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
Quote from: grover on November 07, 2012, 06:30:06 PM
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.
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.
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.
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.
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.
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.
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.
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.
It is code here that your exterior walls are 2x6. Your interior walls can be either.
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.
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.
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.
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.
Are you considering metal framing?
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?
Sorry, meant to say no metal 2x's in my exterior wall framing.
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.
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.
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 Smof 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.
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.
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.
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..
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.
(http://1.bp.blogspot.com/_7UaKc2k_Heo/TOAmeXmpE-I/AAAAAAAABW8/QeNPzVO0WgI/s1600/Wall+E.JPG)
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
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.
Explain to me how cutting down trees 'you don't need' is the problem....If you believe the man made climate change stuff, atmospheric carbon is to blame. (I think this is like debating the life cycle of leprechauns, but I'm just using Al Gore's own arguments here) so ignoring the aesthetics of trees in the vertical position---which I think we'd all agree is a good thing--- if I grow trees, cut them down, bury them, and grow new fast growing trees in their place, haven't I pulled carbon out of the atmosphere and sequestered it?
Your article there is incorrect---when I studied forestry at Humboldt we actually looked at carbon uptake of young trees versus old. Young trees need it for leaf and wood production---the older the tree gets, the slower it adds wood. There was also a significant difference in a young tree's ability to fixate subsurface carbon compared to old growth.
Another incorrect assumption you make is, the ultimate fate of a home's lumber is burning, thus re-liberating the carbon into the atmosphere.
Of the 270,000 homes torn down annually, a little of that material gets recycled, but most ends up in landfill---estimated about 1 billion board feet worth of lumber, buried. Sure, some of that will be re-released as Co2 through microbial breakdown---like forests have been doing since there were forests.
True, there's a negligible increase in hydrocarbon consumption with bigger material. Offset that with the R-21 I get instead of the R-15, without adding a layer of some foam product. You can't convince me a house built with stronger materials won't last longer, and a house that stands for 100 years will have much less environmental impact than three houses that last only 30.
I couldn't find any data supporting what you said from the AWC---do you have a link? All the comparisons I can find compare 2x4 walls 16" OC with 2x6 walls 24" OC. I wish they'd also through in 2x6 16 OC. I suppose at some point the height of a wall in a high wind area will fail by blowing over, remaining intact the whole time...If a wall in the wind is well supported top and bottom, though, the center will be doing the moving---and my money's on the 2x6 wall flexing less, avoiding the creaks and nail pops over time.
(The decision was easy for me---I was required to have these seismic hold downs and they were required to be anchored to 2x6's)
Quote...a house that stands for 100 years will have much less environmental impact than three houses that last only 30.
the above is quite relevant and, IMO, a big reason to start correct at the bottom and do it right with a foundation that will be able to go the distance. )You know where that's leading but I'm not going to beat that horse today.)
So, you say that houses built with 2x4 will only last 30 years? There are millions on millions of example that defy that fact. Even in relative terms there is nothing factual to say that a 2x6 house is more likely to last three times as lo as a 2x4 house...or is there?
FVan...I thought about the chart in AWC and the codes....your codes must be less stringent (at least in your area) as they permitted something even the wood people say is not permitted.
Here is the AWC link. I looked at it a while...am I missing something? Looks like the only real difference is not permitted to use 24" spacing on a two story building. As you have alluded to, there must be a lot of other things to coping with high wind than stud size. Sounds reasonable when you think of the house and how it reacts to wind and the relative strength of wood (even 2x4) on that axis.
As for you concern about nail popping due to flex, you have any facts on the relative flex in 2x4 and 2x6 in walls. I know the flex of a single piece differs, but in a wall with multiple studs close together is there really any difference that has practical value.
As for your words on carbon, I'll pass on debating the big picture.. What you learned at Humboldt State about big trees and small trees and the relative carbon uptake is correct....up to a point One of the main reasons for that is that small trees have a much greater leaf to mass are than larger trees and it is the leaves that use the carbon. But the rate needs to be multiplied by the tree leaf mass to get to the total amount of carbon used. So a small tree with 1/10,000 the leaf mass and 2x the rate is still way behind in carbon uptake. Your other stuff suffers from the same disconnects in facts and there are other places to debate that stuff.
The point is not to use more than you need for environmental as well as structural integrity....not just woo, but oil, water, etc.
Wood sequesters carbon if you bury charcoal, otherwise it cannot be honestly considered to offset the burning of fossil fuels, those are two different carbon loops. The arguments otherwise are pcbs.
A 2x6 wall is stronger than a 2x4 wall. I've built engineered tall 2x8 walls with all framing, sheathing and connections specified, there is a place for each.
Wood is renewable, most forms of energy are not.
Ah---Here it is. it took me awhile to remember where I found the info I needed for my wall. I see the disconnect now---you are only comparing load bearing walls. My roof is supported by three columns holding a ridgepole. My tall balloon framed wall is technically 'non load bearing'---but it does face the wind. We've had 100 mph gusts here, that's a lot of Bending/axial load....
http://www.awc.org/pdf/WFCM_110-B-Guide.pdf (I couldn't see the link on your post)
(http://3.bp.blogspot.com/_7UaKc2k_Heo/TSJpmSqzsYI/AAAAAAAABXw/AzN-o_YSsaM/s400/GEDC0984.JPG) Here's two of the columns
(https://lh6.googleusercontent.com/-5g523Hfwryk/TXvvf5l_2MI/AAAAAAAABYw/NaeyIf3UvAw/s400/ridge+pole.bmp)
And here it is with the ridge pole in place
I used this same AWC reference when drawing my plans. Scroll down to Table 5, page 12. According to AWC's chart--for a non load bearing wall in a high wind area, for #2 grade lumber 16" on center, here's what's allowed--
2x4's max stud length 11'5"
2x6's max stud length 18'5" (Mine are 17' 7 1/2", 18 even with sole and double sill)
2x8's max stud length 19'9"
I figured there was a reason whey you could (would) do it....
Good stuff to know.
I also looked at the 130 mph chart on AWC...that also works with 2x6...so you can take even a bit more!
I take it the back (shorter) wall is classed as a load bearing wall.
On a more general note, from what you say, having a ridge beam means the corresponding wall(s) are classed as non-load bearing for this purpose. I have a guy here who wants to build a shed type roof 16 feet high in front and 12 in back...kind of an observatory...30 x 18 feet. So if it works like this he can use 2x8 in front and go all the way up as long as he uses a ridge beam in the front...probably three posts to support it, maybe 4
Walls that rafters bear on are load bearing irrespective of the ridge configuration. Gable endwalls are typically considered to be non loadbearing. If the roof is a typical symmetrical gable the sidewalls each bear 1/2 of the roof load. If there is a ridgebeam that beam bears 1/2 the roof load and each sidewall bears 1/4 of the roof load. For a shed roof each sidewall typically bears 1/2 of the roof load. 9'9" max height without design @110mph in the WFCM. Tall slender posts need design. Do read the design concepts and foundation section carefully.
Thanks Don, you typed faster than I and expressed my thoughts better. :)
A ridge beam is essential when designing rafters for vaulted / cathedral ceilings with a gable roof and the designer does not want to incorporate rafter ties on the wall top plates. The ridge beam then structurally converts the gable into what amounts to two shed roofs... all gravitational forces go straight down. Standards for heights must be followed or calculated on a case by case basis.
That 16 foot wall would need design analysis it would seem. Maybe another topic as well.
Perhaps this is beyond a simple "more is better" argument. This I know, for years when I DIYed something, it has been my inclination to invest my labor savings into either material upgrades or in many cases, the tool(s) needed to do the job.
Sure, if we were Johnny Lunchbox and were buying a fully financed subdivision home that stretched our monthly payment to the breaking point, every upgrade is one we can ill-afford since we are already buying more house than we can afford. Certainly this was the case in the pre-housing bubble buying euphoria. Where someone didn't flinch at the $22,000 Cherry Kitchen upgrade. Really?
I truly do question the longevity of much modern construction. A preponderance of OSB sheathing, I see houses built with no wall sheathing except for a couple sheets at the corners, nothing but vinyl siding on top of the house wrap. A burglar with a cordless sawzall can be inside in 90 seconds. Can modern construction techniques be better? Sure, if they are utilized. Are trusses, hurricane clips, modern construction adhesives better...yes. If they are used. Too many short cuts. What is the life span of my 6x6 post and beam infilled with 2x6 walls screwed into sill and top plates, sheathed with 3/4", interior sided in 1/2" OAK with a metal roof? I suspect in the 200 year range, longer if a good roof is kept on it. I couldn't have afforded it if I was paying a contractor. But, I COULD afford it with my labor and materials acquired at auction. Is the 3" of closed cell foam in the walls excessive? Perhaps. Still, I was building a multi-generational structure that will be handed down to children and grandchildren.
Frankly, there isn't a real right or wrong answer.
If I am building for my lifetime and maximum energy efficiency, I think 2x6's are the way to go. If my structure is seasonal, and may be sold in my lifetime, 2x4's are good enough. Build to your need, and....desire, and.....ability. And be secure in your decision.
Couldn't agree more.... A lesson I learned from building my first house was, for just a little more money and a little more effort, there's a way to make every step a lot better. Take your OSB example---I could have hired an engineer to figure out where I needed shear panel and put up the minimum, or for less money I could just shear the whole thing. Whole structure is stiffer and slightly more protected. Entire house wired with 12 awg instead of 14. Copper piping, type K (OK you pex people, might be a great product but I know two cases where mice chewed through the stuff)
The difference in cost is only in the hundreds and I see my time in building/repairing as more than that. I'm building ONE house, so saving a little here and there doesn't really pay for part of the permit fees. However----if I were building 4,000 mcmansions, all identical except for the color of the granite countertop, every penny I save means another $40.00 profit so I'm going to build to the very edge of the minimums, even invest in engineering to show me where I can save more. As a firefighter when we're done putting out a house fire we'll tear out drywall lookiing for fire extension---it's an eye opener how cheap houses are built. Roofs barely support their own weight. I've seen type 'M' pipes. HVAC ducting takes crazy sharp turns with flex pipe that could never be cleaned.
Houses are priced according to size and location though, quality of construction is a minor factor.
While I'm all about saving energy I'm not convinced there's that big of an advantage jumping to 2x6 walls alone. If you look at the actual R value of a 2x4 and 2x6 wall (taking into account the framing) they're both considerably lower than the stated R value of the insulation (R9 and R13 respectively if I remember right).
My dad and I are remodeling an old house and he wanted to add furring strips to the 2x4 studs to bring them to 2x6. I ran some rough heat loss calculations and figured that even if the price of natural gas doubled the heat savings would be $55/year. This is in a climate similar to Minneapolis. So yeah, it will eventually pay for itself, but it's not a huge jump and I doubt it will feel any more comfortable in the house.
We're doing the furring strips, BTW. His house, his money. He can do what he wants.
Alan
I generally agree with build it strong and don't wood about a few bucks here and there. I see that too...saving 10 bucks on nails or such.
But not every big house is a poorly built "MacMansion". Just as we like small houses, some like um big.
And a lot are very well built.
Take a look at Outer Banks of NC....they stand to wx that most do not get. 2x4' studs at that.
It's nice that some of us on here build build great and small and strong, but denigrating others does not make our work better.
The point I'm trying to make is, as individual builders it's in our best interest to build well with good materials. The major developers can and do cut many corners.
AS far as whether a 2x6 house will outlast a 2x4 house---if that were the only factor different between two otherwise identical houses, probably little difference. But if everything is equally beefed up---foundation, sheer panel, roof decking, wiring, subfloor, waterproofing, copper, etc---all bumped up to the next level, I believe that it makes a big difference. (Not as big a difference as ongoing maintenance though)
We pretty much agree. Most mass produced houses are built sloppy...at beat finished poorly. At worts structurally not too sound. I goes that last point is the big saving grace for code sand inspectors, et. At least they keep it to some minimum level. I have no doubt you are right, that many of them will see problems in a relatively short timespan. But the way the housing market was is that many people saw the house they moved into as a short term investment to soon flip and make money and move "up". Likely some of that has changed.
I would guess that most people do not really know what needs to be beefed up and what is OK at the code level. Be good to see a prioritized list from what you really should beef up to the lower priority options. Maybe even some cost difference. For instance i put 12 ga wire in my house and not really sure why when here 14 is the norm...I think just afraid of fire. The cost was a couple of bucks. Just did it, but be nice to have a must do vs. could do list for those who don't know where to start.
The point is it is better to overbuild something that needs it more than something that you could live without. My house is a bit of an anomaly but since built an analysis and inspection by two engineers tells me I could have saved about 2k on the wood. My wood is very expensive here, so that likely does not apply everywhere...but I use it as one example.
Around here, 2K is about one house payment (actually I think the average is higher than that) I think it's a good move to use 12 awg wire as there's less voltage drop. The yin to that yang though is cost, and the struggle to stuff those 12 g pigtails into a box. 14 g is a lot easier to pull too.
I kind of look at builds as a spectrum. At one end, you've got Imhotep and his pyramids. A bit labor intensive, but still standing after a few millenia. For a little less labor and a quicker build with less environmental impact, you could pitch a tent squarely on the other end of the spectrum. I understand the attraction to building from a minimalist perspective, but it seems for the amateur owner/builder, tending towards the stronger materials is good practice (Yes---especially starting from the foudation). To me it adds a margin of safety, especially for those of us without an engineering background. So anytime someone asks, I'll tell them 2x4's are fine but 2x6's, in my opinion, are worth the extra money. After having to lift two houses off of piers to pour a perimeter foundation, I'll steer people away from piers when I can. Single glazed windows, T1-11 siding, (failing at my work station right now!) same thing. (Actually I'd never build with roof trusses either but that's just because they kill firefighters. Besides, having a big heavy timber at the top of the house holding the roof up just feels better to me)
My intention when starting this was the question around problems or issues that would come up that I'm not thinking about. I think a 2 x 4 house is strong enough when built correctly.
My thoughts of going with 2 x 6 exterior walls was for the extra insulation possibilities. I don't think I can afford to do the spray on closed cell stuff but I was thinking 2 inches of the blueboard type stuff with great foam around the edges to seal out air. Standard 3 1/2 inch fiberglass on top of that. Don't know what the R value is but should be good.
Quote from: grover on November 28, 2012, 04:32:18 PM
.... I was thinking 2 inches of the blueboard type stuff with great foam around the edges to seal out air. Standard 3 1/2 inch fiberglass on top of that.
Yeah, things sort of ran all over the place after a short while.
3 1/2 finberglass = R13
2 inch blue foam = R10
plus you pickup a little extra with the rigid foam being full coverage, over the studs.
The ideal installation would stagger the seams of two layers of foam but that does cost more.
Mt Don, I think you misunderstood the way I was planning to install the blue board. I was thinking of putting the blue board in between the 2 x 6's and filling the rest with the fiberglass.
Were you talking about full overlay of the blue board on the 2 x 6's?
grover the way I understood him was that if you put two layers and stacked them one on the other and broke the seams at the same location there would be a void that air could penetrate at that seam. By staggering the seams you would not have that void from the outside to the inside. But if you run full sheets from the floor to above the upper plate there would be no seams. But most likely you will piece some. Just make sure that the seams from the 1st sheet and second are not in the same place in the cavity.
I was meaning building with 2x4 framing. Filling the wall cavities with R13 fiberglass. Then sheathing the exterior with two 1 inch layers of R5 rigid foam. That breaks the stud thermal "leak" as John pointed out. Insulates and air seals well. Cutting and fitting rigid foam in stud bays is not my idea of fun. Sheathing the exterior with foam does mean you need to do some special things at doors and windows. The buildingscience.com website has info as do some other sites. Depending on the climate 2 inches of exterior foam is all that is required to make the inside face of the foam warm enough to prevent condensation in the wall.
What climate zone are you?
Climate zone map info (http://countryplans.com/smf/index.php?topic=11967.0)
I think up to climate zone 5 would be covered by 2 inches of foam.
This is for walls with f-glass or other batts in the cavities and covered on the exterior with rigid foam insulation. IF the foam is too thin for the coldest expected temperatures there then is the danger of the inside face of the foam surface getting cold enough for moisture to condense.
There's more info here someplace if we need it.
If you stack R10 over R13, do you add, or multiply, the R values for the total R value of the wall? Would it be R 23 or R 130? Or some other number depending on the space between the two? How do I figure my R value of the wall if it's a layer of caulked Hardie board, tyvek, 1/2" OSB, R21, then 5/8" interior t&g spruce? I can find R values for all those things, I don't know how the cumulative works though. Seems like you'd multiply if every layer keeps a percentage of the heat in (or out)
Additive... but I've never actually tried your method with the BO :)
I've had plans where they were adding everything, there is a boundry air layer with some fraction of an R, the sheathing, etc. ResChek is another method.
From our PM, I haven't found my windspeed/pressure calc, I lost a few in a hacking but did get the formulas to work longhand, just need to reprogram it. Meanwhile wind pressure tables are in chapter 3 of the IRC.
Yes. Simple addition. Except it's not so simple when there are studs covered by foam, for example. That's why the IRC will have a qualifying wall listed as R20 or R13 + R5. The first number (R20) being the required insulation installed in a stud wall cavity and the 13 + 5 being R-13 cavity insulation plus R-5 continuous insulation or insulated siding.
http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_11_sec002.htm
REScheck (http://www.energycodes.gov/rescheck) is a cool tool. It can be fun and educational to work with. I like it as it allows trades to be made; adjust window areas, make one wall thicker, and so on. Our state (NM) requires submission of the REScheck data sheet along withthe building permit application and drawings.
A qualifying air space can add R 1.7 if I remember rightly. But that's really only good for additional radiation value as in having a 3/4" air space between the exterior siding and a foil faced foam sheet. It doesn't do anything when the sun goes down. I'm re-doing our home's east and south facing walls with 2 inches of exterior foam as a two to three year project. Teo layers of foam; XPS next to the sheathing and polyiso with afoil face on top of that; 3/4 air space and then lap siding. I have no empirical evidence but the room I did that to in spring seemed cooler over the summer and now that cool weather has hit warmer than before. New windows helped too. And there I go again running off in another direction....
Is the 'R' scale a linear function, or an exponential one--in other words, say I built two identical structures except one had a net R value of 1 and the other of 4. I heat them both to 80 degrees when it's 32 degrees outside. I shut the heat off. House R 1 reaches outside temp in, say, 8 hours---would house R 4 take four times longer? 16?
Linear. Double the thickness of a layer means half the heat transfer and double the R-value. Similar to electrical resistance.
And it is meant to only measure heat transfer via conductivity IIRC. The numbers touted by those that sell radiant barriers only apply to radiated energy and are not the same as the R-values used for what I call normal insulation... batts, foam... which are thermal conductive insulators.
Right, R is the resistance to the flow of heat. The radiant bubble wraps are about R1 although their performance can translate to much higher if installed ideally. The interior air film I was talking about is the boundry of still air alongside a wall, I've been told the blind can feel it when approaching a surface, I'm not tuned in that well. It has an R value of about .66 on the interior face of a wall and about .17 on the outside where wind keeps it swept thin. Quadrupling the R value will not quarter the building's response or energy use, there are too many variables to make that statement but that insulation will be 4 times as resistant to the flow of heat through it. One variable, windows are ~R2 when the whole thing is done and said. I've built R40+ walls with large expanses of glass. Where do you reckon the heat decided to leave from. Sort of like putting on a down parka but not zipping it up.