After debating between SIP & spray foam, I think my contractor has me convinced to do the foam. But since I am not that knowledgeable about it perhaps someone can help.

This will be a 2 story plus a walk-out basement (total 3 story) with roughly 5200-5400 sq ft total located in NW South Carolina.

I will be using Superior Walls for the walk-out basement.

He gave me a quote for $8,900 to put 3 1/2" thick open-cell foam in my 2x6 walls, from the main floor up to the roof. Then spray 5 1/2" of open cell foam in-between the 2x8 rafters in the roof.

He also stated he would batt it in 1st.

My question/concern is will this be enough to make my home energy efficient enough to lower my power bills substantially?

I should add that I was determined to go with SIP at 1st but his wariness plus the cost factor have me concerned.

Any help would be greatly appreciated!

Hey neighbor- I'm going to building outside Greenville this year. Someone with more knowledge than I have will come along, but the problem I see as described is the heat transfer through all of those studs. This can be dramatically improved with foam panels outside of your sheathing, under your siding. This will break the thermal bridging that really lowers a stud wall's R-factor. Also, make sure your contractor seals everything up good. Air infiltration really lowers energy efficiency. The spray foam will do a good job of that, but watch for other penetrations

Thanks! I assume the cost for the foam panels would be a fairly inexpensive cost to add on? As I want energy effieciency I also don't want to go over my budget. I also would like to throw in the windows we are going to be using:
Simonton Prism Platinum vinyl double hung windows.
 Low E Softcoat (Prosolar);
 Argon Gas;
Double Glazed;
 Double Strength (1/8");
U Factor-.31;
SHGC- .24

Other windows may vary only slightly.

Also, the front of the house faces slightly NE so the rear (with the most windows) faces SE. If it would make a big difference I would like to ask my builder if it could be slightly repositioned. That may not be possible due to the walk-out basement.

And....a friend suggested we extend the fireplace all the way down to the basement. He says since heat rises....While that would be an extra cost does anyone have an opinion on that?

If it helps at all I could email anyone who would like to help my floor plans.

 Again, any opinions are greatly appreciated!

A 3.5" shot of open cell foam cavity in 2x6 16" on-center construction with wood siding will deliver whole-wall R values of ~ R10, but a full fill would bump that to R14 (framing bridging added in.)

Add an inch of XPS or iso sheathing over the exterior and that's bumped up to ~R20 (double what you're talking). Bump the stud spacing to 24" and you'll get ~R21 due to the lower framing factor.

A full-fill spray cellulose will likely cost less than 3.5" of oc foam and if air-tight techniques on the sheathing are used and you get the same sort of numbers, but it performs ever so slightly better due to the additional thermal mass of the cellulose. It'll be quieter too. An inch of exterior foam to thermally break the framing, you're at R20.

Going with a flash & fill of 1" closed cell + 4.5" of sprayed cellulose in the cavities delivers whole-wall values of R15-R16, and adding the inch of exterior insulating sheathing bumps the whole-wall R above R20.

Whether R20 clear walls vs. R10 makes it on a net-present value on utility savings (it usually does, if you're comparing spray-foam R10 to a spray cellulose + 1" rigid approach to R20), but its' a HUGE on comfort levels at the temperature extremes, summer & winter. It's literally half the heat transfer for the wall areas.

Batts are impossible to install perfectly in walls where there are windows, electrical & plumbing, etc. There will inevitably compressions & voids, and they don't generally perform anywhere near as close to their rated R as sprayed or blown fiber does around all of the obstacles. Wet spray cellulose is usually competitive- about the even-money with low density batts, and generally WILL perform to spec, is more stable with R over temp due to lower convection within the insulation, etc. (For more money you can dense-pack cellulose or fiberglass blown behind a mesh making it highly air-retardent as part of the air-sealing scheme, but caulk or foam on the framing/sheathing interfaces is better than mere dense packing.)

Once you're at R20 for whole-wall R, it's the quality of the air-sealing and quality of the windows that makes or breaks it. Minimize window area where you're not intentionally using it for wintertime solar gain. Awning & casements seal better than double-hungs or sliders and offer more egress & ventilation area per square foot of glazing. Sliding glass doors tend to leak air like crazy over time- better to use French doors rather than sliders on your walkout if you're keeping them glazed for the view, etc. Fixed windows leak even less, and are usually cheaper- think about which and how many windows you really need to open ever. Selectively reducing the glazed area by 25% where it's not being used for passive solar tempering can mean low double-digit savings on utilities, and add quite a bit to comfort. Every square foot of U0.31 glazing has the conductive heat gain/loss 6.2 square feet of R20 wall- a 24"x60" window is "worth" 62' of wall area. It doesn't take a large percentage of glazed area to dominate the wall performance numbers (half as much as if you stay at R10 whole-wall values.) If thermal performance is a goal, think about the size & location & function of every window. Going simpler & smaller can be a big boost in performance, and is usually at-worst cost-neutral, often cost-negative (cheaper.)

Designing in overhangs for your massive SE windows to kill solar gain might be tough or impossible given the orientation, but exterior shutters/shades or trellises to introduce seasonal shade may be good options. At least by noon on the solar gain should be dropping off before the real heat of the day sets in. SW windows tend to add to the peak-load of the AC much more than SE windows, so think about how big you really need/want on that side. Big AM solar gain in winter can be a GOOD thing (up to a point.)

5.5" of ANYBODYS open cell goods on the rafters won't meet code-minimum. Best-case you're looking at R22-R23, most would come in just shy of R20. You probably need R30 to make code-min.

If it's a simple roof line, not all cut up with dormers & valleys it'll be cheaper/better to put 2-3" of rigid foil faced iso above the roof deck, with a vented nailer deck above that on furring. That would put an R13-20 thermal break over the rafters, and you could then put blown-in-bag wet-spray cellulose/fiberglass (or R25 batts, if you can do a perfect job) between the rafters for an other ~ R25 without worry of wintertime condensation at the roof deck. A 1" flash of closed cell on the roof deck in the rafter bays prior to the fiber would make it easier to air-seal, and would still allow excellent drying toward the interior. Kraft faced batts would be OK, but no foil facers if you went that route. The foil facers on the exterior iso would reject a good deal of the summer heat, but for overall performance the thermal break over the framing is the bigger benefit. With only 5.5" of spray foam the 8" rafter is an R5-6 thermal bridge sucking performance out of the assembly. Any R you add above the roof deck adds to that number- thicker is better, but anything over 4" gets into more labor dealing with long screws to mount the furring to the structural rafters. Using 2x furring gives you substantial ventilation area under the roof deck , but you need to screen it to keep it from becoming a critter-nesting area.

Going higher than code-min is usually cost-prohibitive with spray foam, but getting air-tightness is key to performance. Using foam judiciously to aid air tightness and putting the bulk of the R in mid to high-density fiber. For large flat surfaces rigid foam is half to 2/3 the cost of sprayed goods (close cell or open), and with taped seams & foam-sealed edges can be made into a very decent air-barrier.

Fireplaces may look good and feel good on a cold winter day, but the air-tightness of the dampers usually leaves a lot to be desired, and an open flue becomes a point of exfiltration, depressurizing the house, and sucking air in through every available crack. (This also is true for furnace/boiler/hot water heaters that are atmospheric-drafted. If you can, only use sealed-combustion/direct vent equipment, or at a minimum, forced draft units.) Heat doesn't rise, but hot AIR is less dense than cold air, so in a room where air is being heated or cooled by some surfaces convection currents will be created. Adding an extra likely-leaking flue for an extra fireplace is more than twice the suck, and costs more- don't do it. The stack effect sucking heat out of the house will be increased slightly by adding a basement fireplace. Air-sealing around the chimney chases between floors (and at the roof deck in a sealed-attic) is also a key element of keeping stack-effect infiltration-drivers under control.

If you're going with R20 whole wall values and an insulated foundation, R8-R12 in EPS or XPS makes sense. Going with 2-3" of Type-I or Type-II EPS would be the cheapest, and supports residential slab-loads just fine. A 2" layer of XPS would be R10, and is typically more expensive than 3" (~R12) of Type-II EPS. But if it comes down to balancing exterior insulating sheathing vs. slab insulation, spend it on insulating sheathing first, but at a minimum insulate the first 2' in from the exterior on the at-grade walkout side- you'll feel the difference in bare feet quite easily.

Thanks for such a thorough reply. I'm going to email this to my builder & see about implementing these methods. I really appreciate your help!

This document showed up in another thread yesterday- well worth a read when looking at new-construction:

http://www.buildingscience.com/documents/reports/rr-1005-building-america-high-r-value-high-performance-residential-buildings-all-climate-zones

(SC is zone 3, in the current DOE climate zone maps.)

For different methods of achieving higher-R walls see also:

http://www.buildingscience.com/documents/reports/rr-0903-building-america-special-research-project-high-r-walls

Pay particular note as to how far the foam sheathing drops, and where capillary breaks are, etc. What I've recommended for you is essentially case 2a in that document, but substituting spray cellulose in lieu of batts for higher air-retardency, more assured completeness/continuity and a bit of thermal mass, and possibly substituting foil faced iso for XPS, which will peform about R2 better than 1" XPS when it's 100F out, and about the same when it's 25F out.

XPS sheathing would have better drying capacity though, and nothing more water-vapor retardent than latex should be used on the interior in an SC climate, for better overall moisture performance. Water gets in by any number of means, but gets out primarily by vapor diffusion. An inch of XPS is semi-permeable, but a foil-facer is a true vapor-barrier, so the assembly must be allowed dry toward the interior if you go that route. Don't even think about using an interior vapor barrier such as poly sheeting with either stackup.

The moisture analysis in that document is for Minneapolis, which has orders of magnitude worse winter-condensation issues in the walls than any location in SC, so it can be pretty much ignored (yours is a very mixed heating/cooling climate with relatively modest extremes & averages. Winter condensation in the walls only becomes an issue when the average temp at the structural sheathing at the interior face of the foam is below the dew point of the conditioned space interior air for months, which in winter would run ~37-40F (assuming 30-35% relative humidity, 68-70F inside.) In Greenville/Spartanburg even the EXTERIOR face of the foam will average over 40F, even in January: http://www.climate-zone.com/climate/united-states/south-carolina/greenville-spartanburg/ With ~ R20 center-cavity on the cellulose and R5 sheathing on the exterior the average temp at the temp at the structural sheathing is 1/5 the difference between exterior/interior, so assuming you keep the average place at least 65F inside the sheathing will avearge 45F+, well above the dew point of the conditioned space air, so it won't accumulate moisture for weeks the way it might in Minneapolis.

If you go with the insulating foam sheathing over structural sheathing, you may want to ponder this detail as well:

http://www.greenbuildingadvisor.com/blogs/dept/musings/where-does-housewrap-go

Thanks, Dana! You have been a great help!

Ok, those articles was a lot to read. Now if anyone can answer a question-& excuse me for not knowing.

What does this mean EXACTLY? I ask b/c when I ask my contractor to do this I want to know for sure.

2x6AF (what is "AF"), 24"oc (I know),  R19FG + 4" R20 XPS  (what exactly)

As I am building in NW SC (Greenville/Spartanburg) I don't want to do overkill with insulating but I do want to enjoy lower utility bills.

Any help would be greatly appreciated!

2x6 advanced framing, 24 inch on center, R19(insulation value) fiber glass + 4 inch R20(insulation value) extruded polystirene

Thanks!

I mentioned doing 2x6 advanced framing, 24 inch on center to my contractor & he is against the idea of 2"oc. he states you will get a flimsier wall by spacing them farther aprart. To be honest, I am not sure why doing it would increase the R value.  Could someone enlighten me on this? I hate not having the facts when I try to push energy efficiency.

On that note, he says it is my house & he will build it however I wish. But he brings up arguments that make sense. I just want to make the right decision.

Thanks!

He was initially going to do 2x6 with 16"oc with regular insulation (not sure R value). But as I want energy efficiency, the more I read the more I get baffled. I want to do this within my budget but I want th elowest possible utility bills for years to come. I know I want the best of both worlds. I read an article that Dana sent me & it seemed that 2x6 advanced framing, 24 inch on center, R19(insulation value) fiber glass + 4 inch R20(insulation value) extruded polystirene would be the way to go. But as my builder said that would result in a flimsier house I have nothing to argue with without the knowledge. So your comments on that would be appreciated. In fact, any comments would be great. The more I ask, the more I get confused. I am just looking for the most affordable, yet energy efficeint way to frame my house & insulate.

For many years 2x4 16” on center was the standard Building practice. Generally speaking going to 2x6 24” OC is equivalent.

Wood is ~R1 per inch and in a typical house framed 16” OC wood is about 25-30 percent of the wall area. So 25% of your wall is R5 and the rest is say R20.
Advanced framing reduces the % of the wall that is wood and therefore increases the % that is insulation. Houses often have huge thermal shorts at the corners , near windows etc. Advanced framing helps to reduce these by requiring less wood to do the same job.
You have to do more work up front to do a smart layout, spec insulated headers, etc, but it installs just as fast. Often builders will spec 5/8 drywall when used with 24”oc framing The other thing you need to do is install horizontal blocking where cabinetry, mirrors, etc will go on the wall. (a good framer would do this anyway

Advantages More insulation, less material, also faster for the electrician. Same or lower cost
 
Disadvantages: More layout time and effort. Less studs to nail cabinetry to. Less to nail the siding to. Some people, including many builders consider it cheap.

http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/26449.pdf is a good summary of very basics of advanced framing.

I know I am late to this discussion, but here is my two cents worth.
Considering your location, I don't think you need 4" of foam outside your framing.
I would suggest 2x6 24" on center, 7/16 OSB over entire building, and 2" foam over that.
This wall will be stronger than a 16" on center with no OSB.
Then add an inch or so of spray foam to seal the walls and fill with cellulose.
This should deliver more than adequate insulation values for SC. Pay closer attention to energy efficient doors and windows, and sealing out air infiltration. These will be bigger factors than added R value, in your climate.

Thank you everyone for your input. I am going to copy & paste this to email him. However, is there anything I can say about it being "flimsy" walls, since it is less studs in place? I know he wants to build me a quality house & he will bring this up. I don't doubt it won't be a quality house but he wil bring up the framing again. & as Eric said, most builders consider it cheap.

Wes, would that increase the cost much? The 2" of foam over the entire house seems it would be expensive, but I don't really know. & would that be a problem in the future of doing the 24" vs 16" in the event we want to add cabinets or anything?

Would it be ok to do 16"oc with the OSB over the house?

I would use 1/2" osb or plywood if going 24" oc. I've had issues with 7/16" osb on 24" centers that aren't pleasant.

Posted By diamonddave1967 on 25 Mar 2011 05:56 PM
Thank you everyone for your input. I am going to copy & paste this to email him. However, is there anything I can say about it being "flimsy" walls, since it is less studs in place? I know he wants to build me a quality house & he will bring this up. I don't doubt it won't be a quality house but he wil bring up the framing again. & as Eric said, most builders consider it cheap.

dave;

the 24" oc is not to cheapen the house, it is a matter of reducing thermal transfer thru the studs. with foam sheathing insulating the studs themselves, there is nothing wrong with 2x4 @ 16" oc with OSB sheathing, it is just not thermally efficient.

Our energy efficient wall design in the 70's was 2x6  @24" oc single top & bottom plates, steel "T" corner bracing 1" DOW t & g styrofoam sheathing (2 x 8 sheets)

However even when I was building conventionally, I never used OSB, it was always 4-ply CDX, 5-ply if it was available

wes; structural bracing can be accomplished without OSB,  with "let-in" bracing instead