Attic insulation under and over plywood.


Attic insulation under and over plywood.
You all have convinced me that compressing insulation lowers its value, and that houses with truss roofs weren't meant to have floors in the attic. But what about leaving the fiberglass that rises to the level of bottom rail of the trusses, putting a layer of plywood in those places where I might have to go in the future, and putting another 4 or 6 or even 8 inches of insulation above that? Wouldn't that be the best of both worlds?
Then I won't lose my balance and fall through the ceiling when I crawl out there, and the fiberglass above the plywood will be compressed when I kneel on it, but will probably spring back pretty quickly. Or I can fluff it up when I leave.
I looked up the R-value for plywood and it is pretty low, but that was plywood used as siding. When plywood is used horizontally, seems to me it eliminates heat loss through convection, even more effectively than fiberglass. I would think even 3/8" of plywood is as effective as 2 or more inches of fiberglass in preventing heat rising through convection. Except around the edges of course, although since it's not a real floor, some edges could be eliminated through overlaying.
There are times when I have to go out from the center of the attic to install wiring, for lights, telphones, smoke or burglar alarms, and speaker wires, plus more. Right now there is a problem with the phone line to my bedroom. A cordless phone is not a permanent option.
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I just built some risers out of 2x4's attached to the joists, and attached parallel 2x6's to walk on. The insulation can then go under the 2x6's.
Bob
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wrote:

You're saying you raised the level for the floor up 4 inches? Im 60 years old and I'm just not going to do that much work.
What do you think about my idea of putting down the plywood and putting more insulation on top of it?

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Your idea is fine as it keeps you from falling thru the ceiling and provides some minimal R value. Just don't think the plywood provides the R value you seem to think it does.
wrote:

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No floor - just walkways to get me across the attic into each of the 4 sections it is divided into.

It should work as long as there is a good vapor barrier at the ceiling/joist level below the insulation.
Bob
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wrote:

Yeah, because putting down plywood is so much easier than nailing that plywood to a couple of 2x6 runners, first.
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Here's how I did it. I made a walkway 23" wide and put sides on it by running a 1x8 on edge along each side. Then the blown cellulose was put in all around and under the walkway. THEN I bought a roll of r-19 in the 23" wide variety, and laid it on the walkway. Now if I need to use the walkway, I just flip the fiberglass over to the side, and put it back when I leave.
--
Steve Barker


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wrote:

Damn good idea and should be standard practice..Access to the cieling for elec lightboxes and such might be tougher but still do- able.. Dean
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Yes, I suppose the walkway wouldn't even have to be nailed down. I screwed mine only on the corners, so 4 screws and the whole thing can be moved.
--
Steve Barker


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mm wrote:

Yea, it should work.
--
Joseph Meehan

Dia \'s Muire duit
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On Wed, 7 Feb 2007 08:30:15 -0500, "Joseph Meehan"

Thanks, and thanks to all.
That's the plan.
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I used furring strips. Easier to work with and you can leave a gap between them so moisture won't get trapped. I also added 2"x2" pieces to the joists (part of a truss system).

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I've done exactly this on a previous house. There was the standard 10" or so of attic blanket up to the top of the joists, then I nailed some plywood strips around to make "sidewalks". I put another blanket up top of everything, even most of the sidewalks. I just moved some out of the way if needed, or didn't worry about it. BTW, if you only plywood some of the areas you can walk, make *SURE* the fiberglass does not cover the edges of the plywood. Otherwise, you will walk off the plywood and right down through the ceiling.
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Back when I had first learned to tape n finish We got a call to My Boss' friends plumbing shop..There was an office built within the shop with a drywall cieling but exposed 2xs above..My friend that worked for the plumbing shop had stepped through the cieling while walking on the 2xs AND carrying a toilet bowl! You shoulda seen His eyes when He told the story! Fear,pride and embarassment all at once I spose..heh heh..Guess Who got to fix the hole.. Dean
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On 7 Feb 2007 10:25:30 -0800, "Andrew Duane"

That would be sad, wouldn't it?
Thanks for bringing that up. The trusses look something like /W\\, and there is a long 2x4 joining them all together at the bottom of each of the V's I will make a distinction between the very middle and the part on the other side of the bottom v's of each truss.
Once I get past those 2x4's, I won't really be doing any walking. Just crawling. So I should be able to feel with my hands to know where the wood is. Not so sure about when I'm backing up, but that would have been a problem even before the second layer of insulation, since I never really looked back. I just went slowly.

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