Exterior rigid foam is the way to go, in my opinion. It provides a great thermal break, allows you to extend the insulation down to the footing, and you can use 2x4 or 2x6 studs. Finding a contractor who is used to doing that and doesn't overcharge for the additional effort can be a challenge.

In a 2x4 wall you can use spray foam but it has to be closed cell not open cell. To meet R-20 requirement (if that is what code says in your location). Closed cell foam is R-7.25 per inch. But that carries it's own added cost. Very rarely do we insulate the exterior walls of new homes using spray foam (cost being the main factor). We frame with 2x6 and insulate primarily with dense packed cellulose. With any of these products it pays to get someone who can install the insulation correctly ensuring no voids or gaps.

Talk to your local codes officer.

If you want economical, spray foam ain’t it. Two staggered 2x4 frame walls with exterior foam sheets and interior fiberglass or cellulose will get you a better thermal break, higher R value, and a much quieter house than 2x6 construction.

There are no circumstances in which a 2x4 wall should be on the table in your location. I have to think you have an idjut for a builder. Which would make me question a whole lot more about him and his recommendations. I think you have a cheap low bidder.

What does your architect have to say about this? Because the home really needs to be designed as a whole system and not field adapted to different construction methodology. Too much is lost when you try to take a plan designed for one way of building and try to adapt it to another.

The architect designed it to be 2x4 with open cell spray foam. He’s employed by the building company.

Are you sure the builder said open cell and not closed cell foam? That would be an R value of about 10.5 which is absurd for a house in Michigan.

Yes I asked him that specific question and he said open cell. He claims that their homes go through 3rd party testing and that they far exceed requirements, but he has never provided me with any specific R-value numbers. I am waiting for those numbers right now.

I would love to know how R value is determined by this 3rd party testing. Ask him for a copy of a report of a house he has recently built. Also ask him what requirements he is using.

I might be mistaken on him saying 3rd party for R-value testing; possibly for something else to do with home efficiency. I will ask for a report thanks for the advice.

So foam does help with air infiltration which is a big item. That maybe tested by 3rd party. Air infiltration is very important but can be addressed in a lower cost way. IMO - it is a way to cover sloppy work and still get decent numbers. Spot spray foam, zip sheathing and tape etc is more cost effective.

I always thought it was common practice to install Tyvek paper over the exterior sheathing in order to provide an air infiltration barrier.

The insulation products and amount will determine the R value. The values are supplied by the manufacturer and the product has to be installed properly.

The builder is either giving you the run around, or is completely clueless about insulation. What is decided should be documented in your contract. This is too important to get wrong.

Is this a tract or builder's home, or a truly custom home? Tract and builder's homes, more often than not, are build the way the tract or builder has learned to build fastest and cheapest. Sorry to have to break the news...

In many climate zones, one of the proven best assemblies may be 2X6 studs, with high density cellulose or fiberglass batts tight in the stud cavities and with exterior grade ply or OSB panels, air barrier/vapor retarder, and 1"-2" rigid insulation panels under the exterior finish material.

Google "residential exterior wall assemblies". There's tons of information out there.

Mike - Tyvex is neither paper nor an effective air barrier. It is a weather resistive barrier. Builders (and Dupont) like to mention that it helps with air infiltration but it really doesn't when installed in the usual manner. I don't think there are many high performance builders who use Tyvex as an air barrier.

Zip walls or taped foam sheathing is a much more effective air barrier.

No, no, no to open cell foam in your area. Rein in your desire for a home "now"...or regret it later. There is no substitute for doing your own research.

I am trying to do my own research and keep finding conflicting viewpoints like this that says closed cell is a waste of money:

https://www.finehomebuilding.com/membership/pdf/184243/021269086NRGnerd.pdf

I am finding time and time again that exterior rigid foam sheeting seems to be the way to go regardless of what you insulate with between the studs.

After a ton of geeking out about wall assemblies, including reading lots of articles and speaking with insulation experts, builders and energy consultants, my favorite assembly is nail base insulation (Zip-R or Atlas nail base) on 2x4 or 2x6 framing with about 3" of spray foam. This gives you great R-value, a continuous thermal envelope and incredible protection against air infiltration and potential condensation issues.

Summit - while I don't disagree, why spray foam at all? My 5.5 inches of blown cellulose is cheaper and more effective. Sure the foam gives an air barrier but good details and exterior foam taped should be good there. Cellulose should also give better sound control.

Birdman - I agree that closed cell is a waste of money. I don't think that is a real conflict. It is generally significantly cheaper to do other methods. But if you were stuck with 2x4s and no exterior sheathing, the closed cell makes more sense. It would cost significantly more than foam sheathing and not be as effective. So no real conflict, just right tool for right limitations.

For a high performance wall, there are 2 options. Double stud or exterior foam. After that, what is actually in the cavity is significantly less important. Most favor cellulose (or Rockwool) based on cost/performance issues. I was going to do fiberglass batts (and increase my rigid foam to compensate) but the sound abatement argument won out. Spray foam in walls is costly and unnecessary since the rigid foam can do better at stopping infiltration.

Now about those windows.....

I would stay far away from that builder and architect.

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There are a number of issues that must be properly designed for in a wall assembly; insulation value, thermal bridging, air infiltration, and moisture mgmt.

In a cold climate like MI the best option is likely PERSIST (or other exterior insulation options) but that is expensive up front with about a 15-20 year payback which most people don't want to deal with.

Next and likely best for most people is a double (offset) 2x4. Design and construction are similar to standard 2x6, cost is only marginally higher, yet it provides much better insulation and thermal bridging performance and if done right will also do well on air infiltration (aim for < 1.0 ACH50) and moisture/mold control.

Next and last is a traditional 2x6. Unfortunately many or most architects and builders don't seem to have the mental capacity to learn new things (see above) and so don't want to do anything but standard 2x6.

More: https://buildingscience.com. GBA also has some good articles on this.

Single 2x4 with no exterior insulation has no place in cold climate construction.

And, as mentioned above, WINDOWS (and DOORS)! If you have many then this may be more important than wall construction from an insulation/energy standpoint.

David,

Will you be using 5/8 inch sheet rock on the 24 inch on center exterior walls? I would be concerned about punching through 1/2 inch sheet rock.

My understanding is closed cell foam is great from getting a high R value in a tight space such as renovating an old house. In new construction you have the freedom to use other methods that cost less and perform just as well.

I also worry that any type of foam has to be installed properly. I have seen pictures of improper installations. They are not pretty.

David Cary--Closed cell spray foam with nail base is my preferred method in a harsh environment when it works with the budget.

I do a lot of homes in Colorado above 9000 feet elevation where the temperature can get below -20º F with 0% humidity outside. The warm moist air inside wants to migrate to the outside. Somewhere in the assembly that air will meet its dew point and condense. Since closed cell spray foam isn't porous there is absolutely no way that can happen.

The difficulty in being able to properly advise the OP is the fact that we do not know the actual proposed completed exterior wall system. We need to know all components from the exterior finish through to the interior finish in conjunction with the applicable code requirements for thermal performance, air infiltration and vapor transmission. There are varying methods of exterior wall system construction that will likely meet these code requirements. The one you chose is dependent upon the cost of construction, ease of installation and whether or not one wishes to exceed the codes minimum.

Mike - yes 5/8 drywall. Should help make the house even more quiet.

Holy cow, there is lots of good advice here but some different opinions. Different opinions can sometimes both be right depending on individual needs. If the builder/owners do not have time to do the research, it is imperative that an architect current with the latest techniques, but not married to the idea that the latest is always the greatest is best is employed. Sometimes nouveau construction techniques are disasters as they age. A good energy rater with new construction experience can be a good alternative if the architect will listen. Even with a good architect, the energy rater should be there with equipment to make sure that the construction meets the set benchmarks for air leakage, thermal breaks, proper insulation application,.... If it does not pass, don't pay. The rater can make sure that the final product does not crash and burn when it is too late to fix very easily by checking on construction as it is happening.

Just to be clear, in Michigan a wall with porous cavity insulation should have an interior vapor retarder membrane. A wall with continuous rigid foam board insulation outside of the sheathing should not have a vapor retarder membrane. A weather/air barrier wrap is not a vapor retarder.

If the IRC is the applicable code, the only accepted standards for R values will be found in the relevant ICC Evaluation Service Report for each specific insulation material.

Here are links to ESR-3458 and ESR-1826 for two low density spray foam cavity insulations.

You should ask the contractor for the applicable Evaluation Service report for the proposed foam insulation and it will tell you the R value for a given thickness. 3 1/2" of the example insulations would have an R-value of 12.5 to 13. I can't say if that meets your code without knowing what that code is but I would guess it is not compliant.

Regardless of the code requirement, I recommend 2x6 studs and 5 1/2" dense-pack cellulose cavity insulation or 2x4 studs with 3 1/2" dense-pack cellulose cavity insulation with an inch or more continuous exterior insulation.

The Kitchen Abode Ltd.

The IRC, if it applies, only lists two kinds of exterior wood framed wall insulation applications: 1) cavity insulation and 2) cavity + continuous exterior insulation. The requirement for Zones 3 through 5 (most of the US) is R-20 cavity insulation or, alternatively, R-13 cavity insulation plus R-5 continuous exterior insulation. An alternative configuration would require a compliance alternative approved by the building department which doesn't appear to be the case here.

What the OP needs to know is that the contractor does not appear to be proposing a wall system that meets the minimum standards of the Energy Conservation section of the building code so he/she needs to ask for proof that it does.

The configuration of the wall system is a secondary issue that is also worth discussing.

This is a complex issue with multiple variables! 2”x 4” vs 2”x 6” wall framing, Open stud corners, ladder T's, Sill sealer, Insulation thickness and type, Thermal bridging, Air Barriers, Vapor Barriers, Home orientation on the lot, The U factor and SHGC of the Windows.

All of these and more are factors that should be considered when deciding what wall system to build for your specific Climate region.

There are people who do studies using Science to answers these questions. The most recent Building code may not even be adopted yet in your area or the building code may even be outdated based on current building science. Do your research and ask questions. Here are a few resources to look at.

https://buildingscience.com/

http://www.eeba.org/resources

JDS - That's the type of information needed to properly assist the OP. Here in southern Ontario Canada the minimum R value for an exterior wall is R20. Major mass builders achieve this using 2X6 studs in conjunction with batt fiberglass insulation. There are other construction methods but for the mass builder this is the most economical and fastest method to meet the code minimum concerning R value.

Agree with ionized, almost all new construction should include a 3rd party energy rater, the most common certification being Energy Star. Involve the builder and rater during the design stage! This contributes to climate appropriate details and holds the builder accountable for performance. Raters (and educated builders) brought in late often results in crummy compromises. Assemble a team early in the design process that welcomes this collaboration.

Blower door test results are currently more important than R-value. I think 1.5 ACH@50 is a reasonable goal that will be cost effective with the right design and assembly. R-1000 walls could perform worse than R-1 walls depending on air leakage.

Exterior insulative sheathing is required by international building codes in cold climates (or approved alternative). These requirements go beyond energy use to include durability and indoor air quality. The sheathing should have a high enough R-value to limit moisture problems in framing (adsorption of humid interior air). Some of the suggestions above could cause trouble because the insulative sheathing is too thin to keep the osb/ply and framing warm enough.

From GBA's Calculating the Minimum Thickness of Rigid Foam Sheathing:

Climate Zone Minimum R-Value of Foam Sheathing

Marine Zone 4 R-2.5 for 2x4 walls; R-3.75 for 2x6 walls

Zone 5 R-5 for 2x4 walls; R-7.5 for 2x6 walls

Zone 6 R-7.5 for 2x4 walls; R-11.25 for 2x6 walls

Zones 7 and 8 R-10 for 2x4 walls; R-15 for 2x6 walls

Notice that sheathing needs to be thicker for 2x6 walls. This is because the extra cavity insulation makes it tougher for the insulative sheathing to keep the framing warm. A 2x4 wall may be the better choice, and can easily outperform 2x6 with enough exterior insulation. With that said, I would probably go with 2x6 in any MI climate, just be sure it has enough insulative sheathing R-value to keep it dry.

Cavity insulation becomes less important with good blower door results and exterior insulative sheathing. In our area, there are not many experienced dense pack installers (cellulose or fiberglass). Due to lack of competition and the extra labor involved, it's equally affordable to use open cell spray foam in wall cavities.

We are proficient in SIPs, the ultimate in wall and roof performance per inch of thickness. I've found the extra material costs balance well with the added labor of exterior insulative sheathing but the new structural sheathings incorporating foam sheathing (Zip+R) have shifted the math back towards stick framing for most walls. Unfortunately for cold climates, the integrated foam structural sheathing offerings are not thick enough to meet the recommended minimums above.

No such thing as a 2x6 wall that meets R20, without exterior insulative sheathing. The industry up there is doing a poor job of meeting minimum building requirements, just like down here.

If you installed R-21 insulation batts why would you need another layer of exterior insulation?

Batts are typically the poorest performing type of cavity insulation. Here is a visual guide of batt installation quality.

Even with a Grade I install (good luck) accounting for 25% typical framing factor drags the whole wall performance well below 20. The bigger problem is that batts almost always results in substantial gaps and voids. Humid air flowing through or within these voids results in mold and mildew on cold framing components. Batts also act as a filter which over time can produce excellent mold growing media.

They can perform fine under the right conditions but as cavity-only insulation with no regards to air leakage they are not the best choice with current state of affairs.

Springtime Builders - Those paper faced batts are not used here, they disappeared in the late 70's. Yes fiberglass insulation permits air flow, that is dealt with via the interior min. 6mill poly barrier and other means to ensure air tightness, exterior sheathing and exterior building wraps are all part of the full exterior wall system. I can google endlessly and find all kinds of examples of poorly/improperly installed insulation.

I'm not saying this is the ultimate/perfect system. It does however meet minimum code requirements and is most likely the most economical way to do so.

I'm guessing your building code prescribes whole wall R-value in which case your proposed wall assembly does not meet the minimum requirement. It might be economical upfront, it might pass inspection but it does not meet the code's intent.

Interior poly may be common in your area but in regions with air conditioning needs, it's usually a bad idea. Air barriers do not account for insulation voids and thermal bridging of framing components. I know you're not here to promote that system but consumers are getting homes that perform worse than what is supposed to be cheapest allowed by law.

Springtime Builders - The assemblies they are constructing meet the full requirements of the code. These builders are huge, they are not building manufactured homes (zoning bylaws do not permit them).

All our homes are airconditioned and of course heated. Temperatures here will rang from around a low of -4 in the winter to a high of 95 in the summer and everything in between. In the summer humidity is often very high so condensation is a major concern all year round.

Perhaps those builders are using a different compliance path but a typical 2x6 wall with cavity-only insulation batts, will end up closer to R16. That seems like weak wall performance for Canada. According to this blog, exterior insulative sheathing (continuous insulation) is required in Ontario. Where is Worthy?

Here's a good BSC article about vapor barriers written by a famous Canadian building scientist. I believe he has softened on poly a bit since then but a solid endorsement in climates with air conditioning you will not find.

Springtime Builders - I like the 2nd article best as the author starts off reminiscing about the Maple Leafs winning the Stanley Cup, "ah the good old days". There's no doubt that thermal performance and moisture/vapor control has been a major concern, ever since the 70's energy crisis when they started to tighten up homes. Back then it was a disaster as the methods used did not fully ensure that moisture would not accumulate inside the cavity. Much better today but not perfect. As you are most likely aware it goes beyond just the building envelope, as they tighten this up indoor air quality and interior humidity control becomes an issue, more equipment and more cost. Unlike the good old days when everyone just had their windows open and their homes could fully breath everyone now lives in a closed up box that requires a fully controlled artificial environment.

The challenge is developing methods of construction that provides the appropriate performance while at the same time it does not drive up the cost to construct. The home builders here are a very influential and powerful group both at the code writing level and politically. Affordability is a major issue here as in Toronto and the surrounding regions an average detached 3 bedroom home is $800,000 plus and it goes up real fast.

Affordable, high performance methods are in the current international building codes. The challenge is antiquated construction practices and poorly informed decisions. 2x6 walls with cavity-only insulation in Canada and "closed up box...artificial environment" descriptions are good examples.

In the good ole days there were no insulation or life-safety requirements. Homes were uncomfortable, expensive to condition and dangerous. As the industry adopts these crucial details, relative costs equalize and health improves.

It is possible to meet the energy conservation requirements of US model codes using one of 3 methods.

The Performance method uses software that allows trade offs between different elements of the building envelope. If the walls are lightly insulated the other elements must be more heavily insulated. Its not difficult. This method takes advantage of high performance windows and HVAC systems so developers often use it for new houses

The other Methods use one of the Prescriptive tables (R values or U value equivalents). These tend to require more insulation and are often used for additions. The U value equivalents table considers surface area so it can be helpful for certain designs. The R value chart is frequently referenced on this forum. I’ve used all 3 methods

For the Prescriptive Method it can be difficult to comply with the minimum wall cavity R value requirement of 20 (no exterior insul. board) since the other elements of the wall system don’t count. Fiberglass batts are R 17 to 18. High performance fiberglass batts are R 20 to 21. Loose fill fiberglass is R 14. Loose fill cellulose is almost R 20. Dense Pack cellulose is R 21 to 22.

One way to view all of this is that codes only establish a minimum and as such no builder is impeded from constructing using what they believe are superior methods, technologies and materials.

There's no dispute that health life-safety is an important element. In respect to indoor air quality this is the direct result of man made materials and the adoption of ever tightening air infiltration requirements. Technology created the problem and now we need more technology as we attempt to overcome the problem.

Just to clarify our R value requirements for exterior above grade wall insulation requirements. This varies between R22 and R29 depending upon the efficiency of the installed heating equipment. The R20 I referred to was for below grade situations such as basement walls, my apology.

Fiberglass Canada has both R22 and R24 batt insulation for 2X6 wall construction.

Michigan occupies building climate zones 5 - 7. Zone 5 is the warmest zone that can still comply with the R20 cavity-only requirement. It looks like Ontario has adopted similar IRC mandatory exterior insulative sheathing. We use the performance compliance path on every home, one of the many advantages to including a third party energy rater. Most raters are not keen on getting too far away from code prescriptions.

For some of the prescriptions, like blower door minimums, it's cost-effective to exceed code. Most high performance builders are exceeding code with exterior insulation as code encourages risky wall strategies, hence the recommended minimum table I first posted about.

Even leaky, all natural homes can have poor indoor air quality. Outdoor air ventilation is now required by current IRC codes and a smart idea for any inhabited enclosed space. It's a life-safety requirement and long overdue measure for modern homes.

Certainly from my past direct involvement in code our codes in most areas were very closely aligned with the major US codes. I did a little checking and our OBC Supplement SB12 that covers this in detail was adopted in 2012, updated in 2016 and I believe there are some further amendments for 2018.

The bulk of new single family residential homes here in southern Ontario would require a minimum R value of 24 based upon the insulation only and the fact that heating equipment greater than 90% efficiency is mandatory. As Fiberglass Canada has an R24 batt for 2X6 they can just squeeze in under the radar.

Michigan code in my area says wall assembly has to be R-20 and R-49 for the ceilings/roof. The builder in question typically uses a 2x4 open cell spray foam wall assembly of R-14 and R-60 for the ceilings/roofs. He does, however, pass code using the performance method as opposed to prescriptive. According to him performance code in Michigan requires no more than four air exchanges per hour (I'm assuming that's measured with blower door test?) He claims his homes usually are at two air exchanges per hour. I am waiting for him to get me info on what their HERS scores typically are.

He has, however, been very open to my ideas and questions with efficiency and is willing to do whatever I want.

All of the information and comments are truly appreciated here. I wasn't expecting this many responses but have learned a lot through the various opinions and recommendations.

Interesting, I'm surprised they permit that level of trade-off. I've always interpreted the codes intent here as a means to address issues such as when one wishes to say increase the % glazing, as this would reduce the overall walls thermal resistance you the had to increase the R value somewhere else to compensate.

Even if it is permitted, if it was may house I would insist that the exterior wall construction be change to accommodate a higher R value. This will have both short and long term benefits, your heating/cooling costs will be lower so gradually you will get a payback and as thermal performance is an ever increasing concern should you decide to sell your home it will be more attractive from an energy consumption perspective. Keep-in mind that an R-14 2X4 exterior wall is like building a 1970's house, brand new it's already 40 years old.

I’m curious how he will achieve R60 at the roof and if there is any HVAC equipment outside of the insulation envelope

The total energy efficiency of the house would meet the current code so it would not even be close to the efficiency of a typical 1970’s house. Get the RES Check software and try different configurations. You might be surprised how important air sealing and roof insulation are. After subtracting the window area, the area of exterior walls might be less than the area of the roof.

i would still use dense-pack cellulose and 2x6 studs. I haven’t used 2x4 studs since the mid 70’s.

What I find ironic is builders are required to have install walls and ceilings with R-20 and R-49 insulation values, but then are allowed to install HVAC equipment in unconditioned attics with R-8 flexible duct work. When will the code be changed to stop this practice?

I'm just referring to the exterior wall construction in isolation to anything else. I might be surprised but I'm not sure that here they would permit that type of trading-off. Also, the builder quoted the OP a $2,500 upcharge to upgrade the exterior walls. Seems like a very minor cost to bump up the walls performance. Should the owner wish to do this in the future after the build it's going to cost 10 times or more than that amount.

Also, there is a limit to increasing attic insulation, insulation weight on the ceiling drywall can exceed it's carrying capacity, if so then either the frame spacing needs to be reduced or a thicker board must be used. In most attics/roofs you can't get that level of insulation around the perimeter so the R-60 will not be consistent over the entire ceiling.

An easy solution to the OP's concerns would be Huber's Zip Insulated R-Sheathing.

It goes up faster than exterior foam board over OSB, provides a good nailing base for classing and avoids the need to furr out around windows and doors.

I'm still curious about the roof/attic insulation and how it is installed. Focusing on the walls can be a mistake.