How much greater will the R value be with foam? Is the cellulose dense-pack?

foaming the rafters in my real word experience is a good thing in our hot humid climate. took me a long time to get here...but I'm a believer.
I do hope that you are pricing open cell and not closed cell.

we do stupid things like putting our equipment and ductwork in the hottest part of the attic.
then we cut holes in the ceiling and don't seal them
plumbing, electrical, supply boxes, bath fans kitchen fans
and my personal pet peeve recessed cans that are not air tight.
so when we do all these crazy things and then dump conventional insulation in the ceiling joist bays, and turn on the hvac system we move air through the insulation.
the more air movement..the less insulation performance.
trades people just don't seal the holes they make..so foam
insulation does the air sealing that trades don't.

when you insulate the roofline you are moving the thermal barrier from the hole filled ceiling to the roofline.
the roof has well sealed holes on the exterior (roof)
and much less holes than the ceiling. so the foam when correctly installed moves not only the thermal barrier but also the air barrier to the roofline taking the ceiling out of the equation.

in this scenerio there is no pressure driven air movement
at the ceiling. the ducts & equipment are now in a semi conditoined space. performance is improved, air is closer to the temp exiting the duct as it is entering the duct.
problems like duct leakage..and yes ducts leak a LOT..
are lessened because now the duct leakage is semi conditioning the attic space.
you don't size the hvac system to include the attic space
it is just the common leaky duct install that most people get.
foam companies like to say that the attic is conditioned..but in reality..unless someone is putting ducts to cool off the attic..it is the duct leakage and lessened heat gain that makes these attics cooler.
they also like to say that the foam will make the attic just a few degrees warmer than the house..itrw it is not 3-5 degrees but 15-20 degrees warmer.

to take it a step further think about the install
that whole 3" is sufficient..not true.
doesn't even meet code. my clients get a full rafter install and all of the rafter faces are covered.
if the rafters are 2x6 then the foam is 6" to 7" with
no exposed wood showing.

the other area that concerns me is where the roof meets the walls...top plates have lots of holes
the foam should seal the top plates and be continous from rafters to attic floor. @ the attic floor the foam has to seal.

I see a lot of bids with 5" average fill
average meaning that some spots have 3" some 4" and some 5"
average fill doesn't mean that you are getting 5x the R-value per inch. it means that overall 5" is the average.
this is a big difference.

look at jobs by the company you are thinking of hiring.
talk to the installer..not just the salesman or company owner. you are paying 3x the cost of conventional insulation so make sure that you know the type of install that you are paying for.
foam should be level without being concave between rafters.
it takes experience to get a good install.
locally the foam companies go through several installers a year. finding an installer who consistantly does good work is a gold mine for the company. they tend to hold on to these guys.

personally I wouldn't put cellulose in the attic of a dog house. but that is my personal feelings. the fine particles of cellulose finds the smallest cracks in the ceiling.
people complain of dust, young children have allergies
folks get sick.
put it in a wall...no problem ..as long as wall is air tight, which usually isn't a problem.
but attics...
breathe in borate treated newspaper particles for a few days and you'll know why.

R-values of foam are usually in the R-4.2 per inch for open cell and 7.5 for closed. differs from brand to brand.
to meet code you still have to have R-values that reach the standard for your area. with foam you are ok with just achieving code, with conventional insulations you do better to invest in higher R-values.

just my experience & opinions..not to get anyone bent out of shape.
I see that OP has been working with insulation options for quite some time, my post is based on what I inspect and test in the field for the homeowner..not the foam company

best of luck

Athens - we have been in our home for 2 years. 4000 in upper 2 floors with 1400 in walkout. Seer 15 HPs with NG as heat on the first floor. We are slightly cooler in NC than you.

We have ductwork and airhandler in attic.

We got a report from our electricity supplier saying we were 40% below our peers in usage (our peers was our new neighborhood with 4500 average sqft). Our peers also had gas heat and gas hot water - we don't so our gas bill last year was $100 in usage. That was the entire year. Even not using much gas we were 40% lower on electric for a grand total of $1600 a year. If you take out heating with electric and backup on the hot water, we were probably only $1000 a year or 65% below peers.

What is my point for bragging about this? There is no way, no how, that foaming the rafters would save 30% of this. Even if it did - the payback is close 18 years. Have I mentioned that we have zero shade trees and I feel like you have some.

Seal the penetrations into the attic, then your only possible reason for foaming the rafters is to keep ducts cooler. I do think you could save about 10% on upstairs a/c this way. In my house, that would be about $30 a year.

Here is another thought. Upstairs a/c generally has a pretty small load. You usually don't have as many windows upstairs. Your ceilings are usually lower. You don't have a kitchen up there. And occupants spend time up there when it is cooler outside. There are no doors to the outside (or if there are, they don't get opened nearly as much). So by keeping that airhandler and ductwork cooler, you are saving 10% or so on a system that is much less than 1/2 your a/c bill (typically).

So I used $30 for my house but that was a really high guess. It also is high since we sleep in an upstairs master that we keep at 65 all night. Even still, I really doubt our upstairs a/c is $300 a year.

I drive a hybrid car which in my opinion pays back about 10 times faster than foaming the rafters. I think solar PV pays back in 10 years in many places. Solar hot water 5-10 years.
I really do think foaming the rafters is about a 50 year payback (and it really could be 100 years)

THanks David for chiming in. I keep coming back to your thoughts on this because the rest I am afraid is marketing hype. We actually have a lot of attic space. Big house and the master is on the bottom floor but single story with attic space above. So the foaming would cover attic above master bedroom and bath (on its on unit), and 4 bedrooms, hallways, craft room and large playroom and finished storage(over 3 car garage) - so that is 2 units covering probably 3500 square feet (when you include entire upstairs and master wing). The foam people (I realize they are biased) say 30 percent savings.

Another question - as far as caulking attic penetrations, my builder said something about fire caulking the penetrations (which I assume are mostly boxes for light fixtures and recessed cans). Is this enough? Should I insist on foaming the penetrations? We have trusses and getting up there safely is a pain or I would do it myself. . .

foam is great. No lies there. But you pay for it. It is one of the few energy boosters that, IMO, you rarely see a return on. When they throw numbers at you, they test the worse, oldest, leakiest house they can possibly find. Of course they will see a 30% reduction. The foam is probably the only insulation in the entire house! Point is, do NOT fall into the marketing hypes foam installers claim. Same with the ICF industry. ICF is a great product, but far from the r values they claim. Do the research, look for unbiased case studies in various climates. Building Science does some, ORNL does some. They find the same thing david is claiming. Foaming, especially in a big house like yours, will not pay off. However, there might be some use for open cell in certain areas you can mix with cellulose. For instance, the small area your equipment is, that can be framed and boxed in, then you can foam the rafters and walls of just that portion, and blow cellulose in the rest of the attic. Cellulose is a great product. It is dense, green, and highly fire resistance. Foam is the exact opposite of that. A simple spark can ignite your entire attic.
Fire caulking will suffice for sealing around penetrations. However check your local code. If you can get by with a standard caulk product, the material is a fraction of the price of fire caulk. However you may need a 20 min rated ceiling enclosure.
Again, first of all, make sure its open cell, and not closed cell foam. Then decide if you want to spend the upcharge. 5500 can but A LOT of caulk.... Finally, I highly doubt you will see a savings of much over 20%, if even that. Then again, there is no way of knowing or comparing. Do the research, find case studies and unbiased reports. They will probably not be as astounding as the foam reports...:)

We used closed cell foam on our entire house, attic, walls and basement. The attic is much more pleasant here in the summer than other attics, but EnergyRater is correct, it's not 5 degrees warmer, it's about as hot as the exterior temperature (98 today). That's still much better than 140 like some attics. I think our electric bills are much better than our last house and our neighbors, but the numbers are always hard to compare.

Would I do it again? Yes and no.

I'd foam the attic. Probably open cell and fill the bays like ER says. Ours is closed cell with the 5" average.

I'd use a densepack cellulose in the walls with foamboard panels on the outside of the sheathing, taped at the seams.

Regardless, make sure you use quality windows and doors that seal well. I'd suggest doing a blower door test after the insulation, doors and windows are in and using caulk and small foam to make the house nice and tight before drywall.

Thanks all. Total for upgrade to foam is 4875 now, because there is a slight downsizing in equipment that results in a 625 savings. I love the idea of framing out the small area where the equipment will be and foaming that - although I think part of the cost of the foam is getting the guys and the equipment out there so not sure if even that would be cost effective.

I'll get more information about the fill level and r value.

foam won't 'ignite'.
a simple site search of any
foam product will show ratings.
as will the 'green' properties.
(which can be misLEEDing)

foam does have a longer payback
which is why I recommend to my clients
to foam only attic & under floors for houses on
piers.
the savings are there. always cost of efficiency
is upfront. savings longterm.

best of luck op

I am really surprised you would recommend foam under a house on pilings. The temp differential is small. Generally if you are on pilings, you have a very mild temp because you are next to a body of water.

I am getting ready to build on pilings and the winter design temp is 27 and summer is 91. It is hard to make any insulation payback beyond code with those design temps.

Seems like the floor is pretty easy to make airtight also.

houses on piers are fairly common here
and not near water.
not so much for new homes, although a few
build on piers..
lots of leakage in floors..a good example
is the 4"x6" under tubs for drain.

lots of older homes used centermatch for floors

Ok fill level for cellulose is 14 plus inches for an R-38 (unfinished attic with only a small portion floored for equipment.). Foaming the rafters is 5 1/2 inches of foam for an r-22. Upgrade cost is about 4600.

I would think that the air infiltration benefit (which may not ever be cost effective anyway) would be outweighed by the reduction in r-value. . . am I right about this?

I realize that some folks say you need a lower r-value for foam than conventional insulation but I am not convinced of that. Should I be?

Oh and next question. . . was reading a message board that suggested a closed cell foam of 2 or 3 inches at the attic floor and then either batts or cellulose above. Apparently more cost effective, you can get an r-50 insulation that way and you get the benefits of the air sealing.

Thoughts?

if your rafters are 2x6, the actual measurement is 1.5x5.5
so 5.5 inches will leave the face of the 2x exposed.
it is better to install a full 6" so that thermal conductivity through rafters is broken.
wood has an R-value of R-1 per inch so this R-5.5 derates the overall install
open cell 7"@ 4.2 per inch is R-29..close enough to R-30 for me.
this will satisfy codes.

the whole air sealing quality of foam and R-values is a mixed bag.
in the work I do, the air sealing comes under a different portion than insulation as there are many ways to
reduce air infiltration.
the goverment program that I work with is now being used as a pilot program nationwide, so it will be interesting to see how others address the foam claims of quanitive values vs R-values.

as it is now, dept of energy and other goverment agencies
do not accept Q-values. its a good thing IMO as each product can't just invent its own values.
R-values are used for the average joe to compare products. with foam...it is what it is. Open cell is approx R-4.2 closed cell approx R-7.5 it varies with different brands.

with your post about foam at attic floor...
now you are moving your thermal and air barrier back down to the attic floor..same as with conventional insulations.
your mechanicals and ductwork are now back in the 140 degree attic..if you have recessed lights the foam won't be sprayed against them so if they are not air tight you not only have hot attic air infiltrating into your house
but the area around the recessed can has no insulation either.
if your mechanicals and ducts were in the conditioned space
this would be a good choice.

this is one of the areas I struggled with in the past.
less cost to foam attic floor...but no benefit to mechanicals and ducts..with homes with those huge 18/12 roof pitches foam @ roofline is costly..
we did a few houses with radiant barriers and foam on attic floor but over these houses didn't achieve the savings (utility)and units were oversized by hvac companies defeating any efficiency there.

www.buildingscience.com has quite a few studies that you
can review with different insulation methods and what the testing of these homes showed to work or not work.
if you do a site search on unvented attics
(sorry but entering rafter foaming wont work..lol)
for your climate these studies will be listed in pdf format.
interesting stuff..if you've a mind to educate yourself.
or if you are looking for input from forums
www.hvac-talk.com in the residential forum will get you
some pro's input. foam and hvac can work well together if each company works with each other. foam = smaller more efficient hvac systems.

realistically you would be looking at about a 10 to 12 year payback..depending on the size of your house, the roof pitch and utility costs.
I try to talk folks out of foam in walls as the payback jumps to 25+ years. 50-100 is unrealistic. just saying..I run the numbers a lot and our highest utility costs in my area are .13 per kwh. approx savings varies also I've had homes that achieved 30% savings on the low side and 50% on the high side..but foam is never the only upgrade.
high efficiency hvac, better windows, air sealing, high ef water heaters..its a package deal in my work.

I remember your build bdpeck:
"I'd use a densepack cellulose in the walls with foamboard panels on the outside of the sheathing, taped at the seams.

Regardless, make sure you use quality windows and doors that seal well. I'd suggest doing a blower door test after the insulation, doors and windows are in and using caulk and small foam to make the house nice and tight before drywall."

glad to know that you remembered my foam boards to exterior of walls..it works for any climate.
hope you are enjoying your new home.

best of luck with your decisions OP.

ER-
why do you recommend blower door tests AFTER insulation? Obviously if CCf is being used as the air barrier, but I always spec it to be done once sheathing is up and windows are installed. This way we can easily find the leaks before insulation is in the way. if we can hit >.2@50 at this stage, we are in good shape. Knowing the final should be lower, hopefully >1.5 or better.

Good question. I would like to have a blower door test done but don't know when to schedule it. Still waiting on front door and back ordered french doors. When should I have it done?

I call for 2 on my ES projects. One once everything is sealed up in the shell (windows, doors, sheathing, exterior air barriers, shingled. also after electrical RI and plumbing RI are done. If using cellulose and gyp as your ceiling sealer, the ceiling gyp also has to be installed, cans and boxes caulked, etc. All exterior penetrations sealed and caulked (outlet boxes, plumbing, etc). If that passes (like I said, I like to hit .2 or .3 at the worse), then insulation and finish out the rest of the stuff. Using air tight drywall, etc. After that is completed, I call for the 2nd one. The goal is .2 at the worse. But its whatever you are after. Passivehouse needs to be .07, which is pretty extreme. But if you only want to do 1, I would say do it at the time before insulation and gyp. in theory, it SHOULD only improve from that number anyway!

We did our blower door after drywall. It was less than 1/2 the ES standard but I don't know the number. I'm not really sure I want it that much tighter.

I have to say that we had a large amount of air leaks that I fixed after the test so I don't think it is particularly hard to hit ES standards. We had a cat door that desperately needed foam and has since become a two door system. We had a large kitchen vent hood that needed weather stripping on the damper and our pull down attic door was just sealed at one level with basic weather stripping. And we could and still can seem some light on our front french doors.

Energy rater - thanks for the reminder to foam the drains. But you have to admit that a couple of plumbing penetrations pales in comparison to bath fans and can lights. Also what is an issue on older houses is not necessarily an issue on new ones. I think foaming the rafters on an old house with duct leakage or unsealed bath fans probably helps whole lot. That some of those ducts might not be insulated, and you are in a totally different ballpark.

I stand by my assertion that foaming the rafters in the South compared to a well sealed ceiling is a 50 year+ payback. My upstairs HVAC cost is

We are not foaming. Had to decide by this morning because they are roofing and needed to know whether to do a ridge vent or not.

Is there any magic to the number for attic insulation? We are planning on r38 cellulose. We have an attic above our master (not accessible from the rest of the attic) with no mechanicals in there. Should we treat this differently? Closed cell foam and batts? More cellulose?

Did I read somewhere David you are upgrading to r-50 in your attic?

code min. is r-38. for a zone 3 (I assume that is what you are) Mins are not always ideal...they are just that...minimums. I would see what the adds per inch of additional cellulose is. Push 45, maybe 50. It should be a very small upcharge. I would guess much above 50 in your climate will start a diminishing return. Around here (zone 6) I tpyiclaly do 55-60. However when you get into those thickness with cellulose, you need to start to be concerned about the weight on the 5/8" gyp.

boy --- r this r that open cell closed cell... guess i have a little learning to do.. yeah know the higher the r value the better - but havent heard the terms open/closed cell yet (any short explanations on differences).

odd i came across this thread as yesterday HVAC company mentioned to me that people are slowly moving towards foaming the rafters - of course the added cost is there. we didnt jump into the specs too much - but it seems that people have different opinions on the idea....guess a quick question i would have---i know they arent sizing for the attic - but wouldnt you still have some heat/cold transfer from the house to attic that would be more than usual if the ceiling itself was not insulated as it is normally done?

for a simple description, they are just 2 types of expanding foam products. The r values vary some from manuf. to manuf. but in general closed cell is around r 6ish up to 7s. Open cell is less, from as low as 3.2 up to around r4. The perm rating of the two vary quite a bit. Without throwing numbers at you, in general, open cell has a much higher perm rate, meaning more moisture can get through it compared to closed cell. However both are good air sealers. Closed cell is, in most cases, one of the best air sealers and highest r products to put in your wall, but you pay for it. In our area, closed cell is over double the price of blown fiberglass, and about 1/3 more then open cell foam. I just did a house where the insulator quoted 3k for installed blown blanket, netted and including "air sealing package (caulking and foaming windows and other penetrations, lights, etc), and 8k for closed cell. Closed cell dries to be hard, open cell stays spongy. However closed cell's hardness can really add structural integrity to your wall diaphragm. In a perfect world where costs are not an option, I would spray closed cell everywhere but the under side of a roof, in which case I would use open cell.

Your ceiling will have heat loss, yes. ducting and your equipment will also have heat loss. The idea of sealing the rafters is to completely enclose all of these items. While you do not want to condition the attic, it is at least still retaining heat loss or helping to prevent heat gains. this is important because it keeps your equipment and ducting warmer in heating mode, and cooler in cooling mode, thus increasing efficiency.

ER-
why do you recommend blower door tests AFTER insulation? Obviously if CCf is being used as the air barrier, but I always spec it to be done once sheathing is up and windows are installed. This way we can easily find the leaks before insulation is in the way. if we can hit >.2@50 at this stage, we are in good shape. Knowing the final should be lower, hopefully >1.5 or better.

are you a builder?

the state program I work with calls for preliminary rating from plans on new construction and final inspection and testing when house is completed. The blower door and duct testing are required on final..because all equipment is installed for us to get model and serial numbers to verify equipment.
I do an intermediate inspection, using ES's thermal bypass checklist. this is not required by the state program. but
at this stage insulation installed, ducts installed heating system installed windows in place.
doors are not always installed at this point.

to test @ blacked in stage...lots of things can be done for air sealing between blacked in and completion.
additional caulking..air tight drywall for example.

I read your posts with closed cell recommendations
are you in a cold climate?

R-30 is code(In central NC and Athens is probably the same). R-40 cost about $200 and saved about $40 a year. I have enough to go up to r-50 after I finish a few projects. I think you do have a cost effective benefit (10-15 yr) up to 50 in our climate but maybe 40 in Athens.

I should mention that $40 a year was based on an energy audit that way overestimated costs so it maybe closer to $20. They had our heat at $1400 a year using 80% NG. Seer 15 and 90% comes to about $500 with todays low NG prices.

I am an architect, but also have put in my years in the field with a building background. I enjoy construction and building for friends and family now, and my own house hopefully starting this spring. the goal is to be close to Passivehous standards. I am in zone 6, about 7500 HDD.
green building has become sort of a passion I am now pressing into my firm and trying to make it a culture in my office.

thx to lzerarc... that is some pretty good info...

http://www.eia.gov/emeu/cbecs/climate_zones.html

must be looking in the wrong place to find
zone 6 as this link only lists 1-5

one of my favorite sites is buildingscience.com
good unbiased tested info..
and ol joe is married to an architect!
I use one of his quotes as my tag on an pro forum
'green building is 80% efficiency & 20% everything else.'
of course he also says that
green building is misLEEDing...

I thought I would jump in on this thread since it is current to what we are looking at.

We are doing a flat roof with cathedral ceilings for over half of our roof areas - so we are planning on closed cell foam, so we don't need to vent etc...

Our other roof sections will be curved cathedral ceilings - again we are planning on closed cell foam under these - negates venting again. Closes Cell should seal us up very well. The flat roofs will have a cool deck membrane.

We are Zone 3 Marine - R30 Min.

Not sure if a blower door test is required by Title 24 in California, but I will look at doing that as well.

montel- read my posts above. I would not recommend closed cell against the roof, rather use open cell.

On a side note...very impressive ceiling!

Energy rater-
check a new website (I do not have a link handy) or IEC. zones go up to 7 (7 being Alaska and some of Canada). Zone 5 and 6 split Iowa right down the middle almost. Minnesota is zone 6.

lzerarc - Thanks for the comments - why do you recommend open cell in this case?

I know some say it helps it breath better, show leaks if they occur sooner etc... However, I was under the assumption that it CCSF would be a better air seal in general and of course a better R value per inch.

Un-vented with open cell would be OK still?

Further Follow up: Just checked our plans - we have 2x6 rafters to fill - so 5.5" only which is R30 in the Closed cell foam we have specified - So I don't think we can switch to open cell, at least for our curved ceilings with a metal roof. We could switch to open cell in our flat roof areas as we have 11 7/8" TJI's.

I am thinking that might be a good solution due to the flat roofs getting a membrane that is also an air and moisture barrier - we might want some more breath-ability on those areas.

CC is far more dense with a much lower perm value than OC. This attributes to its higher r and higher cost. However air sealing abilities are very similar, especially at full thickness. 1" flash and batt situations, CC is typically a better solution. However at 2x10-12 (what
appears to be your thickness) air sealing will not be a factor. Assuming you are using 2x10 up there, that still gives you an r 32 with OC and a big cost savings for the size and volume you are talking about. However with CC you would have an r around 55, which means you could either go higher r or just not fill the entire bay.

What are you using for the walls?

Our large curved ceilings only have 2x6 rafters on top of the glulams so it would have to be Closed Cell...or we would have to fur down on the rafters with some 2x2 or something to increase the cavity space, don't think that is worth it for this job.

For walls we are getting some quotes to compare blown cellulose with fiberglass batts. Will go with blown cellulose if it is reasonable - meaning not a huge up-charge over fiberglass!

Mon-
unless you practiced air tight sheathing (your pictures do not appear to be) and will practice air tight drywall...a blower door test will most likely be a waste of money (unless required for some reason). Also, cellulose performance is not comparable to batts in any way. While r values are very similar, performance of cellulose is much better in various categories. Batts in your 2x6 walls will perform around an r-14. Cellulose will be slightly higher, but also provide an infiltration damper, prevent air convection currents within your cavity, better fire barrier and flame spread prevention, a recycled product, and far more dense for a better sound damper. It can also hold moisture within your walls longer without damage and release it for drying abilities.

I just want to add an anecdotal experience to this discussion. We recently toured a house for sale that had the air conditioner off or at a very high temperature. We live near the GA/FL border, near the water, so it is extremely hot and humid right now. The house we visited was 2 1/2 story cape style. The upper floor of the house was shockingly cool, especially considering the living area is basically the same level as the attic. When we looked into the surrounding attic space, we discovered foam insulation. Foam may not be cost effective to install but as a buyer I certainly find it to be a big plus.

"unless you practiced air tight sheathing (your pictures do not appear to be) and will practice air tight drywall...a blower door test will most likely be a waste of money (unless required for some reason)"

I was planning to caulk seal the exterior seams of the plywood sheathing (using a product like GreatSeal LT-100). Not sure if this would help at all...

We will have some level of air tight drywall - due to sealing required by Title 24 in CA.

What about the effect on the shingles?

Some used to claim placing shingles over unvented roofs would void the warranty. However they are realizing it does not have any major adverse affects on a QUALITY shingle.
Most are starting to refine their warranty coverage to allow full warranty on unvented roofs.

Dear Athens Mom, I believe that blown insulation is a good product and will save you money on your unilities. However, please make sure that the product they are using is non-toxic & oderless. A contractor spray blown insulation under my kitchen sink to fill a hole and it smelled to high heaven. He promised me the smell would subside but it did not, even after a hugh water leak that flooded my entire kitchen, it still reaked. Many of these new products can be harmful to our health which we do not realize or even think about until it is too late. Be very cautious with those 3 precious children of yours. Fresh air and breathing are of the utmost importance. Think of all the so called safe prescription drugs the FDA pushes that are very often recalled due to harmful side effects and even death. Now-a-days you really have to take it upon yourself to do as much research as possible for your own safety & health. Good luck to you! *HUG*