Replies

1. 
   Mongo | Nov 29, 2003 06:36pm | #1

   Pete,

   My idea is that it's very difficult to get a decent performing vapor barrier out of a kraft-faced product when installing it paper face down in an attic floor joist bay.

   Since you're set on FG batts, if you do proceed with two layers of insulation, definitely only have one with a facing. In your climate, the first layer would go paper face down, with the paper towards the warm living space. Subsequent layers over the first would be unfaced. If you use faced for the second, just slash the paper facing multiple times with a utility knife.

   Before you even insulate, use canned foam to try to seal any penetrations in the attic floor. Anywhere air can flow from the conditioned space below upwards into the attic. That dividend will likely pay off more than insulation. Canned foam is inexpensive, and your labor is free. Kind of.<g>

   Another option for a vapor barrier is paint. Many of today's paints perform as a vapor barrier. Were you to repaint the celings of the space below, that could solve your problem.

   Tough to tell, though, as I'm not in your house to see the actual details.

   In case you're wondering, paint as a vapor barrier and the paper facing as a vapor barrier wouldn't really count as two barriers. You can do the faced insulation and paint without having to worry.

   Just to give you more work <g>, before sealing the attic of older homes, it sometimes wise to go into the basement and use foam to seal and penetrations between teh basement ceiling and the cinditioned living space above.

   Stop moist air infilatration at its entry (basement ceiling) and stop it at it's exit (attic floor), control the amount of moisture added in the envelope through day-to-day activities (bath fans, cooktop exhaust), and you're way ahead of the game.

   There are some quirks with moisture in older homes, but my first concern would be the basement ceiling. Second, the attic floor. See how the humidity is over the winter. Then deal with exhaust fans if indoor moisture is a problem.

1. 
   peteduffy | Nov 29, 2003 09:34pm | #2

   Thanks for the input.  The basement is dry, since we're the highest point in the county, but I will foam any gaps that I can get to, both in the attic and in the basement.

   The office is away from any kitchen and/or baths, just a laundry room next to it, and high humidity is not a problem.

   I know the Zinnser white pigmented shellac is a good sealer and vapor barrier, so I can use that.

   Would you recommend loose fill cellulose?  If so, would I need to put down plastic first, or would the loose fill dispers any moisture that does get up there.  I think I read that somewhere.

   THanks again.

1. 
   Mongo | Nov 30, 2003 02:35am | #3

   My first choice would indeed be blown-in cellulose. Realize that they will settle after installation, so blow in more than you need to end up with the amount you want. Initial fluff can depend on the blower and installer technique. Your installer should know how much his jobs settle, if you do it yourself follow the guidlines for the blower/cells that you use.

   If you have nothing up there, it wouldn't hurt to lay plastic down,laying over the joists and allowing it to settle into the bays. If anything, it'll help if you ever have to clean out the attic for whatever reason. Shovel the majority of the cells, then pull the plastic up for clean joist bays.

   Cells does have an ability to hold and disperse water. It's a good choice.

   If you have a lot of air movlement in your attic, some people find that blown-in insulation can shift, or drift, like snow. You can lay Tyvek over the cells, for that is what Tyvek was originally brought to market for.

2. 
   dIrishInMe | Nov 30, 2003 03:11am | #4

   A well vented attic doesn't need a vapor barrier, and it may act to trap moisture where you don't want it - especially if you use plastic. 

   Also, you will find loose fill insulation will fill in better around wires, light fixtures, pipes, odd sized joist bays, etc.    The idea is to have no air pockets.    Where I live, the big box stores rent insulation blowers for not too much money.  You may want to get a price from an insulation contractor also, as I have found that their price is often only a little more than you can buy the materials for since they get a discount for volume buying, and blowing insulation can be a nasty job.  With loose fill, you would have to come up with a way not to block your soffit vents - assuming you have them.   I think that you will find that a celulose product will give you more R Value per inch than fiberglass loose fill which is probably important since you are somewhat space constrained.

   If you really want to use R-13 batt insulation, I say use unfaced, at the very least, for the 2nd layer.  Really though, for Illinois, R-30 would be considered the minimum.   The problem with R-30 insulation though, would be that it would sit higher than your 2x8 joists - unless you got R-30c, which would be the best fiberglass batt type product for your application. 

   Do what mongo said and seal up air leaks before insulation the attic. 

   Matt

   
   

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   Edited 11/29/2003 11:52:10 PM ET by DIRISHINME

1. 
   peteduffy | Nov 30, 2003 07:58pm | #5

   Thanks all for your responses.  I think I'll take back the FG rolls and use cellulose. 

   I'll install baffles so as not to block any air intakes/soffit vents.  The problem now is that there is wood blocking between the roof rafters, right at the attic floor at the eaves.  I guess this was what they used 80 years ago to prevent the insulation from blocking up the eaves, or maybe they did it for some other reason.

   There is a T&G floor that goes in the attic for storage, which I'll put back in after I insulate, so I'm not worried about the loose fill blowing around.

   Now, one final question.  The area I'm talking about isn't very big.  Instead of getting the blower, can I just dump some loose fill cellulose up there, manually fluff it up a bit and make sure if fills all the voids and in between the joists?  I know I don't want it compacted, but the area is less than 20x20, and it seems a blower would be overkill.  Not to mention the mess it would make in the rest of the attic, which is over a garage, and stuff is still stored in up there.  It's messy enough as it is, after taking out the 80 years old stuff.

   Thanks again for all the good advice.

3. 
   jimz | Nov 30, 2003 08:12pm | #6

   Pete:
   While I agree wholeheartedly with using blown in cellulose insulation WITHOUT  a vapor barrier in the attic is best method, my concern is your wiring.  If it is romex, no "problemo".  But if it's the old knob & tube (K&T) wiring, you need to be careful about packing insulation around it, since it needs an air space to cool.

   Rookie

1. 
   peteduffy | Dec 01, 2003 12:25am | #7

   The electrical is ok.  Romex is not allowed in the Chicagoland area, so it is all in conduit or BX.

   Thanks.

1. 
   jimz | Dec 01, 2003 05:41pm | #8

   Pete:  Glad to hear that your electrical is up to par.  There's also a discussion (Nov 26th?) in this folder regarding i.e. "What's wrong with kraft paper".  Take a look at it as well.  In my last reply, I meant to give a "big amen" on the importance of sealing air leaks.  Since reading up on insulating, I'm more convinced that sealing leaks into (1) the ceiling and (2nd) cracks in the crawl/basement areas are almost more important than insulation. And the more I read, I'm also more turned off on fiberglass insulation batts - unless I installed or inspected the work.  Rookie

1. 
   stonebm | Dec 01, 2003 08:51pm | #9

   R-25 fiberglass is available around here and is sized for use with 2x8's.  Maybe look into that.

1. 
   marv | Dec 01, 2003 10:31pm | #10

   I'm about 100 miles from Chicago and have no vapor barrier and blown in insulation.  works fine.You get out of life what you put into it......minus taxes.

   Marv