Expanded Polystyrene directly to cement walls

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  #1  
Old 01-25-05, 11:42 AM
howz
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Expanded Polystyrene directly to cement walls

I have a 1 year old home. I have ordered some Expanded Polystyrene insulation with 1"x3" grooves to accept wood strapping. I want to nail this directly to the cement walls and cover it with vapor barrier. After reading some other comments, I'm worried about problems 2 or 3 years down the road. Some say expanded breathes well and should not have vapor barrier. The manufacturer says to use vapor barrier. Others suggest the 2x4 walls with 1" dead space. Has anyone out there done it the way I am suggesting?
How long has it been and have you had any problems?
 
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  #2  
Old 01-25-05, 06:31 PM
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There has been a great deal of discussion on this subject lately.

People have been installing Expanded Polystyrene directly to basement walls for many years. I do not have a problem with the Expanded Polystyrene by itself. I have a problem with what people do to it. Besides the gaps usually found between the seams, people run wires through it. What this does is increase the probability of a moisture problem occurring. Whereas, studding the wall an inch away from the masonry wall reduces the probability and it is a lot easier to run wires if you need to.

Regardless of the type of insulation you use, if your intent is to heat the basement, you have to install a vapor barrier between the insulation and sheet rock. The reason for this is that insulation slows down heat flow but does not slow down the moisture in the heat. Vapor barriers slow down the moisture flow in heat. So if you do not install a vapor barrier and you heat your basement, you are almost assured that you will have a moisture problem on your basement walls behind the insulation, regardless if you have the one inch gap or not. If you search the web on Relative Humidity (RH%) it will explain to you why I think this way.
 
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Old 01-26-05, 09:57 AM
howz
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Does an air exchanger help to combat against mold problems or does it just delay the inevitable?
 
  #4  
Old 01-26-05, 06:41 PM
MylesOC
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My understanding was that if you have extruded (or expanded) poly styrene flush against the basement wall (no dead air space) and you have uniform coverage with no cracks, holes, etc..., that you shouldn't have to worry about moisture migrating out towards the foam. The foam, as long as you have enough thickness and net R-value for your climate, will insulate the cold surface from the warm air, thus preventing it from condensing. It would no sooner condense behind your warm drywall, than it would on your coffee table. Another advantage, is that moisture in the cement wall below grade needs to dry to the interior. EPS or XPS does have a permeability (e.g.: extruded type 2 perm is approx 1.5) and you need to allow the vapor coming through the foam to be able to permeate through to the interior air. Of course, if you dont have enough insulation against your wall, you will have a cold surface upon which warm moist air will migrate to, condense, and cause moisture build-up and lots of nasties start from there...

Makes sense, or am I misunderstanding anything in my logic?
 
  #5  
Old 01-26-05, 10:21 PM
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Dominant heat transfer mechanism during heating season.

Which is Conduction. Insulation slows down conductive heat transfer and is rated nationally on its effectiveness in retarding conductive heat transfer. R-13 means one thirteenth of a BTU traverses a square foot of this insulation per hour. This is continuous as long as the heat is on in the basement and the masonry wall is at a lower temperature than the temperature inside the basement.

Insulation retards heat flow by retaining some of the heat but it does nothing with the moisture that is in the heat. In other words, the heat is slowed down by the insulation but the insulation allows the moisture inside the heat to continue to flow through the insulation. So the moisture leaves the insulation with that 1/13th of a BTU per hour. Another way of putting this is, at a temperature a lot lower than the temperature the heat was when it entered the insulation.

Relative Humidity (RH%) describes the percentage of moisture content in an object at a certain temperature. So if I have a certain volume of heat that contains 100 grains of moisture at 70 degrees Fahrenheit, let's say it has a RH% of 20%. In order for this cetain volume of heat to reach 100% Saturation, you would have to increase the amount of moisture in it five times or lower the temperature of the heat. This is because heat at higher temperatures, the molecules are very excited and move further apart. The space between these heat molecules is how the moisture molecules travel with the heat. As the heat loses temperature, the heat molecules move closer together, thereby reducing the amount of space for moisture molecules. So if I take the example stated above, the 100 grains of moisture but drop the temperature to 60 degrees Fahrenheit, the RH% becomes 50%. Which means I do not need five times more moisture to reach 100% Saturation, all I have to do is double it. Or lower the temperature more to Dew Point.

Though it may be true that heat condenses on cooler surfaces, that has to do with surface tension. Because if it only did that, it would never rain or snow.

I have debated the so called drying out process with basements for years. Hydrostatic pressure, capilliary action, live and dead load pressures all effect moisture flow, but what dominates moisture flow in basements is Equilibrium Relative Humidity. This states that an object of lower humidity will absorb humidity from an object of higher humidity until the humidity levels are equal in both objects. I asked these questions repeatedly to my collegues who support this type of application. Where does the moisture go when it is expelled from the masonry to the interior of the basement? Does it evaporate? It is already in a vapor form. Does it go out your door when you go in and out of the house? Perhaps it goes down your drain. The answer is that it gets absorbed by the air in the basement and then absorbed by the rest of the objects in the house. Then by the air outside, depending on which objects have the lower humidity levels.

We know that vapor barriers impedes moisture flow inside heat. Besides the fact that it is rated in its effectiveness, we can actually test and observe it. The rule is high towards low. High humidity level gets absorbed by low humidity level; High temperatures gets absorbed by lower temperatures. So we can safely say which way the heat that contains a certain amount of moisture is going to flow during the winter in the basement.

The other part of this is that the studded wall is connected to the framing members of the house. What effect does the vapor barrier has on Equilibriium Relative Humidity? Look at the definition.

When my collegues and I debate over this issue and a whole lot more, there is one thing we do agree to, that is to disagree.
 
  #6  
Old 01-27-05, 10:21 AM
howz
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resercon

I value what you say. You know your stuff. From reading other comments you have made, I gather your preferred method to insulate basement walls would be to stud up 2x4 walls with 1" dead space. I have already purchased a large quantity of 2" EPS and strapping to nail it to the cement walls. I live in a cold climate (as low as - 30C), but 70% of my walls are below the frost line. What would you do to proceed? Would you cover or treat the walls with anything before putting the insulation on? How much R-value should I be shooting for? What grade vapor barrier and where would you put it (between insulation and drywall)?
 
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Old 01-27-05, 05:09 PM
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First and foremost you should check with your local building department on any requirements.

Though I may not support or agree to this type of application, it does not mean that I am right. The people who make papers like the one mentioned have a lot of guts. Because they put themselves out there to be scrutinized by established organizations like ASHREA, Architects and Engineers associations. And believe me, it is not pleasant. However, change does not come by going with the flow, it is done by those who are willing to withstand the beratting from the establishment. My admiration for them goes much further than this expression.

I would not recommend water proofing or installing plastic directly to the masonry wall, unless there is clear signs of water penetration or required by building code.

For the vapor barrier between the sheet rock and the insulation, you have two choices here. One is that you can use 6 mil plastic, it is important that any penetrations in the plastic must be sealed. like around electrical outlets. The other way is to pay close attention to the spackeling of the sheet rock to make sure the wall is air tight and use a very good oil primer. This should be sufficient to act as a vapor barrier.
 
  #8  
Old 01-27-05, 07:04 PM
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I'd like to interject this along with resercon comments. Considerations to make in using rigid is this;

1. If you are just using 1 1/2" rigid and furring strips - A. You need W/T strips to protect the wood. B. The strips can be adhesively applied but they must be solid - mechanical anchors may have to be used to insure that if shelving is installed it will hold. Problem with this is, the penetration into a sealed concrete/masonry surface is damaged and subject to leaking. C. Any electrical boxes will have to be shallow - sometimes makes it hard to wire. D. You must use a fire retardant material over this as per Code.

(Most books, articles about rigid and furring strips fail to say anything about the use of W/T and this will get destroyed and are a good source for mold/mildew with the slightest hint of moisture)

2. Alternative which does add cost is to apply full rigid sheets to the concrete/masonry walls, adhesively applied, then place frame wall against the rigid, then insulate between studs and cover with drywall. The Rigid insulation does then act as a vapor barrier. Do not tape/seal the seams. This allows it to breathe and dry up any condensation that may form.

So here is some more stuff....

W/T is wood treated. International Residential Building Code says "it must be used whenever wood is in contact with concrete and/or masonry". Check it out with your local inspector. This would also include furring strips applied directly to a vertical block wall unless you use the vapor barrier behind it.

If you are considering using 2x2's as furring strips I can only give you my 2 cents worth and you decide;
A. Are you going to have electrical in the walls? Short depth boxes make it difficult to wire. 2x4's would be better.
B. Are you planning or foresee hanging shelves or cabinets on the exterior walls? Not allot of strength and may be subject to splitting easier than 2x4's.
C. I personally can't see how 2" will make a difference in conserving space when you consider the hassle of doing electrical or other carpentry issues.
D. Depending on what you are talking about when it comes to the pre-cut polystyrene, the white foam board, which is the molded expanded polystyrene (MEPS) only is available in R-2 - 3/4" thick, it only costs about $6 per 32 SF. The better quality with R-7.5 is the pink foam - extruded expanded polystyrene (XEPS). This is great stuff but costs more.

Just a note, when you use NON-W/T stock as the 2x2's or 1x3's as furring strips, you have to place a vapor barrier between that and the block wall - you have to attached the furring strips to wall somehow, right? You can't adhesively apply them, you have to use a ramset - this obviously has drawbacks...you just put a hole through the poly making it useless which in turn starts the problem with moisture touching the wood. Second, is if you used W/T or Non-W/T stock and have a waterproofing sealer on your block walls, you just penetrated the block, puncturing the seal coating that was suppose to stop water/moisture...creating possibly a worse problem....water that fills the concrete block cores starts to drain out or will leak in heavy rains. Just thought I'd bring this up. I would do 2x4 walls with R-11 or R-13, insulation would cost about $.02-$.03 more per square foot than the white foam and be better all around. Leave the walls out 1" from the block when framing, apply your poly over the studs apply the drywall and be done. You'll have no problems then.

Note: Most municipalities do not permit using furring strips on masonry surfaces. Call your local building authorities first.

The last thing is that in insulating basements, there is a requirement here in Michigan that will require a minimum of R-11 insulation within the basement. Other northern states already have this as a minimum.

Just some thoughts
 
  #9  
Old 01-28-05, 05:47 AM
howz
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I have 2" EPS with 1"x3" grooves to accept strapping. The grooves are set at 16" centers. I was planning to pre-drill the strapping EPS and cement wall and then nail it with 3" cement nails. After that, I would apply the vapor barrier and then put on the drywall. You do raise a very good point about wall strength for hanging shelves or whatever. Do you think the system I have described would have enough strength? I suppose if I were to drive nails through the drywall and into the strapping I would be piercing the vapor barrier ... I hadn't thought of that. Now I don't know what to do ...
 
  #10  
Old 01-28-05, 06:13 AM
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howz,

With what resercon mentioned, the choice you make will be one that you cannot change. Although what you intend to do is acceptable, it is not my choice either.

I thought I would provide additional information that could prevent you and others from making mistakes. All factors shhould be considered and of course what is allowed per Code in your area. Penetrating the block is not recommended regardless of the fastener. The more information available, the better you can make choices.

You must decide what you want to do. How much was the 2" EPS with grooves?

Does this help?
 
  #11  
Old 01-28-05, 07:22 AM
howz
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Ok, I do want to do the right so I think I'll glue the EPS to the wall, stud up 2x4 walls, fill with fiberglass and seal off with vapor barrier . Do I still need a 1" deadspace?

EPS is $18.5 cdn per 4'x8' sheet ...

PS: Why is it a bad idea to penetrate the cement wall?

Thanks
 
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