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  1. #1
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    Apr 2013
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    Default Insulation/vapor barrier on cinder block home in Florida

    I'm new to this forum, thank you for taking the time to give your thoughts on my question. I live in the central Florida area in a mid 1970's cinder block home. I have had recent health issues that have caused me to have to retire out of my job as a firefighter for the city of Orlando after 10 years. It turns out the cause of my health problems is possibly linked to toxic mold that was found in my house. Black mold was found growing on the backside of all the baseboards inside our home. Full remediation has been done at this point. When our house was built the interior walls on the perimeter of the house consisted of drywall then plastic vapor barrier over a thin layer of non-faced insulation and furring strips, then the cinder block. There is only a 3/4 inch space between the drywall and cinder block.

    I had a home engineer come to the house yesterday and he said that plastic vapor barriers are not usually used in Florida due to the tropical climate and mild winters. He thinks that due to the humid heat outside and the a/c running that the plastic vapor barrier is causing condensation that is running down to the base boards. Every one of my family members that owns a home in this same area have no vapor barriers over there cinder block walls.

    Due to the mold the bottom 4 feet of drywall has been removed on all exterior walls and I am in the process of removing the old insulation and plastic vapor barrier.

    My question is what would be a good insulator to put in between the drywall and cider block that will not act as a continuous barrier like the plastic so I don't end up with condensation and more mold.

    I was looking at different types of foam board insulation which would fit perfectly in the 3/4 inch space between the drywall and block. I realize up north vapor barriers are a must but from what I'm being told down here in Florida it can cause problems like my house.

    Is there anyone on this forum that knows construction in tropical climates?

    Thank you so much for any help. My health is counting on it.
    Last edited by Fireguy911; 04-28-2013 at 08:58 PM.

  2. #2
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    Default Re: Insulation/vapor barrier on cinder block home in Florida

    Have you considered putting the insulation on the exterior side of the block wall. The advantage to this is that the block wall has a lot of thermal mass and will store heat. The insulation on the exterior side will keep the concrete blocks from getting to hot during the day and cold at night.

    You would have to use rigid foam boards glued to the blocks, then a stucco and paint over that. You could apply plaster directly to the blocks on the interior side and paint with a vapor resistant primer and a good top coat of latex paint with a mildewcide added.

    The last step would be to control the humidity inside the house. I don't think anyone makes an HVAC system that works like a car, but a system that first ran the air through an air conditioner to reduce the absolute humidity (squeeze out the water in the air) and then heat it to the desired temperature would keep the relative humidity down inside the house so that condensation never forms.

    You may have to just do with a separate dehumidifier system to keep the RH between 30 and 70%.

  3. #3
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    Apr 2013
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    Default Re: Insulation/vapor barrier on cinder block home in Florida

    I hadn't thought of that. Thank you for responding. I will look into that. I bought a dehumidifier since the remediation and I am averaging about 40% humidity now. I just want to make sure I address the the interior walls properly so I don't have condensation. No sure if a vapor barrier in this climate is a good thing.

  4. #4
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    Default Re: Insulation/vapor barrier on cinder block home in Florida

    The trick is to keep the inside surface of your exterior wall above the dew point for the humidity in the room. Putting the insulation on the outside of your block walls will keep the blocks closer to room temperature so condensation is much less likely.

    If your dehumidifier can keep the humidity down inside your house during the hot muggy summer, you will not have any condensation. In the winter, you need to keep the wall surface temperature above the dew point. Here is a reference that should help you understand.

    http://www.tis-gdv.de/tis_e/misc/klima.htm

    This is a German Dept. of transportation web page, but it is in English.

  5. #5
    Join Date
    May 2012
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    Default Re: Insulation/vapor barrier on cinder block home in Florida

    Tens of thousands of block homes, including my rental in Central Florida, have no insulation outside, just stucco.

    The insulation you need inside is interior-installed foam panels that have an aluminum or mylar backing facing the block to resist radiant heat. Your drywall goes over that.

    Your Florida home needs to breathe, and the heat goes a long way to combat moisture, in concert with an efficient HVAC system designed for the size of your home. Too large an HVAC system will actually be less efficient in humidity control and comfort.

    Call your local power company for a free energy audit.

  6. #6
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    Default Re: Insulation/vapor barrier on cinder block home in Florida

    Quote Originally Posted by daspyda View Post
    Tens of thousands of block homes, including my rental in Central Florida, have no insulation outside, just stucco.

    The insulation you need inside is interior-installed foam panels that have an aluminum or mylar backing facing the block to resist radiant heat. Your drywall goes over that.

    Your Florida home needs to breathe, and the heat goes a long way to combat moisture, in concert with an efficient HVAC system designed for the size of your home. Too large an HVAC system will actually be less efficient in humidity control and comfort.

    Call your local power company for a free energy audit.
    Just because it is not commonly done does not mean that it isn't the best way to do it. Its a relatively new way of building. It is more popular in the desert southwest but it would work just as well in Florida. It really shines where there is a large temperature difference between daytime and night time.

  7. #7
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    Default Re: Insulation/vapor barrier on cinder block home in Florida

    Quote Originally Posted by keith3267 View Post
    It is more popular in the desert southwest but it would work just as well in Florida. It really shines where there is a large temperature difference between daytime and night time.
    There's the problem: desert vs tropical locales. Dry vs humid. The temp diff is not as pronounced most of the year. It is 80 degrees at night during the (long, hot) summer.

  8. #8
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    Default Re: Insulation/vapor barrier on cinder block home in Florida

    Quote Originally Posted by daspyda View Post
    There's the problem: desert vs tropical locales. Dry vs humid. The temp diff is not as pronounced most of the year. It is 80 degrees at night during the (long, hot) summer.
    But he is using a dehumidifier. Condensation is going to occur on the walls in winter, not summer. In the summer, the wall will likely be a little warmer than the room temperature. In winter, the wall will be cooler. If the insulation is on the outside, the blocks will be closer to room temperature so it is less likely that the wall surface will be below the dew point for the humidity in the room.

  9. #9
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    Sep 2009
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    Default Re: Insulation/vapor barrier on cinder block home in Florida

    Use 3/4" Tuff-R in between the firring strips. There are three ways to install it in new const. Install Tuff-R first then furring strips on top. Second option fir the wall then cut TuffR in-between the furring strips. Third option use a reflective barrier over the furring strips with or without the insulation board. Option two looks like your best option.

    You might want to use blue board foam cut in between the firing then reflective shield depending on cost. Bottom line whatever you decide make sure all the mold is 100% gone.

    http://fuhsco.com/details/floridalit...t179_07376.pdf

    http://www.fifoil.com/Builders/Appli...tionInfo/?ID=1
    Gizmo

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  10. #10
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    Portland, Oregon, formerly of Chicago
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    Default Re: Insulation/vapor barrier on cinder block home in Florida

    The problem being encountered here is not interior generated moisture, but moisture that is being driven through the exterior walls where it encounters a cold, impermeable air barrier on the inside. Here it condensates. This type of problem did not exist before the advent of air-conditioned homes and the use of absolute air barriers such as plastic. Those interior walls must let the moisture continue on through. Similarly, wall papers with plastic coatings or metalic finishes should not be used on exterior wall surfaces as they also form impermeable barriers.

    In hot humid climates, if a vapor barrier is to be used at all, it should be on the exterior side of the wall, the opposite of in Northern climates. An absolute vapor barrier such as sheet plastic should not be used at all in either climate. My house here in Portland ,Oregon does have such a plastic barrier in back of the drywall. However, the air in Portland in summer is very low in humidity. Also, air-conditioning is not used here as much as in other parts of the country, so condensation inside the wall is not a problem.

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