I am doing some prelim research for an upcoming project.  I think I will propose double stud as a very high r is requested by the owner.  However I am considering ZIP sheathing on the exterior as opposed to typical OSB to help in my air sealing.  I plan on using an ICF foundation, and continuing the ZIP all the way to the foam where I will somehow tape/seal it to that.  Looking at the Building Science website they shell the cross section of the double stud wall.  However they are calling for the vapor retarder to be on the inside of the inner stud face.  I am curious if this can lead to issues due to the ZIP exterior sheathing and prevent drying to either inside or out if moisture gets in.  I am debating if this should be eliminated?
I can also see it being a PITA for the insulator to have the plastic in the middle of the wall as well. 

Speaking of insulation...talking with local insulators who do dense pack, wet spray and blown blanket, they tend to greatly favor blown blanket.  Its faster, cleaner, does not have a dry time, and has a slightly higher r rating.  I know its not the "greenest" thing to use, but are there any major reasons not too?  I can hit an r-40 and decrease my wall to 10" thick that way too (center wall r).  They also tend to price them (cellulose and blown blanket) similarly.  BB is also a little lighter, so I think I can go r-60 in the ceiling with 5/8" gyp 24" centers they claim. 

thoughts on any of the above?

Greetings,

If your going with ICFs on the foundation, why not use them for the upper floors.  You'll have your strength, sound deadening, higher insulation values, storm and earth quake resistance all in one. Check the "vertical ICF sys"

One of my customers has an icf house about 2500 sf ,. multi level with radiant barrier in  vaulted ceilings and the power company came out and changed the meter because the usage was too low. It also had geo therm.

You can't get "R" 50. It's a myth.  You can get better results with 2x4 construction and radiant barriers(RB). As low as 2 btu/hr/sf when done with my improved method, ceil'g and walls.

We're getting 100 deg days here and my them is set to 76 and the ac runs intermittent about 20 minutes out of the hour, middle of day, AND, low humidity in the house.  The "R" 50 sys can't do that. My house is a radiant barrier up graded sips house we bought several years ago and up graded with RB ceil'g and for now, ceramic paint on interior walls.

I don't recommend sips homes.

The best value for the dollar, my opinion, is the "econodome.com" home with RB. Wish I had the money to build one.

Insulating paint and reflective Barrier in the same post. Wow... That's impressive.
And a myth of r50? Impressive. If you put 10" of XPS, you have just achieved r50. MYTH BUSTED!

Seriously though, Insulating paint.. read the following, and get a good laugh in.
http://www.greenbuildingadvisor.com/blogs/dept/musings/insulating-paint-salesman-tripped-his-own-product

Greetings,  There are NO legitimate , INSTALLED, tests that show that you will get "R" 50 with 10" XPS.  I've been in the insulation business for over thirty yrs and have not seen one yet.  Same with FG and cellulose.

The maximum eff'y I've seen for any bulk insulation is about 4".  After that the roll off is dramatic.  For instance, if you add 6'' FG to existing 6" FG the increase eff'y OF THE SYS IS ABOUT 7.6%. If your ^'' sys is already saving about 80% of the energy that it will allow,( not 80% of 100%), then the add'l 7.6 % of system eff'y is going to result in wasted money.  Various independent labs, universities and even power companies have verified this.  But the government, insulation mfgs and utility companies manipulate the public into using the common type materials because of money.  The US senate has interfered twice to protect the status quo.

I read the article. I have no doubt that the paint didn't work if he used something else rather than ceramic beads,  The problem with the article is that they did not identify the additive.  One paint company used alum chips and that failed,  You cannot coat aluminum with paint, it stops the reflective process.  It is good that this fellow really wanted to do good.  The problem was he apparently did not have the knowledge or back ground to validate what the mfg told him.

When an architect friend told me about RB back in '74 I drove out to Cal to check the mgf and went out to several jobs to see the results. One  job was a 250000 sf shopping area, They use ONE layer of foil stapled to the bottom of the rafters.  It was very hot outside, but, very cool inside.  I decided to start my own business and I have never regretted it.  I'm i n the St Louis area.  My back ground was, R&D machinist, cost est'r and quality control supervisor.

Sorry about the book, I got on a roll.

You do realize the definition of R50, is that you have r.... 50. Point blank. 1" of XPS = R5, times 10 = r50. Simple math.

Whether R50 is worth the cost vs decreasing gains, that's a whole other issue which smarter people than I have researched and agreed upon... (mostly. )

Refer to any PassivHaus literature if you disagree, or any of the Net Zero research.

Tell you what, you build yourself a house, with only insulating ceramic paint in an extreme cold/hot climate and tell me how it goes.

I am not real sure where r-50 came from....

Also I am not interested in ICF all the way up.  There are other advantages, but in our climate, higher r stick framing pays off way better then ICF upper floors.  Any 3rd party testing out there (not funded by the ICF boys) shows ICF in cold climates has marginal advantage thermally vs other options, especially when price is factored in.

Greetings,

I would not build a house using CBs as the prime insulation.

I would use 2x4 with 3 layers RB ceiling and two walls.  The way I install the RB it calculates to about 2 btu/hr/sf on a 100 deg day. I know of no bulk insulation that will come even close to that.

"R" factors do not tell you what the drywall temp is.  It's not the "R" factor you want to know, it's the drywall temp.  Because that tells you the amount of btu/hr/sf. based on the delta T between ceil'g and floor.  For instance it's quite common for FG ceil'g temps to get to 110 deg on 95 deg day, emitting 37 btu/sf/hr.  110 deg is about 25 deg hotter than a radiant heat sys.  IF, the RB surface gets to 110 deg it will only emit 2 btu/hr/sf.  The calculations are based on a 75 deg floor.

As far as researches you have to be careful because you don't know who fund the tests.  Just because they are smater doesn't mean they have the best info.  Believe me. I know.  Been there , done that. For instance if you check the DOE web site for insulation you'll come up with this gem.  RB are not as eff in winter as summer.  Not according to a mechanical engineering handbook. BUT, there is a difference in the mechanics of a ceiling so that would APPEAR to be true.  What DOE doesn't tell you is what type of RB sys they are using  AND to what they are comparing. Just small details.  The RB sys will out perform all other sys according to my 30 yr + experience.  So why does DOE do this? Because, the RB will cut ac use by at least 50% and heating by 30%. That's alot of taxes lost. 100's of billions in fact.

I published an article a few days ago on this forum.  It contains a btu chart.  If you measure the ceil'g temp and check the chart you will see your gain.  Does your "R" 50 house ac run 18-20 total minutes/hour, intermittently, mid day, on a 100 deg day with temp set and hold'g 76 degs?  And, what are your humidity levels?

sooo....about the vapor barrier on the inside...any thoughts on this used with ZIP?

Greetings,

Putting a VB on the inside does not prevent condensation from forming in the insulation. Any fiber type insulation will increase heat flow at least 50% due to condensation. You ALWAYS have condensation in fiber type insulation.

Greetings,

Curiosity finally got to me and I looked up some info on the ZIP sheathing that some of you are planning to use for a wall system.

DON”T USE IT FOR WALL SHEATHING. It was not designed for that purpose.. I did not see on the ZIP website any mention of wall installation, in fact their pictures only show roof application. This material has a 1ppm permeability and will trap water inside you walls and cause them to rot out.

Plus the more moisture you have in your insulation the greater the heat loss thru conductivity.

In very cold conditions there is even the possibility of ice in the walls.

This higher moisture content puts you at greater risk for mold.

If this system is used on a roof application make sure you use a well designed ridge/soffit vent system. The best is at core-a-vent.com.

Unless I get info that would change my mind I would personally not use this product.

If you really want super insulated wall, go with radiant barrier insulation. See Fifoil.com

rbisys-
thanks for the comments, but you need to research more about ZIP sheathing......
THey do have 2 types, green for walls and red for roofs. THe very low perm is exactly the reason I am asking about omitting the VB in the inner face of the wall as the Building Science details show. However they use typical osb sheathing, not ZIP.

Greetings,
Thanks for the info.
I checked their web and did not pick up on this. I guess I'll have to check it again.

AGAIN, having a VB on the inside does not stop condensation in the walls. The process of condensation is EXTREMELY strong.
If the process cannot pull moisture from the inside, it will pull it fro the outside.
It is commonly accepted that even a minimum amount of moisture in the wall, including humidity, will increase heat flow about 50%.
The more severe the situation the more heat flow.
I have seen walls in the middle of a drought with temps at 100 degs, SATURATED with moisture.
Why use a system that is crippled from the very start, when you can use RB and eliminate those problems and have a super insulated house. Also, you do not have to use special products.
The method I advocate emits as little as 2 btu/hr/sf using calculations from a mech. eng. handbook. I know of no other sys that even starts to approach that. Yes it does cost a bit more, because you have use 1/2" and 7/8" steel furring strips, but this works.
On a 100 deg day, electricity out, single story ranch, dark roof, no shade, inside temp never exceeded 80 deg.

incase anyone is curious, here is a reply I got from ZIP's manager of building science. I was surprised...a great, fast response!:

Considering that your house is located in Waterloo, IA (climate zone 5 or 6) per the 2009 IRC , it is a requirement to install either class I (<0.1 perm) or class II (0.1-1.0 perm) vapor retarder on the warm side of the wall. Although the vapor permeance of the overlay on ZIP sheathing is 12-14 perms the vapor permeability of the ZIP System does not differ significantly from the vapor permeability of the OSB substrate. In other words the equivalent water vapor permeance of ZIP panel with overlay would be almost equivalent to the water vapor permeance of the OSB substrate.

As an alternative, per the 2009 IRC you may use class III (1-10 perms) vapor retarders on the interior in a case if you have vented cladding over ZIP panel, which we recommend assuming that interior RH levels are not elevated in the winter. By doing so you will still promote the drying inwards in the case an accidental leak occurred in your wall assembly and ventilation through the cavity behind the cladding will allow for drying outwards. You can achieve this by installing kraft paper faced batt insulation with the facer located on the inboard surface. We understand that your intent is to apply ZIP panel in a double stud wall assembly, and these are typically built either with staggered 2x4 studs on 2x6 base plate or with two rows of 2x4 studs. This construction provides larger separation between exterior and interior sheathing panels and allows more insulation to be placed in the cavity. The more insulation installed will make the exterior sheathing colder and would increase RH in the sheathing over the winter and it may promote some mold growth. Also ensure that insulation placed in the cavity does not sag and leave any big cavity space for the air in the cavity to circulate by natural convection (interior cavity convective loops). The warm air within the cavity hitting the cold exterior sheathing may condense. Also ensure that top and bottom of the wall are properly sealed on interior to prevent any entry of warm and humid interior air into the cavity in the winter time.

TL,DR:

Air Barriers are important. Do them right on the inside.
Rainscreen or backvented siding = Increased ability to dry to the outside.

Vapour Barriers (poly) prevent drying to the inside, so if you can get away without poly, do so.

That 12-14 perms seems... significantly high... I was under the impression OSB/Ply had a perm of 1 or so.

But on the other hand, You could just skip all the insulation, and install a radiant barrier, and you'd have no problems right??

Greetings.

Sounds like he verified what I said.

2x4 with RB. No condensation and much higher efficiency.

I sort of figured the "sarcasm" tags weren't required.

Greetings, there's something else going on in this double wall sys.

Summer condition: The stud towards the i/s wall only has 2" of insulation between it and the exterior wall. But you want to claim a higher insulation value because the wall is thicker. That's cheating. The highest temperature is going to be in that 2". In fact there is a good possibility that the first 2''insulation is very close to the sheathing temp. What have you gained?

The other problem this sys has is that the greatest amount of heat flow considering surface [exposure) is thru the top and bottom plate, particularly the top plate. A true double wall sys has 2, 2x4 wall sys separated by 1" or more air space.

If going from a 6" batt to a 12" batt only increases the sys eff about 7.6 then haw much do you think you're going to save with this ddbl wall sys? Not much.

So, you using all this material and time to get something that is marginally better, at best.

You can't fool Mother Nature.

rb- I really have no idea where you are pulling your info from, it certainly isnt this thread...
12" thick double stud wall made of 2x4s...first of all gives you 5" of thermally broken space between the inner and outer face of the 2x4 walls. yes, thermally broken. That means the top and bottom plates are also 2x4. The upper cavity will be left open to the ceiling cellulose to form a complete blanket from floor to attic. The 2 walls will be held together with scrap osb plywood pieces here and there connecting studs.
Also the outer 2" of insulation is the hottest...so what? luckily, there is still another 10" of insulation!
I suppose all of the case studies and real world findings of near net 0 double stud assemblies are also wrong?
tell me, how much would RB cost to build a 2x4 wall to hit an equivalent r-45? My fully air sealed double stud assembly is about $3.24 sqft, materials. I'm fairly certain you wont be anywhere near that.

I didn't say 12". Most ddbl I've seen were 2x6.

However the ratio of savings to thickness still remains, SMALL. After 3 1/2" the increase in eff is not proportionate.

Comparing, how about the same price as a standard 2x4 plus about 2% more, or less.

In the first place you are NOT getting "R" 45. You're lucky, with the moisture, if you're getting "R" 20. That "R" 45 is a myth, and you have bought into it. That's OK, it's your money and you're happy thinking you have "R" 45. You'll have to admit, the PR guys did a great job convincing you.

But you spent more money and lost alot of sf.

I've got over 30 yrs experience and structures to compare, so I know what works best. That's why I advocate RB.

most of the double stud walls you have seen were 6" thick?... how is that even possible?
show me the studies and numbers that moisture brings the r-45 down to an r20 and then we can go from there. So by that math, code r21 walls are really an....... r-0?....... No one convinced me of anything. I do not listen to reps. They call me every day. I rely on real word studies and findings. I rely on discussions on forums such as these to get unbiased opinions and alternate info. I am not denying RB are not affective. However they certainly arent the be all, end all. Moisture in walls will happen. THe goal is to design for it so it can dry.