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Insulate A Dirt Crawlspace Floor?? - help settle an argument

Insulate A Dirt Crawlspace Floor?? - help settle an argument

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  #1  
Old 02-02-06, 08:50 AM
windowb18
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Question Insulate A Dirt Crawlspace Floor?? - help settle an argument

Please help settle this argument.

Does it make any sense to put blue rigid foam on the floor of a dirt crawlspace - as in directly on the dirt?? We have a 3/4 height partial basement under about a quarter of the house. The rest of it is crawlspace.

We are going to insulate the crawlspace walls from the inside (they already have blue rigid foam on the outside, underneath the siding) with the spray foam, and put poly down on the dirt to prevent moisture.

So, is there ANY benefit to putting blue rigid foam on the floor - underneath the poly? Is that a significant source of heat loss? Or is this just a waste of money/effort with no real benefits?
 
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  #2  
Old 02-02-06, 09:01 AM
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I have never heard of placing any type insulation on the dirt floor. Usually just some heavy Poly to prevent moisture from infiltrating the area. Good luck and watch this post for more answers and opinions.
 
  #3  
Old 02-02-06, 11:26 AM
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Like the people that published that conspiracy theory about how the earth is actually hollow, with thousands of interconnected tunnels built by a race that has since departed, most people don't don't realize that the ground is actually constantly emmanating heat:
http://www.seawana.com/conspiracy_hollow_earth.php
http://www.onelight.com/thei/thei.html

Most of the earth that we see on a daily basis loses its heat to the atmosphere so quickly that we never notice that it is a heat source. However, there is enough heat coming out of the earth to create an entire industry, known as the Geothermal Heat Pump industry.

Similarly, if you put a well sealed building over top of the ground, we provide the opportunity for the heat to accumulate. Of course, heat loss will still occur to the outdoors through the walls, so these have to be well sealed & insulated, with exterior insulation below grade.

However, in a poorly designed crawlspace, heat could circumvent the walls by going through the ground. In this case, a good breathable foam would be recommended: EPS or otherwise.
 
  #4  
Old 02-02-06, 12:39 PM
windowb18
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Further to this......

Ideally, I'd like to use the crawlspace that is in reach from the basement as a storage area. However, I don't want whatever I'm moving around in there to rip the poly.

Can I put patio blocks under the poly to offer support for whatever I store there? Or perhaps put the blocks on top of the poly and use it that way???

We'd want to "finish off" the dirt crawlspace as best as we can. Is there another way to get the support I want for the storage, without compromising the poly? Could you use cement, or wood, or patio blocks etc??? Any suggestions would be great!
 
  #5  
Old 02-02-06, 01:01 PM
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You could use rolled roofing material. What you are looking for is a vapor barrier. I would put down the poly and then cover it with the roofing material. You won't tear the roofing very easily. I may get slammed for that answer but I had it that way up North and it worked. I even had to crawl across it to change the furnace filters once a month.
 
  #6  
Old 02-03-06, 09:27 AM
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The dominant heat transfer mechanism during the winter is Conduction. Heat Loss is calculated from the amount of British Thermal Units lost through conduction per hour (btu/hr.) The greater the degree difference between two spaces the greater the amount of heat loss per hour. For example, because of the bouyancy of warm air the temperature at your ceiling below your attic is much warmer than at your floor. Therefore the heat loss through your attic is much greater than at your walls and floors. Another example of degree difference is when it is colder outside. Therefore the colder it is that year, the higher your fuels bills are. The cost effectiveness of doing an action is determined by the cost to do the action compared to the amount of saving derived from doing the action. So the amount of heat loss which is influenced by degree difference is a determining factor to cost effectiveness.

The "GAS LAW" states for a liquid to evaporate, the liquid must be absorbing heat (getting hotter). For a vapor to condense into liquid, the vapor must be giving off heat (dropping temperature). The unique aspect of this is referred to as the "LATENT ENERGY of VAPORIZATION". For example to raise 1 pound of water 1 degree Fahrenheit it requires 1 BTU of energy provided that the raising temperature of the water does not cause evaporation. However, if you raise the temperature of the water from 211 degrees Fahrenheit to 212 degrees (boiling temperature) you require 970 BTU's. This is because you are changing the state of the water from a liquid to a vapor. The key here is the 970 times more energy (heat) to cause evaporation.

While it is true that we can neither create nor destroy energy, we can only transform it, when this vapor condenses, it gives off this 970 times of heat energy. However, the vapor must condense to give off this energy (heat). Unfortunately in cold weather climates this moisture vapor will get absorbed by the air in the crawl space and structural members of the house and never condenses inside the crawl space. This is because of the Relative Humidity (RH%) of the objects this vapor comes in contact with in a crawl space during the winter. Equilibrium Relative Humidity (ErH%) applies.

So if we apply this to a dirt floor inside a crawl space what happens is the moisture in the ground evaporates. it uses the heat energy not only in the ground to cause the evaporation but also the heat energy inside the crawl space. This lowers the temperature of the crawl space, including the ground. Even though the earth radiates energy (heat) it cannot compete with the 970 times more energy to cause evaporation. If the temperature drops inside the crawl space as a result of evaporation, it increases the degree difference between your home and the crawl space. which increases your heat loss and will increase your energy bill.

The poly you intend to apply over the dirt floor will not only prevent moisture in the ground from entering your home, it also lowers your heating costs. Because it prohibits the evaporation of the moisture in the ground. While most of us understand the greater the degree difference the greater the attraction, most fail to see the relavance of the temperature of the dirt floor inside a crawl space compared to your exterior walls, even if they are insulated. Once the evaporation is prohibited by the poly, the ground temperature would either be the same or higher than the air and exterior walls of the crawl space. In other words installing insulation either under or over the poly will have little or no value. I hope this settles your argument.

In energy conservation there is only one other application that is more cost effective than applying poly over a dirt floor. That is the water heater insulation jacket. What is obvious is the degree difference between the temperature of the water inside the tank and outside ambient temperature. What is not so obvious is the amount of BTU's requires to raise the temperature water verses air; heat loss with water heaters are usually constant and evaporation in crawl spaces is inconsistent. So water heater insulation jackets usually pay for themselves inside of a year with the savings.
 
  #7  
Old 02-03-06, 10:17 AM
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Resercon
Thank you so much. I was aware of the energy requirements for the evaporation of water, but in this application I was entirely ignorant. Today I learned something completely new.
 
  #8  
Old 02-04-06, 06:49 AM
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Doug,

What may interest you to know is that these same Laws of Physics apply to cooling. If you think about it you will see how the condensing of moisture inside a structure increases Cooling Load which increases your cooling costs. Manufacturers' of Evaporator coils use what is known as the SENSIBLE HEAT FACTOR in determining their design, not HVAC installation, for specific areas.

It takes an air conditioning unit a considerable more time to extract moisture from air as it passes through an Evaporator Coil than it does to drop the temperature of that air. In energy conservation the oversizing of AC units results in higher cooling costs and moisture related problems inside the structure.
 
  #9  
Old 02-04-06, 07:11 AM
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Ya, what resercon said.

I would add that how insulation is added to structures here is to apply it underground around the perimeter.
It would be buried just under the surface and if on the outside would be angled to allow water to run away from the foundation.
I might suggest that roofing material would pose a fire hazzard.
It is common commercially to apply a heavy duty vapor barrier to crawlspaces and then cover it with at least two inches of screened gravel.
At work there have been walkways made using patio stones place directly on the gravel.
 
  #10  
Old 02-09-06, 08:58 AM
windowb18
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The questions continue.....

Thanks for everyone's comments on insulating the crawlspace floor. It really made a lot of sense. I understood WHAT things did, but didn't really understand the WHY. (and I also won the argument!)

And thanks for the suggestions for the crawlspace storage issue. I think we'll stick with the gravel/patio stone method.

GregH: Does putting the insulation on the perimeter underground, prevent the frost from getting near the foundation of the house?? (and thus prevent heaving/sinking). As well as act as a way to slope the ground to let the water run away from the house?

There is no weeping tile system for this house, and apparently every spring water pours through a crack/small hole that's in the basement wall (about 2 feet below the surface of the ground). We haven't lived there long enough to see this happen, but the house was in the family, and that's what we've been told. We have no idea if this is due to heavy snow/rain, or if someone is just exaggering about it happening EVERY year, but we're going to assume there's going to be some kind of water coming in in the spring.

Does proper surface drainage help in preventing this? Would proper grading (and potentially adding the foam insulation near the surface level and grading it away from the house) help his problem?? Or is it because below the surface, the ground is too saturated so it's going to happen no matter what we do on the surface.
 
  #11  
Old 02-09-06, 11:43 AM
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Grading will help.

A little excavating to install damp proofing / exterior insulation will help against frost heave and solve the leak problem.
 
  #12  
Old 02-09-06, 11:58 AM
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Insulate A Dirt Crawlspace Floor?? - help settle an argument

Frost heaving is a soil problem/situation and a moisture barrier will do NOTHING to stop the heaving. Elimination of the water or elimination of the elimination of the cold is the way to go. Get your grading to drain water away from the house and eliminate the saturated soil.
 

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  #13  
Old 04-04-06, 08:04 AM
windowb18
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Well......it happened

Well, the water is coming in through the basement walls. Didn't see it actually come in, but the floor was wet. There are several cracks that could have been the culprit, but didn't see which one of them it was.

Can a weeping tile system be installed??? Would this help, and how can it be done. We have a 3/4 height partial basement under about a quarter of the house. The rest of it is dirt floor crawlspace.
 
  #14  
Old 04-04-06, 08:34 PM
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Insulate A Dirt Crawlspace Floor?? - help settle an argument

Before you do anything inside, get your exterior drainage corrected. - Then you can decide on the drains or what to put on the floor.

Correction of external problems is the most effective and economical method to control moisture problems.

Dick
 
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