Replies

1. 
   DanH | May 10, 2009 04:54am | #1

   Foil serves as a vapor barrier (when properly installed).

   Foil, in theory, improves the insulation effectiveness slightly.

   I suppose foil might also slightly reduce flame spread, but I doubt that it's rated for that.

   Since the foil serves as a vapor barrier, it should face appropriately for your conditions. In the far north the foil should be towards the living space; in the deep south the foil should face away. In the temperate middle you get to flip a coin.

   Beware of the dreaded double vapor barrier.

   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
1. 
   td88 | May 10, 2009 05:00am | #2

   Thanks, DanH, so I, simply leave the tabs unopened and lay the batts in the cavity with the foil facing down. I am in northern WI.

   You've answered a second question, which was, since I can't attach a vapor barrier to the underside of joists, the foil is my v. barrier?

    

   td88

1. 
   DanH | May 10, 2009 06:11am | #4

   Note that it's an imperfect vapor barrier, since it's poorly sealed at the edges. Also note that in any old structure with multiple layers of oil paint on the ceiling, the paint creates a pretty effective barrier. Your moisture leaks will be through cracks, around light fixtures, along studwalls, etc.
   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

2. 
   td88 | May 10, 2009 05:35am | #3

   I'm seeing paper and foil faced. What's the difference?  

1. 
   DanH | May 10, 2009 06:13am | #5

   Not much difference between the two. Foil is a little bit better vapor barrier than the plastic-coated paper, and you get the slight (theoretical) insulation improvement with the reflective foil.
   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

2. 
   amillionquestions | May 10, 2009 06:54am | #6

   You are not giving enough info. for a good answer. First of all, do you have any idea what relative humidity your home operates at in the heating season? This is important for a few reasons, the foil vapor retarder is better at preventing moisture migration to the attic space and the fact that you want to replace the 1x floor boards with plywood can be problematic if you are running a high RH since the plywood can present itself as a condensing surface, especially if you are adding additional insulation. You might be wise to re-install the solid lumber floor boards as this material is much better at handling moisture.

   Maybe after installing new wiring you can blow cellulose insulation in which will also handle moisture loads better than fiberglass. Of course it is also important to check for air leakage paths at light fixtures, plumbing chase, duct runs, all the items installed that penetrate the building interior.

1. 
   td88 | May 10, 2009 08:56am | #7

   Thank you, amq,

   You bring up cellulose, which I've considered. A contractor has suggested dense pack to achieve higher R value than the batts but, I've heard dense pack makes future wiring work, etc., quite difficult. My ceiling joists are 2x8 so, I'm around R23 with batts. Small potatoes for this area but, better than 0. Any comments on cellulose vs. batts from amq or DanH?

   Edited 5/10/2009 2:05 am by td88

1. 
   CapnMac | May 10, 2009 11:33am | #8

   Well cellulose will give a much better fill than batts, as it will conform to the spaces.  Batts tend to keep their dimensions which in bays.  When too tight, they can kink, leaving a draft space.  In too big bays, there's an airspace in the gap.  This is one of the reasons why FG batts get really poor real-world reviews.

   Given my choice, it's much rather fish wires through cellulose than batts.  Might be more work, but to are a lot less likely to hook an edge and roll up a batt, or twist it into leaving a gap.

   Since you are in northern WI, you are in the exact sort of cliimate where you need venting to maintain cold roofs.  Which suggests running unfaced batts over the tops of the joists to help protect the ceiling framing fro mthe cold.  Where you need attic storage and access, plywood can be installed over rigid foam, but that can require deft details to do right.Occupational hazard of my occupation not being around (sorry Bubba)

2. 
   DanH | May 10, 2009 04:12pm | #9

   Cellulose could make snaking wiring more difficult. But a lot depends on the scenario.I assume this attic area (since you're insulated below) will be unoccupied, and just used for storage. In that case you could screw down the plywood and be able to lift it to do wiring (the bulk of which I would hope is done before you insulate anyway).
   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

3. 
   DanH | May 10, 2009 04:13pm | #10

   (PS: I specifically chose loose-fill cellulose for our (unfloored) attic. Most local vendors were pushing fiberglass, but I consider cellulose to be superior, especially in an older house).
   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

   Edited 5/10/2009 9:14 am by DanH

1. 
   td88 | May 10, 2009 06:26pm | #11

   I haven't seen dense pack in person but, I understand it's quite hard. Is a fish tape even possible in that type of installation. You mention loose fill in your attic, which is a place you would want max. R value. Why did you opt against dense pack? And before it's asked, yes, I intend to do all of my current wiring prior to insulating but, I try to anticipate future needs with my current choices.

1. 
   DanH | May 10, 2009 08:25pm | #12

   I would guess that you could work a fish tape or rod through dense pack for a few feet, but you'd be ramming a hole, not really fishing.We used loose fill because it's an unoccupied, unfloored attic, and there's nothing to restrain the insulation so that it can be densely packed. Instead you just pile the stuff on. I forget how thick ours is (and it's expected to settle a little), but I'm thinking about 20".
   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

2. 
   td88 | May 11, 2009 01:37am | #13

   DanH,

   What did you do for a vapor barrier with the loose cellulose or were you dealing with new construction and applied from below?

3. 
   cargin | May 11, 2009 05:24am | #14

   td88

   If I was in your shoes, I would

   1.  Pull the floor boards and redo the wiring

   2.  I would put all my junction boxes up on the rafters or up on knee wall studs so that you can access them for changes

   3.  I would install 2x6 or 2x8 over the existing joists. If you put them across the existing joists then you will minimize thermal bridging. Then blow with cellulose. Dense pack is better than loose fill.

          Or  install 2" of XPS foam, blow with cellulose and then another 2" of XPS and then install the plywood

   4. Then install your plywood.

   Here is a link that describes blowing cellulose.

   http://forums.taunton.com/tp-breaktime/messages?msg=117095.11

   Dense pack cellulose is not packed rock hard, with a rental machine there is a limit to how tight you will be able to blow it. It's like loose fill packed down. Most of us have not seen dense pack unless we remove wall covering during remodeling. So guys blow the stuff behind netting so they can see the results of there work.

   Rich

4. 
   DanH | May 11, 2009 07:01am | #15

   Old construction. No vapor barrier, though I had previously gone around and sealed things as well as I could.My impression is that the vapor barrier isn't usually required in a well-insulated ceiling since the temperature gradient and moisture gradient will normally cross at a "good" point.
   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

4. 
   Piffin | May 11, 2009 12:51pm | #16

   "dense pack to achieve higher R value than the batts but, I've heard dense pack makes future wiring work, etc., quite difficult."What's the goal here, to get decent insulation or to make the future work easy?I'd use unfaced batts or blown in insulation. The cells is far superior to the batts for this application. 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

1. 
   td88 | May 11, 2009 06:16pm | #17

   See no reason to limit my assessment of a product to a single issue.