Hello and thanks for any help! I have about 3000 s/f of attic to insulate in Maine. This is new const. with a truss roof 24"o.c. Metal roofing over purlins. Of course the budget has a lot of influence on decisions, but understanding that old saying about insulation being the gift that keeps on giving... How should I spend my insulation dollars smartly? I allways thought about a 12" batt (f.g.) and blowing up to a r 49 ceiling. Recent reading has educated me to the reduced performance of f.g when air can move through it. I have vented soffit and 2 huge gable end vents, I was brought up with the notion that more air moving through the attic the better. That was probably for the benifit of the shingles, and a cooler house in the summer now that I think back. And then there is gravity and wind that I know will eventually mess up and settle anything that I Have blown on top of the batts. So.. it looks like the next thing is spray foam, but at 'bout a r6-7 per inch, that means 6-7 INCHE$$ sprayed in and the low price so far is .85 cents/inch, and I'm lookin at close to $18,000 and that earlier gift that keeps on giving had better earn intrest, compounded daily! But seriously I could block out some or all of the attic ventilation if that would be an advantage. So any ideas from somebody who's not trying to sell me something would be highly apprecited. On another note, some of these guys (insulators) are telling me that once you are at a R-30 or so, your holding in 90% of your heat. I'm not positive on these #'s, but they are not far off. Is this a legit line of thought? If it is it shure helps me think and put things in perspective in terms of cost/result

Use fiberglass with a cellulose cap it makes the fiberglass more efficient. The numbers on saving are true. The fiberglass won't settle. An old trick from my insulation days, was to take a small pump spayer and wet the top of the celloluse near the soffits and it glues the cellulose together like paper mache.

I just priced out a 1900 sq ft open blow with r-30 over 3.5" rockwool . Labor, material, blowing machine rental, and profit, the cost was $1450. The soffits are vented so I will use the pump spayer trick.

Moving more air through the attic isn't necessarily better- it's something of a a "solution-problem", in that it solves some of the problems it creates. The vented attic induces stack-effect infiltration, drawing moist air up from the conditioned space below (if you let it), only to condense on the roof decking & rafters, but with sufficient ventilation capacity it dries out before causing much damage (usually). Read this thoroughly:

http://buildingscienceinc.com/resources/4-Understanding_Attic_Ventilation.pdf

If you're using the attic for storage, etc. any access has to be VERY tight from an air-infiltration point of view, as do any plumbing & electrical penetrations, etc. Foam seal & caulk everything you can between the conditioned space and the attic- it's critical to getting the full peformance out of the insulation.

For a vented attic, new construction in ME, frame it with an "energy heel" extension to the tops of the wall framing to allow full insulation depth right up to the eaves- no thin spots at the tops of the exterior walls, and little capacity for air currents from the soffit venting to move insulation around. Then apply a sealer-layer of a couple inches of half-pound foam (or spot seal with half-pound foam) to achieve a perfect air-barrier. (Just don't mess it all up with recessed lights, etc.) If you can, pressure test with a blower door and spot-remediate as needed with foam sealer. Use vapor retardent paint on the ceiling as the vapor-retarder.

Then blow 12-24" of cellulose in there for ~R45-90. Be sure that the attic floor/ceiling can take the load though, eh? In the event of an actual roof leak or wind-blown water coming up through the eaves you can have some serious weight building before the leak is detected.

If weight from saturated cellulose during a leak is a concern, blowing fiberglass with a 3-6" top coating of cellulose can minimize the problem. When a leak occurs the cellulose layer saturates locally more quickly, and the fiberglass passes it through to the ceiling below. Half-pound foam is open-cell- won't hold the water back, and won't redirect it the way 2lb foam can, or soak it up the way cellulose can. (Scoop out and replace any wet cellulose after any leak events.) In Oak Ridge Nat'l Lab studies, topping off fiberglass with even as little as 2" of cellulose can cure the bulk of fiberglass convection-current losses, restoring it to full performance even at big delta-Ts. In a lab is one thing, in a vented attic it's another- the 6" is to allow for a bit of wind-drift redistribution of the cellulose layer over time, and some installation-depth variability. (Shoot for 6", the thin spots will be still more than 2", a thickness which has been demonstrated to work.)

Statements like "with R-30 you're holding in 90% of the heat" are just CRAP! "90% relative to WHAT- open air, no roof at all?", is the right response. (Indeed, a 6-mil polyethlene tent holds back 90% of the heat, for some arbritrary set of conditions.)

Once you have a perfect air seal to fully block convection & infiltration losses, it's ALL about R-value, which is a directly measured inverse of the conducted heat transer (heat lost) per degree of difference. The only people I ever hear saying "Rxx is all you really need" etc are vendors of foam insulation, which is more a reflection of the return-rate you get with the higher-cost R. So at the cost of more than say R30 of 2lb foam may have negative present-value for the lifespan of the building, whereas with far cheaper-R value from cellulose that negative-return financial Rubicon might not be crossed before R100.

Don't get me wrong- foam is great stuff and the performance is there, but you don't need to live in a foam building to get good performance. If you can get to R60 with a combination of foam + fiber at the same COST as R30 foam, you will have half the heat loss for the money. The greatest value in foam is it's air-sealing ability, which isn't easily achieved by other insulation methods. Closed cell foam is also very vapor-retardent (that can be good or bad, depending on where it's located within the stackup) and adds structural rigidity (valuable for high-wind regions- great for gluing steel roofing and siding to the structural elements.) With 6-7" thicknesses of 2lb foam you might as well go ahead and get rid of the framing-timbers- you've built yourself an all-foam structural monocoque (and thrilled the foam contractor no end! :-) ) I'm all for using foam where appropriate, but it's not the only answer to every insulation problem.

Smartwall: I like your trick of using water to keep the soffit air currents from redistributing the cellulose- hadn't thought/read of that one before! A thin crust layer of cellulose increase would improve it's already pretty-good air-barrier qualities too! (But I don't think I'd go so far as recommending a wet-mist overspray of the entire attic. :-) )

I don't do the entire attic, just the edges with the soffit vent. You have to watch the weight of that much cellulose it will cup the ceiling even when the sheetrock is screwed to furring strips. I've seen it happen in some of our 1980 vintage r-50 installations. It doesn't happen right away, but over time that's a lot of weight.

Yep- plaster & lath holds up under the weight better than gypsum.  I'd imagine OSB or plywood (or joists 12" o.c.) would be necessary to keep R90 cellulose from popping sheet-rock screws over time.  But even when comparing the cost of the additional structural materials to do R90 in cellulose vs. R50 in 2lb foam it sort of fades into the noise, eh? 

With energy heel framing and a 3/8-7/16" OSB insulation-bearing floor atop the ceiling joists it'll handle a lot.  Whether you fill in between the joists with cellulose or just add 8-10" to the energy heel walls is designers-choice.  And insulation-bearing floor idea would allow one to use the joist bays for electrical & plumbing (even recessed-can lights), and if it had glued/taped seams it would be an effective air-barrier as well, even if it too sagged a bit over time.  OSB is a lot more structural than sheet rock, and is a class-III vapor retarder to boot.  With sealed seams and painted with vapor retardent paint prior to insulating it could easily become a class-II vapor retarder, appropriate for Maine climates.

The best bang/buck method that creates a good air seal is first getting closed cell spray foam foamed in only 1" thick over the whole attic, then getting fiberglass blown over that to your desired R value. Be sure any ceiling fixtures are insulation contact. The thin layer of foam will prevent any air traveling between the house and the attic, and the fiberglass gives you your R value. The foam should also reduce the drywall sag on the inside, but I would still recommend plywood/osb behind the drywall ceiling.

Are your trusses raised heel to provide depth of insulation at the perimeter? With a 3' overhang and a 6/12 pitch roof, you get to about 1'-6" for insulation. Up in Maine this kind of thing is probably standard, but here in Tennessee a lot of builders still ignorantly use the regular trusses where your are lucky to get 3" of depth for insulation at the perimeter. Most of the time they don't even bother putting anything at all out there which kills the average R value of the whole ceiling, regardless of what is blown in the middle.

According to testing at the Oak Ridge National Labs loose-blown fiberglass in open blow attic applications under heating season conditions under-performs cellulose by quite a bit even at ~R40-ish levels due to convection issues within the insulation causing it to lose increasing R-value with increasing delta-T.  (This can be "cured" by a top coating of cellulose though.)  The loss of R-value is significant- something on the order of 50% at -10F, a mid-winter temp not  rare in parts of Maine.

In cooling-season environments blown fiberglass is much better behaved (nothing like the issues that occur when the warm side is below, and the cold side above with big delta-Ts. )  But it still has some issues occuring primarily in the upper layers due to infra-red translucency.  Radiated heat passes into the insulation and is absorbed by inner layers causing the peak temp within the insulation to occur somewhere in the top few inches, not at the surface, the peak-temp layer can be 10s of degrees above the attic-ambient temp.  This anomaly too can be "cured" with a top coating of cellulose and/or a radiant barrier on the rafters above.  At R40-ish levels the cooling-season differences in performance between the materials aren't very consequential (or even measurable without difficulty).  The density of the fiberglass also makes a big difference.  High density fiberglass batting performs signficantly better in winter at equivalent R-values than the lower density goods or loose blown (presumably due to reduced convection losses.)

R-values for labeling purposes are at a fixed delta-T- IIRC it's 40F, with a mean temp of 75F.  (Look up the ASTM test if you like.) That doesn't tell the whole real-world story very well since real attics get a lot hotter than 115F, and a lot colder than 35F.

An inch of closed cell foam is sufficiently waterproof that you could literally end up with hundreds of gallons of water up there before detecting a roof leak, which is why half pound foam may be a more appropriate choice for air-sealing- it'll allow leak water drip through somewhere near the leak at the first bit of puddling.  (With an OSB deck/floor it would make it take awhile though- the thinner the OSB the quicker you'd find it.)  With closed cell foam it may travel laterally some distance before finding a drip spot, making the location of the leak difficult to find, and potentially distributing the water to less water tolearant areas than ceilings.

I wouldn't use blown in fiberglass. It can be overfluffed and blown at a settled densities that creates air flow thru the material. I would use a batt insulation with a cellulose cap . Batts have a more consistant density. Depending on the type of blown fiberglass, your either getting the scraps from the batt production or a prime product. I used to use Insulsafe from Certainteed. The fist time we used it we ended with 24" in an attic and the r-value of about 30 according to the bag coverage chart. Blown fiberglass can be used to screw the customer because of the ability to fluff the material.

The same is true of cellulose installers- but the number of instances where this actually happens seems pretty low these days.   IIRC there was a spate of lawsuits & fraud cases in the late '80s early '90s, much of which may have been as much pure incompetence as intentional fraud.  It's true that fluffed cellulose still outperforms fluffed fiberglass, but both eventually settle to a thinner-denser final-value.  Competent & honest installers will show up with the proper WEIGHT for the specified R value and coverage area, and install it all evenly using the installed depth as only a rough guide.  The R-value you're paying for is the SETTLED R-value- the initial value is always higher, fluffed or not.  (I'll bet that 24" fluff-job on R30 was performing at about R50 at moderate delta-Ts the first year, but probably settled to under R40 (with lower convection/better temperature range) within 3 years, approaching R30 in a decade.) 

Still, vet your insulation contractors well and you won't have that problem. If you're not sure, be there on installation day and count the bags. It doesn't take high math to calculate the coverage.  Insulation manucturers sometimes specify air settings  for particular blower models to use for open-blow, to limit the chances of accidental overfluffing, but that's not to say everybody on an insulation crew is meticulous about details like that. (Most is, some ain't.)

And capping blown fiberglass with a half a foot (typically ~R20 coverage, in open blow) of cellulose still "cures" any probems associated with fluffing, and gives even properly-installed FG far more operating temperature range on the low end.

I'd have to disagree that fluffed fiberglass will settle a great deal over time. Cellulose will find it's settled desensity because of the nature of the fiber. Fiberglass tends to stay in the shape it was created. I have proof in my own warehouse. Every time I bought a new ins. blower, we tested over the top off the office area. Last machine I bought was 1980. The fiberglass is still pretty close to the height we blew it at. Plus the nature of most blown fiberglass makes it come out of the hose in small clumps. I don't know of all the blowing wools on the market, but from the material that I've used Certainteed still has the best product. I checkout some of the manufacturers web sights and you can see the material clumping as it's being installed.

I have also been looking at ways to get the most insulation in my new home attic for the $. I'm building an ICF home with full basement (ICF from footings to roof) with ~2100 sq ft footprint. I will also be using 2x4 roof trusses 24" OC. I am located in Arkansas which has a relatively moderate climate, but summer time temperatures can be pretty high. I was wanting to shoot for ~R49 in the attic, and I was planning on going with blown cellulose. My concern has been the amount of weight of all that cellulose on my sheetrock ceiling. I'm planning on going with 5/8" sheetrock in the ceiling, but still concerned. I think what I have finally settled on is installing R13 3.5" thick FSK foil faced fiberglass batts first, with the foil side down and the staple tabs stapled to the sides of the truss bottom chords. This will create an air gap below the foil and will also help hold some of the weight of the cellulose off the sheetrock. Plus, when combined with the ~R13 I will get from the lightweight fiberglass batts, the settled depth of the cellulose is reduced to ~11" to get my R49+. Plus I get a foil radiant and vapor barrier as well. Any thoughts or recommendations regarding this approach?

That's a good data point- thanks for the correction!

Did you blow cellulose over the fluffed fiberglass your experimental attic, or is it now just so thick that it doesn't really matter?

Radiant barriers work best for cooling when applied above the insulation, not below it.  In this configuration you'll get some heating season effectiveness out of it, but at best half the cooling season benefit. (But at R49 in the attic with cellulose as the top layer your attic will not likely be your biggest heat gain anyway.)

Also, vapor barrier on the interior might not be the best approach for Arkansas' mixed-humid ~2000 cooling-degree-day climate:

http://www.climate-zone.com/climate/united-states/arkansas/little-rock/

Building Science Corp calls for keeping the ceilings permeable or semi-permeable in mixed-humid climates:

http://www.buildingscience.com/documents/profiles/designs-that-work-mixed-humid-climate-atlanta-profile/
http://www.climate-zone.com/climate/united-states/georgia/atlanta/

http://www.buildingscience.com/documents/profiles/designs-that-work-mixed-humid-climate-charlotte-profile/
http://www.climate-zone.com/climate/united-states/north-carolina/charlotte/

http://www.buildingscience.com/documents/profiles/designs-that-work-mixed-humid-climate-louisville-profile/
http://www.climate-zone.com/climate/united-states/kentucky/louisville/

FSK faced stuff it probably too vapor-retardent for your summer climate to be on the cool side of the insulation.  You may end up with condensation & mold issues on the lower chord of the trusses during the air-conditioning season if you don't have better inward-drying capacity.  You need a good air-barrier, but a semi- permeable vapor retarder (Don't use vapor retardent ceiling paints either- permeable or semi-permeable latex is key.)

If you run furring strips/purlins 12" o.c. , screwed to the truss chords at every intersection, use 5/8" gypsum with 12" screw spacings it'll hold a LOT of weight without sagging.  Foam-seal all plumbing & electrical penetrations, and avoid recessed can lights (or use gasketed air-tight insulation-contact fixtures if "the boss" insists), and you should be able to handle R49 depths without any trouble. (At R49 it'll be under 2lbs/square foot dry, but fairly hefty if you let it get rain-soaked. :-) )

If you want to use a radiant barrier, hang it ~2-3" under the roof deck, and use perforated highly permeable aluminized fabric stuff (eg. http://www.buyfoilinsulation.com/radiant-barrier-perforated-4-x-250-1000-sq-ft-p-26.html ) not aluminized bubble-pack or impermeable foils.  But whether it makes any economic sense to do so is highly questionable at your insulation levels:

http://www.ornl.gov/sci/roofs+walls/radiant/rb_tables.html#table4

Even at R38, the present value (the most you should pay for radiant barrier to get a 25 year payback, in the ORNL financial model) for nearby Memphis TN, is 6 cents per sq. ft.  if you don't have ducts in your attic, 8 cents  sq. ft. if you do.  (Memphis has nearly identical CDD data to most of Arkansas:  http://www.climate-zone.com/climate/united-states/tennessee/memphis/ )

You'll already have an additional R11 over that R38, so radiant barrier would be worth even less to you.  The material alone costs 12cents/sq.ft., which sounds like a no-win.   For the money you'd be better off spending it on better window shades/awnings etc. to reduce the cooling load elsewhere.  Radiant-barrier paints will get you something like 1/2-3/4 the benefit of RB sheets & foils- if you can get it for 2cents/foot or less (installed price) it may be worth it.
 

Yes we did but just as a test on the shredding rate of the machine, not to increase the efficiency of the insulation. One spot has about 30 inches of insulation in it.

Dana1, thanks for the input.

So, FSK faced fiberglass batts are not recommended in my situation. What about kraft faced or unfaced fiberglass batts?

Also, with 7/16" OSB sheathing running ~$5.50 per 4'x8' (32 sq ft) sheet, and 1x4s or 2x4s running ~$2.00/8 ft, I think in would be less expensive to deck the ceiling with OSB rather than install lath 12" OC. Plus, with the OSB, I could use 1/2" sheetrock rather than 5/8" sheetrock, further saving on materials and labor (cost is a bit more to hang the 5/8"). I guess the next question is whether to put the OSB on top of the truss bottom chords or below? If on top, this would create a 3.5" gap between the OSB and the sheetrock. Any issues with this?

I ran some numbers using prices at the local Lowes and I came up with ~$1.00 sq. ft material costs for the following three options that achieve ~R-53:

1. 7/16" OSB sheathing plus 14" of blown cellulose
2. 3.5" of R-13 fiberglass batts plus 10.5" of blown cellulose.
3. 5.5" of R-19 fiberglass batts plus 9" of blown cellulose.

It's more labor to put the OSB on top of the chords (isn't it?), and it'll likely be more difficult to air- seal. OTOH the 3.5" gap can be use for running the electrical without punching holes in the air-barrier.

There shouldn't be any reason not to use unfaced batts.  Kraft-facings are somewhat permeable, but probably lower permeability than the OSB's average permability.  From a fit & tightness point of view batts are step down from blown insulation.  Unless there's a significant cost advantage,  if you're going an OSB floor to it all doing it all in cellulose would likely outperform batt+cellulose and simplify installation somewhat. It's still under 2lbs/ft^2 at R53, and I expect 7/16" OSB would be good for a heluva lot more than that under any circumstances.

If you are worried about fluffing, just calculate the number of bags the job should have taken for a given depth, and compare it to the number of bags used. If less bags were used than calculated, then it was probably fluffed.

The reason I suggested fiberglass over cellulose is simply for the weight factor, R-60 fiberglass weighs a lot less than R-60 cellulose, so that you probably wouldn't need any kind of support boards, especially not if you have a thin layer of closed cell foam adding rigidity to the drywall. By saving on the support boards, you can afford to blow in even more insulation.

Another option to cut down on air into the fiberglass is to put in those cheap 1/2" foil faced foam boards over the fiberglass, acting as a radiant barrier. With spray foam on the bottom and these boards on the top, there isn't going to be much air moving anywhere through the insulation.

Hey thanks for all the replies. (ceiling insul. real world $$) One huge thing that I left out (it was very late) is that I will be having radiant heat in the ceiling of a small portion of this space (less than 500s/f) and this ceiling radiant is my only option, it can not go in the floor. Can or should I treat this area differently to push? the heat down? , can you push heat or just be sure separate the the radiant from the cold by insulation? A note to Dana1, as to my question about being told that R-30 being 90% or so eficient, another insul contr. gave me a copy of a graph type chart that showed this. I think what they were drying to explain was the "diminishing return" of every dollar after a certain point. Thanks all.

While the heat loss will be higher with a radiant ceiling, if the whole ceiling were at R75+ I don't think it really counts for much, but at R38 it might. What sort of heating-water temps and final R values were you anticipating?

Here'a WAG, (without pullin' out a caculator... )  Heating water under 110F, or insulation value over R75 fuggedaboudit.  Over 140F & under R50 you might want to be 6" deeper over the 500 square feet of radiant ceiling. 

Don't let anybody sell you on a radiant-barrier (unless you want to use the RB as a vapor barrier as well.)  The net effect of the RB is small in a high-R setup- insufficient to rationalize from a cost point of view. (The money is usually better spent on more R-value.)  Setting it up with a reliable 3/4"-1" air gap between the tubing and radiant barrier takes more time than it's worth- fill that space with blown or foam insulation instead. (Just having the gap can set up a potential thermal-bypass air current with even higher losses in some cases.)  Be sure insulation doesn't get between the heat-spreader plates and the celing gysum when you do. It would be hard to blow cellulose in such a way to get enough under the plates that it affects performance, but with expanding foams a droplet under the corner might start a larger seperation as it expands, reducing contact area and thus the heat transfer efficiency.  DO use heat spreader plates on the radiant, not simply suspended-in-cavity.  Plates lower the required water temps by over 10F, reducing the heat loss through the insulation layer by lowering the delta-T.  (A 100F ceiling cavity loses a third less heat through the insulation to a 0F attic than a 150F ceiling cavity.)

The  present-value-goes-negative crossover on the diminishing return per dollar curve happens a lot sooner with 2lb foam with cellulose or fiberglass.  Once you have a perfect air barrier it's all about R-value. Flash & fill (2" of foam for the perfect seal, the rest cheap stuff) is usually a cheaper yet effective way to go at super-insulation levels.