Don't forget that it's not really an apples to apples comparison- while spray foam is more expensive, in our area, you will typically see a considerable reduction in HVAC tonnage needed, as well as other savings. Spray foam still ends up more expensive than traditional pink stuff, but I know that we will end up using it for the long term savings associated with it.

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

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.

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.

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.

Where do you live?

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

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 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.

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.

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

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.

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.

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.