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About to insulate - things to watch for?

Post in 'The Green Room' started by precaud, Oct 19, 2006.

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  1. Rhone

    Rhone Minister of Fire

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    Well, I'm not really sure about the loss of R-Value or that it only applies to fiberglass if true. The examples, one comes from a foam company the other from a quick look talks about loose-fill fiberglass which... loose fill fiberglass is just the junk of the industry, very little in common with fiberglass batts. Don't worry Precaud, you're on the right track and don't Warren about your walls, the issues of fiberglass batts don't apply much when they're installed vertically. In my energy books, fiberglass gets mentioned repeatedly as a bad choice for attics and floors for one reason or another, but those same authors say the problems that plague them don't apply much when they're used in walls, and they use it there themselves.

    My new energy book this year went extensively into fiberglass batts, studies, and results and says fiberglass batts in most cases is acting around 50% but can be worse. Here's a brief synopsis (when installed horizontally). First, to get the full R-Value it needs to be installed to the book, and I've seen reports say when fiberglass is installed too the book it has the same air penetration properties as blown. But, we need to define what's too the book? Ready for this? Each piece/roll has to be "fluffed" to the height it's supposed to be. Then, each piece is supposed to be fit with surgical precision, absolutely no gaps and tight but not too tight. The corners can't be bent up/down or rounded, if going between studs/joists the sides need to be pushed down with a putty knife and pulled back out to ensure the sides are "square". All pieces must be fit tight together, any obstructions need to be cut around the obstacle to maintain a 0% gap (so that it fits like a glove), and can't be compressed. The penalty of failing to do such, is astronomical. My books show just a 1% gap around fiberglass batts will reduce its effective R-Value almost 50%, but it depends on the starting R-Value. The higher the R-Value of insulation the worse the effect. That is, a 1% air space around an R38 batt will reduce its total performance to act more like R20 whereas a 1% air gap around R13 batt will reduce it's performance to be more like around R9-R10. Tomorrow I'll take a picture of the page in my book that shows the chart of just how much R-Value you lose with fiberglass batts with how much air space. Since joists aren't a perfect 16" or 25" O.C., since it's not possible to make glove-tight cuts around obstacles, fiberglass will never reduce airflow or insulate as well as blown cellulose and probably most homes with fiberglass batts in the attic are almost all acting more like 50%-60% what they think it's doing (which the book says also). On the contrary to fiberglass which is nearly impossible to install it correctly to get the full R-Value, blown it's nearly impossible to improperly install it to not get the full benefit. Aren't you glad you went with the blown?

    I just finished installing insulation in my attic, I picked fiberglass batts because I'm not done remodelling and wanted the ability to move it out of the way and put it back. So, I methodically fluffed, carefully placed each piece checking repeatedly no spaces, any obstacle I went around (instead of trying to cut the shape out of the batts) and afterward filled the hole with blown cellulose by hand. There's no way I'd picked fiberglass batts again, it cost me probably 3x more, took me 10x longer, and I probably have about 80% of the R-Value since I was so careful. I'd been better off to walk and destroy the cellulose when it came time for remodelling, and simply fill in the damaged area again with more by hand.

    There is what I call a useful insulation limit. Everytime you double the R-Value you cut your heat loss in half. R1 cuts your heat loss by 50%. R2 cuts it down to 25%. R4 cuts it down to 12.5%. R8 cuts it down to 6.25%, R16 to 3.13% as you can see each time you double your R-Value you cut down your heat loss by 50% each time. But by the time you hit R38 you've cut it down to 1%. Bringing it up to R98 you're still at 1%. For example R60 cuts your heat loss by 0.48% over R38. You have to figure out, is it really worth paying for almost twice the material to reduce your heat loss by 0.48%? In my case (house & environment), with Electricity it certainly is. Heating with wood, after 9-10 years it'll save me a cord, I didn't do it.

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  2. precaud

    precaud Minister of Fire

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    As usual, Rhonemas, I find your reasoning pretty impeccable. I think the reason that the problems don't arise when batts are used in walls is because the top space in the wall is not a ventilated space, and these convection currents are vertical events. There's plenty of flow resistance in a vertically disposed batt.

    Yes, installing batts properly is tedious work and requires great care. I hope your effort is paying off. The one thing I like about fiberglass is it's relative immunity from damage by moisture. If my aging roof starts to leak, the cellulose is going to drink up alot of water and take forever to dry out, probably with impaired insulation value. But I realized that batts would not have been installed properly by inexperienced workers, so I feel the cellulose was the best decision.

    I agree with you on the math of heat loss/R value. But anecdotal evidence I got from people who should know suggested there's more at play than the math. One builder I talked to about it says he recently did a house at R60 in the ceiling and was astounded at the difference it made. He plans on doing R60 to his own house.

    In my own case, I didn't decide on a particular R value. With the crew I had, language differences, etc. I realized it was unrealistic to expect them to put, say, 12 inches in consistently. The easist thing was to tell them to fill it to the bottom of the roof beams. At least then I would know there no dead spots.

    BeGreen, yes, you seem to have found the same info I did on K&T. I examined my wiring, especially junction points, carefully before going ahead. Plus, as stated earlier, in all but one bedroom, the ceiling wiring only carries juice to the light fixtures. There's no way that a maximum 100W draw is going to cause any heat buildup. The problem would come in running 15-20 amps consistently for hours.

    Warren, it sounds like you're doing a great job, and with the humidity you have down there, glass was probably a good choice.

    PS - I said yesterday that my central heat hadn't kicked on yet... today was overcast all day and the heater kicked mid-morning... thumbing it's nose at me...
  3. wg_bent

    wg_bent Minister of Fire

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    What's depressing is that I know what I did in the 1 room in the basement is right, and since I know there is no drafts, the insulation combo of bats and polystyrene is a winner. I sealed the heck out of the sil plate with great stuff also, so it's all nice and tight...but the rest of the house? Who knows. I know the plugs all leak. I feel like tearing all the sheetrock off the walls and pumping in the expanding foam stuff. My friend who insulated that way plus 2 inches of the aluminum backed foam board R15 heats the whole house with 1 cord of wood and a Defiant CAT stove.
  4. Rhone

    Rhone Minister of Fire

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    Well Precaud, I owe you an apology because you were right! I dug around in my energy books and low and behold there's a tiny blurb that states the temperature difference also affects it (see picture). That's all I could find anything about the rated R-Value of batts decreasing with temp difference, doesn't mention how much or to what degree, but something I passed over. I'm assuming it happens to all insulation, nonething I have mentions it happening to cellulose but I feel the higher the temperature difference the more force but I have to assume fiberglass batts is most susceptible.

    Here's the pictures of what this years energy book says, along with the chart explaining how devastating the smallest gaps have on fiberglass batts. Oh well, the book recommends if I have fiberglass to blow cellulose over it saying the cellulose will fill any gaps/cracks I missed so I get full R-Value of the fiberglass batts and add it's own R-Value. Maybe after I'm done remodelling :) Enjoy

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  5. precaud

    precaud Minister of Fire

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    A local energy conservation specialist told me that, if I have cold air coming out of the electrical fixtures, I should seal the opening that allows the cold air to penetrate down the walls in the first place. His point was that no attic air should find it's way downward into the living space or walls at all. Made sense to me. I found two openings over doorway arches that were wide open, and sealed them with styrene and gooey I mean great stuff.
  6. begreen

    begreen Mooderator Staff Member

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    How did you locate these openings precaud?
  7. begreen

    begreen Mooderator Staff Member

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    I believe it's recommended that fiberglass batts be layered in the attic at right angles to each other for this reason. First layer between the ceiling beams, then the next layers put down at right angles to the joists.
  8. precaud

    precaud Minister of Fire

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    By getting up there with a light and looking along the wall intersections...
  9. precaud

    precaud Minister of Fire

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    Seem like it's just a function of the porosity. A material where the air pockets are trapped and sealed won't allow penetration.

    OMG! 50% loss of R value with R38 and 1% gaps! That's huge.

    Yeah, it can wait...! The only downside I've read to doing that is that the cellulose, which is quite a bit heavier than the fiberglass, compresses the batt. Nevertheless, it seems like the way to go.
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