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Floor Insulation/vapor barrier Question

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  • #16
    It's elementary, my dear Taiga:

    Water vapor moves from areas of high vapor pressure to areas of less pressure. As in the case of heat transfer, water vapor moves from areas that are warm to those areas that are cold. Therefore, in the case of a wall, the vapor pressure will move from the hot, humid air found in the summer time on the outside to the cooler, dryer temperature on the inside of the building. This means that water vapor is being driven though the wall cavity.
    http://www.awcitechnologycenter.org/...ture-migration

    P.S: "dew point" calculators are available online....plug in your local conditions to see what the moisture is doin'....
    "– Gas boats are bad enough, autos are an invention of the devil, and airplanes are worse." ~Allen Hasselborg

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    • #17
      Originally posted by cdubbin View Post
      P.S: "dew point" calculators are available online....plug in your local conditions to see what the moisture is doin'....
      Yeah, the internet's pretty cool, huh? Handy for folks who don't have the DP charts just sitting on their desk. So let's take a quick look at some Anchorage stats. In the past week, the highest dew point temp was 66ºF., which occurred only briefly on the 13th. The average dew point temp was 55.57ºF. Your hottest day was July 4th when the temp hit 89ºF with a RH of 35% and a dew point of 58ºF.... If we scrutinize every day of this summer of 2019, we can find occasional instances when the dew point was impressively high, but again, those instances occurred only very briefly. So, if the inside of your stick-frame wall is acting as an active condenser of external ambient moisture during these hot summer temps in Anchorage, either your wall construction and/or insulation R-value is total crap, and/or you're keeping the inside of your structure really, REALLY cold....or the moisture in your wall is coming from somewhere other than the external ambient airmass. You're correct, it is elementary.
      ...he who knows nothing is nearer to truth than he whose mind is filled with falsehoods & errors. ~Thomas Jefferson
      I would rather have a mind opened by wonder than one closed by belief. ~Gerry Spence
      The last thing Alaska needs is another bigot. ~member Catch It

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      • #18
        Sounds like ANC was a real peach this summer alright!...lol

        ....just a couple final Thoughts to Ponder:
        ...when the summer sun shines directly on a wall, it can become significantly hotter than the ambient air temperature....also, building materials like wood, concrete, and insulation are terrific natural sponges, so relative humidity is only a starting point for the amount of moisture contained within a wall assembly. Finally , a "total crap" R-value would actually MITIGATE condensation in this scenario, as there would be less differentiation between indoor and outdoor temps....voila! ...no moisture migration...
        "– Gas boats are bad enough, autos are an invention of the devil, and airplanes are worse." ~Allen Hasselborg

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        • #19
          Buildings are built for people, people exhale moisture with each and every breath, our bodies exude it as well. Doesn't take much science to out-science those who just want to argue a ridiculous point that has nothing to do with the original post.

          If you want to know how to build a building that is vapor tight, AOD is apparently the place to go. From everything I've ever read and experienced, buildings need to "breathe". The way I understand it floors are not the place to install a vapor barrier, walls and roofs are...but then I don't build buildings for a living, maybe some of those commenting here do?
          “I would rather have questions that can't be answered than answers that can't be questioned.” Physicist ― Richard Feynman

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          • #20
            Originally posted by Patsfan54 View Post
            The way I understand it floors are not the place to install a vapor barrier, walls and roofs are...but then I don't build buildings for a living, maybe some of those commenting here do?
            Unfortunately, there are LOTS of people in Alaska who "build buildings for a living", but don't understand basic physics.

            No web forum is a good place to go to learn about anything, unless those involved are actually interested in understanding what they're discussing. Science, by definition, is unemotional. Unfortunately, most people are unable to discuss science without injecting emotion. Typically it devolves into individuals with delicate egos standing round wagging their d**** at each other. ...And then the trolls arrive to snipe from the sidelines.:rolleyes:

            Regardless, when you hear phrases such as: "moisture always flees heat"; "heat rises"; warm weather following a cold spell "draws the frost out of the pavement"; "you don't need vapor barrier in floors"; etc....you know it's likely pointless to try to engage a conversation, and you'll have a long row to hoe if you do. So it goes.
            ...he who knows nothing is nearer to truth than he whose mind is filled with falsehoods & errors. ~Thomas Jefferson
            I would rather have a mind opened by wonder than one closed by belief. ~Gerry Spence
            The last thing Alaska needs is another bigot. ~member Catch It

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            • #21
              Originally posted by cdubbin View Post
              Alaska has the highest average relative humidity of any state in the nation...we're #1!
              RH is well... relative... amazingly enough Fairbanks can have a RH in the 90's on a -40 day, however bring that same air inside and its drier than a popcorn fart.... Cold air doesn't hold much moisture so we can brag we have a high RH... still its a empty boast... LOL
              “We have digressed from a Nation of Revolutionaries to a country of entitlements"

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              • #22
                "You must spread some Reputation around before giving it to Akgramps again."
                ...he who knows nothing is nearer to truth than he whose mind is filled with falsehoods & errors. ~Thomas Jefferson
                I would rather have a mind opened by wonder than one closed by belief. ~Gerry Spence
                The last thing Alaska needs is another bigot. ~member Catch It

                Comment


                • #23
                  Originally posted by Akgramps View Post
                  RH is well... relative... amazingly enough Fairbanks can have a RH in the 90's on a -40 day, however bring that same air inside and its drier than a popcorn fart.... Cold air doesn't hold much moisture so we can brag we have a high RH... still its a empty boast... LOL


                  Suspect quote, but still sums it up nicely....our understanding of how these processes relate to modern construction materials and techniques is imperfect at best....regardless of keyboard experts...
                  "– Gas boats are bad enough, autos are an invention of the devil, and airplanes are worse." ~Allen Hasselborg

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                  • #24
                    Just wanted to stop in and say thanks to everyone. Ended up doing kraft-faced insulation between the 2x6s with 2” closed cell foam board over that as a thermal barrier then covered it all in hardware cloth. Just kicked the new heater on tonight so we will see how she does.

                    Thanks again!
                    Jon
                    Nurse by night, Alaska adventurer by day!

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                    • #25
                      Originally posted by Patsfan54 View Post
                      Buildings are built for people, people exhale moisture with each and every breath, our bodies exude it as well. Doesn't take much science to out-science those who just want to argue a ridiculous point that has nothing to do with the original post.

                      If you want to know how to build a building that is vapor tight, AOD is apparently the place to go. From everything I've ever read and experienced, buildings need to "breathe". The way I understand it floors are not the place to install a vapor barrier, walls and roofs are...but then I don't build buildings for a living, maybe some of those commenting here do?


                      Go make t visqueen tipi without a floor, chuck a wood stove in it and see what happens...

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                      • #26
                        Originally posted by Troy Sharp View Post
                        Go make t visqueen tipi without a floor, chuck a wood stove in it and see what happens...
                        I'm not exactly sure that a visqueen tipi on bare ground would count as a building.
                        “I would rather have questions that can't be answered than answers that can't be questioned.” Physicist ― Richard Feynman

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                        • #27
                          Originally posted by Patsfan54 View Post
                          I'm not exactly sure that a visqueen tipi on bare ground would count as a building.
                          In AK that's called a starter home...
                          "– Gas boats are bad enough, autos are an invention of the devil, and airplanes are worse." ~Allen Hasselborg

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                          • #28
                            Originally posted by cdubbin View Post
                            In AK that's called a starter home...
                            Starter hell.....people live for years and years in not much more than that. Which is always nice when you're trying to build a nice house with those all around. Location, location, location!!!
                            Sheep hunting...... the pain goes away, but the stupidity remains...!!!

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                            • #29
                              But it has to have a blue tarp over it to be truely Alaskan!
                              When seconds count, the cops are just minutes away.
                              '08 24' HCM Granite HD "River Dog"
                              2018 12' Moto Jet "River Pup"

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                              • #30
                                Originally posted by cdubbin View Post


                                Suspect quote, but still sums it up nicely....our understanding of how these processes relate to modern construction materials and techniques is imperfect at best....regardless of keyboard experts...
                                you said a mouthful there.....!
                                “We have digressed from a Nation of Revolutionaries to a country of entitlements"

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