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Home Construction 2 x4 or 2 x 6 framing
Old 12-03-2008, 12:20 PM   #1
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Home Construction 2 x4 or 2 x 6 framing

I was talking to a builder and deciding weather to go with 2 x 6 or 2 x4 construction. He said the 2 x 4 would be a much tighter house because the windows fit much tighter and do not have to be framed in. He also mentioned there would not be that much different between the two in terms of R-Value.I plan on using blown cellulose that sticks to the cavity. I live in Michigan and heat with natural gas. Anyone have any idea of which is best.


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Old 12-03-2008, 12:34 PM   #2
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I recall reading something about this a while back. Because heat rises, most of the loss is through the ceiling and roof. Also, since doors and windows usually dominate heat loss through exterior walls, any gain by going with 2x6/R19 insulation is minimal.
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Old 12-03-2008, 12:49 PM   #3
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I thought the idea of using 2x6's is that studs are on 1 24" spacing instead
of the usual 16". Thus 2/3 as many compromised places in the insulation
blanket, but basically the same amount of lumber. And of course the
option to use thicker insulation in the walls.
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Old 12-03-2008, 12:49 PM   #4
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The contractor I hired to build our house had a degree in construction engineering. I thought I wanted 2x6 walls as well but he talked me out of it for the same basic reasons IB mentions above.

He said a number of studies had all shown 2x4 walls were the best option unless cost was no object. The big factor is the ceiling insulation - the added R factor from 2" more wall thickness isn't significant enough to warrant the added cost of labor and materials.
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Old 12-03-2008, 12:51 PM   #5
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He's looking for the easy way out. 2x6 will give you a little more room for insulation.

Also important is reducing heat loss through the studs. Your blown-in (wet?) cellulose is a good step toward tightening up the airflow through the wall system, but you'll still be conducting heat through the studs. The ways to reduce this is to 1) reduce the number of studs (go with 24" on center instead of 16" OC) and/or go with exterior sheathing that is insulated (1" foam works great--it's not expensive, it breaks the thermal bridge of the studs, and it provides another R-5 on insulation across the entire wall). My personal view: I like 16" OC framing with OSB sheathing and also the foam panels on the outside of the OSB (topped by Tyvek housewrap). In my climate, 2x4 framing is enough. Others disagree, and believe the 16" OC framing is overkill, that the walls are plenty stiff with 24" OC framing, and that you don't need OSB if you have the foam. I'd definitely rather have 2x4 walls with 1" of XPS foam on the outside than 2x6 walls without the foam.

The idea of better, more efficient framing for walls has been looked at extensively with an eye toward reducing waste and overbuilding while improving energy efficiency. Here are two good articles:

Toolbase "Advanced Framing Techniques".

Building Science Corp. "The Futue of Framing is Here."

Your builder will resist using these techniques: It's something he's not used to, he'll have to find windows with deeper frames, etc. It's all been done before, but he'll tell you that it's impossible. It's your house: Read up, decide what you want, hand him the articles you've printed out and let him know what you want, ask him what the price will be. I would think that, with construction down severely, he'd understand that he's not your only option.
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Old 12-03-2008, 12:57 PM   #6
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2X6 will also be less likely to warp. Finger-joints will also cut down on warping and may even be less expensive.
Not sure about insulation properties, but the house is stronger with 2X6s if that is a factor for you.
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Old 12-03-2008, 01:02 PM   #7
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Here's a link that provides info, some already mentioned: http://www.energystar.gov/ia/home_im...doeframing.pdf

If you look at the picture of the framed in window, you might notice that the 2x6 framing gives the opening a three dimensional feel of older construction that's less possible using 2x4 framing. Old houses feel cozy in part because they're substantial, the thick wall will contribute to that effect, provide large sills, and extra wall area to bounce light off of.

The linked document suggests that due to material cost savings, it's a wash between 2x4 and 2x6. I'd imagine that's the case unless your contractor prefers (for whatever reason) to use 2x4, in which case they will make you pay through the nose to build using a technique they're unfamiliar with.

If energy efficiency is your goal, you should talk to the contractor about passive measures that will provide far more savings than additional inches of insulation. Siting the house so that it takes advantage of passive solar, shielding from the predominant wind, well designed overhangs, materials, and equipment; all of the above plus the proper insulation is called for.
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Old 12-03-2008, 05:01 PM   #8
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IMO- go with 2x6 construction at 16" OC with an inch of high-R foam on the outside. 2x6 lets you install thicker batts R15 vs R11. The labor to frame 2x4 or 2x6 should be the same, you are only paying for the nominal difference in material and getting a lot stronger structure. Windows will still have to be cased out either way, and the wider look of a 2x6 window jamb looks better-more substantial- to me than a narrow 2x4 jamb.

I'd also look at sprayed in place foam if you really want to up the ante on energy efficiency. It is much significantly better than batts, seals against air infiltration, and really glues the house together. Higher up front costs but it provides a comfort level you can't get with fiberglass batts or foam sheeting.
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Old 12-03-2008, 05:25 PM   #9
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When we build Habitat for Humanity houses here in Michigan, we use 2x6s for the wall studs combined with the wet blown in cellulose insulation and 1" thick blue foam on the outside under the siding. That, combined with other energy conserving techniques allow them to be heated with a couple of 1200 watt electric heaters while waiting for the furnace to be installed. Anecdotally, it seems like the right approach.
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Old 12-03-2008, 05:53 PM   #10
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Quote:
Originally Posted by runnerr View Post
I was talking to a builder and deciding weather to go with 2 x 6 or 2 x4 construction.
Are those your only choices?

The current season of This Old House is building a modular structure with engineered lumber and foam insulation-- inside the factory. The best part is that it's pre-wired and pre-plumbed, so there's no need to use insulated electrical receptacle boxes or special tricks to keep the pipes from freezing. The indoor walls include removable 36"-high "wainscoting" that pops off to modify the internals as needed.

If you're going for max insulation, there's lots of alternative construction methods-- straw bales, old tires & rammed earth, or even SCIPs.

I don't know if passive solar works in Michigan...
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Old 12-03-2008, 08:39 PM   #11
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I used 2x6's in my first house. Installing windows wasn't a problem since I ordered them with extension jams to fit 2x6 walls. I used 2x4 walls in the current house. I dont think I gained much efficiency from the thicker walls in the first house. It's more important to seal cracks, install energy efficient windows, insulate the attic very well, and install efficient furnace and ac.
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Old 12-04-2008, 05:42 AM   #12
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We went with 2x6 for both the strength and the insulating value...not so much for the winter, rather for the late afternoon summer sun that heats the house. There seems to be a significant difference, comparing our 1993 vintage 2x4 framed home with the new one. I didn't specify it but they are on 16" centers. In fact, I worked in insulation one summer in the 80s and never saw a 2x6 frame on a 24" center. I think that is only allowed for sheds and out buildings in california anyway. If it was me, I would do it the same way again. If cost is an issue, you could look into the finger joint studs...I don't like them, but some do. Another thing you may want to consider is talking to a heat/air contractor: ask them if there is any difference in size requirement for the HVAC units...it may hep you decide. Oh, and if it is possible with your siding choice, do get the inch thick external foam board for added insulation.

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Old 12-04-2008, 07:58 AM   #13
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I'm also involved with Habitat for Humanity. We switch to 2X6 construction to meet the building codes for insulation R value in NY. A few year ago the insulation companies came out with a new 6" fiberglass insulation that had a little more than R19 so you could still squeeze enough in a 6" wall without putting the blue board on the outside when they upped the requirement again.

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Old 12-04-2008, 10:03 AM   #14
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Here are the numbers for the "whole wall" R-values. These numbers take into account the heat loss through the studs, and help explain why, by stopping the thermal bridging through the studs, adding the foam accomplishes more than just adding the same R-value as more insulation in the stud bays. The numbers also include the (minimal) R-value of the 1/2" drywall on the inside. 1/2" plywood and 1/2" clapboard on the outside, along with the associated thin air layer on both surfaces and the impact of typical surface emissivity of the outer surfaces:

2x4 studs with R-11 fiberglass batts: R-11.6
2x6 studs with R-19 fiberglass batts: R-17.2
2x4 studs with R-11 fiberglass batts + 1" foam: R-17.1
2x6 studs with R-19 fiberglass batts + 1" foam: R-22.6
Full 4" stud cavities with blown cellulose: R-13.4
Full 4" stud cavities with blown cellulose + 1" foam: R-19.4

From:"The Visual Handbook of Building and Remodelling", 1990.

Note that this info does not necessarily address which wall system is most cost effective (based on payback period, etc), only their relative insulation values.
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Old 12-04-2008, 08:47 PM   #15
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Quote:
Originally Posted by IBWino View Post
I recall reading something about this a while back. Because heat rises, most of the loss is through the ceiling and roof. Also, since doors and windows usually dominate heat loss through exterior walls, any gain by going with 2x6/R19 insulation is minimal.
Quote:
Originally Posted by samclem View Post
Here are the numbers for the "whole wall" R-values.

2x4 studs with R-11 fiberglass batts: R-11.6
2x6 studs with R-19 fiberglass batts: R-17.2
2x4 studs with R-11 fiberglass batts + 1" foam: R-17.1
2x6 studs with R-19 fiberglass batts + 1" foam: R-22.6
Full 4" stud cavities with blown cellulose: R-13.4
Full 4" stud cavities with blown cellulose + 1" foam: R-19.4

From:"The Visual Handbook of Building and Remodelling", 1990.
Likewise, with windows at about R-3, I really wonder how much it helps to go from R17 to R22 for example.

Hmmm, my semi-educated SWAG on this (back of the envelope and a couple Excel cells) - assume exterior walls are 25% windows and R3; going from R17 to R22 in the wall would only reduce heat conduction by 8.5% for that wall. As IBWino mentioned, the ceilings (and air leakage?) are probably a bigger part of of the heating/cooling bill? So probably less than that overall.

I had also read that that 1" foam was as good as going from 2x4 to 2x6. Interesting to see some actual data on it.

-ERD50
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Old 12-05-2008, 09:52 PM   #16
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Likewise, with windows at about R-3, I really wonder how much it helps to go from R17 to R22 for example.
It's helpful to remember that R-values are really reciprocals of what you
probably want to know: they're degrees square-feet per btu/hour (also
known as square-feet degree hours per btu). The reciprocal of R value,
known as U value, is more useful, I think. Because you can have your
entire house insulated to R-100, except that 1 square foot is insulated
to R-epsilon (where 'epsilon' is an incredibly tiny number), and your
house is very poorly insulated. But if you look at U-values, most of
your envelope is U=0.01, but 1 sq-ft is at U-gazillion; so when you add
it all up, the overall btu/hour per degree is still pretty big, and thus the
overall R-value is pretty low. Not exactly realistic, but it makes
the point (I hope).

Similarly, we measure fuel economy in MPG. Apparently they use a
a reciprocal measurement, something like liters per 100 kilometers,
in Canada. That's more helpful. For example, if you ask the
average non-math-geek person whether it saves more gas to
increase somebody's gas mileage from 10 to 15 MPG, or from 20 to
40 MPG, they'll probably answer the latter. (If we used "gallons per
hundred miles" as the fuel-economy measure, you'd more easily see
that the first person goes from 10 to 6-2/3, whereas the second goes
from 5 to 2-1/2 - so the first saves more gas).

Of course, it's also true that R-values are more intuitive when you're
looking at "series" thermal "circuits". So you can add the R-value of
that outer foam layer to the R-values of the stud spaces + batts. With
U-values, you have to add them as reciprocals - like you do resistors
in an electrical circuit, and like you have to do R-values for elements
that are in parallel (like my R-100 house with a small area with
extremely small R-value).

Hope this all makes sense and is of some interest and helpfulness ...
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Old 12-06-2008, 09:51 AM   #17
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Quote:
Originally Posted by RustyShackleford View Post
It's helpful to remember that R-values are really reciprocals of what you
probably want to know: they're degrees square-feet per btu/hour (also
known as square-feet degree hours per btu). ...



Of course, it's also true that R-values are more intuitive when you're
looking at "series" thermal "circuits". So you can add the R-value of
that outer foam layer to the R-values of the stud spaces + batts. With
U-values, you have to add them as reciprocals - like you do resistors
in an electrical circuit, and like you have to do R-values for elements
that are in parallel (like my R-100 house with a small area with
extremely small R-value).

Hope this all makes sense and is of some interest and helpfulness ...
Yes, that is what I did in my quick-and-dirty calc. I turned the R values into conductance's, and assuming 25% window space, modeled the wall as 1 window conductance unit, plus three wall window conductance units and inverted to get back to R values.



Quote:
Similarly, we measure fuel economy in MPG. Apparently they use a
a reciprocal measurement, something like liters per 100 kilometers,
in Canada. That's more helpful. For example, if you ask the
average non-math-geek person whether it saves more gas to
increase somebody's gas mileage from 10 to 15 MPG, or from 20 to
40 MPG, they'll probably answer the latter. (If we used "gallons per
hundred miles" as the fuel-economy measure, you'd more easily see
that the first person goes from 10 to 6-2/3, whereas the second goes
from 5 to 2-1/2 - so the first saves more gas).
Also true - I heard a DOE or EPA rep a while back saying they wanted to switch the car stickers to gallons per 10,000 miles - which would be much easier to figure cost differences at various miles and gas prices. Hope they do that soon.

-ERD50
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Old 12-06-2008, 10:02 AM   #18
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Slightly unrelated, our current house has "fire stops" in the framing of the ceilings (and maybe the wall?) - 2x4's running perpendicular and bridging adjacent joists every 3-4 feet or so.

While designed to retard the spread of fire behind the walls and ceilings, it has the side benefit of making this the most "sturdy" feeling house we've owned. It's a colonial and there are NO squeaks in the floors, no groans during heavy wind conditions, no popping of floor boards. Even footsteps on the 2nd floor tend to be more muffled.

Just something to ask about if you're building new.
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Old 12-06-2008, 10:36 AM   #19
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..... My personal view: I like 16" OC framing with OSB sheathing and also the foam panels on the outside of the OSB (topped by Tyvek housewrap).
Please, NO! You need an underlayment that expires vapor from inside the home at least. The link that follows is not the only product to use but its features are what you need to specify. Builders will install the cheapest product they can obtain locally, this is nothing to let the builder choose.

Architect Home

Since framing is the discussion I will not rant about flashing, another common problem in today's construction.

Spend a couple $ on time with an architect who has personnaly built his own home or find a member of the Constriction Specification Institute. Their architect members focus on materials.
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Old 12-06-2008, 10:54 AM   #20
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Please, NO! You need an underlayment that expires vapor from inside the home at least. .
Tyvek does "expire" vapor from the wall structure (that's why people use t instead of polyethelene, etc), so please explain what your objection is to its use. The perm ratings (IIRC they are 20+) are far too high to trap moisture. It also stops liquid water transmission and mass air flow. As far as I can tell, it is functionally equivalent to Typar.

There are "smart" membranes that you can specify (they physically change properties based on the gradient of water vapor pressure on each side of the membrane. Here's an example of this product: MemBrain. It gets good reviews.
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