Excellent choice.

External insulating sheathing reduces thermal bridging.

Photo: Dow

Tongue and groove sheathing, as on the house above, reduces air infiltration. Or you can tape all seams.

The decision to use insulated sheathing usually has to be made prior to construction, so there is enough room to install it between other structural sheathing and the exterior finished wall.

If you use external insulation like this and are using a brick veneer, doesn't the foundation need to be wider to accomodate the insulation and still leave a proper brick ledge? In other words, is there a cost for a wider foundation as well as for the external insulation?

You should check out the rvalue of the product you use and the vapour barrier location.

Too small of an rvalue and improper placement of the VP can cause moisture in the walls to condensate. I think that you need at least a 5 rvalue to stop this.

1/2" on corners over 1/2" plywood
1" everywhere else on exterior of walls.
I recommend closed cell foam sheathing board rather
than open cell. closed cell foam boards will be
about R-7 where open cell will be about half.
this is a cost effective upgrade.
all seams should be taped, all openings sealed before
exterior cladding is applied.
caulk the sole plates to the slab or subfloor.
this is the beginning of the air tightness.
insulate conventionally and use air tight drywall
approach to interior.
save foam for attic where most it is really needed.
spraying foam in walls is a huge waste of $$ when
you can make the wall air tight fairly easily.

best of luck.

you will see a much better pay off using exterior foam sheating vs spray urethanes for sure. Make sure the sheathing runs cont. from your eaves all the way past the rim joists as well, not just the walls. Caulk the foam to all the studs and locations it connects to wood framing. Tape all seams. I would recommend going 1" min. vs the 1/2". Labor costs remain the same, slightly more matieral costs. Also talk to your insulator about spray in options such as cellulose or fiberglass instead of batts. Again, more efficient with less air spaces, and overall better insulated house. Put the money in your shell, it will pay you back!

doesn't the foundation need to be wider to accomodate the insulation and still leave a proper brick ledge?

Only if you're covering the rim joists from the exterior. Otherwise, the carpenters just set the framing back on the deck the necessary amount. Or you can split the difference.

In the house above, the foam sheathing is the only sheathing as the structural strength was achieved with bucks between all the 2x6 framing at midpoint on both floors.

I recommend closed cell foam sheathing board rather
than open cell.

I've never heard of open cell sheathing. Perhaps you're referring to expanded polystyrene.

I may need to clarify. The contractor would use the energy shield board on the interior portion of the exterior wall; the drywall would go directly over the energy shield board. It would not be exterior sheathing. As noted before it would reduce thermal bridging and infiltration.

This is about a $3K adder to a 3200 sq foot 2 story house. Any thoughts?

the drywall would go directly over the energy shield board. It would not be exterior sheathing

Energy Shield board is foil covered polyisocyanurate board and it is correctly installed over all framing materials to the exterior, not the interior. Here are the appropriate manufacturer's info and aBuilding America publication on insulating sheathing. The latter also includes illustrations of how insulating sheathing raises the effective R value of a wall over the nominal R value.

Here is a link that might be useful: Guide to Insulated sheathings

sheathing the house with foam board is more cost effective than foam spraying the walls.
I've never heard of foam boards on the interior of the walls. I'd check to see if this is what your builder actually means.
best of luck.

Confused! Digging footers this week . . . thought we would do R-21 (we have 2 x 6 exterior walls). We are slightly north of Atlanta so fairly mild winters and hot summers. Does the sheathing board make sense here? Do we need to make any framing changes, or basement wall changes? We will have a brick exterior.

Thanks!

The US Department of Energy's Office of Energy Efficiency and Renewable Energy considers your specs to exceed the level of cost-effective insulation. (See Link. Scroll down to map.)

Here is a link that might be useful: US Dept. of Energy: Cost Effective Insulation Values

athensmom - I wouldn't even do r-21. You might save $500 in insulation costs by going to r-19 and your increased energy cost might be $20 a year. Just a thought. I am so much further north than you and paid $500 total this winter for heat with r-13 walls. About $100 of that was probably for the walls.

Excuse me on a little math here. R-19 would have got that wall loss down to $70. R-21 $63. Summer is about the same cost for me but maybe 50% more for you. Insulation is probably worth about 20% of what it is for winter. So the walls are costing $20 a year for you in the summer. (50% greater a/c need but 50% better insulation than me). So going to r-21 might save you $2 a year in summer. So you are looking at about $10 a year in savings for r-21 vs r-19.

Lots of guesses and estimates but I wanted to give you an idea what you are looking at. Adding foam sheathing to that would be something like $2000 to save an additional $10.

Focus on air infiltration, not r-value. Then focus on solar gain. In the summer, our window solar gain is about 10 times our wall gain.

(Note - I used my winter and then your summer in the estimated costs so your benefit would actually be less - something like $7 for R-21)

sheathing boards on exterior of walls for hot or cold climates.
see buildingscience.com for your specific climate.
best of luck.

Has the problem with the poly-iso been solved? I've heard of it shrinking and cupping. That was years ago though, and maybe the new formulas do not do that? Just curious as I would like to wrap the exterior of my house with 4 inches of it.

cheap foam sheathing boards break down fast
the more expensive ones do not.
proper nailing patterns, seams taped and holes repaired
make for a good long lasting install.

you must be in a cold climate Johnny..we have 1"
here, I hear of 2" mid state area. never seen 4".
you might be looking at overkill..being in a hot humid
climate 1" suffices. but air sealing has to include above
install, sealing of sole plate to slab or sub floor
and air tight drywall to interior.
you would have to put pencil to paper to see what
is within your budget.

best of luck.

best of luck.