A conditioned attic is part of the home, whether you're using it or not. So you should air-seal it and insulate around the entire space adjacent to the exterior; that's the roof for most of the attic but the floor above the garage too.

You can fill the joist space on the inside of the attic above the garage with cellulose, add draftstopping material above and air seal the garage--caulking or gasketing the drywall and taping all joints.

As an alternative, since the spray applicators will be there anyway, check on the cost of just "flashing" the attic side of the garage ceiling, then adding the cellulose and air barrier.

Here is a link that might be useful: Enclosures that Work in Mixed-Humid Zone-Charlotte, N.C.

This post was edited by worthy on Thu, Jan 31, 13 at 23:53

Are you insulating the garage walls?

Don't know exactly where you are but my uninsulated garage made it below 50 once this year. Raleigh area.

I'd just put a bit of fiberglass or cellulose on the attic floor above the garage. But of course code is going to dictate what you do. I believe R-30 is what is required in such a location.

Are you foaming to r-30 in the rafters? I'm curious what your quotes are?

We are not insulating the garage walls.

The quotes stipulate 5 1/2 inches of open-cell foam in roof rafters and 3 1/2" open cell foam in gable walls.

Thanks

could you explain the conditioned crawlspace?
will you be foam insulating the walls of the
crawlspace or the floor of the house?
hard pipe ducts & heating system in crawlspace?

rather than foam insulating the entire roofline
why not just build a room for storage & put
foam on the roof, walls of the room and foam
on the rest of the attic floor?

without ductwork in the attic it seems like
a big cost just for storage.

best of luck

5.5" of Open Cell foam is only R20. Code is R38. You will probably pass inspection but this is technically WAY below code. Spray foam sales folks will have reasons why its OK but its really just a way for them to appear competitive with other insulation. The air sealing qualities are great but codes don't assume air leaks when they prescribe R value. Some inspectors and municipalities are beginning to catch on to this.

Ensuring the top chords or rafters are completely encapsulated is the minimum I would go. You would need 10.5" to meet minimum building codes.

As for your attached garage, beware of the indoor air pollution concerns that this presents. I would want the air-seal and insulation layer separated at the wall plane of the garage attic and house attic to help separate the air spaces.

Even if you're not yet under the IECC 2012, it would make sense to meet it rather than scamper under. As noted above, some of what you're proposing is inadequate.

See link for summary of 2012 Energy Code.

I would want the air-seal and insulation layer separated at the wall plane of the garage attic and house attic to help separate the air spaces.

That is a detail building inspectors pay great attention to for safety concerns.

Here is a link that might be useful: Overview of the 2012 Energy Code

Thanks Brian_Knight and worthy:

I am not sure exactly what you mean by "I would want the air-seal and insulation layer separated at the wall plane of the garage attic and house attic to help separate the air spaces."

Can you give me examples as to how this can be accomplished?

Our specs for the house are stated for traditional fiber-glass batts and call for "R-38 in attic floor and R-15" in walls. The SPF insulation contractors seem to be implying that 5.5"-6" is "comparable to R-38" when it only technically measures R-20 like you have stated. Is this correct? Any comments?

Thanks again!

"comparable" to and actually being R-38 is
two different things. its a thing that foam
companies do. they want to use quanitive values
adding air sealing value to the insulation value.
it doesn't meet code.

you can meeting cathedralized code
which is R-25 in La. (check with your code specs)
in essence, foaming the roofline is recognized
by code as cathedralized.

foam companies imply several things.
one is the R-value.
the other, if you look at or question the bid
is the 5.5" average fill.
this means that if the insulation is 1/2" to 8"
that it will 'average' out to 5.5"
this isn't acceptable.
insulation depth has to be continuous. no low
spots. high spots are ok..just extra, but no LESS
than 5.5"
actually you should have 6" so that the faces
of the rafters are covered. this will help to
eliminate thermal transfer thru rafters, as wood
has low insulation value.

seperating the attic from the garage is what is
also called...defining the thermal barrier.
you don't want to spend extra $$ foam insulating
the roof of the unconditioned garage space.
so where the roof/attic of the living space
meets the roof/attic space of the garage
there needs to be a wall that can be foamed
to air seal and insulate the garage from the house.
studs & felt paper, foam board or sheetrock can
be installed for foam to be applied to to
seal & insulate this break between semi conditioned
attic and regular vented attic over garage.

in addition to the r-value/quanitive value issue
is the actual install. I'll attach a picture
of 6" of open cell in a new construction roofline.
checking the depth of the insulation is a must.
I take a can of spray paint to mark low spots
for the foam installer to touch up, and a piece of
wire with inches marked off to measure the depth
of the install.
the roof to attic floor (at eaves) is critical.
if this area isn't insulated properly...the attic
will have ambient air entering the attic.

blower door testing is one way to measure & find
these leaks. IF the company testing understands
how to test attic, AND the foam company will come
back..or be there ready to touch up when the testing
is done. again...mark the leakage areas so that there
are no missed areas.

you can get it done correctly, but you'll have to
ask questions and get involved.

best of luck.

Thanks for the excellent response, energy rater la.

Our Ceiling rafters are 2 x 8" so it does not seem that even 6" would cover the beams, as you suggest?

We have gotten 2 quotes for icynene spray foam so far:
Quote 1: Roof Deck 6" nominal;
ext.walls/gables 3" nominal
Band joists 3" nominal
Thermal barrier coating
He wants contractor to frame off the garage and the unheted front and screened porches.

Quote 2: "spray 5 1/2" in attic roofline
"spray 3 1/2" in Gable walls
"Use fire retardtant paint if needed on foam"
He proposes spraying the roof of the garage and the rafters over the garage and not walling it off separately.

Both for icynene open cell. Quote #2 is about $4,000 less.
What do you all think?
Thanks again for all the advice and help!

Tough decisions. Have you started build? Quote 1 sounds more experienced and knowledgeable. Quote 2 makes me nervous with the "if needed" statement. The thermal barrier paint is expensive. Will it cause an upcharge if they end up adding it?

Even if you go with quote 2, you should have builder separate the garage and porches from the attics over conditioned space.

I would get a 3rd quote and have all of them include pricing option for getting to code minimum. Tough to give anyone a recommendation for going with below code construction.

Quote #1

Separating the attic areas over unconditioned space is not necessary.

I've built where the unconditioned (vented) attic covered the conditioned parts of the house as well as a porch roof. I used ccspf over the porch to seal it and then applied blown cellulose over both parts of the attic.

Of course, there may be aspects of your build that make complete separation the more prudent choice.

I'd want an explanation of "nominal". Is that another way of saying "average"? Not acceptable. I'd change the spec to a minimum. And it certainly would not be to a below Code 3".
Quote #2

"Use fire retardtant(sic) paint if needed on foam"

Intumescent coatings are expensive. Not all inspection authorities will insist on igntion barriers for spray foam. Partly, it's because some specific formulations, all of which closed cell, don't require thermal coatings.

I always use closed cell spray foam.

There is an additional consideration that no one seems to have considered: if the local building authority deems the attic to be living space--after all, it's conditioned and you are planning to use it for storage--you need a thermal barrier over the spray foam. Intumescent paint doesn't count.

As pointed out by several posters, the biggest consideration is that the spf seems to be below Code.

What do your approved building plans specify as the required R Values??

Here is a link that might be useful: Making Sense of Spray Foam and Ignition Barriers

This post was edited by worthy on Sat, Feb 2, 13 at 12:21

Unless it changed recently, central NC code in the attic is R30.

I like ERLA's idea about building a storage area up there and avoiding foam altogether. Foam when you don't have to is generally not worth it. You will likely get more R-value from other options. Sure you don't get the air sealing but there are other far cheaper ways to do that.

From an environmental standpoint, there are a lot of chemicals in sprayfoam.

Thanks for the excellent response, energy rater la.
Our Ceiling rafters are 2 x 8" so it does not seem that even 6" would cover the beams, as you suggest?

no 6" will still leave exposed rafters. increasing the
foam to 8" will fill the 7.5 rafter bay with 1/2"
to cover faces of rafters.

We have gotten 2 quotes for icynene spray foam so far:
Quote 1: Roof Deck 6" nominal;
ext.walls/gables 3" nominal
Band joists 3" nominal
Thermal barrier coating
He wants contractor to frame off the garage and the unheted front and screened porches.

I don't like nominal..defined as:.Of or relating to the presumed or approximate value, rather than the actual value.
rather than the actual value. using that quanitive
value again.

I do like the band joists being insulated.
and that this company will seperate unconditioned
area from conditioned area, and only foam the
conditioned space.

in my area, we don't do a coating in attics. any fire rating
comes from the sheetrock ceiling to living space.
if a garage is storage...it isn't a living space,
and if it were any living space would be comprised of
sheetrock.

adding a vapor barrier eliminates the drying
of any moisture that will come from roof
leaks that happen over time.
the reason we use open over closed cell is to
allow this transport of moisture and not trap it
next to the roof decking.

I have seen companies that put open cell under
floors. to stop moisture from ground to foam
a latex paint was used as vapor barrier.

Quote 2: "spray 5 1/2" in attic roofline
"spray 3 1/2" in Gable walls
"Use fire retardtant paint if needed on foam"
He proposes spraying the roof of the garage and the rafters over the garage and not walling it off separately.

spraying the roof of garage sells more product. if
you were planning on adding a living space in this
area, you'd foam the roofline. if not, seperate it
from the area that is conditioned.

seldom do you see companies set up to spray both
open and closed cell foams. usually the same hoses
& spray guns are used for both foams, the guns have
to be fully cleaned between use of different foams.

to me, it just seems like a lot of cost as opposed
to adding a foam sealed room in the attic.
I'd do that, and spray foam the floor.
could you explain the conditioned crawlspace?

best of luck.

Unless it changed recently, central NC code in the attic is R30.

The N.C. Code requirement in Zone 4 where the OP is located is R38 with these two exceptions:

For further details, see Part IV, Chapter 11 "Energy Efficiency" in the N.C. Residential Code.

Here is a link that might be useful: North Carolina Residential Building Codes

Duplicate Post

{{!gwi}}

This post was edited by worthy on Sun, Feb 3, 13 at 10:29

The OP posted: "Our specs for the house are stated for traditional fiber-glass batts and call for "R-38 in attic floor and R-15" in walls. "

Yes, as per the state Residential Building Code.

Now that you're planning to completely change the insulation system and location and reducing the RValue, you should first contact your building authority. You don't want a nasty surprise when an inspector comes in and compares your filed plans with what you've actually done.

Thanks worthy:

Again, very helpful
I will try to determine if what is proposed will actually pass the city and state building inspection and the Spray foam contractors justification for R-20 foam. I fear they will respond with the option for R-30 thickness but at a cost too much for our budget.
Thanks everyone!

What do you all make of this?

Just found this referred report while searching the web: See section 4.2.2 and 4.3.1.5

Says maximum thickness of Spray foam can only be "a nominal thickness of 6" or it is a fire hazard?. Even though the R value is less than code, apparently the inspectors know this and that is why 5 1/2 and 6" pass inspection?

http://www.pwcgov.org/government/dept/development/bd/Documents/007255.pdf

Does anyone know anymore about this and what do you all think?
Thanks again!

a LOT has changed from 2003.
even the componets of foam have changed.

to be on the safe side anyone considering
foam should have a conversation with code
enforcement in their area.
like Worthy said...you don't want a nasty
suprise after the fact.

an explanation of the second exception...
where in a foam insulated attic you won't have
baffles..would be necessary.
I agree that the
roof edge & details need full depth of foam
or any insulation for that matter.

with conventional insulation on attic floor
we use a raised heel at top plate to give
depth for insulation at roof edge (eaves).
without this detail the space limits how
much insulation can be installed on low
pitch roofs. (5 on 12 & lower)

getting to know the folks who will be
doing your code inspections is a good thing
IMO. code officials often get a bad rep,
but they are there to ensure your safety.
from an efficiency pov..there is a big gap
between minimal code requirements & what
you can actually achieve.

best of luck.

Worthy - There has been a change. But just for clarification, a lot of "central" NC is zone 3. Hence R-30. Where did you get OP was zone 4? Did I miss something?

Also R30 appears to be adequate if it extends over the wall top plate - I would think a unvented attic that is foamed would count.

IECC2012 requires R38 minimum in zone 3. The 2009 version R30 is what's usually enforced, pathetically low by most energy experts standards which is why code is changing for the better. I wonder what the 2015 version will require?

Ive seen some experts suggest that R60 should be the roof minimum for the entire country. Some passive house builds are going for R80-100 granted they tend to be predominantly heating climates.

R20-30 roof will probably appear pretty weak 8 years from now. Code minimum is another way of saying "poorest one is allowed to build by law".

Central, you may want to Google "spray Foam insulation" and add words such as "nightmares" or "illness".

Brian - just a point of info. My energy rater predicted a $40 a year savings from r-30 to r-40 (which is what I did). That was based on $1350 predicted heating cost. Since the actual is closer to $300, it is possible the attic upgrade is saving $10 a year. Hardly a big deal in the South. Upgrade to R60 was a predicted savings of $20 more. Actual might be $5. Try to get the embedded energy of the extra fiberglass with $5 savings a year - it is well over a century.

Imposing R60 on the entire country is a ridiculous waste of resources. Drives up the cost of fiberglass for those that really need it.

a lot of "central" NC is zone 3. Hence R-30. Where did you get OP was zone 4?

Here's the IECC 2009 map, which specifies insulation levels down to the county level. (See map below.)

The OP simply said central N.C. But as the original plan specified R38 I presumed it was Zone 4. True, it could be Zone 3 and the designer specified above Code; some designers consider meeting Code minimums the equivalent of getting a "C-" in school.

Interestingly, the proposed 2012 NC Energy Conservation Code specifies a minimum R42 in residential attics in all three climate zones in the state.

In any case, the point is that the OP must contact the building authority to see if they will approve the spf claims that their product applied as they want to is an acceptable substitute for what was in the filed building plans.

*******

Martin Holladay discusses Icynene's claim that it's OK to skimp on insulation.
*******

maximum thickness of Spray foam can only be "a nominal thickness of 6" ...

Does anyone know anymore about this and what do you all think?

I believe that may refer to the max pass thickness on application, that is, how much can be sprayed on in one pass. OC is routinely used in much greater thicknesses.

This post was edited by worthy on Mon, Feb 4, 13 at 16:34

I wouldnt disagree that most of the things minimum building codes have us do ever pay themselves off. I like building codes though and definitely like the direction minimum energy codes are heading. Its not difficult to achieve the poorest performance allowed by law.

I would be wary of putting too much faith in the exact numbers that the software says is cost-effective mainly because the software is designed to protect the user's interests of over-promising on energy performance. People should be building to code minimums and beyond even if the software doesnt agree with some very specific inputs.

The same people writing and updating the energy modeling software are the people writing the minimum codes. I think minimum building codes are WAY behind where we should be right now in terms of cost-effectiveness. Based on where international energy codes will be in 2015, the industry as a whole seems to agree.

If energy prices weren't so heavily taxed by our political masters and extraction, production and transportation constrained at every turn by so-called environmentalists, nationalists and Malthusians, the economics of insulation and air-sealing would be quite different. But that would gore other oxes, which would never do in our modern system of governance by pressure group.

But that's all another story!

I wonder what the real costs of dirty energy would be if it included the indirect societal and environmental costs? Yeah, we just ruined this otherwise informative thread.. sorry!

I am not nearly as knowledgable as the folks that have already commented, but we are building in the Raleigh area (zone 4) and are foaming the walls and ceiling. If we were building 2 miles away- the neighboring county, we would be zone 3. We decided against foaming the rafters due to cost - we are also building a one story house with 5000 sq ft on the first floor, hence a huge attic space and lots of roof deck. We put radiant barrier in the roof so our attic should be somewhat more comfortable than our current attic, but we will see how it fares.

We are getting our icynene foam installed this week. Probably the same company you have received quotes from. We have already discussed the plan with our local inspector and he says the 3.5 and 6.5" will be fine. My BIL recently insulated the same way -company and thickness and his house is very tight and insulated very well.... total electric bill only $150-200/month for 7000 sq ft.

If you are Progress Energy, make sure you check out their new incentive for energy efficient buiding. $1000-4000 rebate depending on how you meet the criteria.

Mom3kids...you say" We put radiant barrier in the roof so our attic should be somewhat more comfortable than our current attic, but we will see how it fares.
We are getting our icynene foam installed this week."

so radiant barrier on roofline, where is the foam being installed?
is yours the house in another thread, with rb roofline
and foam on attic floor???

Yes... you got the right gal. I know some disagree, but we just could not justify conditioning twice the space by foaming the rafters. If you could see this attic space! I also think we will never finish off the area up there. Any last minute thoughts before they start insulation install in the am?

I can't knock radiant barriers! I have
one myself. but I put my ducts in fur downs
inside the house.

I wondered if you have recessed lights & how
the foam company would deal with them.
making boxes out of sheetrock comes to mind..
we have even used foam ice chests. with either,
maintaining a 4" space from can light to sides
& top of box is necessary.

it may not apply to you, if you don't have
recessed lights!

I'd make a pass in the attic to make sure that
bath fans have back draft dampers & that they
are vented properly.
will they foam next to the bath fans??

where are your ducts? if they are in the
attic, make sure they seal well around supply
boxes.

oh and next to last, but not least...measure depth of
insulation in several spots before they leave.
I use a wire with inches marked off & a can of
spray paint to mark low spots.

if you have changes in ceiling heights..these
are called knee walls in the attic. you want to
make sure they are well sealed also.

Let us know how it goes!

best of luck

maybe I missed it...but it seems all of the talk and numbers are over closed cell. why not open cell? I know the pros and cons of each obviously, but recently I have gone to spec'ing open cell for roofs if space allows per r value. Like others mentioned, I always spec code min. values, no matter the insulation type. I catch a lot of heat from contractors because of...which has never made sense to me since they are making more money because of it....
I also never spec inches of product, rather MIN. R VALUE required. Foams vary slightly from brand to brand. This allows bidding to be more even and open to various brands of foams. It also holds all contractors to the same r value standard.

My personal house currently under construction is getting the sloped ceilings foamed in a week or 2. The sloped ceiling is made from 14" I joist and filled with open cell so I could still hit code min. r49 in zone 6. (I do not pay attention to the cathedral ceiling exception). Its only a small area of the roof (about 600 sqft). The remaining 1200 sqft is vented truss space/flat ceilings.

The vent baffles will be installed and foamed in place over the top of the wall to seal that connection. After the ceiling gyp is installed, an attic seal will be shot over tops of the wall plates/gyp connections and electrical boxes to seal the attic plane. r60 will then be blown on top.

I would recommend considering attic seals vs full thickness or even several inches of foam in the rafters. This treats my drywall/ceiling plane as the air barrier, and the foam is only used to seal the cracks. No can lights are in the home.

energy rater-
the details I have come up with with local foamers for cans, bath vents, etc is simple. They take a piece of r19 batt and wrap around the insulated, air tight can. They then foam startig at the gyp, up and over the batt. THis creats a cocoon around the can and keeps a space from direct foam contact. Same thing is done with bath vents. this also allows 6" or so in each direction to move, adjust, replace, etc the fixtures if needed and they are not "foamed shut". Building boxes is what I used to call for, but this is faster and pretty easy to pull off.

Lzerarc, I have heard of companies doing just
what you describe with recessed cans & bath fans.
it has been a while, because for the most
part we are foaming the roofline.
if ducts are in the conditioned living space
then attic floor is foamed.

here,it is uncommon for ducts not to be in attic..sadly.
epic fail on designer/arch imo

most of the thread is about open cell.
as per post #4 in which OP specifies foam type.

I have the same problem in getting foam companies
to install 8-9" of open cell sf insulation.
on a few occasions I can 'make' them install
this depth, but it causes bad feelings with the
company & sometimes my client.
the line from the foam company is that it raises
cost of install.

this tatic to me bears explaining.
when adding to depth of foam insulation,
it does NOT double the cost.
to break it down, the homeowner pays for
the foam company's set up. getting truck
on site, heating the product, setting up the
hoses to spray and prep work.
once this is done, the cost to add more product
is only product cost.
it isn't much more time, as spray foam install is fast.
set up has been paid for. to go from 3" to 6" or
9", the homeowner only pays for the extra product,
and minimal time to install.

this was the discussion in going from 3" to 6".
foam co would say...double the cost, homeowner
would balk. once the homeowner understood that they
would be paying for setup etc no matter if 3",6"
or more was installed, then we could start the
conversation about true costs to insulate more.

as for flash & batt, it just isn't happening here.
if the foam company is on sit, they aren't there
to just spray 1", when they could be on another
job spraying more & making more money. if the
foam co can't convince the homeowner to install
more foam...they simply do not take the job.

now maybe if they worked for a builder & had several
houses to do with flash/batt. but in my area,
the foam salesmen have flat out told me that
they won't waste their time doing flash/batt.
IMO it isn't a bad way to go...just getting a
company to make minimal money when they could
be making more for the same amount of time.

I'm 100% with you on no recessed lights.
this is a trend I keep waiting for its death!
personally why Insulation Contact (not IC Air Tight)
are even still produced is something I don't understand.

even when recessed lights are to be installed
under porches, I have homeowner/electrician purchase
only ICAT. otherwise the boxes get mixed
up during install & types are mixed in the house.
upcharge isn't much per case to go IC to ICAT.

Guess what!

a newly revised Feb 1, 2013 ICC ESR report for icynene spray foam and the thickness is listed as minimums and much more allowed and definitely more than my quotes that will give "nominal" and average thickness. Sigh!

http://www.icc-es.org/reports/pdf_files/ICC-ES/ESR-1826.pdf

What do you all think.
Thanks

4.4.2.2.
the insulation may be left exposed to the attic
without a prescriptive ignition barrier or
intumescent coating.

4.3.1 has info regarding this also.

I think this answers a lot of questions about
unvented attics with foam on roofline & fire rated
barriers.
I'll look it over more later.

thanks for the link!