be substantial air handler driven air leakage using "The Great Outdoors" as the primary return duct, via any & all air leaks that happen to be there. It's usually possible to create reasonable return paths without gutting the house and starting over, but it sometimes takes some creativity. eg, While it's not code legal to use stud bays in partition walls as return ducts in new construction, it's still a legitimate to create a "jump duct" to relieve room to room pressure differences in a retrofit. (In my own 1923 vintage 1.5 story had to take some of those measures.)

  5. Expert Member
    BILL WICHERS | | #5

    It's probably worth pointing out that attic access doors/hatches are classic, and notorious, sources of huge amounts of air leakage. That might be some low hanging fruit to seal up as a first step. The usual way to seal those is with weather stripping and draw latches to pull it tight against the weather stripping when closed.


  6. shrews01 | | #6

    Thank you everyone for the advice. I have another question. When I’m air sealing my attic and crawl, should I use great stuff or is there a better sealant?

    1. Expert Member
      BILL WICHERS | | #7

      Great stuff is pretty standard. I like to use the following materails for air sealing:

      For small gaps (seams, cracks), I like to use polyurethane sealants, usually something from Loctite's PL line. Caulk works better in gaps under maybe 3/16" or so because the canned foam tends to not penetrate and just stay on top of small gaps. Caulk sticks better in this situation.

      For "medium size" gaps (holes, gaps of 3/16" up to maybe a 3/4" or so) I usually use Great Stuff. I always use Great Stuff in the gun. The gun is awesome if you have a lot of sealing work to do, since it lets you reuse the cans over months instead of the "keep going until the can is empty" you have to do with the straw cans. The newer "reuseable" can design doesn't really work well for me, so I stick with the gun. There are plastic tips available for the gun that let you get into smaller cracks (less than maybe 1/4" or so). I like to use those tips to "inject" foam into the gaps. Foam really needs to be INSIDE of a gap, not just on top of the gap, to stay secure.

      For larger gaps, or anything I think will be exposed to thermal expansion/contraction, I like Loctite's Tite Foam better than Great Stuff. The reason is that Tite Foam is denser and more solid, so it seems to hold up better and be less likely to seperate. The downside is Tite Foam is quite a bit more expensive than Great Stuff, so I only use it where it's worth it. I foamed in rigid foam panels in my rim joist with Tite foam, for example, but I use Great Stuff for all the penetrations (wires, pipes, etc.), and "regular" air sealing work when I renovate a wall.


      1. shrews01 | | #10

        Should I use standard great stuff everywhere and the fire block great stuff only near heat penetrations or the fire block everywhere? It seems like a lot of the pictures and videos use the fireblock everywhere

        1. Expert Member
          BILL WICHERS | | #11

          I always use the fire block stuff (the orange stuff) everywhere, because that's what the "standard" stuff is in the can for the foam gun. That might be why you see it "everywhere" too. Contractors tend to like the foam gun since it's more efficient to use.


        2. walta100 | | #14

          I am not sure the fire rated foam its self is any different other than the bright color that allow the inspectors to see that the caulking is present easily.


      2. shrews01 | | #12

        Is that the standard loctite or the big gap loctite that you use?

        1. Expert Member
          BILL WICHERS | | #13

          The Loctite Tite Foam that I use is the normal stuff. I've only ever seen two versions of it, the regular "gaps and cracks" kind, and the more expensive "doors and windows" kind. I've only ever used the "gaps and cracks" kind. It's had no problem filling gaps up to around 1" or so, and I think it could probably handle more. If they make a "big gap" version, it must really expand like crazy!

          I've found the Loctite foam to be noticeable more dense than the Great Stuff foam. It also seems to hold up better when exposed to UV, but it breaks down too -- just more slowly. None of the canned foams I've used can really be used where exposed to direct sunlight.


  7. walta100 | | #8

    If you have decided to take on this project I think it is a great choice but understand it is dirty miserable work requiring you to force yourself into the tightest corners of the attic. It seems impossible that anyone would this work miserable just for money alone.

    When I did my last house I caulked the sill plate with silicone caulking. Lessons learned you must have a clean surface if you want anything to make a seal. Clean every crack with compressed air to remove 90 years of dust before you apply the sealant of your choice. Canned foam is a great choice for larger gaps .25 -2 inches for smaller gaps you often the foam ends up covering the gap without sealing it. For the smaller gap I like fire caulking put a bead of caulk over the crack then with a gloved hand press the caulk into the gap.

    Not gap you see is going to leak air and unseen gaps often leak air. I used my whole house fan as a blower door and incense sticks for smoke to detect air flow thru gaps. Note if you do this turn off all water heaters, furnaces and fireplaces as they could back draft.

    If you do not have a big ceiling/attic fan you could tape a box fan into a window and do one room at a time.


  8. PAUL KUENN | | #9

    PK here from across the lake near GB, WI. Have you done the blower door test to find most leakage yet? What were the numbers? Are you getting help from the state or utilities like we do from Focus on Energy (our state only but I think MI has this type of set up)?

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