Posted By Dana1 on 07 Sep 2011 07:09 PM
I'm thinking you ARE correct- building inspectors aren't neccesarily avid readers (and they're certainly not as a class the best building-scientists.) Legally you should be able to pull this off, but with jerk-inspectors you often have to play patty-cake with 'em or they'll make your life miserable- don't go out of your way to prove how right you were, or how wrong they were, eh? ;-) It was only drafted into the CRC last year, after all, most inspectors are probably still in the dark on that aspect.

I will not rub it in....as much as I would like to considering the attitude and pompousness in which he answered the question.  He even used the word, "verboten," which I thought was pretty funny.

So DANA1, assuming I decide to go spray foam, what is required to meet the air permeable parts of the code.  Does it matter closed or open cell?  What concerns are there as far as moisture buildup?  I think you are a fan of the hard foam above the roof sheathing.  I do not want to do hard foam above the sheathing.  I would like to ONLY do the spray foam under the sheathing then the standing seam above the roof sheathing.

Greetings,

QUOTE: And here he thinks all fiber insulation is low-density low-performance fiberglass too, go figure?

I don't care what the density is, it's low performing. Don't you want to see O.C.s and NBS test results?

QUOTE: rbisys1 - how about if you get a couple of coolers, do some tests comparing cellulose, fiberglass, foam and rb and then we discuss the results?
Been there, done that. Here's what I used to tell school kids to do for their science projects. I usually told them FG and RB to keep it simple, but you can do as many different materials as you want to.

Some plastic containers that you can put a lid on. Flat left overfood containers are good.
Fill them equally with water and freeze.
Wrap one loosely with kitchen foil. Try to keep an air space between the container and the foil.
Wrap The other with cut sections of 3.5" FG. Use tape to hold pcs together.
Take 3-4 dry wall screws, nails etc and push them thru some heavy card board so that they will support the containers so that the foil and FG are not compressed. 16 p should work for the FG unit.
Some of the kids used thermometers with long stems and inserted the tips into the containers from the top so they could keep track of the differences other a period of time. For this test just a visual check periodically should do.

You can use plastic soda cups too. 32-44 oz is good size.

If you do cel you might want to put the cel in a box that gives you about 3-4" all around with the container supported in the center.

Foam you can cut 3-4 blocks or use canned foam and trim after coating container.

Depending on the container size and Delta "T" the FG should last about an hour, The RB about 3-4 hrs.

You're going to get condensation just like you do in real life.

For quickest results you want a warm room. The warmer, the better.

When you do this I don't think your going to have any ?s about which is the best.

Let us know your results.

Oh yes, I would really like dana1 to do this test. Come to think of it I haven't done this one for years, if I can get some time here I think I'll do them again.

Only one person has requested the NBS tests and other material I have. Com' on you have to keep ?ing your beliefs.

[email protected]

Posted By superduty on 07 Sep 2011 08:19 PM

Posted By Dana1 on 07 Sep 2011 07:09 PM
I'm thinking you ARE correct- building inspectors aren't neccesarily avid readers (and they're certainly not as a class the best building-scientists.) Legally you should be able to pull this off, but with jerk-inspectors you often have to play patty-cake with 'em or they'll make your life miserable- don't go out of your way to prove how right you were, or how wrong they were, eh? ;-) It was only drafted into the CRC last year, after all, most inspectors are probably still in the dark on that aspect.

I will not rub it in....as much as I would like to considering the attitude and pompousness in which he answered the question.  He even used the word, "verboten," which I thought was pretty funny.

So DANA1, assuming I decide to go spray foam, what is required to meet the air permeable parts of the code.  Does it matter closed or open cell?  What concerns are there as far as moisture buildup?  I think you are a fan of the hard foam above the roof sheathing.  I do not want to do hard foam above the sheathing.  I would like to ONLY do the spray foam under the sheathing then the standing seam above the roof sheathing.

If the underlayment for the standing seam has a perm rating greater than 1.0 there's essentially NO risk of moisture buildup in the roof decking.  If the underlayment is much less than 1 perm it's best to keep the the material below the roof deck less than one perm,  but even as low a 0.5 perms is OK as long as R value of the  foam is sufficient to prevent condensation in any fiber layer (R5 for your climate zone, per the IRC/CRC).  A 1" shot of closed cell is about R6, and 1.2 perms, but can be difficult to hit consistently- a thin spot could arguably not meet code.  A 2" shot is ~R12-13 and ~0.6 perms which is still pretty good, with zero condensing hours per year.   A 2" shot of closed cell plus 5" of  wet-sprayed cellulose (any density) or 1.8lb Spider blown-in-bag would bring you up to code min. R30.   Interior vapor retarders should be avoided, but if lower density fiber is used an interior air-barrier fitted snug to the fiber would be necessary to get the performance out of it.  Unfaced low density R19 batts under 2" of cc foam would be legal in that stackup, but performance would be well below labeled spec. Blown always has more complete coverage, and density high enough to inhibit convection currents within the fiber is necessary to keep from losing a large fraction of the performance at the temperature extremes (where you'd need it most.)  The higher thermal mass of cellulose will give a slight performance edge over a fiberglass solution, but not enough to pay extra for. (Cellulose would usually be less expensive than 1.8lb Spider or Optima.)

An all half-pound density open-cell solution would take ~9" of foam and would be typically between 2-3 perms, which is fine in Zone-3.  A performance advantage to this solution that 2x4 truss elements or even 2x8 rafters would then have a reasonable interior thermal break over the structural timber, and it would outperform a between-the-rafters-only code-min solution with good margin.

If this is an attic used for storage or if it has ducts & air handlers or any significant air communication paths with the conditioned space it any foam below the roof deck will need an ignition barrer.  3"+ of wet-sprayed Spider or most wet-sprayed cellulose would qualify, otherwise the most commonly used material would be half-inch gypsum.  (The codes have been relaxed on ignition barriers in attics & crawlspaces recently- you may want to google the specific conditions under which you're allowed to fly without it, then see if L.A. city has amended that.)

Going with an appropriate CA Title 24 compliant cool-roof finish on the standing will enhance cooling season performance considerably, and it usually a less expensive up-charge than an interior-side radiant barrier.  Should you ever opt for the latter, it must be a vapor-permeable variant, but from a cost/benefit point of view it's not necessarily going to be cost effective even in a 25 year net-present-value analysis, even were it placed on the exterior of the insulation where the radiant flux is much higher. See:  http://www.ornl.gov/sci/ees/etsd/btric/RadiantBarrier/RBFactSheet2010.pdf 

See the table on p5- Atlanta was used for the zone-3 example. At code-min R values with the ducts inside of conditioned space the annual utility savings are quite modest.  With the insulation placed on the exterior the utility savings would be even less.  The hottest element radiating to the interior space in a between-the-rafters insulation setup would be any exposed rafter edges- there may be a modest payback on painting those edges with a low-E paint, but that's about it.  (Putting up rigid foam as a thermal break on the interior might even beat that on an NPV basis.)

I think I will need to have some fire barrier. I was looking at the gaco open cell which claims to be fire resistant. It seems the foam only solution is the easiest (but probably costliest). The foam in conjunction with cellulose? The cellulose has to be below the foam, correct? I suspect I would need some netting to hold the cellulose below the foam.

In a combined foam/fiber stackup the air-impermeable foam is what has to be at the roof deck. And yes, "blown in bag" or "blown in blanket" are the typical terms used in the industry to describe the netting/scrim systems used. The netting is installed first, stapled tautly to the framing, an the blowing hoses are inserted into slits made at the time of installation. In a sloped roof application it looks like this:

http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation/images/photo_03_netted_cellulose.jpg

(the walls in this picture are wet-sprayed cellulose without the netting.)

This is what it looks like before the fiber (in this case, dry-blown Optima) is installed:

http://hci.frontstepsmedial.netdna-cdn.com/wp-content/uploads/2010/07/Certainteed-BIBS-with-OPTIMA-Insulation.jpg

another example

http://www.emsinsulation.com/images/blowinblanket_03.jpg

If used as the ignition barrier the fiber MUST be wet-sprayed, and have the necessary ratings for use ignition barrier application. Wet-sprayed rock wool is another alternative. The wet-sprayed goods have adhesives that bind it together to keep it from sagging or falling apart even when the front surface is scorched. If dry-blown in bag/blanket, it'll all end up on the floor as soon as the mesh fails from the heat of a fire. IIRC Spider (but not Optima) has the necessary adhesives & ratings, as do most wet-sprayed cellulose products. In a wall system dry blown cellulose adds a substantial burn time, but on ceilings & sloped roofs not so much, due to that pesky gravity thing.

I spoke with a rep from Gaco today.  He believes they Gaco has had their product applied in the City of LA in an unvented attic set up.  He said that if you use their new Gaco firestop open cell foam no additional coatings are needed.  If you use their closed cell foam then a fire resistant barrier coating is needed on top of that.  He said if you plan on having "storage" space in the attic you need a barrier (on top of the firestop product).  A barrier can be drywall or cellulose or fiberglass blanket over the foam.  Or he said you could "box" in the storage area and drywall it.