We went with 2x6 exterior walls because they insulate better than 2x4 - we're in Pennsylvania though - winters are critical! We used R19 batt insulation by Certainteed.

2x6 walls mean you have 6" to fit insulation in rather than 4" so your house will be better insulated. Winters are also more of a problem where I live rather than summers but it works the same. You will need less A/C with more insulation. How does it increase HVAC requirements/costs?
If you want to stay cool also consider large overhangs and a light colored roof.

We went with 2x4s although we wanted 2x6s, for the same reason as che1sea.

The architect who drew the stock plans pointed out that all the windows/exterior doors casings would have to be redrawn, which had we gone with blown cellulose would have done.

The reason we stayed with 2x4s was that we finally decided to insulate the walls with closed cell foam and 4" is as deep as they fill, so it would be overkill.

With energy costs rising, we feel it's worth the initial high cost.(We hope anyway)!

We are building 2979sqft living space in SW Louisiana. It will be costing $12,500 to insulate, with unvented attic.

We are building 6500 sq ft. We've been advised that we should go with 2x4 with blown in cellulose. They are claiming that I will never recoup the cost of the additional cost of the foam and then other modifications that I will have to make such as a higher end HVAC.

They told us that too but they were usually short sighted. Our monthly electric bills are $75-$100 cheaper than a similar styled and sized home built just before ours and we are home all day so the AC runs. Also, the bids we had with cellulose were only about $2000 cheaper than the foam. It was a no brainer. Also consider that you can use your storage space without ruining the items stored because the attic/storage space is cooler. I guess it depends on your bids but I would look at multiple bids on insulation and AC before I made a decision. There is a house in our neighborhood that is a bit larger than you are building and they have 3 AC units. Don't want to see their bills!

Also, I thought you had a builder in the fall. Did something change? Have you started yet?

omeyers,
We are in Illinois.
We build a 1800 s.f. home for us about 6 years ago and used Icynene (foam insulation) on 2x4 walls. We loved it! I think the savings were not that good in this size of homes, they say that homes bigger thn 3,000 s.f. get better savings. I liked the fact of knowing there was no fiber glass flying around (usually the insulation they pace at the rim joist is exposed)
We sold the house last year pretty fast (1 month)and the insulation was a good factor.

Last year we built another house for us, 2,500 s.f. and used 2x6 and blow in Spider Insulation with R-23 (DH just wanted to try something different). I loved the fact that it was a formaldehyde free insulation.
DH wanted to see what people thought about the house (he is retiring in about 6 years and we will move down south)and we had an open house prior the closing - we received an offer the same day and decided to sell the house :( (we paid $5,000 and the attic was R-49)
Now we need a house for us and getting ready to start building.

The thing is, the foam insulation is just R-13 (officially)
and they claim it performs a lot higher than that because it seals better (and it's true). DH wanted to try it again and the bid was 13,000. We supposely save in wood studs, vapor barrier and window extensions but still it is about 40% higher than the SPIDER.
The way I see it, when promoting the house to sell it, isn't it better to say that the house is 2x6 with R-23 formaldehyde free than saying we have a 2x4 with R-13 -but very marbelous insulation?
oh and the foam insulation people say that incresing the stud to 2x6 does not help and the price will be double!!!

What do you guys think? we are still deciding.

see the attached link, it healps to know what R-value to use depending on location

Here is a link that might be useful: Energy Efficiency

omeyers,

To comment on your question this is what I think:

Using R-19 is GREAT (in your state), according to the US Department of Energy (see link).

If you build 2x6 you will have a better constructed house and you will not need to blow in the insulation since there are a lot of good insulation for 2x6 walls that are R-19 and you just place it. If you decide to go with the blow in insulation you will get R-23 that could be considered Fantastic (or as good as it gets - I guess) in your area (the energy efficiency link do not even consider it), and you will spend HALF of the money.
You could use the money difference y better windows.

Good luck with your choice.

We went with 2x6....actually, I don't think 2x4 is even an option here (in PA). Our insulation is R-19 also (which I believe is also standard).

We went with 2x6. We needed R-21 for code. Another great thing about 2x6 over 2x4 is in taller walls 2x6's will have a tendency to twist a lot less.

omeyers

If you are just talking about the benefits of 2x4 vs 2x6 for insulation, I think you should be comparing 2x6 studs with cellulose vs. 2x4 studs with foam. The reason is that if you choose 2x6 studs with foam , they most likely won't fill the cavity completely because you only need a few inches of foam to get a very high insulation barrier. However, they will fill a 2x6 cavity completely with cellulose because of the way it is applied and because it makes sense to do so.

There are other reasons to use 2x6 lumber such as increased load bearing strength as well as straighter boards. But there are increase costs too - not just for the wood - but windows and doors are more expensive due to the thicker walls. In my opinion, the 2x6's are worth the extra cost - but you need to factor all of that in.

One other thing to consider is that if you go with cellulose, it is likely that you will still need foam in some spots in the house where the cellulose won't stick well (areas like the joist cavities above the first floor ceiling) or in areas such as living spaces above a garage where you may need foam to provide the tightest seal you can.

I have 2x6 studs with cellulose and am very happy with the wall strangth and the overall energy efficiency of the house. I had an extra 2 inches of cellulose blown into the attic to bring that up to an R38 level instead of the minimum code which is typically R30. We also used foam in the joist cavities in the basement and first floor, as well as in angled corners where it was impossible to blow in cellulose.

Lets see if I've digested this right:

with 2x6 you get:
that good feeling of having a stronger house
more fiberglass insulation
more expense

with 2x4 you get:
big savings while framing
possibly more efficient but less eco-friendly blown insulation
jibes from father in law about inferior lumber
more money to spend on efficient windows and attic insulation

Does that cover it? I still can't decide.
Sure sounds good to have that bigger lumber framing your house....

Most building codes allow 24" centers for 2X6's, whereas 2X4's require 16" spacing. 2X6's cost more, but you need less of them. More importantly, you have less thermal bridging, which is heat/cold being transferred through the framing elements. I've seem infrared images of houses, and you can see every stud due to this. I wish I could find hard data on how much effect thermal bridging actually has on heat loss. I would go 2X6 unless it won't fit in a tight budget. We hope to use metal SIP's, which have virtually no thermal bridging, and are made with 6" of solid foam, but it's looking like it will be much too expensive. Bear in mind that if you spend a huge amount of money for super insulation, you'll probably never recoup the outlay with fuel savings, but it will probably greatly enhance resale value, and of course, it's 'greener', if that matters to you. If I build with SIP's, it will increase the cost of the house at least $20K, which would buy a lot of heating oil! IMHO, people would be better served by building (much) smaller homes, and learning to live with a little more swing in temperature. We set our thermostat at 60 for heat, and 80 for A/C. I know people who keep their homes at 77 or so year-round. (Steps down off soap box).

I'm with you on the smaller homes. We plan a 2100 sq foot house; I was pushing for around 1800, but had to bend for marital bliss.
I don't understand how people afford the energy costs, taxes, insurance, etc of these giant homes.
Obviously, when it comes down to it, I'll check the numbers between using 2x4's and 2x6's. In the end, I'll rely on that and the advice of my main builder, a guy I've known since childhood, and have trust in.

A better way to make your decision is to consider the Department of Energy recommendations on cost effective Total R Value for your climate zone. (See Link.)

Then consider what way you can achieve those recommendations at the lowest cost in your particular situation.

If you have 10' ceilings I would use 2x6s in any case. It twists less--fewer screw pops--and there's less wastage (discards and replacements) during construction.

Here is a link that might be useful: Total R Value Recommendations

All building codes allow 2x4's @ 24" o.c. There is no structural advantage using 2x6's unless your house is over 3 stories.

I don't know of any increased HVAC costs for using expanding foam insulation. I have found the opposite to be true. The cost comparisons are difficult because no one knows how fast the cost of energy will rise or how long you will live in the house.