New to forum.  Have exterior finshed on ~6500 sf mutil family house. I am living in the 1500 sf basement apartment while I finish the 3000 sf main floor and 1500 sf attic apartment. The house is brick over 1/2 in osb wrapped in foil barrier with 2x4 wall 9ft ceiling, 4/12 roof with 26 ga steel over felt and 1/4 in foam. The house is 54 ft square with eight ft wrap composit porch with Ellision Low e douple pain windows and Marvin doors. Our heat load req is the area is 3200.0 and cool is 20700.0 per DOE.
I had planned to use 2-3.5 in foam exterior walls and 3-5.5 in roof of open or closed cell foam in the exterior wall 2x4, 2x6 roof and aprox 1'' of foam in the craw space and rim joint.. I have estimates for open and closed in the 10-12K range. It seems the open cell guys/gals should be cheaper but have come in about the same, go figure. 
I have just read about the mooney walls  and would conside using this approach as it allows a house to breath and I am DIY type and there is allot to do yet and less money. I understand the the open cell foam will breath also. I do like the adhesive qualities of the foam and that it will stop 98-99 % of air infiltration if applied correctly. 
I am at 98 % wiring and plumbing and will be ready for insulation soon. The insulation for the walls and roof line is a one shot deal and once sheet rock is installed there is no going back.... I would appreciate your thoughts, recommendations and or optons...as my HVAC size (and future comfort and utility bills) will depend on what we decide on the insulation. Thanks, TS

If the studwalls aren't yet up, (sounds like we're too late) an inch or so of foil-faced iso, foil-faced EPS, or un-faced XPS on the exterior of the studs & structural sheathing would be far cheaper and far more effective than any foam you spray into the studwall.  Also, 2x6" studs 24" on center is the same amount of timber as a 16" o.c. 2x4 studwall, cutting the thermal bridging of the studs by at least a third. Taking it a step further would go all out on advanced framing techniques for minimum thermal bridging (sometimes referred to as OVE or optimal value engineered framing.) 

With the center-cavity any more than R3.7-R4/inch there's little more to be gained in a studwall, since the ~R1/inch thermal bridging begins to dominate the heat transfer.   Framing factors of ~25% is a typical for 16" o.c. studwalls, but that can be reduced to under 20% with OVE.  Save the foam-money for the exterior, where it delivers the full-R by thermally breaking the studs, plates and band joists.   Then use sprayed or blown fiber for the cavity, and make a complete fill.   16" o.c. studwall with 3" of closed cell foam cavity fill has a whole-wall R value of only ~R12, whereas  2x6 studwall (non-OVE) full of spray cellulose delivers ~R14-15, and with an inch of exterior iso would be fully R19-20.  Go whole hog OVE on it and you'll be looking at R21-22, for LESS MONEY than a 16" o.c. 2x4 wall full of closed cell foam.

Cellulose also breathes better than open cell foam, is more air-retardent than mid-density fiberglass, and buffers & redistributes any moisture that finds it's way in.  Spray cellulose is dimensionally stable over decades, but for more money it could be "dense packed" at which point it's pretty much a done-deal for a century or more, if packed to the proper density for the climate & construction. (3.5lbs/cubic foot would do it, for anything we're discussing here.)

A 1" flash of closed cell foam on the interior face of the stud bays can help air-seal the studwall, but slows the drying of the structural sheathing toward the interior, which is important in masonry-clad walls.  Only if the exterior foil is UNPERFORATED (and thus highly vapor-retardent) would it be advisable to use closed cell on the interior.  Using air-tight techniques on the sheathing & framing can work as-well, and it's better to put ~1perm (or somewhat lower) foam between the brick and any wood, and leave at least a 1" cavity between masonry & foam (vented top & bottom for convection-drying of the cavity.) That way the brick still dries, the sheathing can dry in both direction, and all of the wood is protected from the high vapor drives of sun on dew or rain-wetted brick.  A 1" EXTERIOR shot of closed cell foam would give you that, but so would an inch of XPS.  Foil facers come in both perforated (high-perm) and smooth (very low perm) variants- look at the perm rating for any foil-faced goods.  With a low-perm facer the brick would dry somewhat more slowly, but the wood is better protected.  Foil facers also act as a radiant barrier in summer, and are easy to detail as an air-barrier with 2" FSK tape & 1-part foam on the edges.

Mooney walls work OK and are cheap, but don't thermally break the plates & studwalls.  The foam-skinned approach is simpler, and still not very expensive with 1" of foam.  If your walls are already framed in, a flash'n'fill w/Mooney wall is still worth it.  If the radiant barrier is a perforated type, use Icynene MD-R-200 (a high-perm closed cell foam that's only R5/inch) as the air-seal, and do the rest in cellulose.  At 1" it would be over 2 perms, and any moisture ending up in the sheathing from the high exterior vapor drives makes it safely into the cellulose, and then into the air-conditioned interior.  In AL wintertime vapor drives from the interior and condensing hours at the sheathing layer few, so 2+ perms of diffusion capacity won't add to the moisture burden in the exterior wood the way it would in a cold climate.

On the basement & crawls, a 1" of rigid XPS as a vapor-retarder against the concrete, and under the slab (or subflooring, if the slab is already poured) is cost effective long term an an AL climate.  The wall-R can be fattened out cheaply with a studwall and un-faced batts using only permeable latex or latex acrylic as an interior finish.    An inch or TWO of closed cell foam on the interior of the band joist & foundation sill seals it to the rigid XPS.  Be sure to use a metal or heavy poly capillary break between the concrete and the foundation sill (if it's not too late.  If it IS too late, there are workarounds.)

In the crawlspace, if you're not putting down an inch of XPS, lay in a 10-mil poly vapor retarder, mastic-sealed to the wall XPS.  A 1"-1.5" non structural concrete rat-slab over the XPS or vapor retarder protects it, and critter-proofs the floor.

Addendum: If you're going with an unvented attic, there too you can do well with a flash'n'fill approach using an inch of closed cell on the roof deck for air-sealing & vapor retardation, filling out the R with wet-spray fiber blown behind netting. (Wet sprayed has water activated adhesive.) And once again, it's usually cheaper & more effective using rigid foam on the exterior, only spot-airsealing. If it's not already roofed, adding at least 2-3" of rigid foam above the roof deck and filling out the R with high-density fiber-BIB at the rafters gets you there. (Batts or low density fiberglass BIB doesn't really cut it performance-wise but 1.8lb Certainteed Optima, 1.8lb JM Spider, or any density wet-spray cellulose do.) With 2" (R10) of XPS on the exterior and 5.5" of cellulose (R20) you'd be at the R30 code-min, ( see: http://energycode.pnl.gov/EnergyCodeReqs/?state=Alabama) but with the foam thermally breaking the rafter/truss elements it would perform measurably better than a code-min house done as mid-density or low density batts between rafters or attic floor joists/truss-chords.

By contrast, 5.5" of open cell foam wouldn't meet code for roof R value anywhere in the US (but 5.5" of closed cell polyurethane would.) At 3" cc foam would only be a bit over half the prescribed min-R. If you go that thin, put at least 2" over the rafters/truss elements as an interior thermal break on the framing. Most half-pound open cell goods takes 8-9" to achieve the R30 code-min. With 2lb closed cell polyurethane it takes ~5" (and with the high perm closed cell Icycene it takes 6").

Don't buy into any foam marketing hype about " ...(x) inches is all you need, since it's air tight and outperforms typical fiberglass at R(z)...", even if your inspector buys into that blown smoke argument. To meet code on a batt installation it's air-permeabilty has to meet spec too (hard to install, and harder to measure), so the "...all you need..." thesis is basically "...this crappy sub-code solution beats the performance of typical crappy sub-code solutions...", which may be true in many instances, but so what? It's still a no-brainer to insulate in such a way that actually meet or exceeds code, and it's even financially viable to go 1.5-2x code on a 25 year present-value analysis if you use cheaper methods. see Table 0.2, page 10:

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

Note, you're in Zone 3, and those R-values are "whole assembly", not center-cavity numbers. The R20 wall recommendation would be met with the 2x6" 24" on center sub-20% framing factor foam-clad assembly described in my previous post. Without exterior foam the thermal bridging of the 2x6 studs means it would take a cavity fill of ~ R75 to get to R20 for a whole-wall number, with the R value of the interior gypsum & structural sheathing added in. But with R5-R6 as exterior foam it you get there with ~R19-R20 center-cavity. With a 16" o.c. 2x4 studwall, 25% framing factor, with no exterior foam, even with R1000 center cavity you can't get there- the 25% framing fraction that's only ~R4 means that with infinite cavity insulation you'd still be at R16 for a whole wall number.

See 2a, Table 3 on page 9: http://www.buildingscience.com/documents/reports/rr-0903-building-america-special-research-project-high-r-walls.

Spray foam (any density or type) is a great way to air-seal , but a very expensive way to fatten out the R, and an inch of closed cell air seals fine, and is still somewhat vapor permeable ( ~1perm ) to allow the assembly adequate drying capacity. Open-cell is harder to install at consistent depths thinner than ~3", at which point it's as-expensive as a 1" shot of closed cell, but far more vapor permeable (which can be good or bad, depending on the climate, and where it is in the assembly.) The flash'n' fill approach is more consistent with closed cell foam.

Thank You for the wealth of information and options. I will try to refine my thoughts based on your input and see if we can come up with a plan for insulation of my house.
The walls are already framed in 2x4, 1/2 " osb wth perforated radiant barrier the exterior brick is installed with aprox 1 " air gap between brick and osb/barrier. Note the 8 ft wrap around porch prevents very minmum water to access the brick.
Based on your input I plan to install aprox 1" of Icynene MD-R-200 closed cell foam as an air-seal and fill interior 2x4 stud wall cavity in high density cellulose. Would installing an additional 1/4 in of sheet foam on the interior of the stud walls before sheetrock be somthing you would recommend with the above foam and cellulose in an attempt to increase the R e.g. ~1 in cc foam, ~2.5 in cellulose + 1/4 in sheet foam ?

I do plan on a unvented attic, sorta. I plan to have a mechnical fresh air vent in each eve for spring and fall air flow, and the HVAC for summer/winter air/heat. The 4/12 roof which is installed with 1/2 osb, felt, 1/4 " sheet foam and 26ga metal on 2x6 16c. In the attic there are a few more option since it was framed for interior room at 5' 8" there is a aprox 10 foot air/and storage gap between the interior room walls and the eves of the porch. At the porch eaves the 36 ' knee wall will be sprayed with 1 " cc foam which will continue up the roof to the apex, as it is a square house. Is 1 " enough in this area or should I go with more ? I can insulate behind the room walls as well as the foam on the eves and where the roof becomes the ceiling I will again ask if I should use 1/4 in foam sheeting under sheetrock and fill 2x6 cavity with hd cellulose with 1 ' +++ ? of cc foam.
Thanks again for your assiatance and recommendations. TS

Is there any type of underlayment between the perforated RB an the OSB, such as housewrap or felt?  Got a perm rating for the RB?

1/4-3/8" fan-fold underlayments usually come with polypropylene facers on them to bring the perm rating down below 1, something  like 0.6-0.8 perms, and it would be better to keep the perm-rating toward the drier air-conditioned interior high, to maximize the ablity of the assembly to pass moisture drives from the exterior inward rather than accumulating or even condensing in the cavity.  Unfaced half-inch XPS has typical perm ratings >2, and R-ratings of ~2.5, which would improve things some, but not as much as you'd like.  It would raise the whole-wall R value from something like R11 to R12.5 about a 10-15% improvement.

Unfaced 1" EPS (bead board, not XPS) on the interior would be ~R4, and 3-5 perms, doubling R-value on the framing.  That would raise the R-value of the a wall with 1" cc foam + cellulose cavity fill from from ~R11 to ~R14+, or about a 25%+ improvement. (Were the foam  it on the exterior and thermally breaking the band joist & sill it would be ~R15).


On the kneewall to roof transition 1" is enough to air-seal, but ideally the kneewall would be at the the same or similar R value as the roof.  If the porch roof is on the south side, the space behind the kneewall is going to get pretty toasty in July. If it's possible to put rigid foam on the exterior side of the kneewall as a thermal break, that would be advantageous. (1.5-2.5" of foil faced EPS, with the foil facing the dead-space behind the kneewall would be cheap and effective.  At 2.5" it's nominally R10 @ 75F average temp, but only R8 ~100F, but that's about where the foil facer is starting to give you some heat-rejection benefit.)

I have spent some time reading the recommended material you listed most of which I should have read before contruction. I am finished with exterior contruction and am trying to determine what I can do at this point to get the R value at a Min R-15 with 2x4 walls. Nothing I read mentioned brick exterior. The house has a 8 foot wrap around porch and is a square house. Brick with perforiated foil over 1/2 " OSB. I could not find a perm rating on my vapor barrier. It appears to be foil with very small perforiations. I should have read more before I started but this is customary building materials in zone 3 north AL. Actually the foil was an upgrade as most houses are wrapped in the straberry wax paper ?, sorry I am not a builder or engineer...What can I do to get my wallls and roof (26 ga steel, 1/4 " rigid foam, felt, framed 2x6 on 24 " C) up to aprox R 38 ? As mentioned previously I plan to use some closed cell foam at some thickness in walls and ceiling and floor/ rim joist. In addition I am now considering filling remainder of wall and ceiling cavity with celloculose and possibly 1/4 in open cell rigid foam over 2x4 interior under sheetrock unless there is a reason not to or a better recommendation. Thanks for any assistance you can provide. TS

The perforated  RB be more vapor permeable (5-10perms, just scanning a few manufacturers' specs) than # felt, which means that exterior moisture drives get into the wall cavity & sheathing more quickly than they otherwise would.  Red rosin paper is highly permeable- a few 10s of perms, and more likely to raise the humidity levels of wood the stud bay if you block moisture from drying to the interior of an air-conditioned building. (It was fine to use as an air-barrier before central AC became the norm.)

The key to keeping the structural wood protected is to allow the moisture that finds it's way from the exterior in to the structural wood adequate passage into the air conditioned interior in such a way that it never condense.  If 1" standard polyurethane foam is used on the inner side of the exterior sheathing as an air-seal & vapor retarder, it slows down the transfer of moisture from the sheathing to into the stud cavity just fine, but puts the sheathing at risk. Using a higher-perm rated closed cell foam like Icynene MD-R-200  (not the lower-perm but higher-R  "- C -"version) gives it a bit of relief (2+ perms), but you still have to let that moisture pass into the air-conditioned interior.  (I was hoping you'd had at least one layer of #15 felt or something, but we're still good, as long as you don't lock up moisture against the wood at temps where it it will condense.) 

If you go any thicker than 1" of any standard closed cell foam it becomes a strong vapor retarder, putting the sheathing & exterior stud edge at higher risk due to the vapor drives of the brick cladding.  At 3" standard polyurethane foams are less than 0.5 perms, about as vapor retardent as a kraft-facer on a batt. If you went with the lower-R closed cell Icynene you'd be at ~1.3 perms, (which is about where just 1" of standard closed cell polyurethane lives) you'd be OK, but that's an expensive way to fill up a studwall cavity- cellulose and interior EPS foam sheathing would give you better bang for buck.

More on moisture drives from brick:

http://www.ornl.gov/sci/buildings/2...54_New.pdf

http://www.buildingscience.com/docu...ick-veneer

http://www.greenbuildingadvisor.com/blogs/dept/musings/when-sunshine-drives-moisture-walls


Cheaper and more vapor permeable than foam would be to seal the stud/sheathing, and plate/sheathing interfaces on the interior of each stud bay with acoustic sealant, or 1-part foam or a good long-life caulk prior to filling the cavities with spray cellulose.  To get the whole-wall  R-value up to ~R15 you'd need 1.5-2" of interior rigid EPS (unfaced) between the cellulose-filled studs and the gypsum board.  At 2" EPS is still semi-permeable to water vapor.  During the cooling season the stud edges would never fall below the dew point of the exterior air, since you'd have ~R8 of EPS between the stud edge and the air-conditioned interior.

SFAIK there is no such thing as 1/4" open cell rigid foam.  The stuff used as siding or roofing underlayments are usually closed-cell (XPS), but also have polypropylene or vinyl facers on them further reducing their vapor permeabity to 0.6-0.8 perms, which is exactly what you DON'T want on the interior of your studwall. (It would have been great on the exterior of the sheathing, under the radiant barrier though.)   Putting a ~0.7 perm vapor retarder of minimal R value on the cool side of the assembly all but guarantees that you'll have condensation in the stud bays when the outdoor dew points hit the high-70s.  It would protect the paper on the wallboard, but it'll raise the moisture of the structural wood.  Both higher R and higher permeance on any interior foam is key.

If you're not willing to give up the 1-2 square feet of room area with 1.5-2" of interior unfaced EPS, go with 1/2" unfaced XPS (~R2.5) sheathing, which will leave you at ~ R12-13 for whole-wall R value, but keeps the interior stud edges above the dew point of exterior air (most of the summer, anyway.)  Half-inch XPS from bigger manufacturers (pink Owens Corning or blue Dow Styrofoam)  runs ~ 2-2.3 perms, which would allow the moisture buffered in the cellulose from peak drives to pass into the air-conditioned interior without issues.   If using other manufacturers (eg Pactiv/Greenguard, sometimes sold as box-store branded goods) read the specs- some have polypropylene facers that lower the perm rating, and in this application you want to keep it over 1 perm, (over 1.5perms even better).

Then, DO make sure to...

A: use a silane based masonry sealer on the outside of the brick to limit wicking up of rain & dew

...and...

B: Make sure that you have both weep-holes in the bottom course and as much venting as you can at the top of the cavity, to promote air exchange between the cavity and the outdoor air.


Both measures reduce the peak and average moisture drives, giving the stud wall more drying time, lowering the risk of condensation in the walls.

Or you could just use 2# foam as I did. hehehee

Posted By BadgerBoilerMN on 09 May 2011 05:03 PM
Or you could just use 2# foam as I did. hehehee

Sure hit could, which would only deliver an ~R13 wall, without a thermal break against the bridging of the studs (with R-infinity of cavity foam might get you an R15 whole-wall out of it though). 

It would also place a near-vapor barrier between the sheathing and the interior. That protects the interior from exterior moisture drives, but raises the risk at the sheathing, since the brick-cavity can no longer dry toward the interior.  It's doable, but the brick MUST be designed to dry via considerable ventilation. Summer humidity and solar-driven moisture drives from a brick wall are typically higher in AL than in MN, but even a MN climate isn't immune.

A full fill of 2lb foam in a 2x4 16" o.c. studwall is a waste IMHO (unless you're doing it to add structural rigidity.)  A 1" shot of cc foam is enough to buy you the same air-sealing, and does it without inserting a vapor barrier that you then need to design-around.  The additional cost of going with 3" cc foam fill and a flash'n'spray with 1" + cellulose is about 2x, but the whole-wall R- value gained by the additional 2" of foam is only about 15%. 

By contrast, going with an all cellulose fill and adding just an inch the cheapest lowest-density EPS foam either outside the exterior sheathing (or inside of the studs under the gypsum) boosts performance even more, and it costs LESS than a flash'n'fill.   If you go with 1" XPS or iso on the exterior, it's closer to 50%, and cost about the same as a flash'n'fill, handily outperforming a 2lb foam cavity fill w/no exterior foam at half the cost.

It makes a lot more sense to plan for exterior rigid in the first place rather than treating the insulation as an afterthought.  The cost is lower, and the thermal performance higher.

Using various tools & guidelines for 2x4 16" o.c. framing with typical framing factors the difference in whole-wall R breaks down this way:

Without exterior foam:

cellulose only in the cavity:     R10

1" cc flash'n'fill w/cellulose:    R11+
....add 1" of interior EPS:       (R14)

2# R6.5/inch cc foam fill:   R12.75   <<

With exterior foam:

Cellulose + 1" exterior EPS:   R14+

Cellulose + 1" exterior XPS:   R15

Cellulose  + 1" exterior iso:     R16  (R17 during an AL cooling season, R15.5 during a MN winter.)


An all cc foam fill is north of $3/square foot and by far the most expensive option listed.

A flash'n'fill runs ~$1.40-1.75/square foot.  Adding an inch of interior EPS adds ~40cents/ foot bringing it up to ~$2-2.25/foot. Still pretty pricey, but better R/$.

If you air-seal with acoustic sealant instead of 2lb foam, and use 1" XPS on the interior instead of EPS you end up at the same R14+ for about ~$1.50-1.85/foot.

Cellulose + 1" exterior XPS or iso costs about the same as a flash'n'fill- it requires some detailing to make air-tight, but it's not difficult.  By putting the foam on the exterior you achieve thermal breaking at all the band joists etc. that can't be done with an interior foam-job, which at best thermally breaks the studs & headers/plates.

Most of the time you'll get more performance per dollar spending on the exterior rigid goods, or spray foam as an air-sealant/vapor retarder.  With the 20%+ framing factors of 16"  on center framing, the thermal bridging of the ~R3.5-R4 studs makes R15 whole-wall values impossible. There is no known cavity fill material that would get you there.  But with exterior foam pretty much the full R value of the foam sheathing gets reflected in the whole-wall number 1-1.

Brilliant as usual, but my foam guy hates you! heheheeheee

I wonder about drying to the inside (though I recognize the value in basement applications). It would seem you have to assume a lot about indoor vapor pressure, which tends to vary more than geographic climate data e.g. cooling, ERV, HRV, open window control systems etc.

I would also note that nothing will save a poorly installed brick veneer.

According to the DOE, northern AL is an interior vapor barrier area - I'd be careful about doing the opposite.

http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11810

In all cases, roof overhangs, low air infiltration, minimal differential between indoor/outdoor pressures, low indoor humidity and either non moisture absorbing siding or a rainscreen gap make the most difference.

Great link jonr. Nothing like a graphic to clear the mind. When working as a licensed home inspector I found poor roofing practice and misplaced gutters the most egregious offenders when water was an issue, but the technical aspects of sheathing were the most insidious.

It's better in mixed climates to not have vapor retardency under 1 perm on either surface, but if you must, in northern AL it's generally better to have it on the interior. But with moisture reservoir claddings like brick an interior side vapor barrier puts the studwall at risk in air conditioned buildings (even in those climates north of the 48th parallel.)

With 5-10 perms on the exterior RB the sheathing itself is more vapor retardent than the RB, but still over 2 perms. A flash of 2# foam brings it down to about 1 perm. But I suggested the high-perm Icynene may be a better choice than generic cc polyurethane, since that would leave it over 2 perms @ 1".  

A half inch of XPS or 2" of EPS on the interior would be a Class-III vapor retarder, lower perm than the sheathing & RB combo. In combination with interior latex it would end up between around 2 perms on the interior. Dew point calculations for Huntsville indicate class-III interior vapor retarders would be sufficient to protect it from winter moisture drives from the interior.

With a flash'n'fill even using lower-perm cc foam (~1-perm/inch) the condensing surface would be the foam (which would have a miniscule number of condensing hours, and zero wicking toward the sheathing), and the total stackup between the sheathing and interior would still be above 0.5 perms.  It would still work, but it would have half the drying capacity.

In this simulation, unvented & vented brick clad structures, in zones 3 & 4 (northern AL is in there) with only 8 perm latex on the interior as the vapor retarder the risk to the exterior sheathing is low in a lower humidity scenario, with only slight risk in the highest humidity scenario. But risk is moderate to HIGH in the unvented scenario in zone 3 if a poly vapor barrier is used on the interior:

http://www.ornl.gov/sci/roofs+walls/staff/papers/143.pdf

(See figures 6 & 7, pp 7 & 8)

I'll stick with my recommendations.

BTW: A cavity wall IS a rainscreen gap, but like any rainscreen, they work much better when vented to the outdoors.

I know what the codes say, and what the experts say, but I also have seen the problems interior vapor barriers have caused in my area.(western KY). I can't imagine using one farther south (N. AL)

Posted By wes on 21 May 2011 09:07 AM
I know what the codes say, and what the experts say, but I also have seen the problems interior vapor barriers have caused in my area.(western KY). I can't imagine using one farther south (N. AL)

Amen, brother wes!

The DOE map is a very generalized map, and doesn't take cladding type into account the way the ORNL simulations do, nor does it take into account the type & placement of the insulation. It's probably about right for  vinyl-sided studwalls with kraft-faced batts, in the portion south of the Mason-Dixon, but not so much for brick-clad or foam sheathed buildings anywhere.

Even VERY low vapor-perm insulation can be used on the exterior of the sheathing in ANY climate, as long as it's sufficiently high-R to keep the average January temp at the sheathing above 40F, at center cavity. In that sort of stackup an interior vapor barrier would be a mistake, since both inward & outward drying would be severely impeded.  With semi permeable foam there is more flexibility to the design, but interior poly would still pretty much a disaster anywhere in the gulf states.  Winters there are so mild it takes only a very modest amount of exterior foam to be protective, summer or winter, any type of cladding, so long as there isn't a strong interior vapor retarder.  A rainscreen gap + 1" of exterior XPS + unfaced fiber insulated 2x4 wall + latex paint on the interior works fine with most any cladding from a moisture POV almost everywhere in the lower 48 (but going higher-R is still cost effective.) 

The D.O.E. vapor barrier map is just a bit silly, and isn't specific enough to be used prescriptively.

If open and closed cell are the same price, you will be getting open cell. No one would/could do a CC job at an OC price! The disadvantage of closed cell is that it cures HARD. (like a piece of plastic) (open cell is very soft) In a new house when it racks from wind and settling the CC foam will break and the air seal will break in areas you will never find. The cost should be about 3 times as much for CC.  You must use CC in the crawl space to keep moisture out! No Option! Put much more foam in the rim as this is where most leakage is. Many contractors use 1.2LB foam and call it closed cell, it is not! Your A/C units should seem small for a conventional house. The 10 to 12K is about right for OC. You want someone with experience to spray for you. Both you and the contractor want to do it on a warm or hot day. Be sure the polyseal job is total and there are no cracks or gaps anywhere. The foam can only seal where the foam is. There is no foam on double and triple studs, on headers and where studs meet plates.  They should be caulked...every single one of them!  Remember you are paying for foam to seal the house, so make sure you seal the house. In fact every place wood meets wood in your house should be caulked. Be sure you have make up air for the dryer, kitchen vents, fireplace, bathroom fan, etc. etc. Other than that it's easy. If you do this right you will pay more for cable bill that any heat or cool bill. You can place a meter on the A/C units to see exactly how much wattage they use.

"the CC foam will break and the air seal will break in areas you will never find." ?

I don't think so.

Per ORNL: With vinyl siding, interior poly is fine anywhere in zones 3-6. Just latex paint is likely to cause problems in zones 5 and 6.

Interior poly can also serve as an effective and low cost air infiltration barrier.

Thanks to all for the great input. I still don't understand all I know, read, and heard about perms and drying to inside outside but I have read or am reading all the info referenced. Let me throw my thoughts out for review based on what I have read and request you all to give me feedback. If money were no issue. As I plan to insulated this house even if I have to wait to go to the next phase..sheet rock. SOoo, Again, 54 ft square brick house on craw space with 8 ft wrap roof covered porch with vinyl clad under porch vinted at eves 360 degree. Aprox 1 " air gap between brick and foil wrap (unknown perm) over 1/2 " osb 2/4 stud wall on 16 " c. There is a 32 " knee at the top of the stud wall that will transition to the 2x6 roof which is 26 g metal over 1/4 " xps or eps ? unknow perm over felt. The roof is 5x12 P and framed to 5' 8" so the is ~1500 sf upstairs apartment, the current plan is for an unvented roof. I will start at bottom and work to the roof.
One inch closed cell (cc) foam under floor (optional), 2" cc floam on rim joist is a requirement. 3 1/2 " open cell (oc) in interior stud wall or 1 " cc foam and 2 1/2 " oc or 3 1/2 " cc ?. 32 " knee wall transition from exterior to roof will have 1/4 xps or eps (for stiffner to spay foam on) with 2" ccf. Interior roof (attic apartment) unvented with ~ 1 in cc 4 " oc or 3"-5" cc foam ? The exterior of the house is finished so there is no options other than sealing the brick. Appreicate your recommendations based on the above. Thanks, TS

A smart interior vapor retarder (like Membrain) rates highly in zones 3-6 and creates a/another air infiltration barrier. So that plus cellulose (no expensive spray foam needed although you could still add it) is what I would use. It pretty much keeps everyone happy - breathable, code compliant, double air barrier (assuming taped or sprayed foam on the exterior side) and does well in all tests.