2 x 4 vs 2 x 6

[grover]

How did you decide between 2x4 and 2x6's for your exterior walls?  Am I looking at a 50% increase in cost's for the walls with 2x6's...wood and insulation?  I would still stick with 16" on center.  Any other issues or challenges besides the cost?

Thanks

[Redoverfarm]

How did you decide between 2x4 and 2x6's for your exterior walls?  Am I looking at a 50% increase in cost's for the walls with 2x6's...wood and insulation?  I would still stick with 16" on center.  Any other issues or challenges besides the cost?

Thanks

I like 2X6's for a couple reasons.

1. Stronger to support upper floors.
2. More room to add plumbing and wiring.
3. More room for larger R-value insulation.  More insulation results in less cost down the road on utilites to heat.

[MountainDon]

To me the extra insulation hasf much greater value than the extra cost of the 2x6's and the thicker insulation. IF the structure was a barn, shed or other non inhabited and non insulated building then sure 2x4's might be fine. But for something that is heated and/or cooled and lived in, 2x6 walls are the the new minimum, for me.

There is the further question of whether or not the building to be falls under any energy conservation codes. Those mostly require higher R-values than what is normally stuffed into 2x4 framed walls.

[MountainDon]

I wanted to add that we are very happy with the 2x6 walls in our cabin. The outdoor temperatures can be only in the 40's F outside and we usually only need one fire in the wood stove in the morning.


It may bear repeating that the commonly available R19 fiberglass is not an ideal match for 2x6 framed walls. Most of those are actually 6 1/4 to 6 1/2  inches thick. When stuffed into 2x6 cavities (5 1/2") the batts are compressed and lose about 1 R-number. There are batts made for 5 1/2" cavities; interestingly it is R21. hard to find sometimes though.

[mgramann]

For my upcoming build, I'm planning on 2x6 walls, but I recently did an addition with 2x4 walls, since that was what the original structure had.  To get the needed r-value, 1" foam was used as the primary sheathing.  If I recall correctly, at the corners, 4x8 1/2" OSB was used on either side, along with 1/2" r-board.  This provided the needed strength for the corners.  In the original structure, metal bracing was used at the corners instead of OSB.

There are advantages and disadvantages to the 2x4 method.  It is cheaper.  Also, it is my opinion that you get a more continuous insulation envelope for the home, as the studs are now partially insulated by the sheathing.  I don't believe it is as strong, but it is definitely strong enough for code, at least in my region.  Still, my upcoming build is further north, and I would like that little bit of extra strength to help offset the snow load.

Just some food for thought to help in your decision.

[MountainDon]

mgramann raises a good point. There is more to it than deciding on 2x4 vs 2x6. When insulation is considered there is the question of type. As I mentioned I'm happy with our cabin as we heat predominantly with wood and have little cooling needs. However, if I was in the design stages for a new full time residence I'd be doing some serious research. I'd be studying solutions on buildingscience.com. Different solutions for different climates.

[flyingvan]

  I'll only build with 2x6's.  My biggest reason is if I put electrical and plumbing in the center of the studs, interior and exterior siding nails won't hit them.  Things like wall furnace vents, drain pipe, etc.  are much easier to cut in.  Warping is a problem here---wood gets cut and milled where it's humid, then I bring it home where it's very dry and boards tie themselves in knots.  2x6's seem to be less prone to warping than 2x4's  I also like that I can put 3 nails into each end of each stud. 

[MushCreek]

The added cost of 2X6's is tiny compared to the total cost of building a house. I know 50% sounds like a lot, but overall, the difference is negligible.

[ColchesterCabin]

The question of insulation type is the perfect question here. If you are going batt insulation or spray foam. My limited understanding as I am just starting the research in anticipation for next spring is that with spray foam, you can get a better insulation factor, saves on the labour cost of installing batts and also depending on the type I think saves the need for vapour barrier prior to drywall or interior finish.

I to looked at 2x4 construction when I started mine with a 1" foam exterior, but I looked at my oerall build and location, factored snow loads and winter environment and I am glad I spent the little extra. The poeple who have stopped by can believe how sturdy it feels and looks.

[yankeeredneck]

It is code here that your exterior walls are 2x6. Your interior walls can be either.

[MountainDon]

HWGA
yankeeredneck, where are you? What code?

The building codes I have seen still list 2x4 as suitable for typical residential construction. However, the energy conservation codes will very likely call for something in the range of R-19 insulation. It is possible to achieve R-19 with 2x4 framing, just not possible with fiberglass batts. My first post in this topic mentioned the energy codes.

To some it may be nitpicking, for me to say that the building code does not call for 2x6 exterior walls. But to me there is important difference.

If the code really does state 2x6 exterior wall framing must be used I would like to see it for my own education.

[Ndrmyr]

Other than a garden shed, I wouldn't consider building a structure that I wanted to endure out of modern 2" x 4"s.  Consider this, a 100 year old home built out of true 2x4's, usually of old growth lumber far exceeded the strength of modern wood.
A true 2"x4"x 12" is .66 of a board foot.
A modern 2"x4" with nominal dimensions of 1 1/2" x 3 1/2" is .43 of a board foot per foot. (1.5x3.5x12 / 144= .43)
A modern 2"x6" with nominal dimensions of 1 1/2 x 5 1/2" is .68 of a board foot.
It takes a modern 2"x6" to come close to the actual dimensions of an original 2"x4" and this DOES NOT take into account the difference in lumber strength.
From this we see that a modern 2x4 has just 65% of the original dimensions.  It might not be out of the realm that it takes a 2x8 from our fast growing SPF (Spruce,Pine,Fir) forests to truly match the strength of old growth, slow growing encroached timber that took 200 years to slowly reach its height.  Growth rings tell all. 
This I know, my father and uncle built a truck barn from rough sawn walnut harvested from the farm and sawn with a tractor mounted saw blade. (Back then, if you said OSHA, someone said "bless you") 30 years later, it was almost impossible to remove a nail, and if it did come out, it made a sound like a wounded Tomcat.
So, long story short, 6 is better than 4 anyday, and, size does matter.

[yankeeredneck]

MD


I live in the Watagua county of NC. Although I in the country, I also have App State University about 20 minutes down the road, Elk River where people like Ricky Rudd and Bob Greise live. Heck, half a mile up the road the is the home the CEO of Buggle chips. I live in a tourist county. Grandfather Mountain and Blowing rock are all with in 20 minutes drives. My brother-n-law is a GC and he as well as the building inspector have both told me that 2x6 is mandatory and code. Now you leave Watagua county and the code is different.

[Native_NM]

The strength of a modern 2x4 building may still exceed the strength of an old building.  It's more than just the studs.  Modern design utilizes plywoods and OSB along with modern fasteners and code that can result in a super structure of sorts. 

Insulation is an important factor, and I agree with Don that I'd use 2X6.  Over in California, however, they have engineered homes that use 2x3.5 and plywood sheeting that is stronger than 2x6's and even friendlier to the environment.

[intelijoc]

Are you considering metal framing?

[grover]

No, no 2x's
Except for possibly the wall around the wood stove.  Not to veer off topic but I was reading a few threads about wood stove clearances and was wondering about metal 2x4 studs in the wall near the stove.  Metal 2x's plus stone plus a metal sheild around a wood stove sounds like a good idea to me.   What ye say?

[grover]

Sorry, meant to say no metal 2x's in my exterior wall framing.

[MountainDon]

The metal studs I've seen arpund here are not rated for load bearing walls, only interior partition walls. There are structural rated metal studs but they are not cheap.  Using metal behind the stove will simply transfer the heat to the next combustible surface, IMO.  If you have a modern stove, a well built one, not a cheap import, most have very reasonable clearances without the need for special shielding. If extra shielding is required to reduce a side or rear clearance the 1 inch air shield technique qorks very well.

Once the building floorplan is set, I'd advise checking into what wood stove is suitable, as a part of the planning process, not after the walls have gone up.

[alex trent]

Lots of good reasons to use 2x6 over 2x4, but on of them is not the need for more compressive strength...which I think ranks as the number 1 concern in building...is it going to break, not how easy is it to put stuff in between the walls.

Somewhere in this thread, strength is raised as an issue.

Even crappy "modern" pine has compressive strength of over 4,000 psi, so 2x4 studs are no problem in holding up the second story and the roof and a lot of snow and ice and fat guys walking around on the roof.

[Don_P]

Current design value for SPF lumber in #2 grade, allowable compression parallel to grain is 1250 psi, perp to grain is 335 psi in SPF (south) this is often the controlling factor.

Buckling is one primary concern with a column. Studs, posts, jacks, etc are all columns.
Designing a column based solely on compressive strength works for columns with a span to depth ratio of 12 or less. An 8x8 post would be appropriate for an 8' post height if you didn't want to bother with deeper math to check for buckling potential, we know it will fail in compression before buckling. Multiplying the Parallel to grain compressive strength of the post times its sectional area would give a post's capacity IF the post has a l/d of 12 or less

If the l/d slenderness ratio is higher than 12 up to the allowable limit of 50 then the column stability factor must be considered. Notice that a load bearing 2x stud needs to be braced in the weak axis, a load bearing basement wall should be sheathed.

If the column is subject to bending, for instance a greatroom gable wall in wind, then the out of plane bending force on the studs is one factor and the compressive load is another, the interaction of those two loads should be accounted for. Hold a thin strip of wood, ends between thumb and forefinger and squeeze. That is an axial compressive load, the load flows down the length of the stud. Note how much force it requires to deflect the stick. Now push on it's middle with the index finger of your other hand. That is bending, your finger is the wind, note the force required to deflect the stick. Now squeeze and push both, the stick deflects easier and further than when acted on by only one force.

A piece of wood in bending resists that force by using the strength of the material AND its' shape. Rather than just comparing gross sectional area, look at the section modulus. That is the geometric shape's ability to resist bending and is derived from the formula bd²/6, breadth (1.5") times depth squared(3.5 or 5.5²) divided by 6. A 2x4 has a S_mof 3.063"³ where a 2x6 has a Section Modulus of 7.563"³. All things being equal (species, grade, span), a 2x6 is two and a half times stronger in bending than a 2x4.

http://theownerbuiltcabin.com/calculators/TT/Simple_column.htm
http://theownerbuiltcabin.com/calculators/TT/44axbend.htm

The design values for most species and grades in older texts are not really much different than now.

[alex trent]

All things being equal (species, grade, span), a 2x6 is two and a half times stronger in bending than a 2x4.

Pretty obvious even without all the math and tables that 2x6 is stronger than 2x4. Point is do you need this strength (2x6 vs. 2x4) or just want it?  If so, better use a 2x6.  But then you need to go back and recalculate  because you might really need a 2x8 for that margin of strength.

[MountainDon]

Thank you Don_P for the explanation / lesson. Once again it becomes apparent there is more to building a wall than buying some lumber and nailing it together after looking at pictures of what others have done. No seat of the pants engineers need apply.

While it might seem obvious that a 2x6 is stringer than a 2x4, what is not obvious is the amount of increase in strength. The taller the wall the greater the need for calculations. That is what the math is all about. And if anyone has doubts about the possible necessity of stronger walls, what about all the severe weather we've been experiencing in recent years? My opinion, my thoughts.

[alex trent]

In regard tom the weather, my opinion is no matter what you build with, don't build on the beach. or in a flood plain...no matter how strong the levees look..

[flyingvan]

Is it strong enough?  That question got me curious--armed with Don's numbers, and using the W.A.G. method of figuring out how much stress my balloon framed wall takes in a 70 MPH wind (not a rare event here)  I don't think a 2x4 wall would have worked.

As far as 2x4's being 'easier on the environment' than 2x6's.  Why??  The matter that makes up lumber is mostly carbon pulled from the atmosphere through the magic of chlorophyll along with sunlight... If builders are sequestering this carbon in walls, couldn't you argue thicker walls are BETTER for the environment?  Add the energy efficiency and environmental impact of a longer lasting structure, too.  Very little lumber for construction comes from old growth forest anymore

[alex trent]

Based on the AWC building guide for high wind areas (110 mph)  2x6's over 9' 9" don't work any better than 2x4 on 16 ' load bearing walls.  Actually, according to that neither do 2x8's over 9'9".

So much for the strength factor n using 2x6's

BTW, I am not anti 2x6......other reasons to use them. I actually do it for appearance since I have no interior walls in my cabin.  Just need to be clear on facts why they should be used.  if strength is the only reason, it fails on that accout.

As far as carbon sequestration...if by sequestration you mean storage, that is precisely the problem....or at least part of it.   I assume we are talking about excess CO2 in the atmosphere here...as in global warming.

So in the long term when the building life is over, here is what happens with the stored CO2...would intuitively seem to be a carbon neutral process, but in fact is not.  Hwer is something I lifted from a published explanation.

"In terms of carbon neutrality, the burning of wood often ignores the fossil fuel used in the harvesting, preparation and transporting of wood.

The carbon dioxide released when burning wood (about 1900g CO2 for each 1000g of wood burnt) is balanced by the fact that this carbon was taken up by the tree from the air when it grew. So this part of the emissions is carbon-neutral. However, many other chemicals are produced when wood is burnt, including one of the most potent greenhouse gases, nitrogen dioxide; although the amounts may be small (200 g of CO2 equivalent per kg of wood burnt), the gas is 300 times more potent as a greenhouse gas than carbon dioxide and lasts 120 years in the atmosphere.

Methane is also produced (70 g of CO2 equivalent per kg of wood) – 21 times more potent than CO2. Carbon monoxide is also produced in large amounts which has an indirect positive effect on global warming. Recent research suggests that particulates too have a positive effect many times greater than the combined gases although they are short lived. Overall, although figures vary depending on a multitude of factors, there is no doubt that wood burning is contributing to global warming."

But the real problem comes when you cut wood that you do not need.  To use a 2x6 over a 2x4 you use 50% more trees...more or less. So if you assign a value of 1,000 points to the CO2 used by that pretty big tree...and that is for both old and farmed trees.  That tree stops using carbon dioxide.   But you plant another tree.  But it is very small. So on our 1,000 point scale, it uses about 5 points.  Next year 10, and a very long time to get to 1,000.  So the net effect is a big loss of carbon dioxide use.  Couple that with the extra fossil fuels used to harvest and transport and it is surely not an environmentally practice.

In general, the less you use for what you need, the better we are environmentally.  A big dump truck has a lot of important uses, but using it to go get groceries..even though it is safer...is not a useful thing to do.