"By the way Dana1, on another post you said that with 25% thermal bridging in walls an R32 is more like an R22. Here normal build is R19 in walls - how much is Rvalue then if houses here are not OVE framed and probably have the 25% bridging?"

A 2x6 studwall with 25% framing fraction,  wooden siding + gypsum, with R19 cavity fill runs ~R13.  Reducing the framing fraction to ~20% bumps it to ~R14.

Add an inch of exterior iso and that's R19/R20 for 25%/20% framing fractions respectively.

I think in the other post the stackup included 1" of exterior foam (which is the only way  R32 @ center-cavity R works out to ~R22 whole-wall.)

Brian,

So the traditional styrofoam baffles are not that good of an idea? You say low cost netting, or perf. radiant foil... is this available anywhere? What other materials could I use. Were you the one that suggested at one time to use pink/blue foam board insulation?

Most installers here do the baffles that look like made out of the styrofoam egg cartons. I like the look of the provent since it looked sturdier than the foam things (but cost more I'm sure).

Dana1 - thanks!

Boontucky-girl,

Perforated radiant barrier is readily available online. The netting is a product sold through insulation supply houses for keeping the insulation in the stud space during fill of open stud cavities. Styrofoam baffles are designed to isolate the end of the joist space that is not insulated from the insulated cavity and to protect the first couple feet up the roof air gap. Any cheap breathable material could be used. Its only purpose is to keep the air gap protected during insulation fill. After fill it has little purpose. Pink or blue foam board insulation would not be appropriate for this application it is not breathable. It could be used for end cap below the air gap retaining the insulation as the vertical barrier.

Brian

In the thickness used for blown-insulation baffles Styrofoam (XPS) is plenty vapor-permeable, but even impermeable rigid-board isn't a problem since one side is exposed to the ventilation air, the other side to an air & vapor permeable insulation exposed to the same air. The vapor permeance of cellulose is VERY high, so there's zero chance of creating a moisture trap with an edge-dam (leaning or not) of say, foil-faced iso, even through substantial thicknesses of cellulose.

If the tapering down toward the soffit is very significant it can undercut the performance of the whole assembly. Cellulose would run ~R3.3/inch at open-blow densities and you'd have 30" of insulation to hit R100 in the middle. But if it tapers down to 10-12" at the soffits, the tapered down area has more than 2x the heat loss per square foot as the middle. Stacking up R6/inch polyiso in the taper would even things out a bit. But hopefully you have sufficient energy-heel built into the truss to get at least R60-75 all the way out over the exterior edge of the wall framing, and from a cost-effectiveness point of view R75 is probably more than "enough". (R75 is the rough guide BSC uses for US climate zone 6 attics see table 2, p10: http://www.buildingscience.com/documents/reports/rr-1005-building-america-high-r-value-high-performance-residential-buildings-all-climate-zones)

In a heating dominated climate the using RB would increase the average heating load slightly- more than offset any miniscule savings during the cooling season, but the effect in either direction is negligible. Perforated RB would be fine to use to keep the soffits clear, but isn't worth paying extra for in an IA climate. Netting is cheaper and works just fine.

If taking a DIY approach to the attic insulation, note that cellulose sold at Home Depot has (always, in my experience) uses sulfate based fire retardents, which are corrosive to metal when wet (it stinks after a time when wet too.) It's better to seek out a source for a "borate only, sulfate-free" goods. All "stabilized formula" or "wet spray" cellulose is sulfate free, and is fine to use in a dry-blown application. It contains a water-activated adhesive to help limit settling over time when wet-sprayed, but doesn't cost significantly more than standard dry-blow goods.

Boontucky-girl,

Home Depot sells non-sulfur based fire retardant insulation. This has been available through them for a long time. I am not pushing Home Depot and I agree that the consumer needs to be educated when picking materials. They may have sold a bad product at one point in some location and still may in some locations. They generally try to provide products that the consumer wants and do not cause issues. Here is the description from their web site of the current offering.

“The 12 in. x 16 in. x 1 ft. R3.7 Blow-In Natural Insulation is an environmentally-friendly insulation made of 85% recycled paper fiber. The insulation is treated for flame resistance with borates that are non-corrosive and provide for a safe home environment.”

If the insulation in his application was wet there was a problem with the building design. Short on ventilation or a leaking roof or something else was wrong. I agree that you should avoid sulfur, formaldehyde and VOC containing fire retardants and preservatives, but the justification and explanation is incomplete.

Edge-dam permeance is not an issue if it is only near the outside edge of the installation. If you are filling to the top deck the barrier is to maintain an air gap which is a different application then an edge-dam. You can fill to the underside of the top stud as long as you maintain an adequate air gap but the material protecting the air gap must be breathable.

I agree that using foam in the taper if the space is less than 12 inches in the heal would be advisable. Foam can cost 10 times as much as blown in cellulose per R-value so budget concerns here are significant. 2 inches of blown in foam will add extra R-value and air seal the underside of the cellulose improving its performance with a reasonable compromise in performance. Was the heal height called out in this discussion?

Loose fill cellulose is an effective air barrier when applied in depths that exceed 24 inches per manufacturer’s application recommendations. The sound dampening of the material is also affected by the extra depth and is significant to the livability of the home. I am always amazed at how much quieter the home is after 30 inches of cellulose is installed. Cellulose is very low cost around 70 cents per cubic foot. In my opinion the benefits of complete fill out way the cost up to the 30 inch range of fill. This is double or triple code in most places. The additional cost is $1 per square foot of attic space. Note that the setup, brake down, and move on site are a significant part of what the insulation contractor is charging you for on a small home. This is why DIY of loose fill has a payback for the home owner over a contractor for small jobs.

I recommended using the least costly netting option. Radiant Barrier was only suggested when asked for alternative materials that could be used. Radiant Barrier application benefits are dependent on climate and buildup of the given design. Radiant barriers range in price from 3 to 40 cents per square foot so the economic justification depends a lot on the product chosen and how it is applied in a given situation.

Brian

Posted By zehboss on 13 Jun 2012 06:21 PM
Boontucky-girl,

Home Depot sells non-sulfur based fire retardant insulation. This has been available through them for a long time. I am not pushing Home Depot and I agree that the consumer needs to be educated when picking materials. They may have sold a bad product at one point in some location. They generally try to provide products that the consumer wants and do not cause issues. Here is the description from their web site of the current offering.

“The 12 in. x 16 in. x 1 ft. R3.7 Blow-In Natural Insulation is an environmentally-friendly insulation made of 85% recycled paper fiber. The insulation is treated for flame resistance with borates that are non-corrosive and provide for a safe home environment.”

If the insulation in his application was wet there was a problem with the building design. Short on ventilation or a leaking roof or something else was wrong. I agree that you should avoid sulfur, formaldehyde and VOC containing fire retardants and preservatives, but the justification and explanation is incomplete.

Edge-dam permeance is not an issue if it is only near the outside edge of the installation. If you are filling to the top deck the barrier is to maintain an air gap which is a different application then an edge-dam. You can fill to the underside of the top stud as long as you maintain an adequate air gap but the material protecting the air gap must be breathable.

I agree that using foam in the taper if the space is less than 12 inches in the heal would be advisable. Foam can cost 10 times as much as blown in cellulose per R-value so budget concerns here are significant. 2 inches of blown in foam will add extra R-value and air seal the underside of the cellulose improving its performance with a reasonable compromise in performance. Was the heal height called out in this discussion?

Loose fill cellulose is an effective air barrier when applied in depths that exceed 24 inches per manufacturer’s application recommendations. The sound dampening of the material is also affected by the extra depth and is significant to the livability of the home. I am always amazed at how much quieter the home is after 30 inches of cellulose is installed. Cellulose is very low cost around 70 cents per cubic foot. In my opinion the benefits of complete fill out way the cost up to the 30 inch range of fill. This is double or triple code in most places. The additional cost is $1 per square foot of attic space. Note that the setup, brake down, and move on site are a significant part of what the insulation contractor is charging you for on a small home. This is why DIY of loose fill has a payback for the home owner over a contractor for small jobs.

I recommended using the least costly netting option. Radiant Barrier was only suggested when asked for alternative materials that could be used. Radiant Barrier application benefits are dependent on climate and buildup of the given design. Radiant barriers range in price from 3 to 40 cents per square foot so the economic justification depends a lot on the product chosen and how it is applied in a given situation.

Brian

Sorry, doing this on an iPad and couldnt figure out how to selectively cut. Just to clarify, homes depot carries green fiber, if you look at the msds for the product, ins541ld, you will see it does contain sulfates. This is the product that zehboss quotes from the website description on the home depot website. The stuff is hard on machines and takes more than stated because they pack the bags so tight, this is from experience. Compare bag sizes for the same weight from green fiber and a premium supplier and you will see what I mean. http://www.greenfiber.com/images/technicaldocuments/831201194905AMMS-6.4-057%20Rev%20D%20Loose%20Fill%20Blended%20Formula.pdf

The product I looked at was not designated as green fiber and is listed as I suggested as borat and not using corrosive componds. I assume Home Depot must stock different sources based on area availability or something. What ever product you are considering, it is a good idea to review the msds of it before installing.

Green Fiber also has a Borate only product that I am sure Home Depot can supply if they are competitive from Green Fiber. If you look at that product it is sulfer free.

PRODUCT IDENTIFIER: Cellulose Insulation, Stabilized Borate Formula PRODUCT NAME: INS735, INS745 Insulation
http://www.greenfiber.com/images/technicaldocuments/81201115908PMMS-6.4-060%20Rev%20C%20Stabilized%20Borate%20Formula.pdf

Here again it is a matter of the consumer knowing what they are buying. It is upto the consumer to order the right material.

Brian

The Home Depot near me has changed cellulose vendors 3x in the past 12 years, but has yet to stock a sulfate-free version to date. YMMV.

Greenfiber has bought up a number of smaller cellulose manufs, and has excellent nation-wide distribution, and seems to be the most commonly found version in box-stores like Lowes & Home Depot. But their dry-blow versions all use sulfates.

Anyl "stabilized forumla" version (any vendor) is designed for wet-spray application and are sulfate-free (or at least should be), and they're perfectly fine to use as dry-blown. If you're not sure what you have, dissolve a couple pellets of Drano in a cup of water and stir in a heaping tablespoon of the cellulose from the bag. Your nose is a pretty sensitive ammonia detector, which would be outgassing from the slurry when there are any sulfated fire retardents in there.

I tend to use National Fiber Cel-Pak, since I have a distributor just down the road from me ( 5 miles further than Home Depot.) Since none of their products use sulfates, there's no chance of getting mis-labeled/mis-bagged product that could cause an issue. But there are others.

Posted By zehboss on 14 Jun 2012 03:54 AM
The product I looked at was not designated as green fiber and is listed as I suggested as borat and not using corrosive componds. I assume Home Depot must stock different sources based on area availability or something. What ever product you are considering, it is a good idea to review the msds of it before installing.

Green Fiber also has a Borate only product that I am sure Home Depot can supply if they are competitive from Green Fiber. If you look at that product it is sulfer free.

PRODUCT IDENTIFIER: Cellulose Insulation, Stabilized Borate Formula PRODUCT NAME: INS735, INS745 Insulation
http://www.greenfiber.com/images/technicaldocuments/81201115908PMMS-6.4-060%20Rev%20C%20Stabilized%20Borate%20Formula.pdf

Here again it is a matter of the consumer knowing what they are buying. It is upto the consumer to order the right material.

Brian

The product is not designated as green fiber anywhere, but the manufacture ID tells who it's from. Your suggestion illustrates how they misle the consumer, yes it has non corrosive borates, then they leave out the part about the sulfates. At 8.98 a bag the consumer is really going for a ride and if their low grade bag is 8.98 what do you think they'll charge for all borate? For comparison sake I pay 6.47 for the same size, all borate and not as compressed, plus hand sorted.

Posted By Boontucky-girl on 12 Jun 2012 11:29 PM
Brian,

So the traditional styrofoam baffles are not that good of an idea? You say low cost netting, or perf. radiant foil... is this available anywhere? What other materials could I use. Were you the one that suggested at one time to use pink/blue foam board insulation?

Most installers here do the baffles that look like made out of the styrofoam egg cartons. I like the look of the provent since it looked sturdier than the foam things (but cost more I'm sure).

Dana1 - thanks!

We use Proventil baffles, what you will run into on a hip roof with deep insulation is unusable soffit venting off the corners because the hip rafter will block the rafter bays below the top of the insulation. Depending on pitch it could be significant. A workaround is a ridge vent designed for hipped roofs since hipped roofs are usually short on traditional ridge and everything thinks mushroom vents are ugly. I would venture to guess the added cost/pita versus payback/roi and it makes no sense for all these weird foam board, polyiso, netting suggestions.

Distributor pricing near me for all-borate Cel-Pak is "in the noise" of the prices charged for the sulfate laden goods at box stores. (It's ometimes less, sometimes more, but always within 10%.) YMMV.

Energey heel - Unfortunately my trusses do not have a true energy heel. What they have is that the top chord is stacked over the bottom chord, so I have at best about 7" of and energy heel (on the exterior edge of the wall top plate). My roof slope is 6/12, all hip roofs, so the perimeter area is definitely a lot less room to fit lots of insulation. So when baffles are installed in each truss cavity, I have about 5" between the exterior edge of the top plate and underside of baffle. The wall is 2x6, so on the interior edge of the double top plate it is almost 8" of space. Greentree - your statement is correct, that at the corners the truss spaces are worthless as vents since the hip rafter blocks it. Would I still want baffles in these just to keep the insulation from touching the roof sheathing, even though they technically won't vent? I have no idea what type of ridge vents we have, but you're right, it's very limited amount of ridge venting.

We have planned 2" of 2lb spray foam on the ceiling sheetrock for both sealing purposes and to add a little bit of insulation, which is more critical at the exterior perimeter. I got one quote back from the spray foamer that said he would fill the gap above the top plate with the 2lb foam for the whole perimeter of the house for about an additional $700. Would that be a bad idea to fill my "energy heel" with 2 lb foam? Like in the purple area of my little diagram. I still need something for windblocking since unfortunately the soffits are already in, and the framer didn't extend the R-board beyond the to pf the double top plate. Would the additional investment be worth it? It would completely cover the double top plate area, and the R-board does cover the exterior of the double top plate, so it is doing something for the bridging.
At best I'm still only getting about an "R30" or so at the perimeters, regardless of whatever R we can achieve in the middle of the roof.

I'm hoping that the extra expense of the skim coat will help a lot since it should take care of the infiltration side of heat loss. But I'm not sure what much more I can do to max. R at the perimeters.

I also think we will need double stack of vent baffles to keep the insulation from blocking that vent space, and reduce windwashing? (Assuming I will get ventilation!)

Putting the ~6" plug of 2lb foam above the top plate of the wall does not create any moisture problems, and will REDUCE the risk of ice damming, since it'll put a reliable R30+ between the warm corner of the wall/ceiling interface and the roof. With the doubled top plate and only ~6" of cellulose at that critical point would be a localized heat leak of real proportion causing localized melting and re-freeze.

I agree with Dana, the 2 lb foam idea is a good one. We would install baffles in all spaces even if they weren't technically being used to move air, in my opinion even with great ceiling plane air seal, I don't want insulation touching the deck with few exceptions.


There is an attic venting formula, dont quote me but it's something like 1 square foot of free air per 300 square foot of ceiling, you then divide that square footage between soffits and ridge or pot vents that is useable. I think you can go up to 60/40 split, google the formula and you'll find it. Soffit makers and ridge makers specify how much free air their products provide so you can pencil it all out.

The foamer can spray right onto the chutes, he'll probably need a backer to spray against above the top plate which could be scrap foam board, scrap fiberglass, as long as the backer is outside of the exterior sheathing plane, dont let him stuff a batt above the top plate and spray against it, thats all you have then is compressed fiberglass above your exterior wall plates.

So, everything sounds cut and dry and easy but coming from someone who has spent many hours on his back or belly in a 6/12 hip roof and attempted 4/12 at the exterior wall it's very slow, tedious, hot, uncomfortable expensive work. For people planning similar builds, chutes and backer above the plate should all go in prior to ceiling finish, sooo much easier.

Thanks greentree. I was thinking the same thing that baffles should be installed, though even there won't be true venting at the corners, the roof would still get an air gap.

I'll check into the venting.

The spray guy wants to come and install the baffles, backing, and spray the walls and above double top plate before ceiling goes up. Then when ceiling goes up, he'd spray on the ceiling and overlap the energy heel area, to make things easier.

The attic venting formulae enshrined in many local codes have no real science behind them. The amount of actual ventilation provided will vary widely by the difference in height between the ridge & soffits, since that's the stack height of the stack effect driving the ventilation.  (A tall 12:12 roof/attic will pull a LOT more air than a 3:12 roof at any given span & vent area.)

In general more ventilation area==>better from a moisture purging point of view, but making the soffit venting cross-sectional area much larger (like 2x) than that of the ridge limits the amount of de-pressurization of the attic relative to the top of the conditioned space, thereby limiting the total infiltration from any air leakage at the upper floor ceiling.

Dana1 - so you are saying that more soffit than ridge vent is good because the attic won't be trying to "suck" up the air inside the house through my ceiling? My pitch is at 6/12, and with hip roofs I probably have more soffit than ridge vent area. I have about 150 lineal ft of continuous vended soffit since there's only 2 gables that don't have it (without counting the garage ) and about 25 lineal ft of total ridge vents.

I'm struggling to find a general willing to go up to R100 in the attic. So I backed down to R75, but they keep telling me the cost of labor to do the osb in the ceiling to support weight does not justify going higher. So they want to bid the min at R50 since it's code now around here, with only 5/8" drywall on 24" o.c. but in fiberglass. I'm trying to reach a compromise of ok, R50 blown in but cellulose over the 2" 2lb foam. Will 5/8" drywall be good enough to support weight without sagging? If I still need to go with the 3/8" osb in the ceiling, I will plan on adding the addition R value, even if I have to rent the blower and tell general just do the foam skim coat, we'll do the rest. Any advice? Thanks.

What do the cellulose installers say about using stabilized cellulose to distribute the weight to the joists?

Boontucky-girl,
        I guess the economy must be booming where you are!  Contractors refusing to do it to your spec!  DON"T compromise you want r100 & OSB they do it your way or they don't get the job!   If you really want to make their life miserable and make them estimate added labor and price it ask for a 2x4 service cavity in the ceiling.  Seriously, that it takes more labor to do what you want is no excuse, you are paying them a profit on that labor and paying for it as well.

"What do the cellulose installers say about using stabilized cellulose to distribute the weight to the joists?"
 It doesn't matter what they say!  IT DOESN"T WORK!  The pressure,on the drywall, midway between trusses is  NOT reduced! Drywall can't support the pressure long term sag or failure are inevitable!