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Wow, man, where can I get some of what you’re smoking? That’s the deepest dialog I’ve ever read here, and it does get deep. I love it. You win the top quark award. Wish I could embelish on the subject, but I have to get back to my paint fumes.
Impressed, Greg
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Ah .. but what about evaporation effect. Evaporation off a body cools it and reduction of relative humidity in the air surrounding a body warms it.
I think humidity and moisture have to be added into the equation.
On the wind breaker over wool sweater question ?
When the wind breaker is removed on a windy day, two things happen: (1) The wind convects the heat off and out of the wool and (2) the warm moisture trapped by the wind breaker evaporates. Do you cool from the loss of heated air or from the evaporation ?
On the other hand, consider damp, cold feet inside a pair of poorly insulated boots.
One way to warm cold feet is to loosen the boot laces. Three things occur that warm the feet: (1) an air space is created between foot and boot; (2) and (3) convection dries the socks (exchanges damp air in boot with lower humidity, outside air).
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Sure. Assume the fg is laying on a flat, impermeable surface - like perfectly applied poly on gypsum board for arguments sake - above heated interior space and a cold, open to the exterior (through venting or whatever means that allow cold air to blow over it) attic above. If you measured the temperatures at different points within the depth of the fg, it would be warmer on the drywall side, cooler towards the attic side. So, since fg presents little impediment to convection, the denser, cold air above will displace the warmer air in the "pockets". The greater the greater the tempertaure difference, the more this will happen. That is the jist of what was shown in the ORNL tests.
*Joe,Sure, all insulation materials fail to bring heat transfer to a complete halt. However, it seems that while all materials lose heat to conduction, some are more apt to also lose heat via convection. From what others have said, and said with a fairly steady voice, is that convective loss through cells is much less than convective loss through FG. I'm not a "cells guy", which is why I'm attempting to absorb and regurgitate all this info. There does seem to be quite an argument being made for cells and I'm leaning toward using them. I just need to pry myself out of the "always done it this way" department.A major part of this stems from the ability of cells to fully pack a cavity better than FG, even when both materials are conscientiously installed. I have seen thermographs, and they do seem to support this argument. I'm lost where my above post leads to a pro-vent argument. None of my ideas were intended to convey the idea of heated air from the living space passing through or around a VB then into the insulation. My idea of the "convective loop" that Steve brought up was of the loop existing IN the batt itself. Cooler air in the attic settles on the batt surface, percolates down, displaces the warmer air in the batts and the warm air is flushed to the surface, upward and out of the batt. The loop is increased with flaws within the batt (delamination) and flaws in installation (not full contact between batt and drywall/stud). I didn't mean to infer there was any air passing from the living space, through the VB, and into the unheated attic. Should that flaw exist, the transported air would, in addition to heat, carry the dreaded moisture. If the flow can't be stopped, then there is the argument for venting. At least there's MY argument! :) There are many variables in getting a good seal in the house envelope. House design (both structure layout and mechanicals), worker attitudes & education/awareness, building materials, and budget are just a few. I do think it's possible to get a decent barrier if you make it a priority. It's not easy, but it's easier during construction then having to come back afterward.
*Steve et al. My introduction to Tyvek was in 1972. Bob Hoppe, then of Brookhaven National Laboratory, told me it had been devloped by DuPont for use over attic insulation to prevent wind or air movement from decreasing the insulation's effectiveness.Here are some references on the subject. See "Natural Convective Heat Transfer Im Permeable Insulations" by C. G. Bankvall in _Thermal _Transmission_Measurements_Of_Insulation_ published by ASTM in STP 660. Bankvall also has another article in the same volume: " Forced Convection: Practical Thermal Conductivity in an Insulated Structure Under the Influence of Workmanship and Wind"In 19888 two Danish building scientists, Clausen and Hoyer,were researching the effects of increased attic ventilation on the R-vlue of insulation. Their findings showed that doubling the airspeed of roof ventilation in cathedral ceilings resulted in a 22 percent reduction in the R-value of the insulation.No one can say that doubling the attic ventilation rate will result in some specific R-value reduction. However, avoid increased ventilation rates[this is another myth that the more attic ventilation the better] to avoid and reduction in the insulation's effectiveness. The Clausen and Hoyer paper was published in the proceedings of the Buildijng Thermal Envelope Coordinating Council (BTECC) S y.mposium on Air Infiltration,Ventilation and Moisture Transfer. BTECC (202) 437-5710.Abe Berlad, fornmerly of Brookhaven n?Ational Laboratory has also done lots of research on the effects of air intrusion into fiberglass insulations. Unfortunately I cannot at this time give you the names of his research report.Many years ago Simplex Industries manufacturers of Thermoply funded research on the effects of wind penetrating exterior sheathing and on into the wall cavity. The research showed a substantial redution in the insulations effectiveness. Simplex's answer to this problem was to use their sheathing. In fairness to them, Holometrix, at the time called Dynatec R/D Company, but still located in Cambridge ,Massachusetts, found no fault with their research and questioned only the magnitude of the reduction. Hope this helps a bit. More later on ORNL findings on the reduction of blown fiberglass's reduction in R-value as tempersature drops. GeneL.
*Regardless of whether it's fg or glass or steel heat transfer is a function of the boundry conditions. Specifically (or generically) surface finish and state of the surrounding air. Forced convection increases heat transfer vs stagnant air any time. I think the fiberglass would be even worse due to the large amount of exposed surface area, and the ability of the air to penetrate it. I can post the equations if anyone cares.-Rob
*MongoIts getting late and I admit I didn't read your post enough to understand your whole message, but I wanted to clear up one point.If you take any material and induce a temperature difference accross it the surface temperature on the cold side will always be higher than the air temperature. Envision this like a graph charted accross a wall (the way it's taught in school anyway). The interior temperature is 70 degrees, the temperature accross the insulation is a line (basically straight) that runs downhill til it hits the outsdie face of the wall. As I rememeber the slope of the line lends it self to a graphical analysis. The steeper the line the better the insulator because the lower the surface temp on the cold side. As I remember (which is open for debate) a well insulated, or superinsulated wall would have a grahical heat transfer line accross the wall tha is asymptotic. This means that the curve would drop off steeply, then gradually flatten out, but never hit the cold side temperature no matter how thick the wall was. The really interesting thing is that adding more insulation could actually increase heat transfer in these situations if the boundary conditions are not conducive to heat transfer. This is a fact, and hard to believe, but we did it in a lab and had to prove it.The gist of the story - If there is a "boudary layer" of warm air above (or just inside the top layer) of the batt, then there is not nearly enough insulation. As I stated earlier in this thread, open faced fiberglass appears to me to be an ideal heat transfer medium (good boundary conditions)-Rob-Rob
*Mongo - I never used tolike cels either, and now I actually decided to put them in my roof!! Jump on the band wagon, abandon reason and follow the herd! (meant in a cynical manner)-Rob
*GeneI think we're looking for a direct comparison between f/gi battsand cells in the same config.- a 5 sided box, with venting air possibly washing over the exposed 6th side???
*Hey Fred,Where did your post go? I was going to read it again to try to absorb a little more of it, and "poof!" it's gone!What the heck is going on around here! Things are popping in and out of threads with alarming increase.Steve
*First, would someone please tell me what cells are? Second, I am currently redoing another house and I am insulating it as I have all my other recent projects by using foiled 1" polyisocyanurate on the inside. I feel that this serves three purposes. First it is a good vapor barrier. Second, I feel that R values are probably close to theoretical. And, third, it reduces radiated heat out in the winter, and in in the summer. The more I read here, the more certain that I never knew as much as I thought, which wasn't all that much in the first place, and the more concerned I become that I am making some horrible mistakes in my buildings. Comments pleaseDennis
*Dennis - cells refers to cellulose insulation - ground up newspapers with a little chemical thrown in for fire resistance.
*Dennis,Are you strapping over the iso board? The foil is only a radiant barrier if it has an air space against it. If drywall, sheathing or insulation touches it the emissivity acts like material touching it.
*No.As I said, I seem to know less and less. Why do you need an air barrier? Wouldn't the iso on the back side of the foil do the same thing to the radiation? Dennis
*Hi Dennis,A piece of foil with an air space on both sides is TWO radiant barriers. With insulation on one side it is a radiant barrier on the other side. If something is touching both sides, it is not a radiant barrier at all, just a vapor retarder if the seams are sealed.Ron
*There was an article in this months Home Energy magazine that talked about the neccessity for the thermal barrier to be in complete contact with the air barrier. Fred has said about the same thing but I didn't understand the why too well until this article. The article explained that when there is a gap or space between a fibreglass batt and teh back of the drywall, the air in that space is warmed through the sheetrock and then is lost through convection. The article stated that testing had shown this to happen in spaces of less than an inch, so in particular batts laid between joists and over furring strips would loose a lot of their R value. They also discussed the need for this complete contact at dropped soffits and such, suggesting the need to make the drywall continous over the soffit. More difficult was teh pop up or trayed ceiling and getting tight fitting, perfect contact on the inside corners.It would seem that any void or gap like where the batt didn't fit perfectly aroung a pipe of piece of romex, would result in the same loss of R through convection. Likewise the greater the delta T, the stronger the convective force would be.
*Steve - You are busted! You must not have fully read Gene's book. In the chapter on insulation he explains exactly what happens to the effectiveness of open batts in an attic. I was amazed. It doesn't fully explain the "why" of what is happening, but it does cover measures to improve the dramatic loss of R-Value at temperatures below 30 degrees .I am slowly becoming a believer in cellulose. If only it had about double the R-value!-Rob
*Bill, Steve et al. Both ORNL and Bill Rose at the University of Illinois performed tests( 1990-1991) that show loose fill fuberglass insulation degrades under cold conditions, but that this does not happen to cellulose.Their tests showed that at 10 degrees F fiberglass's effective R-value dropped over 50 percent.The cause of the degredation is air convection into and withing the insulatiom... verified by infared scanning. Both laboratories found that the convection starts at about 50 degrees F. However, the highr R-value loss does not occur until temperature drops to Zero or below. the good news is that there are not that many regions in the USA where the average outdoor temperature is below ZERO for several months each year. For regions where attic temperature drops to Zero or below for a few hours per year the results can be ignored. The question to ask is how much does this add to my heating bill? Very little. See my recent post about Bankvall and the Danish research into the effects of ventilation air on reducing effectiveness of fiberglass insulation in attics. GeneL
*Fred - could you please elaborate more on the air barrier/moisture barrier issue. It occurs to me that no one has ever explained in straight forward terms the amount of water that exfiltration will carry as opposed to moisture that has to permeate through ordinary drywall. Someone told me a rule of thumb is that air leakage is 100 times more effective at getting moisture into walls than permeating through ordinary drywall.I believe this is why you say that with properly installed DP cels you need no vapor barrier, because it would merely be fixing a problem that does not yet exist. No?-Rob
*Rob,DP takes care of all the holes, cracks, penetrations and spaces that appear after the framing shrinks away from drywall over the course of a few years...What DP does is make the b non-drywall areas work well at retarding.J
*Rob. First. Did you receive the material I faxed to you? Never received an acknowledgement nor did you have any questions. I'm not looking for the T shirt because I did not send you details on the Leger Stud wall. I'm in the process of copyrighting the manual.You are correct about the air leakage moving a 100 times more mosture than diffusion. From Lstiburek's latest book: At 70 degrees F and 40 RH interior, diffusion will move 1/3 quart of water through a 4'x8'sheet of gypsum board--no vapor diffusion retarder. Now put a 1-1/2-inch hole in that same gypsum board and air leakage will move 30 quarts through that hole under same temp and Rh conditions.Of course there is a formula that allows,one to calculate how much moisture is moved by diffusion. GeneL.
*Gene,I am very interested in learning how to build a Leger house. What do I do next? Are you selling manuals?Steve
*Yes, I did get the fax. Thank you very much. I thought your notes were interesting because you appeared to pay very close attention to the cost of these details - which were essentially the same. In my main career I have no regard for initial costs (despite what my boss says) I put in machines that will be there for thirty years. The initial cost is a fraction of the life cycle cost especially if the machine needs constant attention. When my boss and I get into disagreements he says "you have to spend it like it's your own money." I counter by saying "I do, would youlike to come over to my house and see how I have spent my money!!"What I am trying to say is that it is interesting to see initial cost considered so closely. Obviously this is not an apples to apples comparison. It is neat that your work allows these improvements in undercapitalized construction (probably 80% of housing projects - for variou reasons). It deeply bothers me to not see this type of value engineering in house construction that is obviously very over-capitalized. It must be particularly bothersome to you because this is the focus of your work.-Rob
*Rob. Glas you received the material i sent. Because of a screw up by a framer who assumed rather than thinking--he pre -assembled all the header 2x3s only to find that he had to disassemble most of them--I stopped using the 2x3s in an L configuration, and substituted a 4 2x4s. Notch out the end of a 2x4 so it has an L shape. The base of the L is 2 inches wide. the Height of the vertivccal arm of the L is the depth of the header. the thickness of the vertical L arm is 1-1/2-inches.I'll send you a sketch if this explanation insn't clear.For me first cost is a consideration not an Obsession.If I looked only at first costs of sprayed-in PUR foam I never would have used it.I think you would get real excited with my new stud wall. I'm presently trying to find some fair way to price out the package, and make it available.We've invested thousands of dollars for the engineering and see no reason why I should not recover my costs. The package is the 100 page manual with all the engineering calculations, details of how the stud is constructed from 2x3s.Although my stus can be substituted for regular studs, anyone wanting to build a Leger House--MESH house- must see that the the stud is part of a system building. If you follow any of my posts especially on double walls--which I do not advocate any more--you see what goes inot a MESH House. The most importsant element is attitude. If you have a healthy attitude you'll automatically have TQC Total Quality Control.GeneL.
*Steve, E-mail me ([email protected]) your address. I want to send you something that may be of help, and possibly save you from going through Breaktime archives to find my posts. . I am in the process of copyrighting the engineering manual on my Leger Stud. The manual is 100 pages long and contains all the engineering calculations and diagrams of how to construct the stud from 2x3s. anyone using the stud will need the engineering calculations to keep the building inspector happy.Although the manual is stamped with the engineers stamp- he is a registered professional structural engineer in Massachusetts, New Hampshire and Vermont, the stamps are only legal in those states. If your building inspector wants a stamped engineering manual you take the manual to a structural engineer in your state. He of course will check out the calculations but at least he doesn't have to start from scratch.My major problem at the moment is to establish a fair price for the manual. Next I have to write another nabual to explain the WHY of my way.GeneL.
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Can we start fresh with a rational discourse on the topic of insulation? The original R-values thread has gotten too long and convoluted.
Maybe in the new spirit of cooperation we are all embracing, we can trade some useful thoughts.
I'll kick it off with the following post, but I would encourage any and all digressions that might prove fruitful.
Steve
*Hi All,So I'll pick it up with a question that I raised in the 2x6 ceiling thread.What, if any, is the effect of having FG directly exposed to exterior air flow?If an attic floor plane is perfectly air-sealed will you get the same actual r-value from a manufacturer's rated R-30 of FG batts laid over the floor as you will from alternative (not just cells) less permeable insulations at their rated R-values?In other words, are you likely to see any degradation in the performance of FG when when it is not in a closed, six-sided box? Can you get convective currents wicking away the heat in either an open attic configuration or even in a closed wall cavity for that matter?Has any testing been done to this effect?Looking for facts,Steve
*Steve - I believe I have read of tests at ORNL that showed a significant decrease in insulation as the temperature lowered - from the wind washing effect - like 50% at -50 f. No doubt, Gene will have the facts on those te
*Dear interneted insul- types (Add any attachment that suits...ter...ted...ation contractors....ation detractors...etc)Hope you all have some room left in your belly; just a few thoughts to stimulate a little challenging "recourse" during your "Breaktime."Double wall, passive solar homes and their long run of news time via Popular Science, etc...As I followed this thread a decade ago or more, it seemed studies eventually "framed" the heat transfer process refining it down as follows...large convective loops of air movement and laminar flow that would go hand in hand with the idea just weren't observable...their were what appeared to be, scaled micro-eddy transfer through the "air medium."...I have no idea how to explain what "it" all means except that as I learn more about any physics involved in observations, I seem to find philosophical and all other forms of knowledge categorization converging and diverging from the two extremes of nothing and everything...infinitely small or zero to vastly large and universal...And now for some real "What the **** is this ****?....OK life's lived in frames...a time and a space, conditioned by our ability to reach out, in focal awareness, through proper "relational ordering" of all frames perceived, with those yet sought after....I.E.- Modern physics has made huge achievements in knowledge and use of knowledge in sort of a stepped energy (no inter-existence) level way in it's reach down to the infinitely smallest make up of matter, past atoms and electrons and gluons, quarks and more...deeper, deeper the scientists dig running headlong into seemingly "un-scalable walls," only to discover in trial and error another "back door" on and in to the next level, the next, frame.Where does it all lead or end?...There are no ends...life only leads...Who's having "just another day," are you tapping the edge...out of bounds....or just watching the punch clock tick?Fractally,Jack : ()
*Wow, man, where can I get some of what you're smoking? That's the deepest dialog I've ever read here, and it does get deep. I love it. You win the top quark award. Wish I could embelish on the subject, but I have to get back to my paint fumes.Impressed, Greg
*FG depends on air pockets between glass threads to insulate, so to me it would certainly make sense that air flowing through an open FG batt would reduce the insulative capacity of the batt.In simple terms, it's kind of like adding in a wind chill factor. Air movement carries away the warm boundary layer, thus lowering the effective temp and increasing the required heat load on the warm side of the insulated cavity. I just re-read my response and can't make sense of it! Still jet-lagged, time for bed! I guess what I'm trying to convey is that if you go outside on a cold windy day with your windbreaker zipped over a sweater, you're comfy. Remove the coat and the wind howls through the sweater, your chilled. Though the sweater is thick and the windbreaker thin, it's the ability of the windbreaker so stop the air movement against the skin that helps to keep you warm.Nite nite.
*b "What the **** is this ****?i by Adirondack Jack Kerouaci As Ii followed this thread a decade ago or more,i framed the heat transferi air movement and laminar flow air movement and laminar flow hand in hand . . . the idea just weren't observablei the twoextremes of nothing and everything...infinitely small or zero to vastly large and universal... a time and a space,of all frames perceived, with those yet sought after....deeper, deeper . . . digrunning headlong into seemingly "un-scalable walls," . . . discover in trial and error anotheri "back door" on and in to the next level, the next, frame. any attachment that suits...ter...ted...ationWhere does it all lead or end?...There are no ends...life only leads...i frames perceived, with those yet sought after.... i are you tapping the edge...out of bounds.... thepunch clock b tick?Every great writer needs an editor
*Joe, thanks for bringing up additional considerations. My previous post was a wee bit (conservative estimate!!) incomplete...I agree with you that if it were a 6-sided box, with no leaks, that a convective loop, while still possible, would occur at an ever so subtle level so as to not concern me at all. That's also based on the "perfect installation" theory. A poor installation procedure, however, with gaps in the cavity, could result in convective currents within the cavity that could reduce the listed R value of the installed glass to noticable levels.Steve's post, in which he broached an open box such as found in an open attic has more merit, or there is more reason to be concerned with it. If there is a delta T of 50F degrees between the living side of my attic floor (second floor ceiling) and the unfaced batts open to the cold attic air in the attic (attic floor), heat is passing through that insulation. If my second-floor ceiling is a work of art, if the vapor barrier is an impermeable thing of beauty, if the FG insulation was installed in perfect fashion by the manufacturer's own techno-nerds, heat is still passing through from my toasty house to the frigid outdoors. I guess the question is how is it passing? Convection, conduction, radiation?As you wrote, air is a poor conductor of heat. That's the premise upon which FG batts are designed. The woven fibers minimize convection, the air minimizes conduction. Conduction does still occur, though. It does make sense to me that if you do have cold air flowing over the surface of the batt insulation in the attic, that the cold air will "wash" away the warm boundary air layer that is sitting on top of the batt. To regain that nice, even delta-T, heat will conduct at an increased rate until equilibrium is once again reached. I would even suppose that the cold air "wash" would "catch" on the iregular surfaces of the batt, creating mini pressure ridges or pulses in the upper layer of the batt, with the resultant "caught" cold air displacing the warm, previously trapped air. I'm certainly out on a theoretical limb with that, however.I can see justification in the convective-loop aguement. On a perfectly still day, no air flow over that exposed batt face, there will be a delta-T throughout the batt. Some of the "heat flow" or heat loss can be contributed to conduction, air-to-air. We pretty much also agree that warm air rises, or that colder air will displace warmer air, causing it to rise above the cold air (choose your cause, but the effect remains the same). The cooler air at the surface of the batt will want to dispace the warmer air closer to the VB and drywall. The filtration-factor of the glass threads will affect (reduce)the movement of air through the batt, but I can see it happening, albeit on a small level. It's tough to envision a convective loop in a 6, 12, or 18" batt, but personally, I agree that in theory that it can happen. I'm sure on the practical level it does happen, to what degree it affects the R-value I do not know. Does it add up? Is the loss significant? I haven't the foggiest.I've really enjoyed this R-value thread, the discussion on FG vs cells vs foam. Regardless of house size or sq ft building cost, all houses should be built with a decent envelope.