around 16" deep would be about an r50. For cellulose material to buy from my local lumber yard (price matches Lowes) plus gives you a trailer with the bags delivered as well as a Force2 blower (much faster then the cheapos you get from Lowes/HD, I have used both!). Prices would to be about $1200 for a 1600 sqft roof at r60. My insulator bid it at $1900 which also included installing attic baffles and batts to hold them in place. So for the few hundred bucks difference, not sure why anyone would not just pay for someone else to install it. Humping 172 bags of cellulose is a sucky job! He also gave a price to attic seal with 2" open cell foam on the ceiling plan for about $700. This includes wrapping cans with batts and spraying over the batts.

Just be sure to use "borate-only" or "sulfate-free" cellulose in your installations (either DIY or contracted out.) The goods sold at box stores almost universally use a combination of sulfate & borate fire retardents, and it's the sulfates you need to avoid. In the presence of moisture sulfate based fire retardents corrode metals (it stinks pretty bad after awhile when wet too.)

"Stabilized" cellulose formulated for wet-spraying can be dry blown, and is always borate-only/sulfate-free. If you're not sure what's in the bag, a quick & dirty test is to stir a couple of Drano pellets ito water in your brother's coffee cup, then stir in a heaping teaspoon of the cellulose- your nose will let you know pretty quickly by the pungent hit of ammonia if it contains sulfates. No ammonia==no sulfates.

In any attic blow it's important to wrap flues or other potential ignition sources with rock wool batts (inherently fireproof) to provide the necessary clearance from flues to combustibles. Installing cellulose in direct contact with flues would be a code violation, despite the fire retardents. It can survive years or even decades in direct contact, but it's still basically a paper product- even if the borates inhibit the oxidation to just a surface char, it's a very dubious way to treat your house. Rock wool is recycled slag from steel making- if it get's hot enough to melt the rock wool the house is already long gone.

I'm also facing the issue of supporting r 60+ cellulose, I might even want r80,  in the ceiling.  OSB is the way to go but I'm thinking of not putting it up in whole sheets but nailing 1x2 furring strips to each side of each truss with the bottom of the furring strip flush with the bottom chord of the truss then  make 22 3/8" strips of OSB and simply laying them atop the furring strips.  This will give a 1 1/2" service cavity for the ceiling fan boxes & such.  I might consider gluing the OSB to the furring strips,  maybe gluing and nailing the furring strips,  taping the OSB joints and spray foaming the bottom side.  Interior walls parallel to the trusses already have 2x4 blocking between the trusses and the OSB would simply lay or be glued atop the blocking.   To me this makes a much easier DIY (with hired "cheap" labor) project than wrestling whole sheets.   Comments please.

On the concern about "thermal bridging" in the ceiling: The thermal bridges are the diagonal elements of the truss, made of wood (approximately r1/in) with an average angle of 45 degrees so their length is 1.4 times the insulation depth. in my r60 case 18"x1.4 = r25. and they occupy a really small percentage of the truss length certainly less than 10 % In addition the trusses occupy only 6.25% of the cieling area (24" OC 1.5" wide). Using these values what started out as r60 becomes r59.47 with thermal bridging accounted for! In other words thermal bridging represents a whopping 3/16" of insulation depth. The results will be similar only slightly worse for even r38.

I'm planning a new home build myself and want to use blown cellulose on ceiling floor, wanting to go with an R60 design thickness. As we all know the ceiling will sag over time and this totally unacceptable especially if you have a smooth finished ceiling. As some have mentioned sheathing the ceiling with OSB would solve the problem as long as you don't have any downward buckling of the OSB board. What thickness of OSB? 1/4", 3/8" or 7/16"

Lieblers idea would work quite nicely other than it being even more labor intensive and you would not get the full benefits of the additional strengthening of the bottom rafter chord by attaching the OSB to the bottom of the ceiling joist. I have also thought of using spray foam over the entire attic floor for air sealing plus it would stiffen the ceilings drywall to accept the additional loads for the cellulose. But someone pointed out it could become a liability because the foam may not cure properly for what ever reason.

I do know that roofs with trusses 24" on center roofs sheathed with OSB can sag some over time. Although they are exposed to a different environment I'm thinking 20 years down the road if attached to bottom of ceiling trusses it will do the same?

Maybe the answer to the problem of sagging ceiling from the weight of the cellulose would be best solved by using a cheap fiberglass netting stapled to the sides of the ceiling trusses to keep all the weight of the cellulose off the ceiling drywall? Not sure if the same netting that is used for blown fiberglass in the walls would be durable enough, but surely something similar to that product would work best. Building fire code for the attic area might not allow such a netting? Will create a thermal loop between netting and drywall? Any thing mounted in between ceiling joist the netting would have to go over and back down in the ceiling joist line.

I think a more refined solution would be attaching a fiberglass netting to bottom of ceiling trusses, than you attach 2x furring strips 16" O.C. .... This would eliminate the major headache/problems of all the obstacles that you would encounter between the joist. It would complicate mounting recces cans, Hvac registers, light fixtures and things of that nature. Another big question would be how much deflection would there be in the netting after 20 years? 1", 2", 3"

How about this Idea you attach 1/4" OSB to ceiling than your furring strips over it ...... ?

Any special drywall out there in the market that can handle the high loads without sagging? This obviously would be the TICKET if it exist.

Another question, Is all this extra work to get cellulose in the ceiling worth the money and trouble?

In my case I wanted trusses to be 16" O.C. for a smooth finished ceilings ... If I use furring strip 16" I could change my trusses to 24" O.C. and save a little bit of cash.

Just keep in mind I am doing Smooth finished ceiling so there can be NO SAGGING in the sheet rock!

Example of netting attached to ceiling



Would love to bring this topic back for more discussion....


Location: Lagrange, GA
Hot & Humid Climate - Zone 3

Current Idea of Attic Ceiling Design

• Raised Heel Truss design 18"
• 17" blown cellulose R-60+
• Trusses 16" O.C.
  
• Bottom truss chord 2x6 or 2x8 depending on dead loads
• 5/8" Drywall Ceiling
• Interior Ceiling to be finished Smooth

Current Exterior Idea of Wall Design

• 5/8 Drywall
• 2x6 16" O.C. w/Cellulose
• 7/16 OSB Sheathing
• TYVEK Commercial Wrap D
• Two layers of 1 1/2" unfaced 1.5lb density "Type-II" EPS staggered
• 5/4 x 4" Pressure Treated Yellow pine Furring strips
• JamesHardie Board Artisan lap siding - 4.55 lbs./sq. ft

A company called Hammer and Hand i think out of Oregon does a lot of Passive Hauses (SP?). They have a lot of youtube videos to watch. One of the them features one of their approaches. They use osb under the trusses, airseal the OSB (very simple to effectively airseal a single/simple plane of OSB) then use 2x4 on the flats as furring strips to create an access space for wiring and such. I think this would be a good approach given your goals. The OSB is the air barrier (and vapor retarder) and adds strength to the truss system, the furring keeps the drywall off the OSB so IF there is sagging, it won't show in the drywall, and you get a nice 1 1/2" cavity to run some utilities. It certainly adds material/cost, but should be a relatively easy DIY and none of the materials are special order. And the OSB with furring will be strong enough to pile the cellulose like there is no tomorrow!

so for rally high R values on a budget cellulose is the way to go? I saw a video on a owens corning sealing product, it was similar to sprayfoam lot less toxic the installer was not using any protective equipment http://www.youtube.com/watch?v=q4UrjGhB9T0 does not expend as much it's sole purpose is to air seal, probably cheaper too, my only concern with such setups at this point is weight, 16 inch is supposed to be r60? I think somewhere on this thread it was mentioned that is about 3 lbs/sqfoot, say 1000 sqft that is 3000#? add heavy snow load, I do get a bit of that, may need some better structure, especially since I was considering even more walls and floor too, that may add up significantly, I assume it can be used in those applications also. so I guess I have a question for the forum, which one weighs less per R value if you will. http://www.youtube.com/watch?v=UUaRI7PYwmo this is something else I saw that kind of intrigued me, I am assuming polly iso and such will weigh more but I could be wrong. also danas post couple rows down its rather important too, cost and footprint, I guess if over it's life a products initial footprint can be justified I would consider it however it is best to start with a product that is relatively neutral/recicled

Another alternative is to use 1.5” polyiso insulation sheets, tape the joints for the air seal and then strap it perpendicular to the truss cord, blow in 15 inches of cellulose on top of the polyiso and drywall it. Cheers, Eric

the whole weight on the drywall causing cupping got me thinking of the whole weight on the structure question, granted there's all sorts of ways to go about preventing drywall cupping like osb for example, but that adds even more weight to the structure, I'm no engineer but it appears to me that going high R may require some loadbearing details to be looked into, therefore weight / R value may be worth considering beyond drywall cupping.

R60 dry blown cellulose runs about 2 lbs per square foot, R75 runs about 2.25lbs/foot. Yes, you have to pay attention to the dead-load ratings.

If your truss chords aren't rated for that much dead load at 24" o.c. spacing you can drop back to 18" or 16", whatever it takes to give you some margin.

If you want to use half-inch gypsum to support it, running 1x furring 16" screwed to the under the truss chords works, using ring-shank nails on the gypsum. Half inch (7/16" really) OSB is more rugged, and also lighter than 1/2" gypsum, at about 1.45lbs per square foot compared to 1.75lbs/foot. On a roof deck OSB is subjected to far more extreme temperature & moisture cycling than it would ever see on the conditioned space side of the insulation- concerns about sagging from the modest loading of even a couple feet of cellulose isn't really warranted. But some still opt for an OSB air-barrier to carry the insulation load, and use 2x furring (or sometimes even small joists) perpendicular to the truss chords to mount lightweight gypsum, which also provides a small service cavity for running the wiring without drilling through the OSB.

Cellulose has many characteristics that make it a better product for open-blown attic installations despite the weight penalty. At open blow densities it's still sufficiently air-retardent to actually hit it's rated-R in the winter without a top-side air-barrier, and it's opaque to infra-red radiation, giving the full-R performance under a hot roof in summer too. Rodent's are less likely to nest in it than other fibers insulation too.

you must have spent a lot of time doing this all your replies are rather detailed an I noticed a trend with you and cellulose, would it be safe to say its pretty much the choice to make these days, is there stuff like the JM spider for example bit lighter / R value? been meaning to look it up just did not get around to it you probably got the numbers in the back of your head. I am looking into building with a lot of this stuff, I don't have the numbers yet but some Passive house examples I came across mentioned R 60 walls, R 100 roof, somewhere around there have yet to get specific, R 75 @ 2.25? x 1000sqft 2 250 pounds? hmm is that a lot? the design I was going for involved some kind of double rafters, similar to double stud wall, so not the rafters were bothering me but the entire weight of the whole roof I am already making it twice as heavy in the lumber alone might as well plan it like a 2 story load bearing, so that is part of the reason I was looking at a total weight George

Its cheaper to have the truss company build the trusses to your spec's then to add more trusses. They are use to adjusting their engineering to things like snow/wind load, roof cladding etc. To add a few pound per foot is not a big deal to them.

Ceiling drywall (and all drywall) should de installed with screws. Unless you can sink a nail to the proper depth with one blow, you will damage the surrounding structure of the board and weaken the hold of the nail.

Some people have gotten pretty good at doing ceiling gypsum with ring-shanks and nail guns, but for sure it's safer to go with screws.

If you're going for R100 you'll need 16" o.c. spacing and 5/8" gypsum no matter what fiber you're going for. To use new-school fiberglass such as Optima or Spider without topside air-barriers you'd need to blow it in mesh and hit 1.8lbs/cubic foot. That's about R50/foot of depth, or R28/per lb per square foot. Open blown cellulose, which has about 1.5lbs/cubic foot settled density, at about R45/foot of depth or about R30 per lb per square foot. Not much different there.

http://www.nationalfiber.com/docs/ExpandedBagCoverageChart0911.pdf

With lower density 1.0lb Spider or Optima (or the more appropriate fiberglass blowing wools) the fiberglass is far too air permeable, and it will lose quite a bit of performance to convection when the attic is several 10s of degrees colder than the ceiling temp unless there is also a top-side air barrier. 1lb density Spider runs about R45/foot of depth, but weighs ~30-35% less than cellulose of similar R/foot. Getting the lower density fiberglass to perform to spec requires a top side air-barrier, which adds complexity & expense- there is no free lunch. Cellulose is almost always the cheapest/simplest solution to high-R attics.

Bear in mind that if you want a flat, smooth ceiling, you're going to have to true it up somehow, either with a system of firring strips, or LOTS of drywall mud. I strapped mine with 1X4's on 16" centers, which I then shimmed it to get a flat(er) ceiling plane. I couldn't get 1X3's that were true enough not to introduce new flaws in between the trusses. Maybe trusses are better in your neck of the woods, but mine were terrible, right off the truck. Even with popcorn, my ceilings would have been unacceptable if the drywall was screwed directly to the trusses.

My current insulation scheme is to have the ceiling plane flashed with foam (about an inch) and then blown cellulose. Is the foam worth it to seal the ceiling plane? I've looked into DIY kits to seal just the seams and penetrations, but they cost quite a bit, and it would be a lot of work for me. Will a continuous layer of foam add a little support to the drywall?

for what I had in mind was a double rafter setup, similar to a double stud wall, I posted some pics on the other thread, but they are bad quality, similar to truses if you will almost flat roof slight pitch, no attic, the drywall aspect does not concern me much I was considering wood planks 1x maybe 1/2 inch, not sure what's best either on top of the bottom rafter giving a under deck look, or maybe screwed below, in themselves those planks may proved a bit tricky to seal, considering a seam every foot or so, the owens corning pro pink or something of the likes looks interesting to me for airsealing rather than foam, either way perfectly flat drywall ceiling is not a concern nor cupping as the wood boards should handle it, the idea is to have the lower rafters support the ceiling and cellulose and the upper rafters supporting the roof deck and snow load,

all this on a pole foundation, at a first look appears significantly heavy, sturdy for sure just heavy, so I figured an initial thought sizing the foundation poles as a double story building would be a good place to start, that is basically what I had in mind at this point a double story pole house only that one story is within the other rather than on top giving a full all around double stud wall roof floor with the only thermal bridge being the poles themselves,

that is basically what my concerns were, I need to add this up based on my dimensions, as I was looking at R60 walls, R100 ceiling, somewhere in between for the floor, that is a lot of insulation it will add up to a significant load

Posted By jdebree on 20 Feb 2014 06:53 AM
Bear in mind that if you want a flat, smooth ceiling, you're going to have to true it up somehow, either with a system of firring strips, or LOTS of drywall mud. I strapped mine with 1X4's on 16" centers, which I then shimmed it to get a flat(er) ceiling plane. I couldn't get 1X3's that were true enough not to introduce new flaws in between the trusses. Maybe trusses are better in your neck of the woods, but mine were terrible, right off the truck. Even with popcorn, my ceilings would have been unacceptable if the drywall was screwed directly to the trusses.

My current insulation scheme is to have the ceiling plane flashed with foam (about an inch) and then blown cellulose. Is the foam worth it to seal the ceiling plane? I've looked into DIY kits to seal just the seams and penetrations, but they cost quite a bit, and it would be a lot of work for me. Will a continuous layer of foam add a little support to the drywall?

 
Screwing/ring-shanking OSB to the underside of the trusses for supporting high-R insulation and using light dimensioned lumber joists below that with an inch of clearance between the top edge of the joist and the OSB on which to mount the finish ceiling gives you both the flat ceiling and a  service cavity for the power runs, etc.  It's not the cheapest approach, but it's effective.  Then it doesn't really matter of there's some sag to the OSB over the decades, and you have far fewer penetrations to air-seal.

An inch of closed cell foam adds a buck a square foot or more of cost to the assembly, and does squat for long term sag issues.  In new construction you can air seal the ceilings of most homes with a tube of acoustic sealant and a couple cans of foam, and if you take the service cavity approach with the light joists for the ceiling, detailing the OSB as an air barrier won't even take that much.

this is a rough sketch of what I had in mind it's rough and large so I could only take a pic of it at the moment. that is the approach I was considering, instead of osb use finished lumber and leave it at that, I'd have to seal the joints between the boards somehow, a tongue and groove and wood filler or something like that during installation should do the trick to air seal the ceiling, I really would not mind a little extra cost or an extra vapor barrier as I do plan on PH standard, may not bother to get it certified but those are the standards I aim for, just debating weather to have the boards above the lower rafters or below, not sure how lumber compared to osb as far as weight and strength hence not sure of what a proper thickness would be, I'm sure it's a bit better than drywall, may weigh more I don't know, granted may cost more too, but considering you don't have to mud it and paint it regularly may not be so much, and it give a cabin look, than again if the OP was discussing an existing home that is already drywalled all these options may get tricky to implement unless we're considering a total gut out.

The tongue and groove will shrink to much over time to consider using it as an air barrier.

good point and to season the boards for a decade may not be an option also I kindof like the idea of a under deck look alike ceiling or if installed under the rafters as drywall would that would be fine too, but got to figure out a better way to seal it I guess.

is the tyvek paper a permeable membrane? I saw in various PH builds a similar membrane used to get the building airtight usually from the interior, wonder if something similar above the board would do

I HAVE TRYED TO TAKE AN UP CLOSE OF THE ROOF CEILING DETAIL, the girders are supposed to be 3x12 according to the book the rafters 2x10 so if the ceiling boards were to go on top of the lower rafters I'd have approximately 20 inches of cavity to be filled with cellulose, not quite the R100 but that can be tweaked, I modeled an 18 inch wall in therm with double 2x4 @ 24", might need the ceiling boards under the lower rafter to gain more cavity, and cellulose worked out to R63 I believe nor am I sure of the final R number yet, so how would this best be achieved considering PH standards as a goal? I know it has been mentioned an airtight barrier may not be required but that is not extremely expensive so why not? 6 mil on top of the ceiling boards maybe? cellulose to the roof deck, sheathing, tar paper and white aluminum metal roof? does that sound like a plan? I am an amateur so I don't trust my own judgment. the roof pitch I was considering to a minimum read in some books the snow blanket adds insulating value and with the double rafter idea thermal bridging should be minimum, What is cellulose rated for per inch?