I couldn't tell for sure what was specified or how it was to be installed. Ask him for an Outline Spec that lists the important materials, briefly how and where they will be installed and any possible options to be reviewed and selected by you and/or alternates to be included in the bid documents. After reviewing that document with him he can write the full specification.

Once again I will say I would expect more assistance from an architect.

Tell me about it macv. He is expensive too which doesn't help!

His recommendation was to bid all foam. He doesn't work with folks with budgets generally unless they are in the 5 million plus range so all foam is a standard to him. We have a fifth of that budget so we are trying to get a quality build but also being reasonable about where things can be cut.

Don't get me started on the roof - asphalt is a four letter word to him!

Time for a sit down with the architect. He has to understand that it's your house, you are the boss, and he has a professional/contractural obligation to assist you in meeting all of your needs including your budget.

Just to give you a rough idea, we priced foam vs. fiberglass (we didn't price cellulose because I am allergic to it) and foam was more than 3 times the price of fiberglass (and the fiberglass included many interior walls and the foam did not). About $6,000 vs. $18,000. If we had it to do over I would have used foam in the garage ceiling (master is over the garage).

I see it notes a crawlspace. Where are you located? I am assuming it is not somewhere that regularly gets freezing temps?

We used R21 walls (2x6 construction) and R38 ceilings (12" rafters/I-joists).

I'd be more concerned about having good framing details to minimize thermal bridging. Foam sheathing can help with this. I'd go for cellulose with the board foam on the exterior over spray foam throughout.

I'd also want good air sealing requirements/details, possibly with a performance spec that has the contractor hire a 3rd party to do a blower door test (couple hundred bucks) to meet a specified leakage rate at the end of construction.

The last couple of issues of Fine Homebuilding have had good articles on energy efficient envelope/framing details, and Building Science is also a good resource. Southface Energy Institute used to have good fact sheets, but they've re-done their site and some aren't available any longer.

Athensmom - it might be hard to get an architect like that back down to earth. My builder was pretty good at this balancing act - he has built multiple homes at greater than 5 times our budget. But he understands that money spent does not necessarily equal value.

I'll repeat what I've said before many times. Foam in Athens, GA (right?) is a total waste of money. If you have money to burn, there are better fires - like geothermal. Air seal all you want as that is very helpful but foam is an expensive way to do it.

Now - if you have 2x6 walls then you really should have R-19 if you do fiberglass. I personally would rather have r-19 fiberglass than r-13 foam at much lower cost. You can airseal just fine with cheaper techniques. I'd also do r-40 in the attic because with fiberglass, it is cheap.

Budget talk here - 4000 sq ft in NC, $3000 for above code - energy star standard - fiberglass (r-19 in some areas with 2x6 and r-40 in the attic), foamed windows and doors. I personally foamed all penetrations into the basement and attic. I added foam to attic access doors. $18,000 for foam throughout including the attic rafters at code level.

That $15,000 was about what geothermal would cost with the tax credit.

Our total energy bill 1st year was $1600. I suspect half of that was HVAC - so $800 a year. You can never justify anything more on a cost basis only including geothermal or foam. I'm just saying.....

(Now I do have dual fual heat and seer 15/16 heat pumps and a radiant barrier in the attic which costs a few hundred and is probable worth it. I also have solar hot water which with rebates and credits was dirt cheap)

They're spraying foam in our house today. :-) We opted for spray foam for exterior walls, dormers and gables, with cellulose in the attic. If it's vertical, it's spray foam, if it's horizontal it's cellulose. 3000 sq ft 1.5 story house was bid at $6000. This was for 3" foam. We insulated the garage with fiberglass for another $500, and used the leftovers from that to insulate the walls around our bedroom and the a/c unit. It would have been nice to have insulation between first and second floors, but wasn't practical in the space we had.

To have done spray foam on our roof deck would have been another $4500 for 5" foam. Cellulose was $1500 and part of the price quoted above.

Your architect sounds very arrogant, btw. I probably would have lost my temper and fired him already. LOL

Vonda

Thanks for the advice. Glad you chimed in david - I know you have done lots of research on the pros and cons of this and it is good to hear your experience. After all we do have 2 x 6s on the exterior which should allow a r-19 which is overkill a bit :)

These are not really our specs - just a fly by night, headed out of the country first draft for us to go by. Has no relationship to our house - we have a basement, not a crawlspace, etc. I think I am going to send them back saying that they are too rough to work with since they have no relationship to our house and to please get me some that deal with our specifics to review. It is a bit absurd.

I will say though that there is a lady who has designed 3 houses with a top Atlanta architectural firm, and her latest is on a list of the prettiest houses in town (which it is). After commiserating with her she said that she has butted heads every time with this firm and has always stuck with it and gotten what she wanted - she chalked it up to E.G.O. I am not sure I will go back for more though! I do trust him to get the architectural details and proportions right, which is more than some architects do so I guess it is a benefit there.

Thanks for the advice. Glad you chimed in david - I know you have done lots of research on the pros and cons of this and it is good to hear your experience. After all we do have 2 x 6s on the exterior which should allow a r-19 which is overkill a bit :)

These are not really our specs - just a fly by night, headed out of the country first draft for us to go by. Has no relationship to our house - we have a basement, not a crawlspace, etc. I think I am going to send them back saying that they are too rough to work with since they have no relationship to our house and to please get me some that deal with our specifics to review. It is a bit absurd.

I will say though that there is a lady who has designed 3 houses with a top Atlanta architectural firm, and her latest is on a list of the prettiest houses in town (which it is). After commiserating with her she said that she has butted heads every time with this firm and has always stuck with it and gotten what she wanted - she chalked it up to E.G.O. I am not sure I will go back for more though! I do trust him to get the architectural details and proportions right, which is more than some architects do so I guess it is a benefit there.

athensmom,
We are in the same insulation boat as you, and sounds like budget too --- we don't want to spend money where it is wasteful. Our house is about 5000 sq ft, not including the basement. Our estimate for spray foam was about $15,000, and regular, though a bit souped up insulation was about $5,000. We talked to the builder about doing a hybrid, meaning spray foam in the attic spaces and regular insulation elsewhere. This brought the total bill to about $11-12,000. We discussed with the insulation company, where it would be the most efficient, and they believed the attic was the most critical area. I have to admit, I worry about this as DH has never wanted the spray foam (he thinks it is untested in the long term and it might turn out to be a problem, much like synthetic stucco around here). Anyway, I know from several neighbors that those with spray foam love it, they feel the house is cooler and quieter. Additionally, their energy costs seem to be substantially lower than other neighbors without the foam. I am wondering about adding foam in the garage ceiling as we'll have a bonus room there and I know from my current house (no foam) that this room has wilder temperature variances. We haven't broken ground yet either (hope to by next month), but this is still one of those nagging areas of uncertainty for me, so I'm glad you have posted your question. Good luck!

It's usually unwise to offer specific design advice without knowing anything about the exterior building envelope or HVAC systems (you should try to avoid designing a house one element at a time), but for a Mixed-Humid climate you could try using the Huber Zip sheathing system (or a liquid applied air barrier over plywood sheathing), filling the wall cavity with fiberglass (or better, dense-pack cellulose) insulation, and spending the savings on more sophisticated HVAC equipment.

It's all in the sealing details- and what others has said is right. Foam seals, but you pay for it. Take a look at Southface's EarthCraft home guidelines, there is good info there. They're in ATL (me too) and you could visit their offices to peruse lots of energy/materials info.

Next in importance after all of the building envelope and insulation/sealing details is the HVAC sizing. Needs to be right-sized, installed tight, and set up properly.

Very good advice all . . . Our houses are similar size mythreesonsnc - we are hovering around 5600.

I do think we will do foam in garage ceiling if no where else as we have a finished playroom above. . . . the rest, who knows! We do have 2 x 6 construction so we can get lots of insulation just through fiberglass in our exterior walls so it may be wiser to focus on attic and air penetration. . .

Foam the attic
use 1" rigid foam sheathing on exterior of walls conventional insulation in walls and air tight drywall
approach to the interior.

your bonus room will always be hot in a vented attic unless
you take big steps to make sure it is insulated and sealed
correctly.

I would take the savings from the foam in the walls and apply it towards the foam sheating for exterior
and to attic for foam (open cell) roofline install.

you can stop air flow through the walls with the above approach..and for a reasonable upcharge..
you may have to oversee some of the air sealing details
like sealing the sole plate to the slab and sealing any holes to the exterior of the walls before cladding goes on.

once attic is foamed the performance of the ductwork will be improved..duct leakage becomes less of an issue and equipment will all be located within a semiconditioned space.

Size of hvac system should be reduced accordingly.
You would do best to have a load calculation (manual J)
so that system will be properly sized for a home with
less air changes due to less house leakage.These calcs
should reflect the type of insulation (and other things)
and the air tightness that this type of wall construction and foam in the attic provides.

what costs more in one area is often offset by needing less in another area.
This holds true if you make a sealed builidng envelope
because it takes less energy to cool a building with
less leakage.
Better building..less hvac.

foam in the walls and conventional insulation in
the attic is reverse of what is efficient.

best of luck

If you're using fiberglass, there is R-21 insulation made specifically for 2x6 walls and R-15 made for 2x4 walls. When we bid our home insulation (3350 sq feet 2 story + one wall of basement), it was $300 upgrade to use the higher density insulation. We ended up using cellulose throughout at a slightly higher cost (about 10% more), but it included a lot more soundproofing.

Couple items jumped out at me.

1) "Face the fiberglass vapor barrier down." I thought the vapor barrier went against the living space. That would mean that the vapor barrier should face up against the subfloor in the basement/crawlspace.

2) When you come to cutting costs, do NOT give up the formaldehyde free insulation spec. Turns out if you use standard fiberglass insulation it becomes a major source of formaldehyde in the indoor air. Formaldehyde like water goes right through drywall.

3) I would stay away from foam as much as possilble. This is because it has lots of chemicals that will off gas.

4) I would strongly recommend increasing the amount of fresh air that can come in through your ventilation system. By using a DC motor you can control the amount of fresh air coming in. I would plan on the capacity of a complete air exchange every 30 minutes. That is 6 times more than most codes require, but I'm see lots of sick homes.

5) When the house is finished and you have move your furniture in wait for a warmer day and have a knowledgable professional test your indoor air quality. Increase the ventilation rate until it becomes acceptable. You may want to do this again on a cold day as the required ventilation rate will be lower. It may be a pain to adjust the ventilation rate with the seasons, but it is worth the effort. Always err on the side of too much ventilation. The extra energy cost is a bargin compared to the doctor bills.

Ok rich clearly has some experience with "sick" homes causing "sick" people. I'd like to hear the source and get the proof on the formaldehyde issue with fiberglass but cutting it out doesn't seem like a bad idea.

His level of ventilation is certainly energy inefficient and I'm not sure in the South how you would keep the humidity down to a reasonable level.

There are lots of sources of chemicals to the indoor air on a new house. You have to work at all of them to make any meaningful reduction. I personally did no voc paints, cabinets with less formaldehyde, water based poly on the floors. These were all common sense stuff - but things like the paint do cost a bit extra. And $5 a gallon adds up on a new house with a lot of benefit going to the painters. The paint is reportedly harder to match with touchups but we haven't had an issue.

Carpet seems to have gotten better but if I was really concerned, I wouldn't have any.

I think "sick" homes are blamed for many things of which a small proportion are true. There is a bit of religion in some of these things. Just because there are clear examples out there doesn't mean that it is an issue in the majority of new homes.

befor you go jumping to sick homes and adding ventilation
you first have to know if the house needs make up air.

if it does you dehumidify air before it enters the house.

the only way to determine air changes per hour
is to test the house for air infiltration when it is
completed.

we build houses to specs in previous post here in
hot humid La all the time. very few actually fall below
.35 air changes per hour. it is only when the house is
tight enough (below .35 ach) that it needs additional
'fresh' air.
until house's ach is determined..y'all are just talking
worst case scenerio.

I've never understood why folks get all upset
about the insulation in the walls and in the attic.
if it is seperated by an air barrier (well sealed drywall,
ICAT recessed lights and holes between insulation and
living spaces sealed) it is not entering the living space.
the problem is when the air barrier is incomplete
or there are leaks in ductwork that carries voc's into
living space this is what makes for bad IAQ.
if you pay attention to the air sealing details this
becomes a non-issue.

I've seen and cured a lot of sick homes myself.
Once the house is inspected, tesetd and diagnosed
then a solution can be decided until then it is all
speculation.

Build it tight and ventilate it right..but you have to test to see how tight it actually is.
All builders will tell you they build a tight house..but when you set up the blower door to determine the tightness
(air changes per hour) not many require make up or fresh air.

best of luck OP

Without knowing the nature or configuration of the building envelope the best advice would be to study the Building Science recommendations for you region paying close attention to moisture movement and ventilation.

Energy rater - rich mentioned 2 ach. That is pretty high.

This maybe something y'all already know, but last I checked Johns Manville fiberglass was formaldehyde free but the Owens Corning was not. I agree that if it's done right it likely is inside inside the envelope, but I'd rather support the mfr that isn't using the formaldehyde binder anyway.

The use of phenol-formaldehyde binders in fiberglass insulation is not a health problem. Johns Manville has wisely taken advantage of the public's understandable but erroneous perception that no amount of formaldehyde is acceptable in a construction material for a home even though that standard is not applied to any of the common materials that normally contain excessive amounts of formaldehyde especially in the greater out-gassing urea-formaldehyde form.

Sources of Urea-formaldehyde in approximate order of highest to lowest out-gassing (trace elements).

medium density fiberboard (drawer fronts, cabinets, and furniture)
particleboard (sub-flooring, shelving, cabinetry, and furniture)
hardwood plywood paneling (decorative wall covering, cabinets, and furniture)
smoking
un-vented gas or kerosene appliances
permanent-press clothing and draperies
many glues and adhesives
preservatives in some paints
paper towels
paper money
fabric softeners
cosmetics
apples
potatoes
fish

Phenol-formaldehyde containing materials with considerably less off-gassing

softwood plywood
oriented strand board
fiberglass insulation
(When the above materials are encapsulated in an exterior wall only trace elements of formaldehyde should be able to be detected.)

There is nothing wrong with specifying formaldehyde-free insulation but don't imagine that it will have any measurable or detectable effect on the indoor air quality of a new home. For that you should be concerned about materials higher on the list above.

A general design process comment:
There is a tendency for people new to the design of buildings to focus on each element of the building in isolation. This makes the work considerably easier to manage but the resulting design often doesn't work well as a whole, either technically or aesthetically. Always go from the big to the small and back again testing your decisions throughout the design process; don't take the easy straight path.

I'm no expert, just a guy who OB'd two years ago and used closed cell foam.

If I was building again, I'd use foam board on top of the exterior sheathing, taping all the seams. I'd use a spray in dense pack cellulose in the walls, foam around windows and penetrations, caulk everywhere and open cell foam the roof. Then I'd bring in a company to do a blower door test to find leaks before the drywall went up and learn just how tight the house is before the HVAC is finished.

I do believe, no matter how tight the house is, that an ERV is a good investment in air quality.

I'm not saying that foam doesn't work well, I just think there are more cost effective ways to get a tight house.

Certain kinds of foam sheathing boards placed over the exterior of the wall system can act as a vapor retarder which can cause problems during the heating season in a mixed-humid climate if interior humidity is not effectively controlled.

If you recommend R 25 for the walls in this climate, what R value would you recommend for the roof?

who are you addressing the question to macv?
did anyon notice that the OP hasn't replied for a while?
neither have a couple of other posters...wuwt??

We are just putting together specs now and I think we are going to do r-21 fiberglass in exterior walls (we have 2x6 studs for aesthetic reasons in exterior walls in walls, although in our climate R-13 brings you to energy star standards in walls), foam around windows and doors, open cell foam in attic rafters and blown in cellulose or foam in garage ceiling (finished playroom above). At least that is what we think we will spec at this point. I guess we go from there cost wise.

Talked to one builder and he said that was a respectable plan and would certainly be cheaper than all foam. He did think there wouldn't be any need to put the r-40 fiberglass in the attic if we open cell foamed the rafters. . . any thoughts?

What is the purpose of using foam in the roof? Are the rafters deep enough to achieve the desired R value? what is that R value? Are you trying to avoid ventilating the roof?

That sounds like a good plan. I came up with the determination that foaming the rafters was not worth it and my father who has worked in energy conservation for much of his life agreed.

The way my energy audit ran was that I would save $200 a year on foamed rafters. The reality is that my HVAC costs are 50% of predicted so I'd probably guess that would be closer to $100 a year. Just ask (when the time comes) what you would save by doing R-40 in the attic vs foam in the rafters - for me it was over $5000 - that was over a 50 year payback.

Yes - if you foam the rafters with r-40, you need no insulation above the ceiling. You are making the attic conditioned space. That is one of the issues with this approach - you are greatly increasing the volume of air that is conditioned and the surface area for heat loss.

You might also be concerned (rightly or wrongly) about leaks in the roof not showing up until late, about unvented attics not being approved in some jurisdictions until very recently and so the long term implications are not really known in our climate. You might lose a warranty on your shingles but I think they've all come around. You might lose a few months of life in the shingles but I personally don't think that is true. Then there is the offgassing concern. My only point on this is that there is a debate and the savings don't justify it anyway.

Thanks David! I also read that foaming the rafters is better done a year or so after the house is built because the wood in the rafter dries out and shrinks and creates a space.

I am not sure about the unvented attic approach. Maybe I will drop the foam rafters after we get the preliminary bid???

All I know is that this house will be much better insulated than our current 20 year old spec house!

Most of these URL's are for research pulished in 2009 or 2010.

December 15, 2009 the California Air Resources Board and California Energy Commission released likely the most extensive multi-year study of residential indoor air quality; "Ventilation and Indoor Air Quality in New Homes." The title is a little misleading in the homes were built in 2002-04 and tested in 2006-07, which makes them about 4 years old.

Summary: http://www.arb.ca.gov/research/apr/past/04-310exec_sum.pdf
Report: http://www.arb.ca.gov/research/apr/past/04-310.pdf
Researcher's PowerPoint: http://iee-sf.com/resources/pdf/ResidentialVentilation.pdf

The key conclusion:
"Nearly all homes (98%) had formaldehyde concentrations that exceeded guidelines for cancer and chronic irritation..."
The 2% that didn't exceed the guildlines had a measured ACH of greater than 5. They lived with their windows opened. 98% failure rate a pretty good indication that poor indoor air quality.

The typical home exceeded California's Office of Environmental Health Hazard Assessments of 7 ppb by a factor of four at 29 ppb. THe median ventilation rate was 0.17 ACH including opened windows and doors, use of exhaust ventialtion in kitchen and bathrooms as well as use of clothes dryer. That is half the 0.35 guildeline.

2009 CARB study on fiberglass wall insulation off gassing formaldehyde into indoor air. Formaldehyde goes right through drywall like water does. At 73 degrees and 1.0 ACH the room concentration would be 14.9 ppb. Temperatures in exterior wall cavities with sun exposure are much high. Ventilation rate is typical a lot lower than 1.0 ACH. Both would increase the actual formaldehyde concentration. 50 to 75 ppb was measured in several homes built in 2006 with the fiberglass wall insulation the only identifable source.
http://www.healthybuilding.net/formaldehyde/Fiberglass-insulation-formaldehyde-emissions-090303.pdf

Other useful indoor air quality URL's

May 25, 2010 a Conn. indoor air quality consultant published a very user friendly web site associated with a research paper. "LEED Certification: Where Energy Efficiency Collides With Human Health" http://www.ehhi.org/leed/

Comparison of absenteeism between Energy Star building that does not require testing and LEED buildings that requires testing. ALL of the 10% of occupants reporting an increase in sick time were in Energy Star Labeled buildings. For the most part the 45% occupants reporting no change in sick time were in Energy Star labeled buildings. Almost universally the 45% occupants reporting decrease in sick time were in LEED buildings.
http://catcher.sandiego.edu/items/business/Productivity_paper_with_CBRE_and_USD_Aug_2009-Miller_Pogue.pdf

EPAs double standard won't allow their worker's in offices with more than 16 ppb.
http://www.epa.gov/rtp/campus/environmental/s_01445.htm

Unintended consequences of 'green' building codes
http://www.aihasynergist-digital.org/aihasynergist/201002?pg=32#pg32

"it is wise to measure the levels of formaldehyde, to assure that levels are no greater than 27 ppb." (Note: the CA standard was reduced from 27 ppb to 7 ppb in December 2008)
http://www.cdph.ca.gov/programs/CLPPB/Documents/ResEnviroHaz2005.pdf

http://www.IndoorAirAnswers.com

If there are follow up questions, please send an email as well as posting. Thanks

Thanks for the info but the green stuff is not mine - it is from my architects earlier specs for another house.

I did talk to the prospective builder again yesterday and he said he had had great success with the foam on the rafters, recommended a sealed attic and he thought it extended the life of the hvac stuff placed up there. He is going to price foam and blown in cellulose no foam. I also asked about the r-40 batts.

Cellulose should be the spray "dense-pack" type. Some jurisdictions allow it to be sprayed into rafter cavities without ventilation but I still feel uneasy about that.

The cellulose would be a (cheaper) alternative to the foam rafters. He said if we did the foam rafters he thought no other insulation would be needed in the floor of the attic. We are just north of Atlanta so although it does get pretty hot around here, winters are pretty mild.

He seems pretty knowledgeable about this stuff but I guess we all can learn more. He also told me that although fiberglass bats would work in between walls, he would recommend cellulose there instead - something about sound attenuation?? Anyway, it works better at controlling sound between rooms (we want it between our master bedroom and family room). He also recommended a r-30 fiberglass bat in the garage ceiling as a less expensive option than foam there (the space above will be a finished playroom).

Drywall is an air barrier..... use it. There is no reason to add foam insulation over any drywall in the attic., (Air tight drywall approach).
Why not just do a little spray foam in the attic at the leakage points? Wall channels, recessed cans, electrical and plumbing rough ins etc and then install a less expensive loose fill. You can save considerable money and still maintain the thermal integrity and even moreso, the air barrier.

Given a choice, Id rather have a great air barrier and marginal insulation that absolutely perfect insulation package and marginal air barrier.

Since you're having the home inspected by an Home Energy Rater anyway, why not consult with that inspector ahead of time? They can review the whole building plan and make suitable recommendations before it's too late.

Thank you Rollie..love the way you break it down.
It is amazing the difference it made years ago when sheet products became available. Prior to that walls/ceilings were made of individual boards..then all of a sudden 32 sq
ft with no holes in them. Great for reducing air infiltration.
With sheetrock you are sealing all the gaps where the rock joins and if you seal the penetrations you make a lot of air tightness can be achieved.Always seal wall to ceiling joints even if installing ceiling moldings.
The detail work..sealing sole plates,around electrical outlets, dryer venting through walls..caulk is a great thing!
In unvented attucs choosing ICAT recessed cans and not IC cans, sealing all gaps around bath fans.. stove vents
..fireplace vents this makes an excellent air barrier.

Once the air barrier is complete then any insulation will
perform better. what lowers R-value is air movement and misinstalls.

I would recommend that you also insulate the bonus room area. In my climate these are problem rooms as they are surrounded by hot attic air..as opposed to exterior walls which are exposed to outdoor temps. Attics reach 140 degrees here. If you eliminate the foam in this area
you will pay for not installing it in comfort and utility costs.

It just doesn't make sense to me to not use the better method for the area where living space is in the attic...

air seal then insulate walls conventionally
roofline with foam. over bonus room also.
savings from wall foam will pay for bonus room install

best of luck,

Thanks energyrater - there is no living space in the attic. This is a two story house with finished second story space above the unfinished garage.

finished second story space above the unfinished garage..this is the living space located within the attic space.

what did you decide to do??

We are just at the pricing out stage but this is what we are pricing out.

Open cell foam on roof rafters (this will be a sealed attic and will include the attic over the bonus room). We were on the fence about it but both our builder and our architect insisted this was a good idea. They even thought it prolonged the HVAC units stored up there. Don't know if that is true but we went with it!

R-30 batts in garage ceiling (finished playroom above)

Foam sealing around windows and doors and all penetrations.

High efficiency r-21 fiberglass batts in walls - 2x6 - this is a bit of overkill as the Energy Star requirements are r-13 for our climate - but it is not expensive. We decided to do fiberglass batts vs. blown in insulation in the walls because my understanding is that the walls are the least important part of the insulation package (with roof and air infiltration being the most) and there was quite a cost savings.

We decided against pricing out foam board at our builders recommendation but I can't remember why he recommended not using it.

good for you.
now less tons of a/c will be
needed to heat and cool.
making hvac decisions yet?

We have not - just getting a preliminary price for the build right now but I wanted to try to get the specs as close as possible for the most accurate price. That is good to know though!

I was looking through this thread again and what macv said about the foam board and vapor is exactly what my builder said so he prefers not to use it.

A year later-------- any new suggestions for alternatives to spray foam insulation for unvented attic in hot, humid south?