Also, I forgot to mention in my original post that the bedroom over the garage has a window facing west and another window facing south. Thanks!

We finished our build a couple of months ago and have a bonus room above the garage and I seriously considered foaming it as you describe and we instead used fiberglass. We have 1 zone HVAC in our home and the bonus room stays about 5 degrees different from the rest of our home.
With you having the upper level on it's own HVAC it should be able to keep the temp you desire but might work harder to do so. If I could do it over I would foam our bonus room for a 2k upcharge and not give it a second thought.
We have a crawl space foundation with concrete floor and used closed cell foam on the rim joists and crawl space walls and it made a HUGE difference in maintaining a more constant temperature.

Our master bedroom is over the garage as well, and our builder advised us to sprayfoam the garage ceiling with 1" of foam and then install fiberglass. He said he'd done it in a few homes previously and has seen a big difference in comfort level and draft reduction in homes that had foam.

We had it done, and master bedroom is at the same temperature as other bedrooms upstairs -- we have a separate zone for second floor. Because we only put in 1" of foam, and the garage is relatively small at 500 sq. ft. it only cost us $900 (I'm in NE). Once foamed, we then put in R-38 insulation into the joist cavity in the garage ceiling.

Hope this helps

Closed cell foam on the rims and under the floor above the garage is a no-brainer. On the many homes I've built without this insulation, the rooms were always much colder in winter and much hotter in summer than the rest of the home.

The improvement is not from an improved R Value. It comes from the elimination of air leaks.

The walls, which are much easier to seal, can be adequately insulated with other materials.

No shortage of spf applicators in Idaho.

This post was edited by worthy on Wed, Dec 4, 13 at 10:21

I would definitely go with foam everywhere possible. Just finished new build end of summer and am amazed at how low my electric bills are. We are in about 4000 sf house, all electric, and my entire electric bill in Oct/Nov was $124....and that is with wife having every light on in house "to make it lived in and inviting." We are one unit (heat pump), 3 zones, also have bonus above garage, used foam everywhere. We are in zone 8.

War_Eagle,

I was curious, do you know how much of a premium the 'all foam' option was was over fiberglass bats?

Duplicate, removed

This post was edited by ddr000 on Wed, Dec 4, 13 at 15:33

Not exact number but if I recall it was about a $8000 or so more than traditional insulation. The other factor was the tight city codes on new construction almost made it a requirement. We also saved money only having to have ONE heat pump unit for the entire house. I am also looking into getting "energy star" rates through our power company. Have not had a chance to see what that would require.

No matter how you dissect the numbers, using foam insulation rarely makes any kind of financial or energy savings sense.

First: R-value is R-value. If you can achieve the required R value for your climate zone using fiberglass at 2x less the cost of foam, there is no reason to use foam. You will see energy savings much sooner using fiberglass than foam.

Second: 30 to 45% of energy loss in a structure is caused by air infiltration and exfiltration. This means that most energy los is caused by air leakage. That said, the LEAST cost effective means to solve air-leakage problems is to use foam insulation in wall, floor, and ceiling cavities. One can achieve the same or BETTER insulation energy efficiency without using foam of any type by using fiberglass or cellulose and by sealing drafts with caulk...at about 2 to 3x less the cost.

Third: Foam in cavities does not solve energy loss by 'conduction'. Energy is lost in a structure via radiance, convection, and conduction. Any cavity insulation can address radiance and convection, but only insulation on the exterior walls of the structure can address energy loss and gain by way of convection. Unless one applies rigid foam insulation as part of the exterior wall sheathing to prevent heat loss and gain via studs, then spraying foam alone in stud, floor, and ceiling cavities will be a complete waste of money.
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For my money...and I have been building energy efficient homes for 30 years...the best 'bang' for the insulation 'buck' is to avoid any spray foam product...

Use fiberglass insulation in wall, floor and ceiling cavities...

Add a minimum of 1" rigid foam on the exterior sheathing...

Then air seal all joints and penetrations using caulk.
-----------

This method is the cheapest to install...

The most immediate to return savings on fuel costs...

And the most practical.

I caulked my joints and penetrations, then used open cell foam insulation.

Foam is not the "least" cost effective way to stop air filtration. Cellulose and fiberglass alone is less cost effective over the long haul because they aren't effective.

R-value is only R-value if you can ensure that the product is installed correctly. I would be more confident with foam than I would be with fiberglass as far as installation.

I agree with LawPaw. Its tough to make such sweeping generalizations with any insulation product. It depends on climate, location in the house and installation quality. I think its safe to make a generalization however that FG is rarely installed in a way that achieves its rated R value and that it does not stop air movement like spray foam or dense pack fiberglass FG / cellulose.

I think FG batts could be a good choice if its well installed in mild climates for very well sealed wall cavities. It would not be a good choice for between window jambs and framing or the locations that Worthy mentioned. Even well installed FG batts can have considerable convective looping when temps get extreme.

I also feel FG batts are a very poor choice for attic floor insulation when loose fill products are available. All attic floors should be meticulously air-sealed! Another smart use of spray foam is to seal the attic floor and then pile on the cheaper, loose fill stuff (FG or cellulose) to achieve the recommended R values.

Dense packed FG or cellulose is a much better choice but I find that open cell foam is almost equal to costs in our area and it stops air movement better.

Totally agree that the best place for foam is a continuous rigid sheet on the outside of framing or structure which has a much bigger impact on overall R value. 1-2" of rigid foam could easily have a bigger impact than filling a 2x6 wall cavity with foam.

This assumes that the structure meets the current international building codes for minimum blower door test numbers which is rarely the case, even with current new construction. Its possible that the rigid foam example would perform worse if not air sealed properly. If you want to talk about cost-effective weatherization and energy efficiency then ignore insulation products until you have addressed IECC 2012 blower door test minimums.

Air sealing is more important than insulation. Its also easier to measure thanks to a simple blower door test. Dont assume that spray foam in cavities will result in acceptable blower door test numbers.

Also, caulk can work but not as good as tapes and gaskets. Caulk tends to lose its seal as the building components shrink and expand throughout the seasons. High quality caulk is important and its easily wasted on sealing pointless locations, namely walls.

Dont assume caulk will get you to the blower door test minimums and whatever test results you do achieve assume it will get worse over time.

Thanks everyone for your responses. It has been very helpful!

Foam everything! We built a 5200 sq ft house and ended up having to go with foam due to circumstances along the way, and we are so pleased we did. We have 1.4 air changes per hour, and our energy bill has been $110-180 monthly. That is the same as our old house that was only 2000 sq ft builder grade sealing and insulation. We knew it would provide some cost savings, but WOW, we have been pleasantly surprised!

Thats great Mom23kids, I think 1.5 ACH50 should be the minimum for the entire country! Keep in mind things might be much different with all foam but with the 5 ACH50 that is the current International Minimum for much of the country.

A house at 5 ACH instead of 1.5 is considerably more leaky and would probably represent wasted opportunity with foamed cavity walls.

I like hearing blower door test results given instead of just insulation product details. Its usually much more meaningful!

I see location now... I would profess my own ignorance about Idaho's climate.

Since it hasn't been mentioned - if you have geothermal, the financial incentive for foam is lessened.

The context always needs to be considered - climate, energy cost, heating/cooling source.

i have a 5000 sqft fiberglass home with conventional heatpumps. My annual heating cost this year will be about $300 and my cooling is about $100 per year. You can absolutely never have spray foam "payoff" in this environment. Same with geothermal.

I have a bedroom over a garage with fiberglass - no temp differential whatsoever. All about the HVAC damping and ensuring adequate air flow.

i have a 5000 sqft fiberglass home with conventional heatpumps. My annual heating cost this year will be about $300 and my cooling is about $100 per year. You can absolutely never have spray foam "payoff" in this environment. Same with geothermal.

I'm curious, what type of heating and cooling do you have that you are able to figure out what only those costs are? We have geothermal, and there is no way I can separate the costs.

I've found that rooms over garages are very hard to
condition.

there are a couple of ways to address this,
walls shared with attic space are called kneewalls.
on one side is living space (conditioned) on the
other side attic space (extreme heat/cold).

Southface has great info, check page 5 for
visual of air sealing these walls.

http://www.southface.org/default-interior/Documents/airsealingkeypoints.pdf

with these attic rooms surrounded on 6 sides by
extreme attic temps there are two ways to address them.
one is pictured in link. convnetional insulation in
stud bays, foam sheathing, caulked nailed & taped in
place from top plate to bottom plate of kneewall.

the detail on link also shows how to seal for air movement
under floors of these rooms by using foam board, and placing it between floor joists & sealing air tight.
I personally like to cut the foam board to fit tightly &
air seal with caulk. I see people using great stuff..but
am not a fan of the stuff myself. too much expansion
to get a good seal, and over time, it shrinks.

this is a process that is time consuming & detail
oriented. easiest in new construction prior to any
insulation being added to attic floor.

more cost effective than spray foaming the walls
and between floor area. but labor intensive.
so its a easy fast process (spray foam) or
a longer lower cost higher labor install with foam board.

the benefit of creating an unvented semi conditioned
attic space works great in my hot humid climate where
in the summer attic temps reach 130+ degrees in attics.

as we often put our ducts in the attic, the foam creates
a less extreme temp for less heat gain.

install of foam is crucial. temp mix has to be correct
chemical mix has to be correct, temp of area sprayed
is a factor.
foam has to meet code requirements for your area.
if code says R-30 in attic, enough inches of foam to
reach that R-value has to be installed.
seal has to be complete in an unvented attic.
roof connection to attic floor has to be sealed.
install should be level, no belly in or out between
rafters. faces of rafters should be covered.

none of that average fill stuff which means the spray can be less in some areas & more in others so that it 'averages' out to xx inches. low spots & voids will cause problems.

testing for leakage, marking leakage sites with spray paint and having foam company spray to seal is the way I do my unvented attics.
this all has to be established, in writing prior to any work being done. shop companies carefully.
avoid 'average' fills, Kvalues Qvalues. R-values that is what
code looks for. there is No exception for spray foam.

I'm with Manhatten all the way on spray foam in walls.
long payback when a better option is to put foam sheathing
on exterior of walls & pay close attention to air sealing details. search southface site for air sealing pdfs..great stuff there!

I've never recommended spray foam in walls after
running the numbers for my climate & seeing 25+
year paybacks. and I've done these numbers lots of times,
not just for one house.

(btw hey Manhatten..long time no see)

if you chose to use these details of air sealing for
the tradeoff for this better insulation is SMALLER
hvac system. it only makes sense people if you
weight the benefits of upgrades against each other.

get a load calc for the house including all types
of insulation, window info, air tightness tight not
leaky or average & the size needed lessens.

bigger is not better, it is just lack of correct education
in the trades & misinformatin to the homeowner to sell
them more equipment than needed.
you don't size the system for the 10 days a year
of 50 people in the house & then pay for that the other
355 days.
two stage units, variable speed air handlers are great
things that vary with the needs of the house as they
change. these are good investments.

if you are truly interested in making your house
efficient, hire an energy rater. specific to you
information with inspections, testing & verification.
unbiased working for you.

resnet.us is a good place to start.
new construction, existing homes we do it all.

best of uck.

I foamed sealed all my ceiling sheet rock joints and other areas where I could see light coming up from below before I installed loose Cellulose in my attic. I walked around up there in the dark with the lights on in the house.

Anyway, I forgot to seal a couple of recessed cans. They are covered with a fiberglass bat then cellulose to a 15" depth.

Despite that coverage, I can feel the cold air blowing out of the opening around the rim. Do I now try to seal it from below?

I was amazed that much air pressure could make it through the insulation, but I suppose that cold air is looking for a way down with the hot air looking for a way up.

I now see that air ceiling the attic floor is the most important air seal because that it where you will see significant air pressure pushing the cold air in.

you can take the bulb out & get mfg name &
model number and purchase an air tight insert.
this installs from inside the house by clipping
the spring hooks into the holes in the housing
of the recessed lights.

once these are installed, drop the trim of the
recessed light. often the cuts in the sheetrock
are oversized & covered by the trim piece.
I use a mastic tape to seal these oversized cuts.
hardcast brand 1402 mastic tape. other brands
are not as strong & thick as this brand.

switch to cfl's or led's as the prices on led lights
decrease.

best of luck.

The cans themselves are airtight, I just need to seal the cuts in the ceiling.

I will try the mastic tape, thanks.

All cans are LED retrofit inserts (with trim built in), but they do not air seal to the ceiling.

We don't have any insulation on attic roof..House was build 3 years ago and have lots of problems...What is the best way to insulate?Hot and humid here in Ga..

mousje...
what kind of problems?
why not start your own thread so that
we can help you?

piggybacking threads leads to lots
of confusion in replys.

best of luck from hot humid La.

(and hey to manhattan...nice to see you posting again)
I'd never ever say foam everything seeing payback periods for 'everything'. there are cost effective ways
other than foam that provide same levels of tightness for much less $$.
just what I've learned in my analysis of homes in my decade & a half in the efficiency biz. my non biased, independent, no dog in the fight experience.

Are you limited to siding options with rigid foam on the exterior walls? We are planning on a mix of cedar shake, stone veneer and brick.