2x4 Framed Exterior Walls and Energy Code Compliance

[GeneDavis]

If you can get the structural performance you need with 2x4s, and can get the thermal performance required for ResCheck with sprayfoam in the cavities and Huber Zip-R Wall sheathing, is there a hook in the code that says you MUST frame with 2x6?

 

Because I am being told there is by someone who is not (and I think cannot) citing the code language.  And I cannot find any.

 

2018 IECC and 2018 IRCC.

[DRAWZILLA]

58 minutes ago, GeneDavis said:

If you can get the structural performance you need with 2x4s, and can get the thermal performance required for ResCheck with sprayfoam in the cavities and Huber Zip-R Wall sheathing, is there a hook in the code that says you MUST frame with 2x6?

 

Because I am being told there is by someone who is not (and I think cannot) citing the code language.  And I cannot find any.

 

2018 IECC and 2018 IRCC.

I use 2x4 framing with r-15 in the walls all the time but this is California where the energy code is tougher than the ICC codes, I also use the computer method where you can trade off different methods.

[Gawdzira]

In California also. I can get my engineer to design for 2 stories with 2x4 framing unless I have a tall wall at stairs which then goes to 2x6. Some of the more structurally stringent walls also require 2x6 but a standard wall is fine with 2x4. Local codes vary.

[DRAWZILLA]

27 minutes ago, Gawdzira said:

In California also. I can get my engineer to design for 2 stories with 2x4 framing unless I have a tall wall at stairs which then goes to 2x6. Some of the more structurally stringent walls also require 2x6 but a standard wall is fine with 2x4. Local codes vary.

My engineer lets me use 3x4 full height studs at stairs

[Ed_Orum]

In New York, the 2020 Residential Code TABLE R602.3(5) allows 2x4 @16" o.c. to support one floor with the roof or habitable attic above   So basically that means a two story building.  However, depending on the wind zone, you may need to go 12" o.c. or 2x6.  Then you need to throw in the seismic zone.  But I do 2x4 @ 16" O.C. all the time and use either R-21 Spray Foam or R-15 Fiberglass with exterior continuous insulation.  The exterior continuous insulation also helps with the Prescriptive Res Check.

[SkullMesaRanch]

On 9/6/2021 at 9:30 AM, GeneDavis said:

If you can get the structural performance you need with 2x4s, and can get the thermal performance required for ResCheck with sprayfoam in the cavities and Huber Zip-R Wall sheathing, is there a hook in the code that says you MUST frame with 2x6?

 

Because I am being told there is by someone who is not (and I think cannot) citing the code language.  And I cannot find any.

 

2018 IECC and 2018 IRCC.

Hey Gene,

 

Right now at Lowe's the price of a 8' 2X6 is three times the cost of the comparable 2X4.  As someone getting ready to build a small house and barn I really would like to use 2X4 construction if it saves money.  One of the 1st things people ask when you say you're building a house is "Are you using 2X6 construction?"  I don't understand how this became a status symbol.  Most of heat goes out the roof not the walls and insulation is so good now that the extra 2" of insulation isn't buying that much.  If I use 2x4 construction on my exterior walls I feel like I can't tell anyone except the framing contractor.  Even then I'll call first to make sure they'll do it.  The labor cost should be less with 2X6 exterior wall construction, but I don't know if it would swamp out savings in 2x4 material costs.

[Joe_Carrick]

1 hour ago, SkullMesaRanch said:

Hey Gene,

 

Right now at Lowe's the price of a 8' 2X6 is three times the cost of the comparable 2X4.  As someone getting ready to build a small house and barn I really would like to use 2X4 construction if it saves money.  One of the 1st things people ask when you say you're building a house is "Are you using 2X6 construction?"  I don't understand how this became a status symbol.  Most of heat goes out the roof not the walls and insulation is so good now that the extra 2" of insulation isn't buying that much.  If I use 2x4 construction on my exterior walls I feel like I can't tell anyone except the framing contractor.  Even then I'll call first to make sure they'll do it.  The labor cost should be less with 2X6 exterior wall construction, but I don't know if it would swamp out savings in 2x4 material costs.

Having visited Cave Creek in the winter I know it can get pretty cold and of course in the summer it can get pretty hot.  That said, you should be able to use 2x4's if your design meets the energy requirements.

 

Just make sure you don't have any plumbing in the exterior walls as the pipes could freeze where the insulation is compromised.

 

2x6 construction isn't a status symbol.  It's totally a matter of what's needed for structural and energy requirements.  If the structure isn't too tall (wind load) and the insulation needed will fit in 3.5" then 2x4's are fine.

 

[SkullMesaRanch]

2 hours ago, Joe_Carrick said:

Having visited Cave Creek in the winter I know it can get pretty cold and of course in the summer it can get pretty hot.  That said, you should be able to use 2x4's if your design meets the energy requirements.

 

Just make sure you don't have any plumbing in the exterior walls as the pipes could freeze where the insulation is compromised.

 

2x6 construction isn't a status symbol.  It's totally a matter of what's needed for structural and energy requirements.  If the structure isn't too tall (wind load) and the insulation needed will fit in 3.5" then 2x4's are fine.

 

Hi Joe,

 

Thanks for the reply.  If you were building a small simple house (1500sqft livable) would you use 2X4 construction in today's building environment?

[KristjanM]

Back in 1974 when I started as a carpenter, we used 2x4's. At some point the building code changed and we went to 2x6's. It was only to accommodate R20 batts in the walls due to the change in insulation requirements. We could also go to 24" oc for the 2x6's as 16" oc wasn't needed for any structural reason. 2x4's are entirely okay. The only thing you have to satisfy is the insulation requirements.

[DRAWZILLA]

we very rarely use 2x6 studs here, but it doesn't get very cold. sometimes I do need a 1" exterior foam insulation to get the model to comply. 

[Greg_NY61]

Same here in Jersey its always 2x4 wall with R-15 insulation, unless it's upgraded to 2x6 wall.

[buck_taylor]

On 1/5/2023 at 12:26 PM, SkullMesaRanch said:

Most of heat goes out the roof not the walls and insulation is so good now that the extra 2" of insulation isn't buying that much.

 
Heat travel towards Cold in ALL directions. It doesn't matter the orientation. Hot air rises because it is less dense than cold air.

We insulate attics (and floors) with more insulation because it is easy (costs less). More heat escapes through the walls than the ceilings in most structures. The formula is: Surface area x U-Value. There is an orientation component to the air film layer used in U-value calculations (vertical through horizontal), but there is no component in U-value calculations that concern whether a component is part of a ceiling versus a wall.

2x6 walls are structurally stronger than 2x4 walls. 2x6 studs cost more (more material, weight, volume, etc). If you don't need a 2x6 for structural reasons then DON'T use them. A decade ago the nominal cost between a 2x4 and 2x6 was pretty nominal, so it was a pretty easy solution to utilize a 2x6 wall to meet the energy codes.

The IECC Energy codes look at the thermal performance of the wall assembly. A 2x4 wall with a continuous rigid foam insulation layer (inside or out) has a lower U-value than a 2x6 wall with just cavity insulation. The IECC Building code covers structural requirements. You as the designer (or builder) must design the building to meet both components of the code.

I would suggest anyone reading this start looking at the IECC2021 codes, and play with the corresponding (web-only currently) version of ResCheck to get an idea of what's to come with a much bigger emphasis on building assembly U-values.

IECC Codes

ResCheck

 

[DRAWZILLA]

Here in California the required 2x4 or 2x6 is what the project as a whole calc.s out to. Mostly new construction goes with 2x6 exterior walls but it all really depends on what climate zone you are in and does the whole project as a whole calc out to work with 2x4 walls or not. Most of the time with additions I can use 2x4 walls with r-15 insulation, it really depends on windows and what's inside that matters.