yes to both.
as per reply on building forum.

best of luck.

Where do you live and hot does it get in the summer? If you are not going to use the AC very much then it may not be worth spending the additional money on a more efficient AC. In general a SEER rating of 15-16 is the sweet spot for most parts of the country. You should find out which brand and model the builder is specified. Most likely it is a builder grade which should be avoided if possible.

If you don't upgrade the walls will they be R-11 or R-13? Is the added insulation rigid foam insulation over the sheathing or something else?

I hope you have more than one AC and furnace planned for this house. It will be very difficult to keep a consistent temperature with only one system.

mike home: We're in central SC so we use the AC quite a bit. The builder specified a Carrier SEER 13. There are two separate units for the house. The equipment for the upstairs will be in the attic and the equipment for the first floor will be in a crawlspace. I'm researching sealed crawlspaces now.

I believe that the contract is for R-13 unless we upgrade to R-15 for $485.

Thanks for the help!

Lex - r-15 is a nice upgrade but hardly major.

I live in central NC and did r-13 wall despite other upgrades. We have a similar size house - 5300 but 1300 in walk out basement so it probably heats like a 4500 sqft house. Our NG bills this year were about $300 and I suspect R-15 would save about $20 a year. Likely you are warmer but you may like your house warmer than ours. There is far less savings on a/c - less than $5 a year I suspect.

I don't know if you have posted it before but what are you motivations? Strictly dollar return over 10 years? Best environmental practice? Dollars over 20 years? All of that matters (obviously) in how much to upgrade. Be careful following the advice of those that live in harsher climates.

My 2012 energy bill - $150 in NG, $1300 in electricity. Last winter was an anomaly - this year is already $200 in NG.

David,

My motivation is roi over 10 years and comfort, especially for the second floor because of the open storage space behind the bedrooms. We had some crazy high ac bills in our last house (2700 sq ft), I suspect because of an inefficient unit (which died after inspection but 4 weeks before we closed) and leaky duct work in the incredibly hot attic. There was only a room over the garage and it was seldom used so that thermostat was keep high in the summer and low in the winter.

I think if you foam the attic, you solve all the problems with your last house.

I built recently at the NC coast and we had 2 two ton heat pumps. It cost $1000 to upgrade both to seer 15. That also gave a better warranty. I think seer 15 is nearly always worth it in our climate. Now foaming the attic makes the payoff for seer 15 longer but still probably reasonable. Now if you told me you were building extremely tight and really minimize the East and West windows and shade the south ones, then seer 15 might not be worth it.

That is why these questions are so hard to answer. Everything is ... it depends. But a decent generality is that if you have to have East and West windows in SC, seer 15 is worth it. One could build a house with a $100 a year a/c requirement in SC for seer 13 and then it wouldn't be worth upgrading to seer 15.

I know you've decided to foam the roof deck but I always have to be the skeptic. My electric bills last year were $350 total for the 3 hot months. I am absolutely sure that foaming the attic would have saved some money. I am pretty sure it would be less than $50 a year. While we a/c longer than 3 months, those bills also include everything else electric. So almost 1/2 those bills are not a/c so I think they are a pretty good estimate of the total annual a/c use.

Foam salesman will of course differ in their estimates. But the foam mostly only helps the upstairs system and my house (and probably your house) has 2/3 of the a/c use downstairs. Even if the foam saved 40% of my upstairs bill - it is about $50. Now foam also saves in winter but is often justified in a/c use.

Comfort upstairs would be helped by rigid foam on the knee walls. This is a far greater ROI although honestly it still probably exceeds 10 years. I think you might be overkilling it to overcompensate for your last uncomfortable house.

yes, get the 15-seer unit. If available, look into a variable speed blower. This will help with humidity removal.