Always wondered what the R stood for until I opened up the wall of a breezeway Saturday to install a slider and found Reynolds wrap stapled to the studs. Not an “aluminum foil like product” but honest to God Reynolds wrap. Now if AL is a better heat conductor than air, wouldn’t that mean it has a negative R value?
Oh yeah…the exterior of the wall was vinyl siding and foam board directly on the studs.
Niceeeeeeeeeeeeee
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Replies
They were using it for its reflecttance of radiant heat loss. Where it touched the sheathing, it would have no R. If the side facing the cavity was still fairly clean and shiny, it would have an R value of about 1.6!
Some unscrupulous manufactures are claiming unreal R values for foil faced bubble paks and foil on foam boards. How about 2" expanded foam + foil = R48!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
The R value is the inverse of the k value for a material as tested to ASTM standard 236. k is in BTU's /deg F temp dif/hr/sq.ft. This is the heat flow through the test piece of insulation material.
My dad had an old Dept of Interior (before DOE) farmers handbook from just after WWII that showed the results of actual wall testing.
2" rock wool with Al facing was better R-value than 3-5/8" with draft paper.
LOL about the R48 claim---Only way I'd beleive the R48 was if it was measured at near the melting point of foam - since radiation is proportional to the difference of the 4th power of absolute temps.
BTW, when I was a kid we had a house that had an "expanded" foil insulation.The house was built around 52-54. At the outside layer was foil on paper. Not sure of the inner layers and I don't remember how many that there where. It appeared be be shipped flat and then opened up. When opened the layers where separate. Don't really remember, but it might have been 1/2" to 1".You could see it in the attic kneewalls. Don't have any idea if the same was used other places or not.
Bill:
Had seen it advertised in the US as late as mid 80's but have never run into the muliple foil layers up here.
Some unscrupulous manufactures are claiming unreal R values for foil faced bubble paks and foil on foam boards. How about 2" expanded foam + foil = R48!!
So if I keep those bubble packaging and glue some Al foil to it, I can claim to have r48 walls?! Cool!jt8
"The difference between greatness and mediocrity is often how an individual views a mistake..."-- Nelson Boswell
I looked it up and came up with:
R-value measures a material's capacity to impede or resist heat flow. The "R" thus stands for Resistance, with a higher value denoting a higher capacity for this desirable performance factor.
Here's the (pretty elaborate) engineering explination. It's been about four years since I've taken a heat transfer class, so don't chew my head off if I get something wrong.
First, let me explain the U value.
Insulation (and everything else) resists heat transfer through it. The resistance of a given material is truly given by it's U value, (which is the inverse (1 divided by) the R value. For example, if you have R10 insulation, it's U value will be .1. )
U value is important because it has units of BTU/(Ft^2*hour) * 1/(Degrees F). Basically, what this means, is that we can use this to calculate the heat loss through something. Have a U value of .1, a 1 square foot area, with a 10 degree temperature difference? You're going to lose 1 BTU/HR.
Now, here's where it gets confusing: we can take the inverse of the sum of the inverses, and get the u-value for the entire system. In plain english, this means add the R values, then take their inverse to get the U value.
You have a wall with an interior air layer giving a R value of 1, R13 insulation, and two layers of sheetrock with a combined R value of .1. Your R value for the entire wall system is therefore R14.1. Your U value of the wall system is therefore 1/14.1 or 0.0709, meaning that the wall will loose 0.0709 BTU/Hr per square foot per degree temperature difference.
Engineers like R values because we can add them. It makes the brain hurt a whole lot less than working with U values. I'd write more, but I'm off to fix a window regulator.
My apologies (and thanks) to everyone that took time to write detailed serious replies. I guess my pun was lost : "R value = Reynolds?"
Have to work on my sense of humor ;)
So you are saying the R value of common 1/2 inch sheetrock is .05?
be scratchin' chile's head
half of good living is staying out of bad situations
Nope. Just that I'm too lazy to look it up.
Actually, I just did. It's .45, at least according to the first site that came up on google. Sorry.
Actually, this is a pretty good site...
http://coloradoenergy.org/procorner/stuff/r-values.htm
Edited 5/10/2006 8:55 am ET by chile_head
yeah, I always rounded it off to .5 for fast estimating.
Always made me wonder how a lime board like that could have the .45 when a 1/2 inch asphalt impreganted fiberboard product only gives something akin to a .66.
be a chile cookoff
half of good living is staying out of bad situations
But 1'' of foil faced fiberglass duct board is R 4.3.
be itchy and not chilley
Spheramid Enterprises Architectural Woodworks
Damm, I miss that stuff
Actually I had hoped it was more as last year I'd had the opportunity of buying 100 4x9 1/2" sheets at a giveaway price I now have sitting out back.
Broke a treelimb unloading it.
be sometimes can be fun being poor
half of good living is staying out of bad situations
Actually, we practicing engineers use the published data in the form it comes in and appropriately convert it to the units as necessary to for the application. Not trying to "chew your head off", but if your going to post as an engineer, at least be accurate. For technical correctness, "R" values apply to opaque materials and "U" values apply to translucent/transparent materials. Nothing of practical value is lost in the conversion, however, and the two are used interchangeably.
FYI, the inside air surface has an equivalent R value of 0.68 for a wall (0.61 for a ceiling), walls are properly treated as a composite structure with the standard 2x4, 24"o.c. framing acounting for an average of 10 - 15% of the wall "surface" giving an adjusted insulation value of 80% of the insulation alone (spf framing lumber has an R value of 1.0 per inch of thickness), 1/2" gypsum wall board has an R value of 0.45 and the outside air surface (@15 mph) has equivalent R value of 0.17.
I've yet to see the publishished thermal properties of Reynolds Wrap. Maybe ASHRAE has a subcommittee working on it?
Edited 5/10/2006 10:11 am by Tim
I'm sure it depends on the Reynolds number.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
"if your going to post as an engineer, at least be accurate."
"(spf framing lumber has an R value of 1.0 per inch of thickness)"
I think you'll find the R value of softwood lumber usually stated as 1.25 per inch. If I remember correctly ,cedar is rated as 1.3 per inch.
I don't know what you use in Canada, but my preferred reference for such is the ASHRAE Fundamentals, Chapter 25, Table 4 "Typical Thermal Properties of Common Insulating and Building Materials-Design Values". Tha reference lists a range from 0.89 to 1.35 for common framing lumber materials. 1.0 is a reasonable choice. The value of 1.25 is closer to the edge of the range than I would knowingly select.
You ever see cedar 2x4's?
No but I have seen manufactured cedar "log homes" advertised as highly efficient with only about 6-7 inches of wall thickness.....R8-9!!
From Forest Products Laboratory:
"For example, the conductivity of structural softwood lumber at 12% moisture content is in the range of 0.1 to 1.4 W/(m×K) (0.7 to 1.0 Btu×in/(h×ft2×oF))"
........= R 1.43 to 1; with in field final lower wood moisture content of 7 to 9-10%, the R values will be a bit higher....so maybe 1.25 per inch ain't bad!!!
Engineers like R values because we can add them. It makes the brain hurt a whole lot less
Which is where the ASTM number get "weird," as they seem to insist on using k = u. My old brain always remembers k as the coefficient of smoothness/roughness for fluid conductors (pipes or ducts or what have you). Keeping track that k is a resistance value for ductwork (and/or pipes) on the mechanical pages, while also remembering that ASTM is using it as 1/R makes my brain hurt . . . Occupational hazard of my occupation not being around (sorry Bubba)
You should be in computers. Forget about any sort of single-letter abbreviation, and most TLAs (three-letter acronyms) have been recycled a half-dozen times. You can probably establish a computer nerd's age within three years or so by asking him to define three or four TLAs.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
You should be in computers.
Oh, but I am . . . <sigh>
You can probably establish a computer nerd's age within three years or so by asking him to define three or four TLAs.
Too true. Or use IRC in conversation about conversation--some of the blank looks are telling.
I've gotten to where I rely, sometimes, on whatis' Every File Extension i nthe World: http://whatis.techtarget.com/file-extension-list-A/0,289933,sid9,00.html
If only to try and sort out what progam is needed to open that crucial file . . . Occupational hazard of my occupation not being around (sorry Bubba)
IRC:immediate response chain
import regulations coordinator
information resource center
Information Retrieval Companies, Inc
installation reference clock
integrated R-loop controller
international reconditioning center
international reply coupon
International Rectifier Corporation
International Resistor Corporation
Internet Relay Chat
interregion communication
inventory responsibility code
issue resolution center
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
[wry grin] Wonder which one _I_ meant . . . <g>Occupational hazard of my occupation not being around (sorry Bubba)
R value is largely irrelevant outside of the laboratory.
"R value is largely irrelevant outside of the laboratory."
I disagree. ALL of the buildings for which I have engineered heating and cooling systems were built outside of the laboratory. All of these buildings were constructed using relatively standard materials, with published or measured and tabulated "R values" and "U values". Those values were quite relevant in determining the thermal performance of the envelope and consequently, sizing the heating and cooling systems and equipment. (The difference that Experienced and I are debating IS, for all practical purposes, irrelevant to the overall performance of a wall as used in standard construction.) All of these systems function well and as expected using "R value" as a critical input to the design. While I can reference many projects in which changes in the envelope performance were relative insignificant compared to other heating and cooling loads of the space, R values are hardly "irrelevant" in any well designed structure.
Edited 5/12/2006 9:02 am by Tim
"All of these systems function well and as expected using "R value" as a critical input to the design. While I can reference many projects in which changes in the envelope performance were relative insignificant compared to other heating and cooling loads of the space, R values are hardly "irrelevant" in any well designed structure."
An "input" among many, sure, but choice of materials based upon their other attributes, looking at the design of the structure as a whole, and any number of other considerations are far more important than R value in terms of thermal performance. R value is overused and overrated relative to it's importance, IMHO.
-The poster formerly known as csnow
In my line of work, HVAC system design, knowing the measured, estimated, reported or typical thermal properties of materials in the building thermal envelope is necessary, therefore, completely relevant.
I make no assertion about the relative importance of this particular property, nor its proper level of "use". That is a perception and/or an opinion, that you expressed.
I think it would be more accurate to say that computing R values to a precision of better than 10-20% is wasted effort, and insulation itself is a wasted effort if sufficient attention is not given to infiltration.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
Hardly. A room with high R and high infiltration will still have less heat loss than low R and high infiltration. Nothing makes R insignificant except already adequate R values.Infiltration is very important and accounts for (typically) a very significant portion of any heat load. But that in no possible way makes R-value *less* important, at least until the point where you run into diminishing returns.R is *extremely* important. In addition to R, infiltration is also *extremely* important, window choice importance is dictated by glazing area but is also typically *extremely* important. What is NOT good, is that R is MISUSED or POORLY RATED in some products. and it's not the be-all and end-all of course, and many people think it is. Those are problems, but again, they do not make R-value less important.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
But given a choice between high R value with bad infiltration, and low R value with very little infiltration, I'll take the latter. Infiltration can easily vary by a factor of 10 or more, in two seemingly identical structures.In a structure with bad infiltration (which is true of many homes built before 1950 or so, and a fair number built up through the mid 80s), you can double the R value and have very little to show for it.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
>Nothing makes R insignificant except already adequate R values.I've been struck by how fast one reaches the point of diminishing returns. The software I use shows precious little difference in loads between R30 and R40 and, for sake of argument, R60. My pet peeve is all the building systems that claim R48 or whatever for maybe 2" of insulating material. Arrggghhh. btw, I don't thing you and Dan are disagreeing on R and infiltration, youse are just using different language that makes it seem like you're disagreeing while saying much the same thing. Sorta like Miller Lite's "Tastes Great" "NO, Less Filling"
R60 is half the conductive loss of an R30 structure. If your conductive loss at R30 is already low, then yes, you don't get that much more there. Of course what you think is low now, and what you'll think at $5/gallon for fuel may be two different things... remember the paradigm you are viewing all of this from. At one time, insulation itself was seen as overkill because energy was so cheap. Of course *before* you double from an R30 to an R60, you'd want to make sure you were maximizing your dollars by making sure the windows are good, your anti-infiltration measures are solid, etc. In many cases, going for top-flight windows and halving their assembly U factor (or doubling their R from, say, 3 to 6) would probably be a much better first choice than doubling insulation from an R30 to an R60.It's pretty hard to put so much insulation in a structure that it would never pay itself back though... well, depending on your climate as well of course. Insulation is the gift that just keeps on giving...-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
>It's pretty hard to put so much insulation in a structure that it would never pay itself back thoughWe start our buildings with continuous spray polyurethane foam. We could technically go to any thickness at all be/c there are no structural members than limit the size. But there has to be a limit somewhere. My house has 3" of foam and the hvac bills max at about $100/mo currently (lights and frig separate). How much would another inch save? It'd cost probably $8k for that inch for the 11k sf surface area. If I borrowed that 8k at 6%, the debt service would be $480/year. It wouldn't cut out hvac bills in half...there'd be no payback.Certainly as utility costs increase the economics change, but there are definite limits on the insulation.
"..and insulation itself is a wasted effort if sufficient attention is not given to infiltration"
Within the confines of what most would consider normal or standard construction practices, both should be equally addressed. And within most construction practices, they are inseparable, in that most efforts to increase insulation values over average or normal levels, also improves the air leakage properties of the structure. The converse is not true however, since improvements in the air leakage properties of a structure do not always improve the insulating value of the building envelope.
Infiltration, BTW, in the absence of gross mechancal misdesign, is primarily a wind driven function, and secondly a "stack" function. If you have a one story house that is not subject to direct prevailing winds, infiltration is much less of a concern than insulation. If you have a multi-story home in a high wind area, attention to infiltration could very well be more important.
"If you have a one story house that is not subject to direct prevailing winds, infiltration is much less of a concern than insulation. If you have a multi-story home in a high wind area, attention to infiltration could very well be more important."
Tim:
I have had a blower door since 1981 and worked in Canada's R2000 high efficiency home program until 1992. From my experience, you have to apply equal effort to both insulation and uncontrolled air exchange in all buildings. You can work with theoretical concepts such as wind, stack, & mechanical drivers of air change, constantly changing neutral pressure planes but in untouched older homes, 30-40% of a heating bill was air exchange.
In both air barrier system design/execution and insulation choice/installation, excellence is required. Don't slack off one for the other.
In addition, infiltration affects comfort significantly more than the numbers would suggest.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison