My house build is financed mostly by a construction loan. I have calculated $2,380 in the cost of rigid foam $160 in material to bump out window and door openings 2" $80-$160 in Aluminum $300 for labor to get Aluminum fabricated for the bottom $40 in cap nails $300 in 1x4 furring strips $140 in 4" exterior screws screws for fastening furring strips $40 in tape for foam seams which accumulates up to about $3,550. Then additional math included for the loan interest on that money which I figure $400 per 1k @ 5% interest on 15 year note. This brings the grand total of the rigid foam on exterior of my house to $4,750. This does not include the labor or time I will have in installation. I was pretty set on doing this foam install until talking with local builders who told me I was silly and to spend money elsewhere. My brother suggested spending the money on foam instead on ceiling insulation as he said the majority of heat/cool is lost through the ceiling & windows and not the walls. I was hoping I could mull this over a bit more with some of you more familiar with this data and building technique. I must add that I am in Zone 5B along Nebraska/Kansas border. I plan on living here for the next 15-30+ years! I will have my main source of heat be an electric heat pump. I dream of a wood burning stove for additional comfort. No gas furnace in my house due to no gas line near by.

I guess you could do a Manual J on both versions to see what the difference in BTU loss would be. From there, you could figure out how much you would save by using a smaller heat pump. Someone with a lot more knowledge than me could figure out what your cost per BTU would be so you could see what your electrical savings would be. Your numbers work out to $26 a month, and I have no idea if you would save that much.

We moved from a nearly uninsulated home in FL to a very well insulated ICF home in SC. Our summer power bills are 1/3 of what they were in our old house, saving $200/month in the hottest months. That's a really extreme comparison, though. For me, though, the biggest difference is in comfort. If the house is really tight and well insulated, you can set your thermostat lower because the house will be very uniform in temperature rather than having cold spots. We can coast through warmish and coolish days in the shoulder seasons without HVAC because our house maintains temperature so well. I have no idea how much effect (if any) that the ICF plays in that. Lastly, the house is just more comfortable for the reasons stated. It would be worth it to me just for the comfort factor. I don't know how much difference the foam would make over just conventional construction.

From a broader point of view, you can look at the life span of the house, and what the energy impact would be over that period of time.

I'd look at different types of foam and thicknesses (for example, 1.5" EPS). There are thermal bridging and moisture benefits over no foam. Tape and maybe furring strips should be needed either way. But also look at adding more cellulose to the ceiling (because it's inexpensive, not because more heat is lost through the ceiling).

I did forget to add that I ran a heat loss calculation. I came up with saving 2,370 BTU per HOUR at the -4F outside design temp for my climate area. My cost for a KWH is currently about 10 cents. I and I believe everyone feels that energy costs will not go down in the future and they will rise. How much, we don't know. But knowing I save that many BTU per hour, does it equate to a $26/mo saving? If I end up with a 25 or 30 year bank note, that becomes $19 a month but for 30 years...not 15! Apparently 1 KWH is 3412 BTU. So this would mean a savings of 10 cents every hour the system is running, right?

I get 7 cents per hour savings, while it's -4F outside. Less when it's warmer. What you care about is over the entire year.

It seems to me that if your going to try and come up with a cost/benefit analysis based on a 15 or 30 year time span then you will need to make an attempt to predict energy price increases over that same time period. Simple inflation will make your $/hr savings calc. more palatable in say 5 years hence. If your energy prices trend even greater than inflation then even more so. Saying that you only get $0.07/hr savings now and that will be the savings for the next 15-30 years is too simplistic.

I'm struggling with the same kinds of decisions myself. The biggest factor I keep running into is, you'll only have one chance to install the most energy efficient stack-up you can afford once in a new build. After that, it is a not nearly as cost effective pain.

I will say I am at the point I have done heat loss calculations, talked to local builders, and talked to the power company. Of course these people may have narrow minds, the heat loss calculator sheds the most light. I also am at the point in my build and budget that I should start trimming away the fat. I have deemed the exterior foam to not be as the best benefit per dollar on efficiency at this stage. I will be able to benefit from adding foam insulation to the ineterior of my basement - at least the walls that are the walkout side instead of add additional insulation to the already insulated 2x6 main floor walls. I would not be able to afford a nice patio door if I used foam on the outside in terms of budget so I now will hopefully purchase a decent patio door (Everyone is saying Pella, my jaw drops at the prices) but perhaps something in between Pella and Jeld Wen that is insulated and air tight.

This does open a new bit of steps I wasn't considering but am going to strive for....
1.) Taping my OSB Joints with 3M All Weather Flashing
2.) Caulking/Sealing the exterior of the two top plates joint before the last 2' strip of OSB is installed (If I can get it done in time!)
3.) Taping all house wrap seams
4.) Extra detail in attic insulation
5.) Sealing all the points between inside stud wall and exterior OSB

I have also decided if energy rated double or quadruple 20 years from now, I should have the option to replace my siding and install foam then. I don't plan on buying a siding that will last 50 years and still look nice. I expect it to last 20-30 years.

"My brother suggested spending the money on foam instead on ceiling insulation as he said the majority of heat/cool is lost through the ceiling & windows and not the walls."

"I will say I am at the point I have done heat loss calculations..."

Since you ran the heat load numbers you should be able to figure out just how LITTLE the energy savings of going from R49 to R75 in the attic would be. The cost of bumping up attic-R isn't much, but the heat loss of an R49 ceiling is small relative to code-min windows or walls.

Windows are a pretty big fraction, but the ceiling losses are negligible compared to walls at code-min.

It sounds like you've settled on roughly a code-min house (sometimes referred to at "the crummiest house that is legal to build" :-) ) on financial analysis grounds, looking at it strictly as an NPV of future energy costs problem (which is probably only half the true value of adding foam). But a IRC 2012 code-min house built with obsessive attention to air sealing and the continuity & quality of the installation of the insulation and not too much total window area is not going to be an energy pig.

Above-grade foundation walls and band joists can also be a large chunk of the heat load. IRC 2012 code min basement walls would need R15 continuous foam, or R19 in a studwall (which could be a serious mold hazard.) The same performance can be had with air tight R5 foam trapped against the foundation by a 2x4 /R13-15 studwall with only the finish paint on the gypsum as the interior vapor retarder. (Kraft faced batts would be OK, but unfaced is preferable.)

A foam-over 2x6 wall stackup with at least R8 on the exterior is much more resilient than without it, due to the much more moderate peak moisture content of the sheathing. If going code-min with no exterior foam, back-ventilated siding (vinyl siding would qualify, or other types of siding mounted on furring) adds a lot of resilience by improving the drying rate to the exterior. Using a smart vapor retarder like MemBrain (a 2-3 mil nylon sheet) between the finish gypsum and the studs/cavity-insulation detailed as an air barrier will cut the interior side moisture drive by an order of magnitude without appreciably reducing the drying rate toward the interior. Combined, those two measures add a lot of low-cost resilience to the wall stackup. An 800 square foot roll of MemBrain is about $100 at Menards, cheaper in quantity through distributors it's- not a huge material cost. The labor cost of installing it in an air-tight fashion would about double that. The total cost is well under the cost of repair/mold remediation for even one small piece of wall.

" I don't plan on buying a siding that will last 50 years and still look nice. I expect it to last 20-30 years."

How sustainable it that?

How cost effective is that?

If not going with foam (which would definitely be a vapor barrier) on the outside of the wall, you are suggesting an internal vapor barrier that has been argued time and time again? I know it would make things seal up well, but I have heard and seen numerous issues with it collecting moisture or not preventing moisture from drying. I am not sure I understand 100% of your last paragraph about needing back ventilated siding (on furring strips) if I am not going to use foam. Siding is installed directly over house wrap in most cases unless foam is used then the furring strips are required. I don't see any builders install siding on strips around here, but I suppose it would be beneficial as a rainscreen but not necessary in building.

Furring Strips: what are you using for siding? If it's vinyl, the furring isn't necessary since it is self-venting. If it is wood, the furring will help hold the paint on the wall - maybe that's "not necessary" since you can always repaint, but it does decrease maintenance and increase the longevity of the siding. As for expense, you can use 3/8" plaster lath which is less than $.05/LF.

" I don't see any builders install siding on strips around here" And you are sure that all the local builders are using "best practices" in their houses?

Siding will be LP Smart Side or Vinyl.

No natural wood. LP Smart Side is a combination siding I believe.

SmartSide is a manufactured wood product; same applies. And depending on how the wood product holds up, it could very well be more susceptible to moisture long term than solid wood. You can wait to find out, or do it right.

Okay, I'll check into installing lath over my house wrap. Not sure how I will like that in terms of additional holes in the wrap. Maybe I can put sealant around the nails.

So in terms of the house wrap, pro tape the seams or against taping the seams?

the best & easiest method for air sealing is to tape the sheathing & caulk the edges of the wall when the sheathing is being applied. ZIP sheathing is builder-friendly & has a corresponding tape. "House wrap" is easy to put up, but don't count on it for air sealing, but if you choose to use it for that purpose you will need to tape all the seams, figure out how to seal the top, bottom & side edges as well as seal all the siding nails. Practically impossible.

So in essence, taping the sheathing is the practical air sealing method?

yes

As Dana suggests, I'd seriously consider MemBrain on the interior. Unlike polyethylene, it is "smart" and will improve moisture performance and can act as a second side air barrier (which, due to same-side convective flows, is better than just one side). It can also be used on the ceiling (where there is typically no exterior sheathing to tape).

MemBrain is not a vapor barrier- it's a variable permeance vapor retarder, which behaves almost like a vapor barrier (under 1 perm) during the winter when the proximate air is dry (under 40 % RH). But it becomes more vapor open than latex paint when the entrained air in the stud cavity at the membrane rises to 70% RH or higher. This regularly happens when thesheathing is cooking off it's wintertime moisture burden in the warmer daytime temperatures of spring, or if there is a bulk-water incursion from wind-driven rain or mis-lapped window flashing. The drying rate is just as fast as if there were only latex paint as the interior vapor retarder, but the rate at which conditioned space diffusion reaches the sheathing is reduced by an order of magnitude compared to only latex paint. This gives the assembly a LOT of resilience.

In climate zone 5 as long as the siding is back-ventilated it doen't absolutely need it, but it's cheap insurance. In zone 6 if the sheathing is OSB or plywood even with vented cladding it would need either a class-II vapor retarder (like "vapor barrier latex") or a "smart" vapor retarder like MemBrain, but not if the exterior sheathing is fiberboard or gypsum (either of which is about an order of magnitude more vapor permeable than OSB, which enhances the drying rate toward the exterior.)

See: http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_7_sec002_par025.htm

Dana & Others,

Assuming Zone 5B - Cold Winters, some wet...some dry + Hot Hot summers, some wet...some dry. So every temperature with every humidity possibility here is what we are talking about.

If I want a energy efficient house without going over my budget (*important because if I go over budget, I'll flop on the mortgage payment as time presses on, and makes this all pointless*) --- I will plan on one of two sidings, Either a thick vinyl siding or the Diamond coat LP Smart Siding. After siding, I will have installed: Greenguard Raindrop 3D rippled House Wrap **Taped on every single inch of seams, unless told not to..** > then 7/16" OSB > 2x6 Stud walls 16" O.C. with 1.5" Furring strips to allow extra insulation which will be > 7" thick Thermafiber Mineral Wool Insulation R-30 > and then MemBrain > 1/2" or 5/8" Drywall > and lastly PAINT.

How can this be improved upon without too much extra cost?

Questions are: Should I tape the OSB Seams, at all?
Should I be diligent about taping every inch of seam with the house wrap?
Should I have any concern with MemBrain in my climate conditions with my choice of insulation, paint, and siding?

Bonus: Why does LP Smart Side not suggest / require the siding be installed over a rain screen? They have warranty on the product but the local supplier said it was non-issue. So I just want to inquire more into it.

Thanks!