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I have a home design with 2X4 exterior walls. A few of my friends are builders and some suggested redesigning for 2X6 exterior walls with added insulation to help combat the cost of cooling (in Texas) during summer. The others say it’s not worth it. Does anyone else have an opinion?
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I live in a state that's bigger than Texas and hotter. We use only 2x3's. The stud size has little bearing on cooling ability ( that should elicit some responses ).There is is no reason why you couldn't pack enough insulation in a 3 inch cavity to overcome your problems.
regards
mark.
*I have read at least 3 articles on this subject, and although I cannot lay my hands all of these at this moment, I do know that all were written with respect to savings on *heat* bills. Here is one article for you to read:http://www.askthebuilder.com/cgi-bin/column?217 Another article, (JLC 6/98), says that money is better spent on high tech insulation sheathing than thicker walls. In this article, _Two-By Debate Continues_ it says that the payback time for 2x6 walls in Minneapolis (once again a heating climate) would be aprox 78 years.Another publication "A Builder's Guide to Energy Efficient Homes in Georgia, J. Tiller and D. Creech, Governor's Office of Energy Resources, 1990. Available from the Georgia State Energy Office, 2080 Equitable Building, 100 Peachtree Street, NW, Atlanta, GA 30303-1901, (404)656-5176. 125 pp., Free (softcover). " has an article addressing this topic, which may be more beneficial to you as it is written more from a cooling standpoint.In addition, here is a web site that you may find useful:http://www.eren.doe.gov/consumerinfo/
*Mark,2x3's as studs? Couple that with foam sheathing, and houses won't be safe from baseballs.
*
Hmmm---a trailer park in Hell, Alaska? JRNicholson
*Steve- There are a lot of variables here, and many cost strategies. Here in Houston, 2x6 walls are seldom seen. It really pays off in a climate with 50 degrees or more difference inside to out. If you want 75F inside, and it is 125F outside, the extra R-value pays off. How many days like that do you get? Even then windows leak like a seive, no matter what you do. 2x6 is great for tall walls and ballon frames, but as for A/C savings, ask local HVAC people what they think. It is a regional thing.
*
2x6 = R19......
2x4 = R11......
You make the call.
Ed. Williams
*There is a dense pack insulation for 2x4 walls that yeilds an R-14 or R-15,ask your building supplier to check it out. As I recall it only costs about 20-25% more.John
*Steve,You are probably right. That's why we use cavity brick most of the time. As for strength..our homes are designed to withstand wind speeds of up to 60 metres per second..( you do the conversion )by law, and we have to personally warrant structural for 6 years or we lose our licence. All 3 inch frame unless the wall is over 3 metres then we bump it to 4 inch for support against lateral pressure.regardsmark ( Queensland Australia )
*Mark-Is your actual stud size 1 1/2"x2 1/2"? Just wondering if your nominal sizes have the same the same reduction to actual size as ours.John
*What? You mix inches in your metric.
*In designing the home I'll be building this fall, I performed all the heat load calculations on a spreadsheet, mostly to determine what effect changing certain parameters would have on the total heating load. 3000 sq.ft, 2-story home w/ natural gas in Seattle. 2x4 R-13 walls: 38,000 btu/hr. 2x6 R-19 walls: 37,100 btu/hr. Not much of a difference. Of the heat loss that is NOT due to infiltration, 6,200 btu/hr was lost through windows and doors, 5,800 btu/hr was lost through the 2x6 walls, 6,700 btu/hr lost through 2x4 walls. After looking at the calculations, it seems to me that the most benefitial ways to reduce your heating or cooling load is first by minimizing infiltration, second by upgrading your windows to the highest-insulating double-pane windows you can get with special coatings and gas.
*Can you build new residential construction with 2x4 walls in WA?JonC
*Converting here..........thinking...thinking..35mm x 70mm......yep..sounds about right.
*G'day Mike,Yeah...ambidexterous. Because I was raised with both systems ( showing my age ) us older chippys do mix it. For instance we'll order 3x2's ( we order opposite to you guys ) at so many meters long. ( probably easier to say 3x2 than 70 x 35.)For all measurements on site we use only mm ( no centimetres). However say we are standing a frame and need to nudge it along a little we revert to imperial! "To me an eighth."Confusing?regardsmarkp.s. Mike, after a concerted effort we have lost the mtres.
*Curious ........what is considered state of the art in your area in terms of insulation and windows. Many of the new tract homes that I saw seemed notoriously inefficient. Single pane mill finish windows, short roof overhangs, R 11 insulation ......I haven't done any calculations but it seems to me upgraded insulation and windows would pay for itself in reasonable amount of time. I did notice that smaller builders leaned towards 2x6 framing. Your thoughts?
*The metric versions sound awful artificial. Note you find yourself saying 2x4 first. Maybe that's part of why Americans stuck with English -- the dimensions are literally quite human (e.g., foot, yard). You know, Americans being such romantics and all. :)
*
Gentlemen> I have built many many houses with staggered 2x3s on 24-inch centers on 2x6 plates. They are still standaing. No problems.
Indeed, one can get an R-24.5 insulation R-value--with a 2x3 stud, using sprayed-in PUR--which will add structural strenght to the wall--and 1-inch of RFBI on the exterior. Youm won't drive a baseball through this wall.
If you take into account the thermal bridges caused by the framing: wall studs, solid headers, cripples, 3 and 4 stud corners, top and bottom plates, etc., and then calculate the R-value of a 2x6 R-19 wall, and the R-value of a 2x4 R-11 wall you get a shock.
ak Ridge National Laboratory (ORNL) did exactly this and found the "real" R-vslue of a 2x6-R-19 wall is actually R-13.8. The 2x4 R-11 is actually R9.9. The difference then, between the two is too small to justify the added cost of the 2x6 and the necessary extended jambs. The 2x4 with high density batts and 1-inch of rigid foam board insulation (RFBI) on the exterior is far more economical than the 2x6 wall.
For those of you who would like to read about this see The Journal of Light Construction for September 1997; Custom Builder page 8, Spring 1996; The March 1996 issue of ASHRAE Journal; the March/April 1995 issue of Home Energy, Also search Breaktime archives. GeneL.
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What's the metric equivalent of an RCH?
*
No matter what you spec, the final performance is mostly affected by the quality of installation. How many rough jobs have you seen with holes in the foam sheathing from an errant hammer, or insulation that's not installed correctly around the electrical boxes, or gaps in the sill plate because of a chip in the concrete foundation wall that wasn't fixed before the deck went on or the foam that slipped out of place as the plate went down.
I have 2x6 because of personal preference (nice wide window ledges, thick walls look nice, etc.), but if you have to make a choice between the extra cost for 2x6, and hiring some of these companies that seal up everything, I'd opt for the sealer. We always say that one aw s#%t wipes out all the atta boys you've ever had, and one quality mistake can wipe out all the benefits of 2x6.
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Yes, but only if you have nat.gas heating.
*Gentlemen. Oak Ridge National Laboratory has done considerable research inot the "real"R-value of some 18 differencr wall combinations. They found that when you take inot account the framing shport circuits and thermal bridges, the 2x6 R-19 wall is now actually R-13.8. The 2x4 R-11 wall is actually R-9.9. Obviously then, the difference between the two is too small to justify the added cost of 2x6s--even 24-inces oc--and the extended jambs. The 2x4 wall with 1-inch of rigid foam board insulation (RFBI) on the exterior is more cost effective.I've built many, many houses with 2x3 studs in the form of staggering them 24-inches oc., on 2x6 plates. As for the single stud 2x3 wall, it can achieve an R-value of R-24.5 with sprayed in polyurethane foam (PUR) and 1-inch of RFBI on the exterior. You won't throw a baseball through this wall.GeneL.
*You can build with 2x4 in washington as long as your WSEC calculations show the actual U*A value is greater than the target U*A calculations. Many homes go up in the Seattle area with 2x4's and XPS foam on the outside, usually with acrylic stucco covering the foam. DH
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State of the art? Mighty arguable term, I would say. For me, in this hot and humid climate, R11 walls are plenty. My window upgrades consist of white frames and tinted glass. Serious roof ventilation is critical, however. One could save a bundle on energy by using 1" thick gas-filled, vinyl clad thermal break windows (lowEglass), and R50 ceilings with 2x6 walls, foam sheathing and housewrap. However, the house may sweat and rot to death before any payback is realized. While throwing money at the problem, let's double the cost of decking with Kool-Ply. All that stuff may pay off somewhere, but here, forget about it. The first place I look for energy savings is HVAC. Too many AC subs throw together the return air chases, leaving them to draw hot, dirty attic air. That is hard on the system, not to mention the power bill. Some even gouge you with too big a system that won't cycle long enough to remove the intense humidity we have around here. Ouch! First, you pay for more than you need, then, it turns your home into a mildew farm. In Houston, a house must breathe to live.
*
Well Mike being upside down we refer to them as HCR's
*Gene , when you say a staggered wall 24" on center do you mean 24" center to center on the outside and 24" center to center on the inside or 24" centers stud to stud resulting in 48" centers on on any given wall plane . Just curious , Chuck . BTW after the big energy crunch of the mid to late seventys we saw a move to 2x6 exterior walls [ in Eastern OK ] but for the last fifteen years or so 2x4 has been the norm . I have absolutely no technecnical info to back this up but in our climate I firmly believe you lose or gain far more heat thru the ceiling than you do the walls . Chuck
*I always thought the 2x6 wall was a mess I would muc prefer a 2x4 wall with r-13 in the wall and 1/2 foam over the exterior ply this way the r-value is equal and the window and ext. door jambs are a standard 4 9/16.
*I asked your Q to Gene -- he means 2x3's staggered in/out 12" oc, so the inner and outer sheathings each contact studs 24" oc.
*Chuck. I wanted to acknowledge that i read your post. Andrew is correct. The outer studs are 24-inches oc and the inner are also 24-inches oc, staggered so that there is a stud every 12-inches.The eventual wholeale changeover to 2x6 studs was done without considering the cost consequences. By the bye. There are thousand of houses in OK that have sand covered attic insulation brought in through wind turbine--whirrly bird--vents. GeneL.
*Chuck, andrew et al. I forgot to mention that the staggered 2x3 wall is less costly than the same wall built with 2x6 studs. One can get a furhter reduction by using full width rough sawn plates: 1x6s. Also forgot--I have said all of this in past posts now in achives--to tell you that in my version of this wall there are no 2x6s used for fenestration--doors and windows. That is no 2x6s are used for king studs and trimmer--header--studs. What's the point of breaking the thermal path with offset 2x3s and then mucking things up with 2x6 studs? Andrew. If you e-mail me your address, I'll send you two drawings of how this was done. You can then post them on Breaktime. as I don't know how to do that. GeneL.
*Gene- Your mention of no king studs begs the question of how headers, window and door frames are handled. Maybe this will be answered on andrew's post. Windows and doors have jambs that would break the thermal barrier, it doesn't seem that a couple of king or trimmer studs would have much impact compared to the window and door jambs(or the fact that you have a window or door period)John
*Done. FYI, you can get the e-mail addresses of individuals by clicking on their names (assuming they didn't lie when they registered).Regarding staggered stud -- what is your opinion on Icynene, assuming you don't use it for structural reasons? It is easy to get here; polyurethane inquiries got nothing but "huh?" I'm think of using it as a sort of sir-sealing skim coat over netted cellulose.
*andrew - over at JLC's board there is a gal named Sue V. who is always talkin' about that stuff. You might check her out. Very knowledgable (almost as if she has a vested interest). - jb
*Icynene is the soft spray on stuff that will not let air through . I plan on puting it in my shop some day. price was higher than fiber glass but not out of line when you figure in the better peformance.
*Used to know a Sue V. .... Nice, and a smart lawyer. Married to what's his face now."Ice" is very expensive -- rigid-foam XPS level prices -- quote I got was $1.75 sf to fill 2x6 bays -- and not exactly a wonder-product ... aside from very competent marketing and friends at TOH. But it does appear to have its uses.Cellulose is just so cheap ... like me. Hence my thought of blending the two. I know that Icynene is the only approach so far that the local inspector's office believes will obviate venting. Its selling point is this cavity-filling air sealing, but ironically I don't think I'll need it for that, with a dense load of cellulose behind it and a more-or-less unbroken layer of drywall below. Interestingly, the installer claimed that Icynene is somewhat moisture permeable by diffusion.
*Jim , she pushes that stuff like she owns the patent does'nt she ? We used a spray in foam insulation on a resteraunt expansion last year . The owner wanted the ceiling opened up to expose the rafters and joists and it was'nt feasible to use ridgid board on top of the deck [ They had just put a new roof on ] We had two to three inches sprayed on and I was pretty impressed with the performance .The open ceiling made up about half of the existing building and after a light snow last winter I drove by and the snow was nearly all melted on the end opposite where we did the work but not at all above the foam . Chuck
*Gene, good point on the PUR foam. Material cost and few competing applicators seem to drive the price up, but the benefits overall seem solid/real world.Downside? Retrofits. Know what's going where, and don't go changing things later.
*JRS. Excuse my poor explanation. The jambs in my staggered 2x3 wall are 2x3s: the king studs that are nailed to the inner and outer headers are 2x3s. There is a 1/2-inch thermal break between the studs. The trimmer studs that supports the headers are 2x3s.There is a 2-1/2 inch space between the trimmer studs.As with the double 2x4 wall one can use a sheetrock return in place of extended jambs. hope this makes sense.Andrew. When I use PUR I use a high density version to add structural strength to the wall. I frame the staggered 2x3 studs in the weak direction: the wide-2-1/2 inch face of the stud is what you see.The strong direction would be with the narrow-1-1/2 inch face visible. By the time you read this you will have received my e-mail. It was your mailing address I wanted not your e-mail. Sorry. GeneL.
*Don - what this Sue V. told me was that the price is sometimes double or triple FG batts. You might want to look into BIBS fiberglass if you haven't already. Far superior to batts (IMHO) and only about 10% more than high density batts. Great stuff. - jb
*Hey Chuck - yeh, I get the distinct impression she's a dealer, distributing literature to anyone who'll take it. Seems like a good sport though. - jb
*Andrew. Icynene is a breathable non-structural foam. The question then, is if one wants air sealing which route does one choose: Icynene--expensive, or dense pack cellulose-- less expensive? By the bye. The Canadian research on the air sealing ability of cellulose (Laboratory Testing Of Dense Pack Cellulose For Attic Insualtion) is finished. But for some reason --two years now? the results are not yet published. Unfortunately this Canadian material is no longer free. Perhaps Canadian members of Breaktime --who can obtain the papers free of charge-might post them. No copyright problem since it is government funded research: CMHC paid for the studies. All they require is to acknowlege the work originated with CMHC. For you Canadian who are interested CMCH--Canadian Housing and Mortgage Corporation has a toll free line 800-668-2642.GeneL.
*Boy could this discussion go on and on!Let me throw this in.What about the added costs of windows and doors for 2x6 vs. 2x4 wall framing?Here in my neck of the woods these could be special order items $$$$ ! Any coments?
*JerryIf your suppliers are gonna stick it to you for jamb extensions, make your own returns. . . it's dead simple with a table saw, and a tape measure. . . I do my own regardless.-pm
*
Hello GLW (and everyone else),
Since you are talking about building your house in Texas, this makes a significant difference in HOW you are allowed to build it.
A significant part of Texas is located on the Gulf Coast, and very strict building codes will prohibit building a structure with staggered walls. In 1997, our building codes along the Gulf Coast (reaching inland about 100 miles) was upgraded to Hurricane Zone/High Wind Zone. They are very specific about building specifications, and very strict about enforcing them.
If you live south of Austin, then a 2 x 6 wall design is very practical, and very easy to do. It will significantly lower your heating and cooling bill (although we do have mild winters, but TERRIBLY hot summers). As for the doors and windows, some brands are custom ordered for the added jamb width, some are stock. In my region (Southeast Texas) the suppliers carry both in stock, and the wider jambs add about $12.00 to the price of a door (whether interior or exterior).
Another option is to use R-13 wall insulation with a 2 x 4 stud wall. This will give better insulating power than R-11, and does not add to the cost of the structure. (R-11 and R-13 are the same price here)
One more thing you can do is to call your local utility company and ask them to send you info on making your home energy efficient. They will have all of the info you need for your area, and will help you decide if 2 x 6 walls are a good value, help in reducing heating costs, etc...
Just my two cents worth from Texas.
James DuHamel (Owner, J & M Home Maintenance Service)
*
A substance can be solid, liquid or gas (or plasma). H2O at ordinary earthly temperatures can thus be ice, water, or vapor. With diffusion here, we're talking only about the vapor phase. Diffusion refers to the movement of vapor molecules through something such as Tyvek, or even just through air in a room. Because the vapor molecules move back and forth through the medium randomly, they will tend to distribute themselves evenly over the area open to them. In extremely rare cases they could all be on one side or the other, but such a state is as unlikely as flipping heads a million times in a row.
Now, what sets the rate of diffusion is mostly is the size of the holes. Imagine putting a piece of cardboard with holes (the diffusion barrier) in the middle of a coffee can and adding ball bearings (the molecules) to one side. Shake the can (simulating the random movement of molecules above absolute zero) and gradually the bearings will work themselves through the holes. Some bearings will come back where they started, but the net result on average will be a roughly equal distribution. Make the holes bigger and the "diffusion" will happen faster. Make them too small and it won't happen at all.
Polyethylene has really small holes, fiberglass has huge ones. The rule of thumb in a heating climate is to make each layer more permeable as you move to the outside. This ensures that moisture in the wall will be able to move out easily. If it can't get out as fast as it is coming in from the living space, the relative humidity will rise -- that is, the water-carrying capacity of the air at that temp will start maxing out -- and it might just condense -- become a liquid -- on the surface of whatever is cold and blocking its progress. Complicating things is that the wall space gets colder as you move to the outside, decreasing the amount of vapor the air can hold. Liquid water = problems.
Better?
*Bravo!
*Yes, much clearer, thank you. (I still don't know if this is how Steve meant it though) So, you seem to make a case for an impermeable vapor barrier between the warm interior air, and the wall cavity. "...each layer more permeable...". Am I reading you right? When you say "...fiberglass has huge holes...". Relative to what? Huge compared to cellulose? This fiberglass I'm talkin' about is not like the fiberglass in batts. It is different. Looks like cotton and doesn't have the loose fibers. It may be the same at the molecular level, but not in the wall. I'm not sayin' that this fiberglass acts as a vapor barrier. I'm sayin' it needs a separate one, but it out preforms dense pack cellulose as far as R values go. Another advantage is that you can get some tremendous R values in the ceiling, since this stuff doesn't settle. Don't I remember that as a problem with cellulose on a lid? And I'd still like to hear how cellulose compares pricewise with batts. jbvalues.
*Is there any finished drywall in this scenerio? If so how does it figure into this? Does all the warm moist air just pass through it? If so, does it just pass right back out or does it condense on the poly and make it soggy?Knowing less and less about insulation and venting daily, in fact, I now know less than nothing.JonC
*What's the expression, an expert is someone who knows more and more about less and less until they know everything about nothing at all?The drywall isn't much of an insulator so you'd be as likely to see condensation on its surface as on the poly. I've heard plenty of stories of condensation on drywall, esp. with cathedral ceilings.YB, the case has been made here by Freddy and others that the poly is a bit too much, because under the right conditions the wall might otherwise get a chance to dry inward to get rid of its moisture load before it causes problems.Fiberglass fibers provide no real barrier to air movement, so water vapor will be able to traverse them pretty quick with plain old air movement. The BIBS I don't know much about -- does the binder make it airtight or just keep the fibers from settling? Your description of it sounds very appealing, despite the bad press that blown-in fiberglass (without binder) got. If it "needs" poly, though, it sounds like it can't contain moisture well.I hope a cel guru drops by ... it does settle in the attic, but you could always throw more up there & exceed your intended thickness by enough that it came out right. Pricewise ... I think a 25 cubic foot (after blowing) bale was like $8. That's enough for maybe 25 sf dense pack in a 2x6 space ... pretty cheap. Again, the one application it fit great for us was retrofit -- if I removed an outlet or otherwise made a hole, it was enough to insulate the wall using DIY equipment. Cellulose's problem may be that it is TOO cheap and generic -- not enough profit to be made by pushing it. Look how well Owens-Corning did by coloring its product pink -- whatever it takes to make your product look special.
*JonC - Here in WA we are required to use either a poly vapor barrier or the walls have to be painted with a vapor barrier rated paint. There is a primer that a lot of builders use, called "moisture guard" that the two counties I work most often in accept. We don't seem to have extreme enough temperature differences here for condensation to form on walls or drywall. I believe the vapor barrier stops the water vapor from penetrating the cavity on warm air, which suspends more water than cool air. When this happens in cold climates, the air eventually cools as it moves through the wall and can no longer hold the same water (I think this is called reaching it's dew point). The vapor then turns to liquid, and gets the interior of the wall wet.This relative humidity thing that andrew tried to explain to me a couple months ago was the key for me. If the only water borne vapors come from the outside, and the outside air is cooler, you don't get this problem, because the deeper in the wall the air moves, the warmer it is, and the more water it can suspend as vapor. At least that's how I understand the usefullness of the vapor barrier.Now, if you're sayin' that the lack of a vapor barrier allows the warm air in the room to absorb moisture from the wall in certain situations, then you have to concede that water moves the other way in other situations. What moves one way, would have to be able to go the other way as well.Not only that. If difussion is a principle of physics, it seems to me this would be a continuous process in a wall with no vapor barrier. The warm air would be DRAWING moisture IN through the wall. The only way to stop this would be to stop air movement. A vapor barrier would be one way of doing this, as would insulation that stopped all air flow. If NO air moves through DP Cells, then maybe it is ripe for condensation when used with a vapor barrier. Maybe what these guys are sayin' is that the vapor barrier is too much when used with DP Cells. - jbps - does anybody understand how those airplane engines with the cylinders around the outside work? I never have been able to understand that one!
*Jim and Andrew,Glad you guys are enjoying the physics end of it.But I think you are missing an important distinction. A vapor barrior and an air barrior are two different things. The reason you eliminate the interior diffusion (vapor) barrier in a DP cells wall is that it serves no positive function. Research has shown (I've heard repeated here many times, though I've never independently verified it) that the primary way moisture is introduced into walls is via gross air-movement, which is different than via diffusion. A substance can be airtight yet still allow diffusion of water molecules (ie:Tyvek, drywall, cells at high densities, etc.)The reasoning goes that DP cells will eliminate the majority of moisture loading by stopping air movement. What moisture does work its way in via diffusion, will also be able to dry out via diffusion--to the outside when it is drier outside than in--and to the inside when it is drier inside than out.The terminology for the poly layer in standard construction has indeed changed to reflect this thinking. It is now called the air/diffusion barrier. Its primary purpose is really to air-seal the wall/ceiling, not stop diffusion. It has the unfortunate secondary property of being a diffusion barrier as well, which to my understanding is a negative property as far as the drying performance of a wall or ceiling goes.Steve
*ChadS. By over hangs /i assume you mean eaves? The depth of the overhang should be determined by latitude. When I did the first Leger House I made the eave depth 24 inches. As the months went by and spring approached we found the 2 feet was too much as it kept much of the sun out in March and april. Eighteen inches in 42 degrees north latitude is just about right. GeneL.
*Great! As for condensation on the walls, the problem isn't temp. difference across the wall, but the wall SURFACE being below the dewpoint of the interior air. If the interior air is too humid (close to its dewpoint) or the wall too cold (below the air's dewpoint), condensation (dew) forms. Think about real dew -- the nighttime air, with a fixed amount of vapor in it, cools in place and releases moisture.Also, it doesn't matter to diffusion whether the air is warm or cold -- the vapor will be mindlessly distributed around regardless. It is not "drawn" to warm air -- rather, it moves from areas of greater concentration to areas of lesser concentration because of random motion (like the ball bearings). Because warm air can hold more water molecules, and because we tend to keep the insides of our houses fairly humid, the usual direction of diffusion during the winter is going to be outward. The difference between warm and cold is how much vapor the air can HOLD before releasing condensate -- and this, not diffusion, is where we start talking about relative humidity. (Air can be supersaturated under some circumstances too.)As for vapor moving, keep mass air flow and diffusion separate. You can stop air movement WITHOUT stopping diffusion -- that's what Tyvek is supposed to do. Air movement can move moisture really fast, much faster than diffusion, so it is the one to keep your eye on in building construction. Air movement is to diffusion what the can in the previous example would be like WITHOUT the cardboard barrier.Polyethylene stops both air flow and (almost all) diffusion. It's just too effective for a breathing wall.P.S. That's called a radial engine. It's not a whole lot different; like a "regular engine," the crankshaft has different connection points for each cylinder so that each cylinder firing has maximum effect. So cylinder #1 might fire when the crankshaft and propellor are at 0°, #2 at 45°, #3 at 90°, .... and #8 at 315°.In the real world, the cylinder firing order is set up to reduce vibration and provide more or less continuous power. I used to be a flight instructor and own a small airplane that I serviced myself, the only reason i know this stuff. Dewpoint is real important when considering cloud formation and icing in flight.Gosh, I'm pretty sure there's some work to be doing now... Oh yeah, a posthole to dig.
*
Jim, What is BIBS , is that the stuff that is wraped?
*Don - BIBS stands for Blown In Blanket System. It is the single most impressive thing I've seen in our industry in many years.They stretch a 1/4" fiberglass mesh across the wall, staple it tight, then blow in a mixture of loose fiberglass (looks like cotton) with a bit of glue (that keeps it from sagging). It gets batter R values than cellulose and doesn't have the moisture/mold or settling problems. You can also blow it as thick as you want. When I asked the dealer, he said they can blow it 4' thick if you want.The cost was about 15% (I think) higher than batts the job I used it on last year and I couldn't believe how well it fills the cavities. I mean, it COMPLETELY fills them. You can actually feel the difference in the house after they install this stuff, no echos or air moving through the walls. I won't be thinkin' batts on anything I build, especially for remodeling, with all the oddball framing in the walls. Maybe the most amazing thing to me is that I had never even heard of this type of insulation and I've been remodeling and building around here for over 20 years now, and read a few trade journals a month. Really Don, this stuff is great. Check it out. The thing is, it is a franchised system, so there will only be one dealer in your area, and none of the other dealers will mention this stuff, so you'll have to hunt for it. Believe me, it will be worth it. I joke around and tell tales sometimes, but this stuff is for real. - jb
*Hi Jim,It sounds like BIBS is a far cry better than batts, but I have a few reservations. Is it really an effective air sealing method? Does the manufacture claim it is? Does it require a seperate poly air/vapor barrier beneath the drywall? Also, what is the recommendod method of installing BIBS in cathedral ceiling applications? Is it blown up against vent chutes? I thought it was not good to have FG in contact with the roof deck. If I was going to the trouble of blowing insulation, I would (and do) use cells.When blown in to densities of 3.5 lbs/cu/ft, cells will completely air-seal the walls and will not settle, plus it requires no moisture-trapping poly layer. My understanding of cells in terms of moisture is that cells evenly distributes what moisture does get into the walls, thereby allowing it to stay below mold-inducing concentrations until it has an oportunity to dry, which it can easily do since no moisture-trapping poly layer is used. My understanding FG on the other hand, is that being hydrophobic it will wick the moisture into the surrounding framing and sheathing, creating localized areas of high moisture content, which can lead to mold, etc (this being the reason you don't let batts come into contact with roof decking). PLus, the poly layer slows its drying ability during times of low interior moisture load.Steve
*
Steve. Jim forgot to mention that cellulose may be used with the BIB system. In the BIB system I believe fiberglass has a slightly higher R-value than cellulose, because a higher density fiberglass is used.
One negative of the fiberglass BIB systrm is that a poly VDR must be installed over the BIB mesh layer. Given that sprayed-in cellulose can be sprayed-in without using glue--it stays put in the walls- why is the mesh necessary with the fiberglass BIB system?
I don't know if BIB seals as well as dp cellulose. But it is used anywhere cellulose is used.GeneL.
*
Hello JM,
He could also check with his insulation
contractor because there is now an R-15
available for 2x4 walls.
*Hey Steve - Here in WA the code does require, and the contractor reccomends, the vapor barrier you asked about. Are you sayin' that this is proof that the fiberglass doesn't completey seal the air flow? 'Cause if you are, I think you have a good point. Beyond that, I don't have any problem with the application of a vapor barrier, as I've always thought that was an excellent way to keep the warm air from moving through the wall, thereby limiting dew point created moisture in the cavity. But believe me, I am no expert on this stuff. As far as cathedral ceilings go, the rep told me that they can and do completely fill the cavity if they can in fact seal all air flow. It is very rare here though, and the counties they serve require that this be specced by an architect. (maybe a thin layer of lcynne?) Usually they install a baffle to maintain the air space between the insulation and the deck.Like Gene mentions below, the R values are pretty good with this stuff. They can blow a dense pack and get R-25 in 5+1/2". With their standard blow (I didn't ask lbs/ft) they get R-23 in 5+1/2" and R-14 in 3+1/2" wall. What can you get with cellulose? I've never used that either, but it sure seems like the insulation of choice here at Breaktime.The rep also told me that the fiberglass will not absorb water in a vertical application. That water will pass right through it. This may be exactly what you're sayin', I'm not sure what you mean by hydrophobic. But I guess if water does somehow get into the wall, it will just make its way to the first horizontal framing and collect there. What it won't do, is damage the insulation. Is the same true for cellulose? Maybe we should move this conversation to the HVAC section so we don't ruin this thread. You think? - jb
*Gene - I don't think that they can spray the fiberglass to a vertical surface and have it keep it's shape. I think the mesh is required to keep it from "sagging" out of the wall until it dries. The reason they can't just spray it behind a vapor barrier is that it displaces so much air, the mesh lets the air out.Just as an aside, the staplers these guys used were really neat. Pneumatic upholstry staplers. They pulled the triggers and could regulate the feed rate so that it was a continuous sound. Unbelievably fast. You guys have probably seen these before, but I hadn't. Impressive. - jb
*
Your metric stud is a little thinner and a little wider than our 2x3. My house is built with 1" thick redwood - a popular construction technique here in the 50's, no wall studs, just a 2x6 horizontal stiffener midspan and 2x6 door and window surrounds.
Ever use metal studs our there in Queensland?
*
I finished my brother in laws house this march, a 2000 sq foot cape cod. We used 2x6 studs with r-19 insulation on exterior walls. with 5/8 sheetrock throughout. He keeps the house at abour75 degrees. His electricity bill was under 100$. Normal bill would be about 160 to 175. It was under 1000$ to go to 2x6 studs. We normally use a/c 7 to 8 months a year. And I will be visiting him if a hurricane comes, what price on peace of mind?
*Hi Jim,I think it's fine to keep the thread going here. This relates to whether you need a 2x6 wall or not. What led to this tangent is the thought that a 2x4 wall, with a superior insulating and air-sealing system ought to be more than sufficient, and a staggered-stud wall even better. It's not the thickness that counts, it's how well you use the space you've got.I don't think that cellulose is very widely used, even though it's talked about alot on Breaktime because of a few people who feel pretty strongly about it. Here in Central New York only one of the dozen or so builder's supply places carries it. There is exactly one blower available for rent in a 60 mile radius.I've only used it a few times myself, but I'm very enamored with the claims of its ability to insulate and airseal in one step and in a manner that doesn't depend on plastic and sealants for the air seal.If BIBS fg can perform in the same manner, at a higher R-value, it would seem very worthwhile to me, but dependence on a poly layer for an air-seal bothers me.Living in a plastic bag just seems intuitively bad to me. If it is true that the primary moisture load on the house framing is from moisture-laden air movement rather than diffusion, any way you can stop the air movement that still allows the cavities to dry by diffusion in times of low humidity seems better than trying to stop it with a sheet of plastic (and inevitably failing to some degree) which will only inhibit its ability to dry out in times of low humidity.Steve
*Cellulose was a great choice for us in an old house with solid plank siding (i.e., lots and lots of air leaks). It sealed and stuffed the wall effortlessly. Air leakage through the outlet boxes had been bad enough to draw bits of fiberglass in and to leave star-shaped dirt marks on the wall around the outlet wallplate. If you were in a situation where you'd stripped the walls out, there would be a greater variety of insulation strategies to choose from.
*From the pictures I've seen, hurricanes disassemble rather than break houses.
*Hey Steve - I looked in Webster's and the applicable definition for "diffusion" seems to be "...an intermingling of the molecules of liquids, gasses, etc." Are you sayin' that without the vapor barrier, a gas (air) and a liquid (water) will meet in the wall, and the air will absorb the water (evaporation) thus drying out the cavity?I guess we can leave it up to the original poster when we should transfer this conversation. So GLW, let us know when you think we've disrupted your line of thought, and we'll skeedadle. OK? - jb
*Actually, the gas doing the diffusing is water vapor. Water vapor is not water droplets but individual water molecules, a true gas. If the concentration of water vapor is less is one direction or another (that is, it is "drier"), the molecules will tend to move in that direction. It is natural for the concentration of water molecules to tend to average out by random motion if they're not trapped in one place; how quickly they do so depends on the permeability of the material. Permeability relates literally to the size of the holes in the material' also important would be its hydrophilic or hydrophobic nature, controlling whether liquid water could wick through it to resume diffusion on the other side.
*
Not at all. This has been very interesting. As far as information is concerned... more is better and too much is just right! Thanks.
*
Now hold on there andrew! Slow down and explain that in carpenter talk. I am asking Steve about vapor barriers. When we get our terms straight, I have another question regarding moisture that enters the wall through the siding. But I'm tryin' really hard to get this stuff straight.
By the way, I do, now, understand what you were tryin' to tell me about relative humidity in warm air. At least, I had it explained to me in a way I could believe. So while I do have a tractor speed brain, I can get there eventually, it just takes a little longer. - jb
*
My two cent worth is as follows:
If a 2x4 wall will work structurally then go with the 2x4 wall and add a layer of rigid foil faced polyiso to the wall. You pick the thickness (R-value) that you want to add. I, too would use the R-13 between the studs. Detailing is the key to an efficient wall. Start at the sill with sill sealer, better yet use a urethane caulk bedding before setting the sills. Avoid gaps and holes where not required in sheathing and framing. Use a quality infiltration barrier, I prefer Tyvek,and some reports show it is the most stable and efficient over time. Caulk gaps before wrapping. Use high quality windows and doors- they are what will lose the most energy- and look at the building lifetime, not how long you're going to be in it, when assessing payback. Use the little plastic barriers around switches and outlets & other electrical; it's unreal how much air can pass through an electrical box. Insulate that foundation. Add a vapor barrier in the crawl space (if there is one) to reduce excess moisture migration. Ventilate the soffits and the ridge of the roof, if it's pitched; i.e.: let the roof breathe and let out heat & moisture. If you can afford it, and have the space, build those overhangs out as far as you can stand it, but make sure they still look good and aren't going to sag.
I think that might be worth a nickle.
*
Gene,
Yes I'm referring to eaves as overhangs. I would advise doing sun angle calcs. if you're after any kind of solar gain. Since GLW is building in Texas, I am suggesting deep eaves/overhangs to reduce solar gain. Taking a cue from old buildings with verandas or covered wrap around porches that are often found in Southern climates. I'm in Montana's high desert and get minus 40 Winters and 105 Summers, usually. Well designed eaves are essential here, too. It's all a part of the packaged assembly though.
*
OK, andrew, man, let's focus on one issue at a time, OK? I think I got overloaded there, and mixed things up. I think I understand the process of difussion (thanks to your patient explanation).
Now, let's talk about condensation. As I understand it, condensation occurs when the temperature on one side of an solid object is sgnificantly higher than the temp. on the other side ( there are probably very specific ratios of these temps., but I don't know them). I also think the moisture forms on the warm side of this object. Do I have any of this right? Thanks - jb
*Steve - If I'm willing to admit that fiberglass is not an air barrier (like apparently DP cells) what is wrong with giving it the help it needs in that regard via a poly barrier, thereby eliminating it's shortcoming and utilizing it's superior insulating ability? - jb
*Liquid droplets will form on any surface, or in open air if "seeded," that is below the ambient dewpoint -- i.e., a relatively cold surface. Nothing else matters. Like the sweat on a cool glass of lemonade on a summer day.Interestingly, water vapor or liquid water can be supercooled -- that is, cooled beyond the point it should have changed phase. Then anything disturbing it will make it suddenly change state. For example, freezing rain is supercooled water, where rain falls through colder air and freezes on impact. Pretty dramatic stuff if you've never seen it -- breaks branches off trees, rips out phone wires, etc..
*
Have any of you had experience with insulating concrete form wall construction for homes? I heard some advertisements on a product called Greenblock.
*
...still pondering that one andrew, something there is troubling me, this definatly seems closely related to relative humidity...gears are grindin'...
*Hi Jim,Because the poly creates its own problems. If there are breaches in the poly layer that admit gross air-movement, as there will inevitably be (think electrical boxes, seams in the poly, all the drywall screws you punccture it with, gaps under soleplates, picture hangers and other owner-induced punctures, etc), then water will get into the walls, where the poly layer will inhibit drying, which I'm told is accomplished mainly via diffusion.Think about a tattered tarp over a piece of upholstered furniture left out in the rain. Water will make its way through the torn tarp into the sofa (analogous to a wall under high moisture load via air-borne moisture). It stops raining (the humidity drops) uncover half the sofa. Which half will dry quicker?Steve
*ChadS. thanks for the feedback.I agree with you on the sun anglke calculations. The Leger house is in Massachusetts. What amazed me about Florida was the stingy overhangs. It as though they has no more cooling problems than we in the North have heating problems. GeneL
*
If you are interested in building a better house and saving energy, forget wood framing and check out insulating concrete forms. http://www.insulatingconcreteforms.com
*
Hey Steve - sorry, had some family matters to attend to this weekend, but I've been thinkin' about what you said.
So your overall line of thought seems to be that for any insulation to really be effective, you have to stop air movement between the living space and the wall cavity, and you don't have confidance in poly vapor barriers to do that. On the other hand, you believe that DP Cells are an effective air movement barrier. Is that your argument in a nutshell? - jb
*Gene,Have you compared DP Cels to Icynene to PUR on a $/R/Sq. Ft. basis? Here on Long Island, Icynene was a better choice than DP Cells because NOBODY could do DP Cells. The higher R value of PUR may offset the cost (plus the gained square footage of the thinner walls with PUR). What dollar figures have you run across?Ron
*Jim,Find one of your kid model airplane engines and hold on to the prop while you turn the engine. That is how those old ones worked.The "holes" in DP Cells or Icynene are very small, on a molecular size. Since an H2O vapor molacule is smaller than nitrogen, what little H2O that gets into those insulations with air difusion will difuse thru the insulation very quickly keeping the air/water vapor below the dew point.Ron
*A quick updateAs Gene already knows I'm trying to track down a copy of this research for one and all, but have discovered that the research was funded by Hydro Quebec, and they are sitting on it right now, with no immediate intent on publishing or allowing CMHC to publish.Haven't stopped the search, but emails disappear into cyber space sometimes with out reply. Maybe I need to get a translator, my french ain't real slick. . . I'd ask Gabe but he probably doesn't wanna know!! ;}Also, I think the papers were written in French, and may not come with an English translation. . . they're a bit parochial about that!!!-pm
*Jim,The point where the relative humidity is 100% is the "dew Point". As you cool a given mass of air and water vapor, the amount of water vapor that it will hold decreases. The ratio of the amount of vapor that is in the air to the maximum that it will hold (as a percent) is the "relative humidity". When the air is cooled to the point where the relative humidity is 100% or contacts a surface at or below that temperature, condensation will form. So as long as the air doesn't contact a surface or object that is below the "dew point" for that air, no condensation will form (even at 99.9999% humidity).Ron
*Hey Ron - yeh, I finally got that part clear in my head (after hearin' it several times, from several different people, in several different ways). I think I understand "relative humidity" and I guess I have expanded my idea of "condensation" to the way Andrew explained it. And I do think they go hand in hand. You would be amazed at how many people think the same thing I used to about condensation bein' caused by temperature differences on two sides of a solid object (that, of course, is just ONE example). Must be the easiest illustration our Earth Science teachers could give us in 7th grade.In reality though, I am still having a hard time envisionong a room where the interior surface of the wall has a great enough temp. difference for condensation to occur. Certainly, it would have to be in a situation like Steve Zerby describes, where the air if leaving the room faster than it can warm the surface. I can't put a finger on my next question, so I'm lettin' it tumble around in my head a bit. Thanks for your explanations - jb
*andrew - yeh, I think you're right. Thanks - jb
*
Food for thought:
Why is it that in humid climates, when you get up in the morning, the grass, windows, your car, etc. are covered with "dew" or condensation droplets but the concrete never is?
Chris
*
Chris - I'd say that the concrete is way more porous than the other objects you mentioned, and the moisture works it's way into the pores instead of lying on the surface. But, ah, I don't think "dew" is condensation, I think it is percipitation. (not that this matters for your question). - jb
*Hi Jim,Just saw your reply today for some reason.I do think that efffectively air-sealing the insulated cavities from the interior space is the surest way to prevent moisture from getting into the cavities and causing problems.I'm not saying poly and FG aren't an effective insulation system, just not very tolerant of user abuse and sloppy installation.Poly can indeed air-seal, if carefully installed and protected from ruptures, but it seems to me that Dense-packed Cells (or foam, or any other insulation that in and of itself forms an air barrier) is a more fail-safe approach. And as I said, should the walls become overloaded with moisture, from either vapor or leaks from the exterior, I think having the poly layer in there will actually prevent the wall from drying out as quickly as it could with alternative methods.But I'm just pissin' in the wind here, as I've not much experience with cells. I'm just spitting out my interpretation of what others with far more experience have told me and others in the ongoing debate here at Breaktime. Sounds good on paper to me though (no pun intended).Steve
*Hey Steve - Glad you found this, I've been giving it a lot of thought. As far as lacking experience with this stuff, that is of little matter to me. You explain yourself well, and have an open mind, and obviously have thought this through much farther than I have. I just hope that you can help me gain a better ubnderstanding of this complex subject.Now I agree that a poorly installed vapor barrier is of little use, so let's assume that we have installed it correctly, lapping all seams and sealing the openings on all electrical boxes, and sealed all penetrations between levels etc.I am having a problem understanding your "difussion as a benefit" theorey. It seems to me that if the moiture can diffuse OUT through the wallboard in certain situations, it would have to be able to diffuse INTO the wall under other conditions. Not only COULD it move either way, it seems to me it would be constantly trying to equalize the vapor content on opposite sides of the wallboard by it's very nature. Therefore, it seems to me that a vapor/diffusion barrier would be critical to keeping the two sides separate. Is it possible that this is the rational for this building practice? - jb
*
What happens when you install cedar lap siding over the insul. board? Isn't there a tendancy for the nails to pull through thus damaging the siding? Has anyone successfully constructed 2X4 walls, plywd. sht'g, insul. bd with lap siding over without getting "wows" in the wall?
*
My guess, and it is a guess, is that the concrete holds the heat from the day better (thermal mass) and the dew drys as fast as it forms.
Rich Beckman
*My guess is the same as Rich , with an added thought the grass is many thin leaves that cool very fast , if you had thin blades of concrete it would more than likely have dew on it.
*UhhDew b iscondensation, and if the surface ain't cold, then the air born moisture doesn't condense upon it. . .as stated above concrete holds the heat from the day longer because of it's mass ergo no condensation. Also, i curingconcrete gives off heat as part of it's curing process. . . for how long I don't know, but it takes years for it to reach it's eventual tensile strength.-pm
*JimI too have been wrestling with this since I came to Breaktime and started reading new theories. I havei sucessfully used poly & batts for years, and I have also (again very recently) taken apart poly/batt walls that were installed well and never tampered with by homeowners, which were as good as the day they were covered over. But I have to agree that penetrations by errant screws (careless d/wallers, picture hanging plugs etc.) and poor sealing around electrical boxes (almost an art) can open up the wall to vast amounts of moisture carried by draft because f/g is not inherently a good air sealer.If this wall gets soaked, it would take much longer to dry out back through those same holes, if it ever really would, because it would be seasonally subject to more of the same type of infiltration. If however, there was no plastic barrier, and the insulating product was of a type that would effectively seal against infiltration by draft,(denser,tighter to framing etc.) then any moisture absorbed by diffusion (apparently relatively insignificant) would be able to diffuse back out over a larger area, whence it came, when seasonal conditions reversed.I take great care with sealing poly at plates, electrical boxes, window/door penetrations etc., but not all installers do, and then there is always the homeowners/handymen/renovators who will live there for the next 100 years. They can't be discounted or effectively planned for. . . this then seems the great downfall of the poly/batt system: longevity? Maybe.-pm
*Yes, of course. I am not exempt from occasional idiocy. But I did get the warm concrete part.Rich Beckman
*Hey Patrick - Yeh, I see your guys point about the vapor barrier bein' kind of delicate and subject to damage. I have to wonder though, how much moisture is actually going to enter the cavity though a picture nail hole, especially one into a stud. And I am no big fan of batts, that is why I am so gung-ho about this BIBS fiberglass. It is WAY better air sealing wise and the fibers are completely different than the spun glass in batts. Why wouldn't the moisture in the wall work it's way out through the exterior sheathing? - jb
*I think dew is the result of air temperature dropping to the point that the water vapor in it falls to the ground, regardless of the temperature of the ground. This process may be called "condensation", I don't know. But it is not dependent on the surface temperature of whatever the dew falls onto. The night air is cooler than the ground. But, as usual, I could be wrong. - jb
*I am from a humid area and dew does collect on concrete. Slabs tene to absorb that little bit of moisture though. And as to sealing the house up we are having trouble with housed sealed to tight. We are seeing a lot of sense in allowing wall cavities to breath.
*But if the dew is falling, how come it has never fallen on me?Rich Beckman
*Norman. good point. However, if we are going to use wood framing why not do it in such a way that it minimises the problems Patrick mentions? GeneL.
*I don't know. Is it because you don't remain in one position long enough for it to build up far enough for you to notice? Maybe it has something to do with your body temperature bein' warmer, so that moisture is again absorbed by the air around you. Believe me Rich, I don't know. I had these same problems all through school, but now, I can take the time to reason through these problems, at my own speed. Good thing we had a vocational program in my high school, or I'd a never made it through.Pretty fascinating stuff though. And I'm sure glad we can all bounce these ideas off each other. - jb
*JimThe nail holes into a stud isn't the issue, it's the ones between studs, but even that's small compared to voids around electrical boxes and window and door penetrations, and just plain poor quality installation. I know how careful I am, and how much time it takes to do it right. . . I also know that every other guy out there doin it is a hacker, just tryin to make a buck, and your number one carp ain't the guy you want stuffin insul and fightin with poly.A system that doesn't depend upon state of the art installation is probably going to save a considerable amount of deterioration in the majority of applications. Eliminating poly, and using an insulating product that doesn't depend upon it would seem to be a wise move. The old axiom Keep It Simple, Stupid comes to mind.If the building is sheathed with modern sheathing products, all of which are supposedly waterproof, not much moisture is going to wick out that way. -pm
*Patrick - No arguing with your logic there. So how does this dp cels system compare to batts for costs? - jb
*
I definitely feel it's worth it. Another option is using cellulose insulation as opposed to regular fiberglass. this way the cost increase is only pennies per square foot and you get the comfort of staying with the conventional 2x4 framing.
*
Jim
No idea. . . never used the stuff. .. it's difficult to impossible to DIY it around here. . . no product, no equipment, and I don't know if any installers are even available in my area. Not to mention the fact that I don't trust many other "professionals" to step foot on my site. . . the world is full of bozo's and most of them work in construction!!! And I imagine insulation contracting would be a haven for the bozo set!!!
Better let Steve, or Gene, or Fred answer this.
-pm
*Dew is condensation. The air gets saturated with vapor as it cools, and the blades of grass (or whatever) trigger the condensation.An interesting example: you know how your breath fogs on a cold day, and when it's even colder air from your nose (which has less moisture) fogs as well? I went to school in upstate New York, and used to walk across a birdge over a creek to get my coffee transfusions. My breath would fog only on the bridge, because the creek below would raise the humidity to the saturation point. It was a dramatic effect, beginning and ending at the creek boundaries.I also discovered the temperature I define as "nose-hair cold." That's the temperature at which your nose hairs freeze, approximately 5° F in my experience. The Northeners here know what I'm talking about!
*Ja, Sure, you betcha!As a native Minnesotan, I can attest to the nose-hair freeze point being somewhere between 10 degrees and zero. Now in places where it is really cold, like Mpls. where is has been known to drop to 35 or 40 below during really cold snaps, there is also the phenomenon of chest-pain cold, where it starts to hurt in your chest just to breath.Steve
*andrew - are you saying that these "...blades of grass (or whatever)..." are colder than the air? - jb
*Jim,Since H2O vapor is smaller than nitrogen, what little moisture gets into an insulation with very small spaces such as DP cells or Icynene will difuse out faster than the air (80% nitrogen) can bring it in. Since the spaces in FG are so large molecularly you would not get the same benefit.Ron
*
I have a home design with 2X4 exterior walls. A few of my friends are builders and some suggested redesigning for 2X6 exterior walls with added insulation to help combat the cost of cooling (in Texas) during summer. The others say it's not worth it. Does anyone else have an opinion?