Ok, I appreciate the answer-but how should I reply to my contractor when he states that the house would be "flimsy"? He is referring to the walls being less sturdy since he would be moving it from 16" to 24".

& the question about future issues putting up cabinets or anything else--would less framing be a signifigant problem?

How much of a difference would going 2x6 16"oc with foam sheathing be? Would it lessen my energy efficiency considerably or just slightly?

I know I'm beating a dead horse but I was hoping on making a decision by the end of this weekend.

Again, hate to keep asking this when everyone is giving me good suggestions. But I would like to find a line in the middle where it seems energy efficient, structurally sound & within budget. If someone could suggest which of thes options may be best with those 3 factors to consider?

OPTION #1--2x6 16"oc with 3.5" of open cell foam (R10). Add a "full fill" (R14 with framing bridging added in). Add an inch of XPS or ISO sheathing over the exterior (R20).


OPTION#2--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


OPTION#3--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.

Posted By diamonddave1967 on 26 Mar 2011 02:37 AM
Ok, I appreciate the answer-but how should I reply to my contractor when he states that the house would be "flimsy"? He is referring to the walls being less sturdy since he would be moving it from 16" to 24".

since normal construction is 2 x4 @ 16" oc going to 2 x 6 @ 24" is pretty eqivilent the "let-in" bracing takes the place of the OSB sheathing. It is a means to acheive the best thermally performing wall with equally performianc structurally.

SIPS,  any kind of SIPs,  would be the best wall and 3 times stonger than wood frame, but your contractor talked you out of that too, you are searching for someone to agree with your contactor, but his agenda is not the same as yours, he is not unique and typical of most conventional builders -  he does not want to get out of his comfort level.

It is a a battle between doing something newand better and doing the same old-same old

If I was doing my house over I would go with advanced framing techniques (california corners, partition bridges etc) 2X6 on 24 rather than 16" centers, with all the places where sheathing meets framing caulked and foamed where you can't caulk, outside seams of sheathing caulked, all sills caulked, band joist 2#cc foam, 1 or 2 inches of foam board on outside of sheathing, and spray cellulose or fiberglass in the wall cavity. I think this would give you less expense and excellent bang for the buck. If you are going to go with 16 inch centers, there is no reason not to use R21 fiberglass batts as long as you make sure it is installed properly, but do all the caulking, foaming etc first, and use the exterior foam board to mitigate thermal bridging. Since fiberglass batts are probably the least expensive form of insulation, it will save money, but it MUST be installed with great care.

-Rosalinda

As a retired engineer and mech. contractor, I would build the walls 2x6 on 24oc with roof trusses resting directly on the 2x6. I would add 2x4s cut in half horizontally on the inside studs 24oc. A full 2x4 starting on the bottom works better for future baseboard and full 2x4 could be used where cabinets are hung also.This gives a 7 inch thick wall with only 1 3/4 inch for thermal bridging from the 2x6 wall stud outside to inside. I would not add foam to the outside . This should reduce the contractors concern for the flimsy wall.

That idea makes sense to me. I suppose if one only wanted 6" walls, they could do a similar thing by using 2x4s 16" OC and then crosswise with 2x2 pieces. With no racking issue, one could skip OSB and just use 1" foam.

2x6 24" o.c. sheathed with OSB or ply has structural capacities similar to 2x4 16" o.c. construction- it's VERY standard stuff in cool-weather country.

Option 2 is probably going to come in the cheapest, but requires a bit more care on the air-sealing end. Option 3 is generally easier to air-seal (but don't count on the flash foam alone to seal leakage at the framing plates or at the sheathing seams.)

The horizontal chords on the interior framing is also referred to as a "Mooney Wall". It has higher thermal bridging than with exterior foam due to the grid of 1.5x1.5" cross-points, and doesn't thermally break the band joists, plates and headers, etc., but if the exterior walls are pretty simple it can be a cheaper way to go, and far outperforms standard studwall construction.

See: http://www.builditsolar.com/Projects/Conservation/MooneyWall/MooneyWall.htm

Cutting in bracing to be able to skip the structural sheathing for a modestly thinner wall is effective as well, but I'm more comfortable with a structurally sheathed wall in hurricane country. YMMV. The amount of bowing and flexing potential of the sheathing on the windward side is much increased without OSB or ply to support the insulating foam. It might be OK with 2-3" of closed cell cavity fill though, but even then the penetration resistance to hurricane blown debris would surely be lower. Depends on the cladding/siding, I suppose.

I feel your pain, Chris, but unless he switches contractors it's probably not a good idea to use SIPs if the contractor isn't comfortable building with them. OTOH I'm not too keen on using a contractor who would spec something bare code-minimum on wall insulation and LESS than code for roof insulation. Not having been party to the conversations or knowing the local alternatives it's hard to say whether it's the right outfit to be using or not. But to be sure, getting R20 whole wall values with SIPs is dead-simple, and getting reasonable air-tightness out of a SIP takes a lot less detailing. The "newer and better" aspects isn't always clear- one of my office mates lives in a 23 year old SIP house that has lots of "issues", but most of those issues are pretty well understood now (better than in 1988) and the industry has addressed them. But what SHOULD have been an R25 high performance house in his case is thermally underperforming my circa 1923 stick-built from an annual primary energy use point of view. (Done right, with newer tech SIPs and a better installation it would outperform my place by ~25% rather than conversely.)

Posted By jonr on 28 Mar 2011 06:41 PM
That idea makes sense to me. I suppose if one only wanted 6" walls, they could do a similar thing by using 2x4s 16" OC and then crosswise with 2x2 pieces. With no racking issue, one could skip OSB and just use 1" foam.

2x2 crosswise will not prevent racking

Dana 1;

I am sure his builder is a fine builder, but is too afraid to step out of his comfort zone to build with a new system. I see it time after time owners wanting SIPs or other alternative systems only to be talked out of it by their builder. You are correct something needs to give the builder or the product. But I was a little suprised to here 2x6 @ 24" oc called flimsey? there is more board feet of stud in a 2x6@ 24" oc than 2x4 @ 16"

2x2 crosswise will not prevent racking

OK, I guess that leaves full sheathing, sheathing at the corners or diagonal metal straps?

Posted By cmkavala on 29 Mar 2011 12:34 PM
Dana 1;

I am sure his builder is a fine builder, but is too afraid to step out of his comfort zone to build with a new system. I see it time after time owners wanting SIPs or other alternative systems only to be talked out of it by their builder. You are correct something needs to give the builder or the product. But I was a little suprised to here 2x6 @ 24" oc called flimsey? there is more board feet of stud in a 2x6@ 24" oc than 2x4 @ 16"

True, but there are fewer fasteners between the sheathing and studs, and a bigger span for the sheathing to flex, which may have been the builder's gut reaction(?).  Hard to say...

Beats me- 24" o.c. 2x6 construction, has long been a standard construction approach in much of the cooler-weather US, and it's well understood that the loading specs on it are so similar to 2x4 16" that nobody batts an eye at it anymore in places with code prescribed R-values above R13 for walls.

Dana 1;

you can simply tighten up the nail pattern from 8" to  6" or 4"

Single top plates are flimsy until you get your temp. bracing on and its more difficult to straighten the walls. 24"oc has more wall deflection than 16" and panel and wallboard spans are also stretched, they can seem flimsy as in increased vibration and under high wind pressure. Sort of the same problems/complaints heard when using min. engineered floor systems.
He's probably worried about callback, remember he has to warranty it.

greentree; 

you are correct when stretching any wood to 24" OC , one risks bowed/twisted studs, but with 2x6 it is less of a problem. Makes a good case for metal framing that is done @ 24" oc because every stud is straight and drywall is absolutely flat. drywall and plywood spans @ 24" oc are very common when applied over trusses.  In daves case he is not in a hurricane zone , so wind pressure is probably not much of an issue

All true- tighter nail spacing does nothing for the flex, but the density of cellulose insulation takes some of the vibe factor out, and even an inch of close cell SPF on the sheathing in a flash & fill stiffens up the sheathing and goes a long way toward hurricane-proofing the wall by gluing the sheathing to the studs & plates, etc.

This is all pretty standard stuff with standard solutions, but if the contractor hasn't dealt with 2x6 framing (even with double top plates, rather than the full-on OVE approach to fully minimize bridging) I can understand some initial wariness. But maybe it's time they got on that learning curve- this is 2011, after all, not 1981 (or 1971)- this 24" o.c. 2x6 framing has been around for quite awhile now.

OTOH, a 2x4 framing package with TWO inches of exterior foam is a somewhat better performer for the same wall thickness, but more expensive due to the greater quantity of rigid foam, and may add some design issues around how to best hang the siding.

Anyone considering using 2x6's for wall framing should pay particular attention to the quality of the wood.  A 2x6 being stiffer than a 2x4 can not easily be pulled into place if it is just a little crooked.  So buy at least No. 2 grade and then be prepared to sort the pile before you begin framing.  Use the crooked studs as shorter pieces for openings and braces,etc. to get around the problem with trying to twist a full length into place.  Been there and done that with No. 3 and it resulted in more work with less quality walls.

Since I have seen studs made out of fiberglass, I have hope that someday we can get beyond wood with all of its problems.

Posted By Dana1 on 31 Mar 2011 12:06 PM
All true- tighter nail spacing does nothing for the flex, 

It does improve rack / shea rand  is Florida's answer to improving wind resistance to plywood sheathed roofs (which is 24" oc.) in hurricane zones. It is also is the prescriptive method for hurricane wind mitigation for older homes being re- reoofed

Posted By cmkavala on 31 Mar 2011 05:12 PM

Posted By Dana1 on 31 Mar 2011 12:06 PM
All true- tighter nail spacing does nothing for the flex, 

It does improve rack / shea rand  is Florida's answer to improving wind resistance to plywood sheathed roofs (which is 24" oc.) in hurricane zones. It is also is the prescriptive method for hurricane wind mitigation for older homes being re- reoofed

I think we all agree on how it improves the racking aspect.

I've not seen any hard analysis on how much hurricane-proofing you  get with a 1" ccSPF flash'n'fill on the sheathing, but the improvement in structural integrity @ 2"  or better of SPF is pretty astounding- it's like gluing the whole thing together with Gorilla Glue (and then some!)  I have to believe even at 1" there's sufficient surface area in contact with the stud to do some real good.  I suspect the 2" & 3" solution has been better studied since at those depths it meets code for R-value on walls in most of the southern US without additional insulation.

diamond....  google  "Mooney wall"
all cellulose,  much  cheaper than foam...  a net  wall R-value of  19

cellulose in the rafters R-33  (  2x10 )
if you  have an attic  i'd blow  R-60  ( 18" loose blow )

your windows are  acceptable   (  u of .3 would be better or  .29 )

what are you doing for the foundation .. full  basement ?  crawl space ?  slab on grade ?

sorry...i went back and looked...walk-out basement with superior wall

what about the slab ?

here.... we'd  do a poured wall.... 1" of eps on the interior then a 2x4  cellulose wall inside that...

about an r-18 wall
 the slab would  have 2" of 2 lb/cf  eps  under it.... for you ...maybe 1" (r-5 )