Whats up with insulating a Basement anyway??


Old 01-21-05, 08:32 PM
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Angry Whats up with insulating a Basement anyway??

I have spent the whole evening on google searching for information on how to insulate a basement.

I can tell ya, anyway it’s done, someone says its wrong, and someone says it’s right.
Study after study says insulation will get soaked with moisture, but if you go to the insulation manufactures sites they say it doesn’t.
I will be trying something new on my basement...

I guess if it works I will be the god of basements, and if it doesn’t work I will be just another expert who is wrong.
For reference here is the plan
Please feel free to post your comments.

The first thing I will do is to seal the walls.
I will dry lock the cinder block walls.

Then I will build a sub floor.
1. I will place 15lb tar paper in 3" wide strips on 16 inch centers, this will leave bear concrete between each sleeper.
2. On top of the tar paper I will place 1X2 pressure treated sleepers on the floor, again on 16” centers.
4. On top of the sleepers I will place a 6mil plastic film.
5. On top of the 6mil plastic I will place a 5/8" plywood sub floor, keeping the floor 1" off the perimeter wall.

Then the walls.
1. Using 2X4 studs I will frame the walls, again keeping them 1” off the cinder block.
2. I will insulate the perimeter walls with fiberglass insulation, again keeping the insulation 1” off the cinder block wall.

My theory here is to provide airspace and a ventilation path for the air all around the addition.
The air gap will vent into the garage. Air from the garage will circulate over the ceiling, down the wall and across the floor, and back to the garage.
I will also hang a small dehumidifier from the floor joist above the drop in ceiling to help pull moisture from the air space.
This may seem like a lot, but without digging the house up, it’s the only way I believe I can prevent moisture from soaking the insulation.
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Old 01-22-05, 07:46 AM
MO Darren
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Im with you...Go for it! so many methods
Old 01-22-05, 07:52 AM
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Same question

I posed the same question in a thread around the first of the year. I got quite a response. Sounds like you are heading in the right direction? Do you really need a sub floor if you have a good qaulity carpet pad with mold resistance?
Old 01-22-05, 08:00 AM
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Question Moved

Hello: Steve

Your question pertains specifically to insulation, not basements. The insulation may be in the basement, but the question pertains to insulation.

In this insulation topic, very likely you will obtain far better information to your questions than in the basements topic. Thus the question was moved into this topic.

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Old 01-22-05, 09:28 PM
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Keep moisture out & let it escape from house.

All the Laws of Physics concerning moisture apply throughout the house. However, some of these Laws dominate more than others in different parts of the structure. This is what leads to all the confusion around ventilation, insulation and vapor barriers. For example, ventilation in an attic accomplishes the extraction of moisture through Equilibriium Relative Humidity (ErH%). It does this because insulation nor vapor barriers stop heat or moisture flow and the low vapor permability of most roofing materials. On the other hand, ventilation of a crawl space basically have the same processes, ErH%, insulation and vapor barriers, but you have to include capilliary action (suction). Which by the way dominates in the crawl space and has very little affect in an attic. This is the behavior of moisture in the ground in the crawl space. In both the attics and crawl spaces, the moisture is being generated outside these spaces. It is good to note THAT A MOISTURE PROBLEM EXIST WHEN THE MOISTURE THAT IS BEING GENERATED IS GREATER THAN THE ABILITY OF A PROCESS(S) TO EXPEL THE SAID MOISTURE.

What makes basements so much different than crawl spaces or attics, is that moisture is usually generated inside the basement when they are finished. People cook, wash clothes, shower and live in the basement. All of which generate a considerable amount of moisture and none of which are done in either attics or crawl spaces. You compound this with the fact that attics and crawl spaces are between the outside and the inside of the house, but the basement is in direct contact with the outside. The same can be said about your outside walls upstairs but then we have to consider the effects of capilliary action. Which has very little effect on your outside walls upstairs but has a tremendous effect on your masonry basement walls.

You ventilate attics and crawl spaces because they are between the outside and inside the house and you do not ventilate your upstairs or basement walls because they are in direct contact with the outside. The walls primarily use a Water Shedding System to remove moisture from those parts of the structure. What this explicitly implies is that the materials used in the construction of these parts of the house will absorb moisture and will be used to expel that same moisture.

If your cinder block walls are dry it indicates that you have good site grading, good soil drainage and good roof drainage systems. It also indicates that the basement walls are a major source for the extaction of moisture inside the basement. If the cinder blocks has signs of moisture stains, I would recommend the water proofing system, this includes not only the Dryloc but also addressing the outside water shedding systems. But if the walls are dry, I would not recommend water proofing them.

The one inch DEAD AIR SPACE has several functions. One is that it is a capilliary break. Convection not only transfers heat from one object to another but also moisture. For example, if I dip a corner of a tissue into water, eventually the entire tissue gets wet. If I do the same but I tear the tissue in half and keep them apart an inch, the half that I keep an inch away will never get wet, capilliary break. If I do the same but allow the two halves to touch, both halves will get wet, that is what movement of air will do (convection). So with DEAD AIR SPACES you want as little or no movement of the air, which means you do not ventilate the dead air space.

To SUSTAIN a HEALTHY INDOOR ENVIROMENT you have to reduce the probability that a moisture problem can occur. This is accomplished by maintaining your outside water shedding systems and controlling the amount of moisture generated inside the basement.
Old 01-23-05, 06:23 AM
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I agree with everything you have said, and I can see that my plans are breaking some of the dead air principals.
I have done everything I can short of digging up the basement and re-sealing the walls from the outside.
I (for the past 2 years) have had no "water" in the basement, but during the demolition I found plenty of evidence of a high amount of moisture.

Again, my situation is slightly different. The home is split level with a 1 car garage located in the basement.
The opening and closing of the garage door "shocks" the air temp in the basement with temperature change and humidity.
I am very worried that the insulation will get soaked with moisture and start mold growth.
I figured that I would never be able to account for the influence of the garage air influx. This is why I had decided to add the dehumidifier and draw the excess humidity.
The ventilation for the 1” air space is mainly to allow the dehumidifier to work.
Every insulating design seems to have its draw backs when it comes to basements, and I have been unable to find any design that doesn’t cross some line for me.

Please post back and let me know if you feel I am making a grave mistake. All I want to do is to build a comfortable living space that will be as maintenance free as possible.

For refrence I have 2 pictures of what I have found so far behind my walls...and its scary. The previous owner finished the walls with furrowing strips and rigid insulation. After removing the walls and insulation this is what I found.

What a mess
Old 01-23-05, 09:10 AM
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A picture says more than a thousand words.

The white stuff on your concrete block not cinder block is known as effluorescence. A salt deposit when moisture permeates mansonry. What caused it? Without question the electrical outlet and the hole for the electrical wire. Remember what I said about convection, it not only transfers heat from one object to the other, it also transfers moisture. The void in the concrete block is a dead air space, the holes in the block caused convection in this void and accellerated the capilliary action between the ground and the inside of the blocks. To say what the previous owner did was dumb, is an understatement.

By the way, this is exactly what will happen if you try to ventilate a dead air space with a dehumidifier.

When you were young, did you ever blow up a balloon and put it in your freezer? When you take the balloon out after a few minutes, the balloon is smaller. What this illustrates is that when you heat air, it expands and when that same air cools, it contracts. When the heat comes on in your house it expands, where do you think it went, if the house cannot get bigger like a balloon?

So if I consider that the capilliary break was nullified by convection, in fact it was probably accellerated, and compound it with air transported moisture through heating air expansion, I am astonished that the blocks are not cracked.
Old 01-23-05, 10:27 AM
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Starting to see the light!

Your making a believer out of me...
All of the rotten wood and termite damage starts at those holes, and all of the effluorescence is only present in those areas also.

I understand everything you have said, and it makes sense to me.
Using the standard building techniques, and building the walls leaving a 1" air gap, I will still have the parimeter 1" gap open to the cieling cavity.
The floor will be sealed inside the walls.
I can keep the air dead, but the 1" gap around the room will be open to the 18" cavity over the dropped in cieling.
Is there any great problems with the different air volumes?

The other question for me would be, lets say 2 years from now I have a clogged downspout or something like that, and I get water in the 1" air gap space....how will it drain out?
Old 01-23-05, 12:04 PM
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As long as you prohibit the air from moving, the space above the drop ceiling will not make a difference.

Cleaning out gutters and downspouts is part of annual maintenance. It is only expected that water may build up against the foundation wall periodically. If water should penetrate the concrete block, it will eventually be absorbed by the materials surrounding it. Only if you allow the problem with the clogged downspout to continue for a prolonged period of time will the moisture problem affect your Indoor Air Quality. In other words, temporary set backs are normal, failure to address the source of the problem (moisture) determines the severity of the problem.
Old 01-23-05, 12:49 PM
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Thank you very much sir.

Ok you've sold me.
I will build using standard building methods, and build my sub-floor inside the walls. I will make every effort to keep the dead air space..... dead.
Thank you very much for taking the time to explain this to me in easy to understand terms.

I have alot of cleaning up do do now.

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