# insulating basement floor



## Ron6519 (Mar 28, 2007)

A working dehumidifier is important on LI. I don't see the need for a vapor barrier.


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## real time (Sep 1, 2015)

OK but can we seal the floor?


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## Gary in WA (Mar 11, 2009)

Seal the floor with tar&felt/liquid moisture barrier/sheet goods, insulate with rigid foam board; http://buildingscience.com/documents/insights/bsi082-walking-the-plank?searchterm=slab%2520vapor%2520barrier

no moisture; http://buildingscience.com/documents/bareports/ba-0309-renovating-your-basment/view

Humidity is high due to missing vapor barrier if walls are insulated with rigid FB already. Use foil-faced FB on the wood rim joists.

Gary


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## real time (Sep 1, 2015)

Thank you, what type of liquid barrier would you recommend for the floor?


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## SeniorSitizen (Sep 10, 2012)

Why would anyone just assume all basements have high humidity and do all the mentioned above without actually accurately checking ( no hair hygrometer ) what the humidity actually is?


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## real time (Sep 1, 2015)

The humidifier gets a reading above 60% and after the humidifier brings the reading down to 45% its filled with water.


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## Ron6519 (Mar 28, 2007)

Never saw the need to put anything on the basement floor on Long Island. I always put down ceramic tile and an area rug. And on Long Island you always need a dehumidifier or the humidity levels will get into the 70's. Crawl spaces into the high 80's.
There are water episodes in a basement. Window wells can fill up and cascade into the house, hot water heaters fail, laundry tubs overflow, washers drains get loose. If that happens, all that crap you put down on the floor will need to be removed.
Makes no sense to me.


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## real time (Sep 1, 2015)

I understand what your saying but why not seal the floor anyway?


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## Ron6519 (Mar 28, 2007)

real time said:


> I understand what your saying but why not seal the floor anyway?


I think you need to decide the finished floor material before you start putting down anything. Whatever you put down to seal the floor must be compatible to the finish material going down.
I had unfinished concrete. I put the thin set directly onto the floor. I could have sealed it, but I wanted to make sure the bond from tile to concrete was not compromised.
I really don't know how much moisture you will be keeping out with an applied liquid sealer. There is nothing you are going to do to eliminate the need for a dehumidifier on LI.


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## real time (Sep 1, 2015)

OK thanks


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## Ron6519 (Mar 28, 2007)

SeniorSitizen said:


> Why would anyone just assume all basements have high humidity and do all the mentioned above without actually accurately checking ( no hair hygrometer ) what the humidity actually is?


The Op is talking about her house on Long Island, NY. ALL the houses in Long Island, NY have basements with high humidity unless extraordinary measures have been taken and the house is fairly new.
You don't need a measuring device as long as you have skin and are alive when you get to the bottom of the stairs.
The hygrometer is useful in knowing how well the dehumidifier is functioning, though.


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## SeniorSitizen (Sep 10, 2012)

A hair hygrometer is useful to the people selling them and that's about it.


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## AllanJ (Nov 24, 2007)

The primary reason for a higher humidity in the basement during the summer compared with the upstairs is that basement is at a lower temperature due to the soil/ground/earth temperature all around the foundation.

The same air, slowly circulating between outside and upstairs and basement, becomes of a higher humidity when it is cooled down, here, by the basement walls and floor.

When the humidity gets high enough, water condenses out of the air, first against the walls and floor.

The secondary reason why basements are more humid is due to ground water slowly seeping in where most of it evaporates into the basement air.

When you finish the basement with porous materials, there is an insulating effect keeping the concrete at lower temperatures and increasing the chances of condensation. And the water that does condense has a harder time diffusing out of the materials and evaporating.


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## AllanJ (Nov 24, 2007)

editing time exceeded and forgot what changes were made last so entire post reproduced below.

The primary reason for a higher humidity in the basement during the summer compared with the upstairs is that basement is at a lower temperature due to the soil/ground/earth temperature all around the foundation.

The same air, slowly circulating between outside and upstairs and basement, becomes of a higher humidity when it is cooled down, here, by the basement walls and floor.

When the humidity gets high enough, water condenses out of the air, first against the walls and floor.

The secondary reason why basements are more humid is due to ground water slowly seeping in where most of it evaporates into the basement air.

When you insulate the basement, it keeps the concrete at lower temperatures and increases the chances of condensation. And the water that does condense has a harder time diffusing out of the materials and evaporating.


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## AllanJ (Nov 24, 2007)

editing time exceeded and forgot what changes were made last so entire post reproduced below.

The primary reason for a higher humidity in the basement during the summer compared with the upstairs is that basement is at a lower temperature due to the soil/ground/earth temperature all around the foundation.

The same air, slowly circulating between outside and upstairs and basement, becomes of a higher humidity when it is cooled down, here, by the basement walls and floor.

When the humidity gets high enough, water condenses out of the air, first against the walls and floor.

The secondary reason why basements are more humid is due to ground water slowly seeping in where most of it evaporates into the basement air.

When you insulate the basement, it keeps the concrete at lower temperatures and increases the chances of condensation. And the water that does condense has a harder time diffusing out of porous materials like carpet and batt insulation, and evaporating.

A subfloor like Dricore provides an air space under the carpet or other finish flooring. Together with a radon remediation system, moisture under the subfloor can be better gotten rid of.


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## life_aquatic (Oct 24, 2012)

I got some free samples of this stuff that I think will work well in a basement (and provide a small degree of insulation because of the gap between the concrete and the plastic. 
http://www.modutile.com/slate-look-interlocking-basement-floor-tiles.html
The only drawback I see is that it might "sound" cheap or not solid. But one recommendation I read was to put some geotextile underneath to deaden any noise of the plastic hitting the concrete.


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