Raising Attic Floor for more Insulation?

The house we are moving into has a Nice, Large attic with a plywood/pressboard floor over 2x6's and 2x8's depending on the spans.
The insulation is blown in Fiberglass, but only 6-8" max.
The attic was DESIGNED for loads by the original owner/builder as I have seen the blueprints.
What I want to do is take up the floor, put down something that will raise the floor 6-8" and put in that much new insulation (no vapor barrier of course).
I don't plan to do the entire attic this way, just a 10-12' "path" down the middle, the rest can just have more insulation put on top of what's there... but to be able to put stuff in the attic AND insulate UNDER it....
As this will have MINIMAL load on it, what would be the best material to use?
2x6's or 2x8's would obviously work, but seem like overkill, and costly in material.
If my Time is not worth anything, Can I build a "truss" that looks like a comb that sits on every joist and raises a 2x4 up 6-8"s?
There USED to be product like Attic-Dek that would keep the insulation thick, and still be easy to use...
Ideas and thoughts are welcome...
Bob
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Bob Sisson wrote:

I guess that would work. you would have to have some plywood gussets or something in place of truss plates. and i bet a lot of your "comb teeth" would not contact the underlying joist.
how about this...run 2x6's 48" oc standing up on edge running perpendicular to the existing ceiling joists. then run 2x4's on top of them parallel with the ceiling joists, stacked over them to facilitate insulation installation.
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Bob Sisson wrote:

IMO the easiest way to redo.....
Remove the insulation in the area you want to have the "10-12' "path" down the middle" & use the removed insulation in the areas of the attic
replace removed insulatin with foam board or spray in foam ~R7 per inch
you get the higher R value you want w/o any modifications to the structure....only down side is foam is more $'s than fiberglas :(
cheers Bob
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cutting and fitting rigid foam between joists is laborious and doesn't work that well because of the inevitible gaps (plan on getting a few cases of Great Stuff). Also expensive--5 1/2" would run you about $1.75 a square foot. Also, I have to find out where bob is getting R7 per inch foam. in these parts, our rigid extruded polystyrene is R5 per inch. (polyiso is R 6 per inch, but its a lot more expensive and doesn't work well if you have to cut it to fit between joists) plus, in a 2x6 cavity, you will be unlikely to fit 5 1/2" of rigid. I think 5" or R 25 is the max you will fit in practice. considering that you can get an R21 fiberglass batt in the same space, thats a small gain for a lot of trouble and expense..
spray foam is an option, if you can afford it and don't mind the hassle of tracking down a contractor. where i live, $850 is the minimum setup charge for a contractor to blow in icynene. also, you would have to over fill the joist cavities and saw off the excess with a saw. you will have to mask off everything you don't want stuck full of foam. spray foam makes a MAJOR mess.
so it's hard for me to see that foam is the "easiest way". fiberglass has its uses.

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marson wrote:

I'm getting R7 off the mfr's packaging / info but I guess like most stuff the mfr is a little "optomistic"?
http://www.dow.com/styrofoam/na/iso/tuff_r.htm
looks like "new" iso value is 6.5
http://www.sizes.com/units/rvalue.htm
fiberglas is ~3.3 which is about 1/2 of iso
the best he can do with fiberglass is a 2x6 cavity is R18 / 19 & I got the feeling he was after more
also how well does fiberglass R value holdup up over time
when I said easiest, I meant for the small area he had in mind.....no structrual mods
I agree the spray is a mess & the iso cutting / fitting is a bitch but again it seemed like he was doing a few 100 sq ft
and maybe the loss of few inches of head room is meaningful (or not)
cheers Bob
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Bob Sisson wrote:

Have you considered insulating the attic ceiling? Your attic will be much warmer in the winter and cooler in the summer. You may need a ridge and soffit vents along with those styrofoam air channels for proper ventilation if you go this route. My thinking is that the less the temperature differential the lower the heat loss will be. And the free bonus is a more comfortable attic.
--
Art

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One red light I see not mentioned above that I saw was removing the existing plywood. If it is nailed at all, I can see a LOT of popped sheetrock nails in the ceiling below. Whatever you decide, I would do it on TOP of the existing floor.
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Another thought to consider. I have about 8 inches in my attic, I priced getting another 8 inches blown in and was told $2,800.00 With the HVAC cost I would save I figure probably 10 - 12 years to break even. Hell, I'm 75 now. I didn't do it. :)

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Good GAWD man! I'm having my whole house walls and ceilings done for $1200. It shouldn't cost you more that $200 to add 4" to your attic unless it's the size of a football field or something.
--
Steve Barker



"Glenn" < snipped-for-privacy@kc.rr.com> wrote in message
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I said to the guy that I had been out of the market for several years and I had no idea how much things had gone up. He said before he gave me a quote, what would you expect to pay. I said 5 - 6 hundred. He said no way, things have gone up more than that. My memory may be bad on the price he gave me a year ago but it was really high. I didn't bother shopping around because I really wasn't that interested.
One thing that may make it higher here. *We use United States citizen installers*.
.
Another thought to consider.&nbsp; I have about 8 inches in my attic, I priced <BR>&gt;&gt; getting another 8 inches blown in and was told $2,800.00 With the HVAC <BR>&gt;&gt; cost I would save I figure probably 10 - 12 years to break even.&nbsp; Hell, <BR>&gt;&gt; I'm 75 now.&nbsp; I didn't do it.&nbsp; :)<BR>&gt;&gt;<BR></BODY></HTML>
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That was one thing I made sure of with my salesman. That there would be Americans doing the work. He said most definitely.
-- Steve Barker
Another thought to consider.&nbsp; I have about 8 inches in my attic, I priced <BR>&gt;&gt; getting another 8 inches blown in and was told $2,800.00 With the HVAC <BR>&gt;&gt; cost I would save I figure probably 10 - 12 years to break even.&nbsp; Hell, <BR>&gt;&gt; I'm 75 now.&nbsp; I didn't do it.&nbsp; :)<BR>&gt;&gt;<BR></BLOCKQUOTE></BODY></HTML>
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Got to watch that expression. Mexico is in the Americas too. <G>
<DIV>I said to the guy that I had been out of the market for several years and I had no idea how much things had gone up.&nbsp; He said before he gave me a quote, what would you expect to pay.&nbsp; I said 5 - 6 hundred.&nbsp; He said no way, things have gone up more than that.&nbsp; My memory may be bad on the price he gave me a year ago but it was really high.&nbsp; I didn't bother shopping around because I really wasn't that interested.</DIV> <DIV>&nbsp;</DIV> <DIV>One thing that may make it higher here.&nbsp; <STRONG>*We use United States citizen installers*.</STRONG></DIV> <DIV>&nbsp;</DIV></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>
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Don't have to watch shit. a mexican is not an American. that will not change.
-- Steve Barker
<DIV>I said to the guy that I had been out of the market for several years and I had no idea how much things had gone up.&nbsp; He said before he gave me a quote, what would you expect to pay.&nbsp; I said 5 - 6 hundred.&nbsp; He said no way, things have gone up more than that.&nbsp; My memory may be bad on the price he gave me a year ago but it was really high.&nbsp; I didn't bother shopping around because I really wasn't that interested.</DIV> <DIV>&nbsp;</DIV> <DIV>One thing that may make it higher here.&nbsp; <STRONG>*We use United States citizen installers*.</STRONG></DIV> <DIV>&nbsp;</DIV></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>
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responding to http://www.homeownershub.com/construction/Raising-Attic-Floor-for-more-Insulation-4602-.htm jbeuckm wrote: Between 7 and 12 tomorrow morning, Menards will be dropping new 2x8's in my driveway so I can raise my attic floor. I'm building on top of the existing storage floor and blowing in the recycled stuff when that's done. Also 2" foam on my knee walls. $475 should give a tax refund of over $100 since I ordered this year. Wish me luck!
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I kinda missed the boat originally because I didn't notice that he said he had a plywood floor on top of the joists. in that case, i would leave that intact and insulate on top of it. heck, I'll even eat some crow here and say bobk was right and that he ought to lay down 2"-4" of rigid on top of the plywood and screw new plywood directly on top--no sleepers required--just some long screws. I insulated a cabin floor that way once and it worked great.
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