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Thread: Insulation, Knee Walls, Cathedral Ceilings

  1. #1

    Insulation, Knee Walls, Cathedral Ceilings

    Construction question here.

    House built in 1981. Before i bought it, attic was completely finished out w/ cathedral ceilings. The attic/2nd floor has a couple bedrooms, an office, bathroom, a storage room. The HVAC wasn't properly reconfigured for the space so, in the summer, it's always 5*-8* hotter up there than on the main floor. That is the problem I'm trying to solve or, at least, make less severe. Winter, it's fine because heat rises. I live in zone 4, so we swing from 0* to 100*.

    4' knee walls create the only remaining unfinished "attic" space. There's approx 9'x25' unfinished space above the front rooms that I can access. I can't access the closed off space at the back of the house.

    Insulation is 6" or 8" of blown-in, appears to be rock wool. Only level with the top of the joists. Knee wall is faced w/ fiberglass batt. I have no idea how they insulated the cathedral parts, but it's insulated with something as I can see the can lights ghosting through snow during winter.

    Part A of my plan is to roll R30 unfaced batts perpendicular to the joists.

    Part B is my specific question:
    The knee walls. They have paper faced fiberglass bat affixed to them. Paper side to the interior, fiberglass to the un-insulated space. Since they're only a 2x4 wall, I want to increase the insulation there - due to the cathedralling, it basically acts as an exterior wall. I want to put 1" foam board (R5) over the batts, running perpendicular to the studs. Maybe eliminate some thermal transfer through the studs.

    But what foam board to use? Faced? Unfaced? That reflective stuff? Which way would it point (in or out?) Does the foam board itself act as a vapor barrier? I don't have any problems now and don't want to create any by trapping moisture in the fiberglass. That's my major concern; creating a new problem.

    Any advice?

    Thanks.

  2. #2
    Join Date
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    Sounds like we have the same house plans. I just had some duct updates done to my system when we replaced it and ran a new trunk up to the attic to push more air up there. The other upgrade was adding a large air return downstairs to help move the air from top to bottom, has made a huge difference, is almost consistent upstairs as with the down. Might take a look to see what your air return to duct ratio is and make sure the system is moving the air it needs to. I only had two air returns in the whole house and both were upstairs, the HVAC was starving for more air to circulate.

    Part A sounds like it will work, though just adding more cellulose on top would also work, just be sure your ridge vents don't get clogged in either case and air can circulate up into your attic and you have adequate ridge or gable vents for the air to draw out of the attic, both for moisture and heat build-up reasons.

    Part B, I think I'd find the wider rolls of insulation that they use for wrapping ducts or in morton buildings to hang over the knee walls, it's probably got as good of an R value and could put a slice in the foil side to let it breath if you're concerned about the moisture barrier.
    Darren

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

  3. #3
    Join Date
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    Step one have a real HVAC guy come look at your system. Tons of HVAC systems are done with little to no knowledge of how they work or how they should be installed.
    A real HVAC guy 9 out of 10 times does not come from your home heating oil/propane supplier. Step 2 have a blower door test done to find out what is really needed to improve the performance of your insulation package. Step 3 do the insulation updates that the testing company recommends.
    It could be worse You could be on fire.
    Stupid hurts.

  4. #4
    Well, you two hit the problem(s) on the head.

    Chuck - Yeah, I know that's the right answer, but that's $1,000's vs $200. I've looked into it. Just getting the audit done will be a couple hundo. Then they're going to want to run new returns and install a new re-sized system. The current system is about 12 years old and running like a top.

    Darren - You basically got it. Upstairs has 6 vents but no returns. Rest of the house has 4 returns. Really, I think just adding even one upstairs would make a huge difference on the airflow. But looking at the thing, I've got like R9 in the walls and maybe R15 in the settled, compacted ceiling.

    As for ridge vents... well... I dunno. They didn't allow space for venting when they cathedral'd it. I believe they stuffed the rafters with insulation and nailed off the drywall. I don't have a ridge vent, just a few box vents on the back side of the house. No gable vent, as there's no area to vent. Even though I've got soffit vents, I don't see any pathway for air; it's not circulating. Based on some things I've seen, I assume this work was done in the mid-late 1980's.

    I'm not able to find a product like you're describing. I see pre-cut batts that are 24" wide and 48-96" long. But nothing looking like I can hang.

  5. #5
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    Quote Originally Posted by David Agnew View Post
    Well, you two hit the problem(s) on the head.

    Chuck - Yeah, I know that's the right answer, but that's $1,000's vs $200. I've looked into it. Just getting the audit done will be a couple hundo. Then they're going to want to run new returns and install a new re-sized system. The current system is about 12 years old and running like a top.

    Darren - You basically got it. Upstairs has 6 vents but no returns. Rest of the house has 4 returns. Really, I think just adding even one upstairs would make a huge difference on the airflow. But looking at the thing, I've got like R9 in the walls and maybe R15 in the settled, compacted ceiling.

    As for ridge vents... well... I dunno. They didn't allow space for venting when they cathedral'd it. I believe they stuffed the rafters with insulation and nailed off the drywall. I don't have a ridge vent, just a few box vents on the back side of the house. No gable vent, as there's no area to vent. Even though I've got soffit vents, I don't see any pathway for air; it's not circulating. Based on some things I've seen, I assume this work was done in the mid-late 1980's.

    I'm not able to find a product like you're describing. I see pre-cut batts that are 24" wide and 48-96" long. But nothing looking like I can hang.
    Giving correct advice is going to depend on where you're located, vapor barriers are used differently in different parts of the country. Typically they are on the side that is considered the warm zone.

    I've got some rafters that also are the ceiling joists on the back of my house. Hard to tell if the roof vents are actually doing anything there, but like mine, if you're not seeing water stains or drywall tape popping off then chances are that you're not having much of a venting issue.

    I'd also recommend having a good HVAC guy (or gal) come and look at your system. They can be sure the condenser and A coil are cleaned, check the freon to make sure it's right (too low = bad, too high = bad also), check the fan speed to make sure the air is getting cooled enough (this one gets overlooked a lot, it needs to be slow enough to cool down the air, not just force it by), and check to see if the system is getting starved for air on the return side, which sounds like it could be based on the number of vents. It may be as simple as needing to add some cheap dampers to the main trunk branches or lines to zone your system and get the air pushed where it's needed.

    Here is something similar to what I was describing insulation wise, it's used to wrap hvac duct, and is about 4.5 R value.
    http://www.zoro.com/johns-manville-d...g&gclsrc=aw.ds
    Darren

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

  6. #6
    Like I mentioned, I live in climate zone 4, and our winter lows are in the single digits with summer highs around 100 +/- a few degrees. The kraft paper on the existing insulation is towards the conditioned space. Concern would be a second barrier could trap moisture between them?? I dunno.

    Yeah, the HVAC is working as designed. We get it checked every 2 years. We've got a 19 degree differential.

    Thanks for pointing me towards that duct wrap. It's only 1 R less than the foam board, but about 60% the cost for the area I'm doing.

  7. #7
    Join Date
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    Your concern about the big problem is spot on, I don't have a real answer but have a few docs that might help confuse you further. I suspect that open cell non backed won't probably cause to many moisture problems maybe (but not really sure :P).

    Building Science has a nice overview of moisture barrier usage and visualizations that helped me understand what they are actually supposed to do:
    http://www.buildingscience.com/docum...vapor-barriers

    I'd recommend spending some time there looking at some of the other related docs as well, I've learned a lot from that site:
    http://www.buildingscience.com/@@sea...tic+insulation

    The energy star folks also have a decent overview of fixing attic air leaks. They gloss over a lot of the potential issues, but I think you'll likely want to be solving some of these problems as Chuck noted or you're swimming upstream in a fast moving river so its worth cross checking this while you're in there.
    https://www.energystar.gov/ia/partne....pdf?3806-ab01

    No relation (that I know of) but here's another fairly useful method of increasing the insulation depth of a wall (there are a ton of explanations on the Mooney Wall out there, this was just a quick hit that explained it reasonably well):
    http://www.builditsolar.com/Projects...MooneyWall.htm

    You might also consider seeing if you can rent an IR camera or find one cheap and get some images of the house when there is a nice temperature differential. That plus the pressure test is what most of the auditing folks do. The pressure test is harder to DIY, but the thermal imaging is getting simple and cheap enough it seems achievable. (some phones can apparently do some ok imagery now even: https://play.google.com/store/search...l&c=apps&hl=en iphone https://www.google.com/search?client...utf-8&oe=utf-8 or https://itunes.apple.com/us/app/ther...545954932?mt=8 - disclaimer I've never tried any of these for anything like a house so have no idea how well they work in that regard, but the resolution looks pretty ok on a lot of them).

  8. #8
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    Quote Originally Posted by David Agnew View Post
    Well, you two hit the problem(s) on the head.

    Chuck - Yeah, I know that's the right answer, but that's $1,000's vs $200. I've looked into it. Just getting the audit done will be a couple hundo. Then they're going to want to run new returns and install a new re-sized system. The current system is about 12 years old and running like a top.

    Darren - You basically got it. Upstairs has 6 vents but no returns. Rest of the house has 4 returns. Really, I think just adding even one upstairs would make a huge difference on the airflow. But looking at the thing, I've got like R9 in the walls and maybe R15 in the settled, compacted ceiling.

    As for ridge vents... well... I dunno. They didn't allow space for venting when they cathedral'd it. I believe they stuffed the rafters with insulation and nailed off the drywall. I don't have a ridge vent, just a few box vents on the back side of the house. No gable vent, as there's no area to vent. Even though I've got soffit vents, I don't see any pathway for air; it's not circulating. Based on some things I've seen, I assume this work was done in the mid-late 1980's.

    I'm not able to find a product like you're describing. I see pre-cut batts that are 24" wide and 48-96" long. But nothing looking like I can hang.
    While doing it right the first time may seem to be to much money to spend it is way cheaper than doing than doing it twice.
    It could be worse You could be on fire.
    Stupid hurts.

  9. #9
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    Side note, looked closer at some of the phone ir camera apps and they're bunk. Did find one USB camera with meh resolution for $200, so maybe hour for the future.

  10. #10
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    Quote Originally Posted by Ryan Mooney View Post
    Side note, looked closer at some of the phone ir camera apps and they're bunk. Did find one USB camera with meh resolution for $200, so maybe hour for the future.
    I looked at those a while back also, not worth spending money on. A simple ir point/shoot temp sensor from HF may be a good $10 - $15 investment. You can point it at various points on the wall on a warm day and instantly see where you need to do some work.
    Darren

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

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