# Very Very Confused on Insulating a Basement



## daveswoodhauler (Dec 15, 2009)

As the post reads, I keep on reading conflicting information on what type of product to use when insulating interior basement walls, and whether or not to use a vapor barrier. (Had a thread up regarding my furnace, but didn't want to confuse things) Seems like its not a cut dry answer, as it depends on your climate)

1.) I have not completed a heat loss calculation yet (thanks for the tip), but my question is mainly on whether to use rigid foam insulation or bat type insulation.
2.) Also, in the spring/summer, I will be taping plastic to the walls and floor of the basement to determine if I have a moisture issue or condensation issue. (Summertime it smells musty, but no signs of water/leaking....never any puddles after heavy rains)

Foundation is completely below grade, and the ceiling joists in the basement are insulated with R19 Bat insulation. We will be finishing off 2/3rds of the basement.

I have been monitoring temps in the basement, and the coldest I have seen is 53F when it was about 13F outside. (Temps are being taken from the far corner of the basement, furthest away from any light/furnace etc..)

Some things I read states that R10 is needed for the basement, other items I see is R19 is needed.

I would like to go with the rigid foam board insulation, but its max is about R8 for 2" think, so I guess I would be putting up additional layers. (The reason I am thinking about rigid vs bat is that even though we don't get water, and I don't think we have a moisture issue, it does get a musty smell downstairs, and have read that the regid is better versus moisture.)

Again, just looking to see what others have done as I have read so many articles my head is starting to spin, and many of them conflict each other.

Thanks.


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## tutu_sue (Dec 15, 2009)

There are R-values to comply with the energy codes. There's a cool free program you can download to see what's required for your state and town:  http://www.energycodes.gov/rescheck/download.stm


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## blades (Dec 15, 2009)

If I remember correctly, vapor barrier first, then vertical stringers (studs)/ insulation then another vapor barrier ( if using ridged ins, fiberglass bats come that way) dry wall ( recommend moisture resistant).  You can also add ridged insulation on the exterior of the foundation to a depth equal to or a little greater than the frost line for your area ( couple foot worth at least) from the top of sill plate down or where ever the exterior finish starts.


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## Jack Straw (Dec 15, 2009)

I have a finished basement and I have to use a dehumidifier during the warm months (woodstove seems to take care of it in the winter). If you have a musty smell, I would invest in a good dehumidifier.


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## daveswoodhauler (Dec 15, 2009)

Thanks both. The part I am really getting the conflicting info is on the vapor barrier issue....just don't want a basement full of mold.


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## dave11 (Dec 15, 2009)

The modern recommendation is to use NO vapor barrier or retarder on the inside of basement walls in cold climates. Use unfaced batts, or better, rigid foam/XPS that is vapor permeable, like foamular or Dow's blue board (NOT the SuperTuffR, which has the radiant barrier and is vapor impermeable). The basement walls need to be able to dry to the inside. 

Batts will work, but I dislike using them in walls, because over time they usually slip and pull away from the wall. In fact, it is hard to get them tight to the wall without compressing them, which would greatly lower their R value. Any air space between the batt and the wall will greatly lower your insulating value. Rigid foam cut to fit, tight to the wall, is much better, but more than double the money.

R10 is adequate for a basement, assuming all the walls are below ground. 2 inch thick foam generally gives R10.


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## fbelec (Dec 16, 2009)

dave11 said:
			
		

> The modern recommendation is to use NO vapor barrier or retarder on the inside of basement walls in cold climates. Use unfaced batts, or better, rigid foam/XPS that is vapor permeable, like foamular or Dow's blue board (NOT the SuperTuffR, which has the radiant barrier and is vapor impermeable). The basement walls need to be able to dry to the inside.
> 
> Batts will work, but I dislike using them in walls, because over time they usually slip and pull away from the wall. In fact, it is hard to get them tight to the wall without compressing them, which would greatly lower their R value. Any air space between the batt and the wall will greatly lower your insulating value. Rigid foam cut to fit, tight to the wall, is much better, but more than double the money.
> 
> R10 is adequate for a basement, assuming all the walls are below ground. 2 inch thick foam generally gives R10.



hi dave
when you say air space between the batt and the wall which wall are you talking about? the basement foundation wall or the new sheetrock wall?


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## dave11 (Dec 16, 2009)

fbelec said:
			
		

> dave11 said:
> 
> 
> 
> ...



Well, technically the answer is "Which ever wall you're trying to keep heat from passing through." 

In a basement, that would be the block wall or foundation wall, so you'd want to have your insulation as tight to it as possible. Leaving even tiny air pockets between the insulation and the wall leaves room for air to migrate, or at east to loop up and down, thus bypassing your insulation. This is why batts don't perform as expected in walls, even if properly installed.


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## Gooserider (Dec 16, 2009)

I would tend to say that http://www.buildingscience.com/ is probably your best reference source on the latest and greatest "how to" advice on insulating a basement, etc...  

You would need to read their pages, but my recollection is they suggest vapor permeable wall construction so that the walls can dry to the inside, and possibly putting a layer of drainage mat against the walls as well...

Gooserider


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## Fi-Q (Dec 16, 2009)

I went with 2 in of Soya base Urethane (http://www.heatlok-soya.com/). I think it'S the bast insulation / vapor barrier / sealant that can be put in a basement. But it is not as cheap $$ as foam board.


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## daveswoodhauler (Dec 16, 2009)

Thanks Folks. I am trying to get R13, but 2 inches of the foam board only works out to R10.
I looked at the building science docs, and it would seem that its ok to place a combination of rigid panels and batt insulation, correct?
I guess I am thinking of covering the walls with 1" of rigid panels, then framing the walls with 2 X 4's and then using batt insulation.
Any concerns with this approach? (Or just use 2 inch rigin on the walls, frame in, and then use 1" rigid in between the studs....but then that would leave an airgap)
Back to the drawing board.


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## tutu_sue (Dec 16, 2009)

You're good with the 1" panels with studs and batts as long as you are sure to tape the joints in the rigid panels.  The panels have to be fastened to the walls with screws and furring strips.  We used tapcons.  Here's info on how to do it:  http://www.buildingscience.com/documents/reports/rr-0308-renovating-your-basment 

You don't have to worry about the air gap when you have continuous taped panels.


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## dave11 (Dec 16, 2009)

ilikewood said:
			
		

> Thanks Folks. I am trying to get R13, but 2 inches of the foam board only works out to R10.
> I looked at the building science docs, and it would seem that its ok to place a combination of rigid panels and batt insulation, correct?
> I guess I am thinking of covering the walls with 1" of rigid panels, then framing the walls with 2 X 4's and then using batt insulation.
> Any concerns with this approach? (Or just use 2 inch rigin on the walls, frame in, and then use 1" rigid in between the studs....but then that would leave an airgap)
> Back to the drawing board.



You can get rigid foam panels up to 4 inches thick, or R20, if you really want to go beyond R10. The difference in heat loss rates though gets smaller and smaller as R value goes up. 

In my basement, I put up 2 inch deep  pressure-treated furring strips over the block walls, then 2 inch foamular between those, cut on a table saw. Counting the R0.5 of the drywall covering, it gives me R10.5, is airtight, and only took off 2.5 inches from each side of the room perimeter.


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## dave11 (Dec 16, 2009)

tutu_sue said:
			
		

> You're good with the 1" panels with studs and batts as long as you are sure to tape the joints in the rigid panels.  The panels have to be fastened to the walls with screws and furring strips.  We used tapcons.  Here's info on how to do it:  http://www.buildingscience.com/documents/reports/rr-0308-renovating-your-basment
> 
> You don't have to worry about the air gap when you have continuous taped panels.



I don't deny there are those who do it this way, but if you leave an air gap between the rigid panels fastened to the wall, and the FG batts, then you are lowering the R value of the assembly. Air will circulate in that gap, even if just convection loops, and transfer heat from any surface it touches into the surrounding, uninsulated colder surfaces. Not to mention that any open but secluded space, particularly in a basement, tends to allow rodents, carpenter ants, termites etc. to take up residence without being seen. I've seen enough of it to know to never, ever leave an open space in any type of construction, if it can be helped.


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## fbelec (Dec 16, 2009)

dave 
how much r value will be lost if there is a air space between the solid and batt insulation? i ask because windows get some of their r value from the air space between each layer of glass. and gas.


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## dave11 (Dec 17, 2009)

fbelec said:
			
		

> dave
> how much r value will be lost if there is a air space between the solid and batt insulation? i ask because windows get some of their r value from the air space between each layer of glass. and gas.



Well, the air space between window panes is generally filled with some inert gas, or at one time I think was a vacuum, which is why these windows are so prone to failure, at least regarding their insulating value, if their seal is disrupted and the gas leaks out, and air comes in.

The air space behind a wall is very different. Even if you could seal it airtight, which would be a big job, at some point in the near future the airtightness would disappear, as wood shrank and expanded with the seasons, etc. If you leave an airspace between two layers of insulation, or between your insulation and the colder surface, and there is any contact between that air and the room, then heat will be able to bypass your inner layer of insulation via conduction through the air. Worse yet, by convection, if any sort of draft is established. 

Now of course if the air passages between the room and the air behind your insulating layer are very small, you might not have much of a reduction in R value. But you will have some, plus the likelihood of convection loops forming in the long vertical spaces. This also will reduce your effective R value, but by how much, probably can't be calculated outside a laboratory.

Best, in my opinion, to avoid it altogether, by not designing any insulating assembly with free air inside it.


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## NEDLAX (Dec 17, 2009)

If your going to finish the basement with studs and drywall i would spray foam, closed cell only! at least 2" is needed to be called a vapor barrier. you can spray more all depends on how much money you have or money you want to save down the road.  Spray foam 2" typically takes about 12-15 years to pay for itself over choosing batt insulation keep that in mind.  Just make sure to cover the foam with sheetrock or fire barrier.  Also when the guys comes to spray leave the house for a day most manufacturer dont want homeowners around for 24hrs.  30% of your heating energy is lost to uninsulated basements food for thought.


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## dave11 (Dec 17, 2009)

NEDLAX said:
			
		

> 30% of your heating energy is lost to uninsulated basements food for thought.



There's no basis for saying that without seeing a heat-loss analysis for his house.


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## velvetfoot (Dec 17, 2009)

Here's what I did:
https://www.hearth.com/econtent/index.php/forums/viewthread/33963/P0/

Bear in mind I STILL haven't put any drywall on it.
Hopefully this winter after other stuff.
I think it will work.


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## Gooserider (Dec 17, 2009)

Air spaces in a wall can be a mixed bag, it all depends on how big they are...  If they are the right dimension they can actually be insulating, but that is difficult to achieve...  To a first approximation the bigger the space the worse it will be for convection losses as you can get bigger and bigger convection loops...  Another big factor is the amount of temperature difference there is between the inner and outer surfaces - if the insulation is thick enough that there is little or no difference between the insulation surface temp and the sheetrock temp, there won't be much convection once the temperatures have stabilized...

I agree that it is best to minimize air voids in a wall structure, but I don't see them as causes for panic either...

Gooserider


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## daveswoodhauler (Dec 17, 2009)

Thank for all the help folks....some good advice here.
Just found out a bigger problem I have as I found a crack in the exterior of the basement, and it goes the entire way from top to bottom, and the crack is also on the inside of the wall as well and looks like the prior homeowners tried to repair, and then the put up sheet rock along the whole side of the wall. Frosts me that they did not indicate this issue on the disclosure form, but now I know why they framed in one wall and ran some rough electrical, insulation, but never finished it.  I can probababy dig down the front and repair from the outside, but its right next to the concrete steps, and if I dig the steps are going to collapse in.....might be leaving this one to the pro's


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## dave11 (Dec 17, 2009)

ilikewood said:
			
		

> Thank for all the help folks....some good advice here.
> Just found out a bigger problem I have as I found a crack in the exterior of the basement, and it goes the entire way from top to bottom, and the crack is also on the inside of the wall as well and looks like the prior homeowners tried to repair, and then the put up sheet rock along the whole side of the wall. Frosts me that they did not indicate this issue on the disclosure form, but now I know why they framed in one wall and ran some rough electrical, insulation, but never finished it.  I can probababy dig down the front and repair from the outside, but its right next to the concrete steps, and if I dig the steps are going to collapse in.....might be leaving this one to the pro's



Sorry to hear that. If you used a buyer's agent when you bought the house, he/she might be able to advise if you have any legal grounds to pursue the sellers. Depends on state laws and how the sales agreement was worded, and how long ago was the sale.


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## velvetfoot (Dec 17, 2009)

How long have you been there? 
Have you seen some wet Springs?
Sometime things are better left alone.


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## daveswoodhauler (Dec 17, 2009)

We have been there since the fall of 2005.
I pulled off the drywall and insulation last night where the crack appears on the outside, and found the same on the inside.
Crack isn't really that large...appx 1-2 mm and runs from the top to the bottom of the interior wall.
The good news is that I really don't see much of a water stain on the wall or bottom plate...some discoloring on the bottom plate, but seems to be ok. No mold, but I can feel the cold air moving from the exterior to inside where the crack is above grade. I put in gutters all around the house when moving in, so I think that has helped.
I guess my next project will be using the sealing compound in the exterior, and then the outside as much as I can when the spring is here.
At least that way when I can get all the framing/drywall and insulation down, I can have a good view of any water penetration in the springtime.
Just afraid that even if I get the crack filled in, the constant freeze/thaw cycles over time is going to have the crack reappear, and I am now debating if I want to have that on my mind all the time.


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## dave11 (Dec 17, 2009)

ilikewood said:
			
		

> We have been there since the fall of 2005.
> I pulled off the drywall and insulation last night where the crack appears on the outside, and found the same on the inside.
> Crack isn't really that large...appx 1-2 mm and runs from the top to the bottom of the interior wall.
> The good news is that I really don't see much of a water stain on the wall or bottom plate...some discoloring on the bottom plate, but seems to be ok. No mold, but I can feel the cold air moving from the exterior to inside where the crack is above grade. I put in gutters all around the house when moving in, so I think that has helped.
> ...



Is this a concrete block wall?

Is the crack the same width along it's whole length, or does it widen at one end?

A full-thickness crack in a foundation wall, especially if any movement has occurred, probably should be looked at by a reputable company for an opinion, even more so because you're going to cover it up. The crack formed for a reason. Masonry doesn't move much from temperature changes, but the surrounding soil does, especially if kept wet. 

Are you sure there are no other cracks? There's often a "partner" crack on an opposing wall.


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## Gooserider (Dec 17, 2009)

For what it's worth, someone in another thread mentioned this Sanitred outfit as a possible source for stuff that might be useful in lining a thermal storage tank...  Not sure if it would be suitable for that application w/o doing some conversation with their tech support department folks as its not mentioned, but they were doing a lot of pushing on basement waterproofing and radon control applications...

I am NOT recommending them, but it does look like interesting stuff if one believes their claims, (I did feel my "hype" detector going off)  and it sounds like your crack is the kind of application that they had in mind for the product.  Might be worth talking to them and seeing what they have to say.  The stuff is pricey, but probably less than a lot of the alternatives, and might be good IF it works...

Gooserider


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## daveswoodhauler (Dec 17, 2009)

Thanks Dave.
Its a poured concrete foundation wall. The crack is in the center of the wall (Foundation is 36 feet long by 24 feet wide), and wall height is appx 8 feet high.
From the looks of it, it looks like the crack started from the top and worked its way down.
Looks like the crack ran about 4 feet down when the prior owners tried to use some bathroom cauling or something, and now the crack runs from top to bottom...guessing the last 4 feet of crack is from 2005 to now.
I would say the greatest gap is about 1mm..so its not like there is light shining through....might try to take some pics later.


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## dave11 (Dec 17, 2009)

ilikewood said:
			
		

> Thanks Dave.
> Its a poured concrete foundation wall. The crack is in the center of the wall (Foundation is 36 feet long by 24 feet wide), and wall height is appx 8 feet high.
> From the looks of it, it looks like the crack started from the top and worked its way down.
> Looks like the crack ran about 4 feet down when the prior owners tried to use some bathroom cauling or something, and now the crack runs from top to bottom...guessing the last 4 feet of crack is from 2005 to now.
> I would say the greatest gap is about 1mm..so its not like there is light shining through....might try to take some pics later.



The gradual lengthening of a crack, if that's what happened, suggests a gradual settling or subsidence on one end of the wall or the other. But in that case, the crack should be at least a tiny bit wider at the top than at the bottom. Is that the case?  

But if you're convinced that the crack has been growing, it really should be looked at by a foundations guy. Just sealing it might make no change in the end, if it keeps growing (ie. widening).


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## daveswoodhauler (Dec 17, 2009)

Here are a few pics, and I found a similar crack on the opposite wall:


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## daveswoodhauler (Dec 17, 2009)

2 more on the opposite wall


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## dave11 (Dec 17, 2009)

If I had to guess, I'd say those are likely to be shrinkage cracks in the concrete wall that occurred after pouring. There appears to have been no displacement. These are usually not progressive, and sometimes happen naturally, though it often reflects a lack of proper reinforcement of the concrete when it was poured.

But I'd still suggest you get a REPUTABLE foundation repair company to take a look. One with references. If the cracks are due to shrinkage, they'll probably tell you it's okay to seal them and cover them. 

And make sure to keep your outside foundation walls well-drained.


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## NEDLAX (Dec 19, 2009)

dave11 said:
			
		

> NEDLAX said:
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> ...



Its a rule of thumb in the industry for unisulated basements as per terry brennan the go to guy for basements and how to condition them.


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## fbelec (Dec 20, 2009)

don't know about the 30%, but my house totally changed  when did basement work. i insulated with kraft faced 3.5 inch R13 and sheetrocked. only 3/4 of the basement. my basement went from high 30's to mid 50's. my upstairs floors were 10 times warmer. as far as gas for the boiler i'm not sure how much i saved there because i've been heating with wood since we moved in, in 2001. but i can say using the same wood stove that i went from having to feed the stove all day and night to 1 fire a day in shoulder season, and when it's normal cold 2 fires a day. and when we like the past few nights dipped into the 5 to 10 degree temps feed the stove with small fires in day and stuffed at night. no leaks, no mold. but i do run a dehumidifier in the summer. if i didn't the musty smell would be there. humidity always sinks to the lowest level of the house. the only thing i did as a precaution was to use pt 2x4's on the floor for the base plate. i have good sized spaces between the finished wall and the foundation wall. i have a 4 inch pvc pipe running around the wall. the finished wall is not to cold to the touch when it's in the 50's down there. and it takes 3 days to drop the temps from 70's to 50's when the stove goes out.


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## velvetfoot (Dec 20, 2009)

fbelec, are you talking about a stove that is in your basement?


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## semipro (Dec 20, 2009)

The way I'd do it: 

- Use the Building Science publications that I suggested in your 1st post as a guide (or whichever B.S. doc applies best to your situation)

- Use layers of foam to get the R value you want.  Build the walls to the interior of that. 

- Don't create/install a vapor barrier.  You want a wall that breathes. I believe that's what B.S. and others in the know suggest.  If you install a vapor barrier then moisture will get trapped in the wall somewhere, potentially causing problems. Unless a vapor barrier was installed outside or underneath the concrete, water *will *come through the concrete.  Standard concrete is not 100% impervious to water, not nearly. The key is how to deal with the water that makes its way through. 

- Avoid air gaps if at all possible.  The problem with air gaps is not so much loss of insulation as it is a moisture problem.  If air can infiltrate then moisture can get in.  The water in the air will condense on the cold face and could cause problems.  An ideal wall provides structure and insulation without retaining moisture (or critters). 

- Use a product like Densarmour for your wallboard. It uses non-organic materials that don't provide a substrate for mold to grow on. http://www.gp.com/build/Product.aspx?pid=4659

-  There are gauges that can be installed across masonry cracks to monitor movement.  I suspect if you don't see signs of water migrating in (usually staining or mineral buildup) that you seal the best you can and move on.  Maybe you want to build in an access panel to allow visual monitoring of the crack.  There should be re-bar in there provide the structural strength that's needed. 

- Consider the coating you put on the wallboard.  Don't use anything that will act as a vapor barrier like vinyl wallpaper or oil based paint. 

- Don't put wall sill plates in direct contact with the floor.  Use the thin blue foam insulation made for that purpose or similar.

- Insulate the concrete floor also if you really want a comfortable basement.   I think B.S. covers this as well.  

- Put some Boric Acid powder (e.g. Roach Proof) in the bottom of wall cavities for potential bug issues.


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## fbelec (Dec 20, 2009)

velvetfoot said:
			
		

> fbelec, are you talking about a stove that is in your basement?



no, just using regular fiberglass insulation and what it did for my house. not a whole lot of money and 6 years with no problems.


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## redhotz (Dec 20, 2009)

Gooserider said:
			
		

> For what it's worth, someone in another thread mentioned this Sanitred outfit as a possible source for stuff that might be useful in lining a thermal storage tank...  Not sure if it would be suitable for that application w/o doing some conversation with their tech support department folks as its not mentioned, but they were doing a lot of pushing on basement waterproofing and radon control applications...
> 
> I am NOT recommending them, but it does look like interesting stuff if one believes their claims, (I did feel my "hype" detector going off)  and it sounds like your crack is the kind of application that they had in mind for the product.  Might be worth talking to them and seeing what they have to say.  The stuff is pricey, but probably less than a lot of the alternatives, and might be good IF it works...
> 
> Gooserider






I used Sanitred in my basement 4 years ago. I highly recommend it. It should be applied to bare block. It is a 2 part epoxy polyurethane. It's about $90.00 gallon. I used 4 gallons. It does what there web site says. I was skeptical at first but after trying it, I was sold. I had a lot of leaking cracks, some up to a 1/2". They have a filler for wide cracks. No leaks anymore, no condensation. Check it out.


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## Brian in Michigan (Dec 21, 2009)

I tried the stud wall and 3-1/2" of insulation with a vapor barier on a poured wall. After about a week there was so much water behind and on the face of the plastic, I ripped out all of the plastic. The rest of the walls I put in 1-1/2" foam board. All of it glued to the walls and then I used furing strips on the face of the foam board. I used tapcon screws to drive thru the furring strips and foam board into the concrete. This way no wood came into contact with the concrete and the drywall sets away from the insulation. It's been like this for 10 years and no problems.


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## daveswoodhauler (Dec 22, 2009)

Semipro said:
			
		

> The way I'd do it:
> 
> - Use the Building Science publications that I suggested in your 1st post as a guide (or whichever B.S. doc applies best to your situation)
> 
> ...



Thanks for your help Semipro.
I was thinking of going the route you explained so well, but if I read your post right, all the insulation would be between the walls and framing, and then I would have an airspace in between the studs? (Again, thanks for the help, just want to make sure that I understand correctly)


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## dave11 (Dec 22, 2009)

ilikewood said:
			
		

> Semipro said:
> 
> 
> 
> ...



I won't answer for semipro, but I believe he does mean to build a frame wall on the room side of the rigid panels. You could add 3.5 inch batts between these studs if you like, though again, you should do a heat loss analysis to see if its the best use of your money.

The problem with doing it this way is that you remove a significant amount of floor space. If you use 2-inch rigid foam, then 3.5 inch studs, then 0.5 inch sheetrock, you'll have removed 6 inches of floor space all around the basement perimeter. If your basement is large, you might not miss it, but you might want to measure it out and see if you're happy with the result, before you do it.


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## daveswoodhauler (Dec 22, 2009)

> I won't answer for semipro, but I believe he does mean to build a frame wall on the room side of the rigid panels. You could add 3.5 inch batts between these studs if you like, though again, you should do a heat loss analysis to see if its the best use of your money.
> 
> The problem with doing it this way is that you remove a significant amount of floor space. If you use 2-inch rigid foam, then 3.5 inch studs, then 0.5 inch sheetrock, you'll have removed 6 inches of floor space all around the basement perimeter. If your basement is large, you might not miss it, but you might want to measure it out and see if you're happy with the result, before you do it.
> 
> ...


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## ansehnlich1 (Dec 22, 2009)

I didn't read this whole thread, I admit.

We built our home 3 years ago here in Pennsylvania. Code required basement wall insulation. We have an aluminum faced rolled fiberglass attached to our poured foundation walls with hilti fasteners.

Have had no moisture problems

When/If I decide to finish off any areas in the basement I will simply stud the wall along the insulation, no problem.

Oh, I could tell a HUGE difference in the basement as soon as the insulation went up.....it was amazing.


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## semipro (Dec 23, 2009)

ilikewood said:
			
		

> Semipro said:
> 
> 
> 
> ...



Yeah, the way I was suggesting would leave an airspace between the studs.  To tell you truth I wouldn't use more than 2" thickness of foam because my basement is below grade so the exterior basement walls should never see a temp below about 50F.  I'm not sure about your situation.  I think Dave11's suggestion to put fiberglass batts in between studs is a good one if you're using full sized (2x4) studs.  That is, as long as the batts used are unfaced so no vapor barrier is created.  However in most cases, you don't need to use full 2x4s when framing the wall if you're attaching the studs to the wall through the foam with something like a Tapcon and this creates a pretty stout wall structure. You can use 2x2 studs instead but you won't want to pack 3.5" thick batts into a space 1.5" deep because it won't give you much R value.  

If you want more insulation than initial 2" of foam will provide than it would probably be best to put up the 2" foam against the wall, install the 2x2 studs on the face of the foam and to the wall, then insulate between the studs with 1" foam.  If you can afford the interior space loss, use full 2x4 studs and insulate between them with either more foam or unfaced fiberglass batts as Dave11 suggested. 

I hadn't thought about it before but if you want to avoid any possible mold issues by removing growth substrates (wood in this case) you could use metal studs instead of wooden ones.

If any of what I've suggested conflicts with the guys at Building Science, I'd do it their way.  Those guys know what they are talking about and are highly respected in the profession.  

Good luck!


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## semipro (Dec 23, 2009)

Dave11, 
Your avatar mesmerizes me.  I keep finding myself staring at it.


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## velvetfoot (Dec 23, 2009)

Two layers of foam with strapping tap conned to the wall in between with sheet rock on top attached to the strapping could take a good hit, have a complete thermal break, R20, and not support mold.
(The wood strips at left are used to brace the top layer when gluing to the bottom layer.)


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## dave11 (Dec 23, 2009)

Semipro said:
			
		

> Dave11,
> Your avatar mesmerizes me.  I keep finding myself staring at it.



Ha! Semipro, let me tell you what it's meant to represent. That figure is me, chasing after the "perfect burn" in my 30NC.

Regards.


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## SPED (Jan 4, 2010)

Gooserider said:
			
		

> I would tend to say that http://www.buildingscience.com/ is probably your best reference source on the latest and greatest "how to" advice on insulating a basement, etc...
> 
> You would need to read their pages, but my recollection is they suggest vapor permeable wall construction so that the walls can dry to the inside, and possibly putting a layer of drainage mat against the walls as well...
> 
> Gooserider



As soon as I saw this thread I was planning on suggesting that site.  +1, great website and they have downloadable pdfs on how to do it.  I followed their recommendations, foam board then unfaced batts in a stud wall, then sheetrock, then latex paint so water can slowly get out if it does get trapped.  3 yrs since I did it in my basement and no probs so far.  I did thoroseal the walls first and make sure I had no leaks as well.


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