Get real world estimates from outfits in your area. Pricing on most any material varies by region.

It cost me right at 5k for the walls on a 2400 sq ft house.
Walls were 9 ft and that included rim joists.This was poly foam at 3 inches thick.I also used one inch sheeting on the outside for a total of 4 inches of foam. We used blown in fiberglass in the attic 15 inches thick. So far heat bills have been not too bad.
http://ncfi.com/

Get quotes locally, but I'd suggest looking into building with 2x6 walls, using 1" XPS sheathing instead of OSB, with plywood corner bracing and 1/2" XPS over that. Tape all the seams, foam protrusions and caulk framing gaps, then use a blown cellulose product. Your house will be almost as tight as a spray foam house, but with less thermal bridging and a lower cost for the whole package.

That said, I paid about $0.85 a board ft for closed cell foam in Charlotte, NC.

Our fiberglass quote (R21 walls, R38 ceilings, many interior walls) was less than $6k. Our foam quote was over $18k and didn't include any interior walls. So, 3 times higher. Here at least. I have an independent energy star consultant run and numbers and the payback was about 20 years.

Its about $165 per sq ft here.
Sue glad to read the years of payback. I found the same
numbers have held true for several years now.
dbpeck..we have a company locally that does a blown rock
wool in the walls. In 2x4 wall he consistantly gets R-15
and with foil to exterior of wall and well sealed,
along with an air tight drywall interior we regularly achieve .25 air changes per hours in these homes.

The hvac system tonnage is reduced and these homes achieve
a good ROI and energy savings.

I do recommend foam in floor of homes on piers thats a no brainer
For people dead set on using foam, I generally try to present to them to these simple facts, cost and payback, and encourage them to do the walls as described above, and foam the roofline or attic floor.

just what I have found in the past audits!

best of luck OP.

Figure the cost of spray foam at 3-5X more than the cost of fiberglass insulation.

Remember that not only does spray foam cost more, spray foam must be thermally isolated with drywall or similar products to keep it from igniting in a fire.

This drives up the cost for most spray foams vs fiberglass considerably and makes spray foams not even a consideration in most cases.

While there is some savings in energy costs by using spray foam (mostly because of their air barrier qualities), you can still get the same result using housewrap and fiberglass for 5X less cost than foams.

Because of the cost, foam insulation is rarely the best choice for insulation and foam can take decades to pay for itself with little (if any) return on investment. VERY POOR return-on-investment with any spray foam insulation in any climate...

...Especially in these troubled housing times when one cannot even count on their home appreciating in value despite whatever 'upgrades' they consider.

Don't be fooled. Avoid spray foams.

I wanted to do the XPS sheathing (since we bricked the whole house) and then do 2x6 walls with blown or fiberglass batts, but I ran into so much resistance from every framer on even doing 2x6 walls ("You're overbuilding the house, it will cost sooo much more to use 2x6s") that I didn't think I could find one willing to not use OSB and use the XPS sheathing instead.

So I used the foam, and spent a lot more money than others to achieve the same airtight home.

I think now, I could've been forceful enough with contractors to get it done, but 7 months ago, I wasn't as battle tested as I am now.

Spray Foam is a good product, but not cost effective.

We have soy spray foam product in the walls and under the house. We love it and think it was worth every penny.

I'm afraid spray foam on the underside of roof decks will come back to bite a lot of people down the road. Despite claims of 'open cell', I have yet to see a sample that allows water to pass through. All roofs eventually leak and the ones with spray foam on the underside are going to trap the leak water between the wood deck and the foam where it will go about it's dirty work rotting the deck and possibly even the trusses before there is any indication of trouble. Probably be best to only use the foam with a very leak resistant roofing material like standing seam metal roof.

Spray foam insulation in Houston, Texas should run between $0.35 and $0.40 per board foot, or between $1.20 and $1.60 per square foot of 2x4 wall space.

Where do you live?

You can also check out http://foaminsulationforum.blogspot.com
for foam insulation-focused discussions.

Here is a link that might be useful: Foam Insulation Forum

I'll go check out the forum later. So, is 1.20 open cell costs and 1.60 closed cell costs foam guy?

I've learned that this foam or not foam discussion is
usually like the powered attic fan vs no power attic fans.
People who understand how houses work or should work
vs people who do not understand.

For years I've promoted walls with foil/foam to exterior
with conventional insulation, and air tight drywall approach. It works for much less of the cost. Achieving
.25 air changes per hour is easily done when air sealing details are completed.

That said, foam works great in houses on piers to foam
the floors. Comparing the air seal, lessened labor to install the upcharge is worth the time & labor savings.

The problem that I see still is the downsizing of hvac
in homes that achieve both tightness and efficiency.
I guess it bothers me that so few contractors put together the whole package. Better windows, better walls, tighter house, smaller havc..homes should be built to work as a system, and not one overpriced product with others of a lesser quality. All these upgrades should include a hvac
sizing (Manuel J) that actually calculates these upgrades
& their benefits and sizes the hvac system accordingly.
Whole house approaches are the best.

I did the foam insulation in my exterior walls and in the rafters. The cost was a premium of about $7k over fiberglas insulation.

I have a non-vented house like they do in the midwest. I'm in Memphis.

My house is 4800 SF and my utility bills run around $200 per month.

I did the ROI on the foam vs fiberglas insulation.

I have several friends who went the fiberglas route and their bills are running anywhere from $450 - $650 per month and their houses are smaller. (4,200 - 4,500 sf)

I don't know who did the ROI for the guy that said the payback was 20 years, all I know is that the payback for me will be around 3 years.

I find it interesting that people are concerned about thermal bridging when talking about foam insulation. Correct me if I'm wrong, but isn't thermal bridging also a concern with fiberglass batt insulation in the walls?

The R value of wood is pretty good and since the studs are on end, the temperature sees 3 1/2" of wood that it has to go through to get into the house.

Thermal bridging is so minimal that it probably isn't a concern unless you are in Alaska.

I have a 2400 square foot home, ten foot side walls, cathedral ceilings. Just got a quote for one inch in all exterior wall, 3 inches in kitchen and bathroom, (because of the way that these areas extend over the basement foundation) and all cathedrals filled, 2789.00 very excited about this bid. will still have to blow in but should make a pretty air tight home.

I live in Austin, TX and I built my house last year and used spray foam insulation. Off the top of my head I don't remember the bids I got for fiberglass, but the foam for my whole house was about $6,500 and it was just over double the fiberglass price. My house is about 2,300 sq ft with some cathedral ceiling and my energy bills are about 30-35% lower than my neighbors for homes of similar size.

It's funny that somebody mentioned thermal bridging. The contractor I hired (Thermalshield Foam Insulation) explained thermal bridging to me and actually demonstrated what it was on a section of my roof. I have 2x6 rafters and the spray guy was covering the rafters with the foam. When I asked why (because most of the pictures and videos I saw didn't show that), the contractor said that a lot of heat actually transfers through the wood on a roof and that covering the rafters with even a thin layer of foam locks out of the the thermal bridging. But he said in walls, unless you put a foam board on the outside, there's not much you can do.

Spray foam is a great product. I promote spray foam over other insulation but accordingly to application.
There is alot of benifits that are not mentioned with foam that other insulation does not do.
I use foam to control rodents and insects- for whatever reason they do not like it and stay out of it and do not borrow thru it.
As with fiberglass and cellose insulations insects and rodents like to live in it and make tunnels all thru it making air gaps. main loss of BTU's and air filtration.

Also the bonding of spray foam to walls-that makes a tighter building with less BTU loss, air infiltration and more strength in building[up to 50% more]
so over all, pay back should be between 3-5 years.

Remember agood spray foam will reduce the size needed for your air and heating units and costs.
It does costs more but a good job pays for itself and never have to worry about what is lurking in your walls.

You only pay for insulating once but your billing just keeps on coming!How much you pay is up to you.
There is some poor workmanship done which will reduce the effect of any insulation job. Any more??
Randal

I just priced out 3" of Spray On Foam. The price installed is $2.60/sq. ft. Everyone always talks about saving and paying back through your energy bill savings. Here is the math for my site:

200' of wall 12' tall = 2,400 sq. ft. @ $2.60/sq. ft.
This amounts to $6,240 for 3" spray on foam with an R value of approximately 20-21.

2X4 inch walls with 16" Bats has R of 11. Cost for insulation is $0.38/sq. ft for material plus installation, which you can do yourself. Cost for same area with bats is $912.00.

Next analyzed comparison of energy cost savings to go from an R-11 to an R-21. The cost savings was around $140 annually.

Cost $5,328 more for spray on, but that includes installation. It would take at least 40 years to recover the cost. It just does not pencil out yet.

I do believe it is a good product as it will seal very well. For my application, I am going with the old fashioned pink stuff. You need to see what works best for your situation. Maybe it is far more in my area due to limited competition.

You have to look at new home with walls open and those old homes or homes sheetrocked or plaster and laft are you going to tear down that to make it air tight now add that cost plus blow in insulation breakdown if you don't seal correctly compared too where there is one install of spray foam or injected foam plus the holes you put in your walls and wholes for electrical wires and outlets add to leaks with batted where spary or injected foam comform around it. Things that should be consider in cost eval. And mold and mildrew resistant and other benefits

It is important to note that actual real world tests have shown that actual "as installed" R- values of fiberglass batt insulation are in reality somewhere around 1/3 to 1/2 of their commonly understood/advertised to be, and "rated", R -values. That plus, the "air-tightness" of a structure is quite dependent on the effort put into the proper installation of moisture/vapor/air intrusion retarders. If you want to use batts, you would be best served by building with 2 X 4's filled with batts, or even better, rice hulls, with two 1" layers of foam board on the exterior.
That's right, rice hulls, they don't rot or burn nor serve as food or nesting materials.
But whatever one choses for "infill", real world research suggests that current maximum ROI/payback values are obtained with two 1" layers of foam board running in opposite directions on the exterior side of the stud walls, and the most effective ROI for using batt insulation is currently the foam on top of 4" of batts.
Then again, if you figure ROI based soley on current costs of electricity/fuel,and NOT on life cycle costing, your actual long term casts will be greater than you expect.
Check it out...

Handyman, I don't see where you get only 140$ savings annually. Around here in East Texas I know during the summers a friend of mine saves about 150 a month on a 3K sf home thats open celled at the roof and open ceiling.

Not to mention he went with a highly energy efficient 3 ton unit instead of a larger 4+ ton or two 2-3 tons. That probably saves another 20% on electricity nobody has mentioned. Because not only does the unit not have to run as long because of lost heating/cooling, you can trade up to a much more efficient unit. Some are the difference between about 1500 watts. The lower units run a bit more continuous but I think energy draw wise it works out better, think of turning a computer on and off constantly. Coupling with a HRV ventilation system would make it even more efficient.

I think this would almost make the realm of PV solar panels doable, as you could get a 3k SF home roughly down to 50-75% with some leds of an average comparable home meaning you'd only need about a 5000 watt system at roughly 9K to have a zero utility bill. If your bill "being very energy efficient" averaged 100 a month thats only 7.5 years before your solar power would pay for itself. And lets get it straight a lot more people like myself could pay more upfront and shell out 9 thousand for a solar PV system vs 18-25 for a comparable system due to having a much lower HVAC electrical cost and better home insulation.

Couple this with rising electricity costs, more energy efficient cars, like the new ford fusion electric or sonnata, and led light bulbs and for roughly 20k "EVERYTHING mentioned in most of the above, insualtion an extra 6k, 10 Solar, 1k leds, 3 extras like sun following panels" you could be off the grid in 7.5 years and getting money back from the electric company, "not to mention the savings of not spending between 1-2 a year in gas, and 1-4 in power bills"... I would love to hit that x mark in 10 years knowing I was saving about 5+ a year in power and gas... I would be taking so many more trips in the car not worrying about pushing my 13mpg sequoia around.

"well at least thats our game plan on our build".

Note I didn't include the cost of a 40k Fusion gas/electric hybrid nor the gas electric sonnata. with one of those not having to pay 3 a year in gas nor 500-1000 annually to charge it would net roughly 4k annually for most commuters.

That would mean a 40K car would take 10 years to pay itself off entirely just in gas alone and charge alone :)

Total savings annually would be rougly 100 "monthly bill" x12 =1200 + 3K gas and 1k charge would be 5,200 and zero bills :)

Then all you'd need is a well, heirloom seed, and septic.

I saw a famly do this in hawaii, I think it cost him roughly 40 wo the car for what I think was around a 5K SF home about 10 years ago.

I would also like to point out AIR EXCHANGE. My sister in law is an architect. She said look up
http://www.venmarces.com/
They make ERV or energy recovery ventilators for well built homes. While they aren't cheap they can make your AC even more efficent while reducing energy costs and making your home more comfortable.

A good note, is to pick a north facing lot in the south and a south facing lot in the north so you get sun to heat and can put your windows on the north side in the south :)

I also think evergreens on the north side of the home in the north and shade trees for midday and afternoon in the south drastically reduce energy cost and make the outdoors more enjoyable.

I perfer whole house dehumidification systems
with fresh air intake. for my personal existing home.

if I could start fresh..1" foam sheathing to exterior
of walls...sill seal..crazy air sealing details.
ductwork in side living space, air tight
barrier between living space & attic.
foam under floors for house on piers.
aside from the exterior sheathing, sill seal
under sole plates, I've retrofitted my
house with every thing listed above..
foam for floors is scheduled..but not yet
installed.
dropped my Kwh by 1000. bills are half of
what they used to be.

if you know how and where to seal it can be
done for a very reasonable cost. being able
to blower door test my house has helped me to
achieve this.

best of luck.

My $0.02 worth. We are mid-atlantic region, greater metro DC area. We completed a custom home late 2011, which included blown foam all exterior walls above ground + roof of course. Our cost above fiberglass was an extra 17k. Not sure cu ft or board foot or however you measure, but the floor square footage above ground is about 3350 on two levels (1.7 story).

We have not crunched the numbers, but DO DEFINITELY feel a tremendous difference having the foam. When we allow the house to cool naturally in evenings during shoulder seasons, that has an almost adobe effect, leaving the home cooler all during the day the next day. the house does not heat up as quickly, and holds both heat and coolness wonderfully. We use far less AC than (our rental) last house with no foam, and less heat for same reason. The house just seems more temperature consistent. We would absolutely recommend, and do it again ourselves.

Good luck - hope that helps!

I wonder if extreme air tightness is worth the trouble.
A house needs to be ventilated some way or another. So for every sealed crack the HVAC needs to work harder. Cold drafts are not comfortable but does it really increase heating costs?
Obviously I'm not talking about fist sized holes in the wall. Just those invisible imperfections

build tight ventilate right.
yes it is worth the 'trouble'.

some of the worst infiltration areas are 'invisible'
covered by grills, trim kits & hidden from sight.

recessed lights, oversized cuts at supply boxes,
unsealed return air, oversized cuts for bath vent fans.

house has to breathe is contractor speak for
not understanding that controlling where fresh
air comes from is important.
dedicating a fresh air intake is much healthier,
efficient & smarter than leakage behind crown
moldings from hot attic.
people invest in tstats that can be controlled
by iphone...but sealing ducts is much more
efficient use of time & money.
air/duct sealing isn't rocket science, and has
a fast payback with instant results.

heat loss through ceilings has a huge effect
on heating costs.

starting a new thread may get you more
results than piggybacking an old one.

best of luck.

The house itself does not need to breathe. Most homes are insulated with fiberglass or cellulose, and it is actually the insulation that needs to breathe in order to dry the condensation that forms where the hot and cold temperatures meet within the walls. In actuality, 25-40% of the energy used to heat or cool a home is lost due to air leakage through crevices, rim joists, outlets, window frames, heating ducts and the like. For optimal energy efficiency, closed cell spray foam is the best choice. Closed cell foam stops air flow, moisture penetration, and provides a high R-value. You should incorporate a dedicated fresh air supply into your HVAC system, after creating the building envelope with closed cell foam, to be sure your home is 'breathing' for the right reasons.

Linda - Foam It Green
www.sprayfoamkit.com/home-owners/residential-applications

Linda, open cell insulation stops air flow as effectively as closed cell. I realize that open cell can allow moisture penetration (leaving aside the question of whether it actually does if the interior is finished and sealed properly).

As far as cost, open cell insulation is often a very economical option that provides most of the benefits of closed cell insulation.

The installer is just applying closed cell foam as I type this and I have a 4' crawlspace and he is charging me $1.50 a sf for 3" on the rim and 1" on the walls.

Here is a link that might be useful: Foam Video

Open cell foam does stop most of the airflow, and it costs a bit less than closed cell foam; however, it is spongy and can retain moisture. There are at least two ways that moisture can get inside the wall. Water vapor can migrate into the wall, which a properly-installed vapor barrier should prevent. The second way moisture can be present in the wall is via condensation. The warm air from inside the home will meet the cold air from the outside somewhere within the wall cavity. Where the two temperatures meet, moisture is created. When one uses only open cell foam, the condensation will form within the foam, but won't be able to dry out because the airflow has been cut off, potentially leaving wet insulation which could lead to unhealthy mold. Building science offers that, if a home is heated during the winter months, the best way to prevent condensation from forming in a wall is to be sure that 50% of the R-value in the wall is closed cell foam. The remainder of the cavity can be filled with open cell foam, fiberglass, or any other insulation. Because the cells of closed cell foam are solid, they can't hold moisture. By following the 50% rule in external walls, the hot and cold temperatures will be forced to meet within the closed cell foam, condensation will be neutralized, and you'll have a wall that is air-tight and moisture-free, making the use of closed cell foam as the first line of defense against Mother Nature well worth the investment.

Linda - Foam It Green
http://www.sprayfoamkit.com/videos-a-how-tos/insulating-a-2x6-wall

Check out RetroFoam of Austin and Houston Texas. RetroFoam is Non-Toxic, Retards mold & mildew growth, Environmentally Friendly, Fire Retardant, Stops Heat & Air Loss, Seals Cracks/Crevices, Nooks and Crannies that rob you of your heat in the winter and air conditioning in the summer.

Sound Reducing, Pest Resistant, No Messy Cleanup. RetroFoam is an inject able foam that we inject into you walls from the outside saving you between 30% to 50% on your utility bill.

Here is a link that might be useful: RetroFoam Of Austin and Houston,Texas

Spray insulation costs vary depending on the type of spray foam and the exact product used. For a guide on Icynene costs, a very effective spray foam, there is a very useful blog that can be found here: https://www.massfoamsystems.co.uk/insulation-faqs/how-much-does-spray-foam-insulation-cost/