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Old 10-25-14, 09:21 PM   #61
ctgottapee
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You want the final underfloor foil based poly-iso to have the foil side facing down, not up.

Heat flows from hot to cold. Your crawl space is never going to be warmer than your main floor. In winter the main floor will be much warmer.
The effective R value for a downward facing radiant barrier towards an open space in such an application is R16 by itself (excludes the poly insulation value). You have to tape the seams with foil, and shore up the ends.


The reason they want the air seal, besides the obvious air leakage, is for moisture issues. Same reason the local wants vapor permeability, as they assume you can't fully seal every single nook so there always needs to be a way for the structure to dry, and most flooring and sub flooring combined is not vapor permeable.

I'm going to violate that rule too by using a foil. The only way to make it vapor permeable cost effectively is by poking small holes in it, which also makes it open to air. There might be a product out there that laminates something to a foil sheet that is vapor permeable, haven't seen it and would likely cost a fortune.
I'll have to pay attention and watch for any leaks, and if I do have them, not just assume all will be ok, but to dig in the floor and make sure.

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Old 10-26-14, 09:53 AM   #62
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Quote:
Originally Posted by ctgottapee View Post
...You want the final underfloor foil based poly-iso to have the foil side facing down, not up...
Please help me understand this...

In my understanding, the reason for insulation is to slow, as much as possible, the passage of heat energy from the interior of a dwelling, to the great heat-sink in the sky.

Regarding the foil layer of the last poly-iso, it seems to me that having the foil facing "in" would help reflect the radiant component of heat, back into the insulation assembly.

Having the foil facing "out" would help reflect the radiant component of the meager energy in the crawl space, back into the crawl space, and away from the insulation assembly.

Please clarify.

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Old 10-26-14, 11:47 AM   #63
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The foil face doesn't work like reflecting like light does on a mirror facing you, although it will reflect light.

It prevents radiant energy from 'radiating' off of it, or away from its face.
With the foam installed under the floor, foil radiant barrier facing down, the foam insulation is taking on the heat from the floor above, slowing its transfer due to its Rvalue. That energy will try to transfer through the foam to the colder air below by radiating off the outside face. A radiant barrier prevents that energy from radiating off the face.

This is why a radiant barrier facing down installed in the attic can cut cooling costs in typically warmer southern climates. It stops the heat from radiating down off the hot roof. Of course heat will still travel via convection and conduction.

The radiant barrier's generic Rvalue is that under test conditions which always have heat flowing in the test condition. It has little use facing up in a crawl space as the crawl space is never going to be warmer than the floor above. An accurate "installed" Rvalue would show that.
Both real world heat flow and proper install methods is why the govt got all over the case of the radiant barrier promoters. Unless you live on a volcano, there is no effective Rvalue for the barrier facing up in a crawl space.

Another example: They wrap the guy who just finished the marathon in a thin radiant sheet - the radiant layer on the outside prevents his/her generated heat from radiating away keeping their heat close to them [their sweaty clothing and cool weather at that point are sucking the heat away]

The "Reflectix" sales site is a pretty good example of effective Rvalues in various situations [if the exact build conditions are followed for the typical climate zone]. They were thoroughly sued so their case examples are legit, although they don't explain them thoroughly - in some examples the other insulation used provides most the installed Rvalue, you can figure it out with comparison and a little math. They even removed the attic radiant Rvalues due to the US climate variance. In the winter, a radiant barrier facing into a cold attic does no good unless you live in the tropics basically.
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Old 10-26-14, 02:42 PM   #64
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Quote:
Originally Posted by ctgottapee View Post
The foil face doesn't work like reflecting like light does on a mirror facing you, although it will reflect light.

It prevents radiant energy from 'radiating' off of it, or away from its face.
With the foam installed under the floor, foil radiant barrier facing down, the foam insulation is taking on the heat from the floor above, slowing its transfer due to its Rvalue. That energy will try to transfer through the foam to the colder air below by radiating off the outside face. A radiant barrier prevents that energy from radiating off the face.

This is why a radiant barrier facing down installed in the attic can cut cooling costs in typically warmer southern climates. It stops the heat from radiating down off the hot roof. Of course heat will still travel via convection and conduction.

The radiant barrier's generic Rvalue is that under test conditions which always have heat flowing in the test condition. It has little use facing up in a crawl space as the crawl space is never going to be warmer than the floor above. An accurate "installed" Rvalue would show that.
Both real world heat flow and proper install methods is why the govt got all over the case of the radiant barrier promoters. Unless you live on a volcano, there is no effective Rvalue for the barrier facing up in a crawl space.

Another example: They wrap the guy who just finished the marathon in a thin radiant sheet - the radiant layer on the outside prevents his/her generated heat from radiating away keeping their heat close to them [their sweaty clothing and cool weather at that point are sucking the heat away]

The "Reflectix" sales site is a pretty good example of effective Rvalues in various situations [if the exact build conditions are followed for the typical climate zone]. They were thoroughly sued so their case examples are legit, although they don't explain them thoroughly - in some examples the other insulation used provides most the installed Rvalue, you can figure it out with comparison and a little math. They even removed the attic radiant Rvalues due to the US climate variance. In the winter, a radiant barrier facing into a cold attic does no good unless you live in the tropics basically.

This is all very interesting.

Do you have sources that elaborate, validate, verify, explain or experimentally prove what you have just written?

Best,

-AC
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Old 10-26-14, 09:24 PM   #65
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google reflectix insulation, just another company selling foil bubble wwrap, [i'm not recomending their product] but one of the first and distributed it in stores so they got sued a lot, and via settlement started posting honest installed Rvalues. Look at there installed listings, like Attic, Crawl Space, etc for effective installed values. I believe they have a whole house charts showing examples used all over [keep in mind it's restricted to their specific conditions.]

google how radiant barriers work and you'll get the same concepts. from reputable sources. or google 'convection, conduction, radiation heat energy' to get a low down on heat transfer.
Building Science Corporation is probably one of the best sites for actual real building science; plenty of case studies, and i'm sure an explanation there.

you won't find a lot of info because most reputable building sources understand that there isn't much advantage except for very specific cases to use such radiant barriers, and there are often tricky details to manage. Rvalues for most radiant barriers going up, or horizontal in walls are similar to common insulation that is often cheaper and easier to install. It only became popular as disreputable firms could crank the stuff out cheap and make confusing claims - it is in no way new. It's why common foil backed poly-iso has never had the wild Rvalue claims for the radiant barrier, as it was produced by large reputable firms, although it can be used to achieve additional Rvalue.

just remember a radiant barrier is intended to prevent heat transfer via radiation due to the low emittance of the radiant barrier, ie the low ability to radiate heat from itself.
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Old 10-26-14, 11:11 PM   #66
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I think ctgottapee is correct, the very low emittance of the shinny side is the reason.

Your IR gun won't work correctly on low emittance surfaces.
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Old 10-27-14, 01:49 AM   #67
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Quote:
Originally Posted by ctgottapee View Post
google reflectix insulation, just another company selling foil bubble wwrap, [i'm not recomending their product] but one of the first and distributed it in stores so they got sued a lot, and via settlement started posting honest installed Rvalues. Look at there installed listings, like Attic, Crawl Space, etc for effective installed values. I believe they have a whole house charts showing examples used all over [keep in mind it's restricted to their specific conditions.]

google how radiant barriers work and you'll get the same concepts. from reputable sources. or google 'convection, conduction, radiation heat energy' to get a low down on heat transfer.
Building Science Corporation is probably one of the best sites for actual real building science; plenty of case studies, and i'm sure an explanation there.

you won't find a lot of info because most reputable building sources understand that there isn't much advantage except for very specific cases to use such radiant barriers, and there are often tricky details to manage. Rvalues for most radiant barriers going up, or horizontal in walls are similar to common insulation that is often cheaper and easier to install. It only became popular as disreputable firms could crank the stuff out cheap and make confusing claims - it is in no way new. It's why common foil backed poly-iso has never had the wild Rvalue claims for the radiant barrier, as it was produced by large reputable firms, although it can be used to achieve additional Rvalue.

just remember a radiant barrier is intended to prevent heat transfer via radiation due to the low emittance of the radiant barrier, ie the low ability to radiate heat from itself.
There is a possibility that you are right... but I strongly doubt it.

You have no link to any source of credible information that will support your point of view.

You can not cite any specific experimental evidence that will support your assertions either.

And you want me to Google, and keep on Googling until I am convinced that you are correct?

I'm afraid that you are not making a strong argument to support your point.

And using the outcome of a lawsuit as a proof of scientific truth? Oh boy...

My father was a lawyer, and a very good lawyer, but even he would never confuse the outcome of a legal dispute with scientific truth. He knew the game of law too well.

If you really do think that legal outcomes prove science, then the Scopes trial proves that Charles Darwin's theory of evolution is heresy and no school should be allowed to teach points of view that can't be found in the bible.

-AC
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Old 11-03-14, 04:49 PM   #68
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A/C BSI-009: New Light In Crawlspaces — Building Science Information

Much info on water movement.

See figure 7. Looks like your job. Note that the shiney side goes down.
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Old 11-04-14, 12:18 AM   #69
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That's the best explanation I have seen. This is a subject where there are many (conflicting) old wives tales with no real explanation that have to be taken on faith, so it is good to get a reasoned and understandable analysis.

The penultimate paragraph was particularly interesting for me:
Quote:
What if I don’t want to completely encase the floor framing? What if I want to go with Figure 9 and Photograph 6? That works if the crawlspace does not get too cold—in the summer—if it is coupled more to the outside air than to the crawlspace ground temperature. Elevated crawlspaces with open piers work fine in this regard (Photograph 7).
This ties in with the approach at my house, where the crawl space is only really ventilated in the summer, by removing solid covers from the crawl space access points. I guess covering these in winter is intended to prevent cold air flowing through the crawl space to prevent it getting too cold, and opening them in summer allows the warmer summer air to raise the crawlspace temperature. So the approach taken back when my house was built in the 1890s is actually backed up by current understanding. Who'd a thunk it?
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Old 12-09-14, 10:30 AM   #70
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I know it hasn't been real long, but have you been able to notice a difference in energy consumption? I know you previously didn't really heat the kitchen directly, and now you do. Did you see anything interesting when you had the thermal imaging camera?

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