Insulation for a cinder block basement

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Old 06-06-16, 07:01 AM
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Insulation for a cinder block basement

We have a basement in new jersey that is below grade cinder block walls. There is currently 2x3 studs attached to the exterior walls with no insulation or drywall on them. Need help 1) determining if the studs should come before insulating the walls or 2) if we can put rigid foam board between the studs before adding drywall. If we leave the studs in place and add the foam board, do we need to include a plastic covering over the studs to effectively create a complete vapor barrier. Any help would surely be appreciated.
 
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Old 06-06-16, 07:11 AM
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Hi mohave,
I'll be quick:
1. All moisture issues need to be resolved before finishing a basement. Even when a basement looks dry, gallons of water in the form of moisture vapor are probably passing right through those blocks.
2. Blocks are especially difficult as when hollow they communicate all around the foundation.
3. Untreated wood should not be in direct contact with walls or floor.
4. Attaching a continuous covering of rigid foam board (you should check the code requirement for your location) holds the woof away from the walls and acts as a vapor "retarder". A vapor retarder will allow a small amount of drying to the inside, since it can't dry to the outside. Then additional insulation can be installed between the studs along with any wiring needed.

Some reading
Understanding Basements | Building Science Corporation

Bud
 
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Old 06-07-16, 06:15 PM
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Thanks Bud,
We also have had a mold remediation crew in there and one of the things they did was apply a waterproofing to the outside walls. They said I could now put unfaced batt insulation on the prepared wall and then a plastic 4 mil sheathing over the studs followed by the 1/2 inch drywall. They want me to stay away from the paper faced insulation. They also highly recommended a dehumidifier. Does this sound like a good approach.
 
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Old 06-08-16, 04:26 AM
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If you look at photograph #2 in the link above you will see what you would be building, not good.

The Mold crew most likely didn't achieve what they claimed. Waterproofing an exterior wall, especially a block wall, is an extensive process and cannot be done after construction. It requires a waterproof membrane under the footings and floor sealed continuously to a similar membrane glues up the exterior side of the foundation. I'm certain that didn't happen in your case. Liquid water and especially moisture vapor has no problem moving the full height of those walls.

They said to avoid Kraft faced fiberglass. The Kraft facing is paper and can feed the mold. Well, that paper is made out of wood which is what those 2x3's are, more mold food.

I know you want to save those studs that are already in place, but the right way to proceed would be to remove them and apply a continuous layer of rigid insulation across the inside of the walls. If you choose to not do that and take the risk of leaving the studs in place, at least DON'T use fiberglass insulation and don't use that plastic vapor barrier.

The objective here is two fold. One, to maintain a warm inside surface so that any humid inside air that leaks into those walls will not find a cold spot where it can deposit its moisture. Outside moisture is only part of the moisture problem. Second, avoiding the plastic vapor barrier will allow some drying to the inside to prevent an accumulation of moisture from the outside. And yes, a dehumidifier and conditioned air from the house may be necessary to keep the humidity low and air fresh. You know that old basement smell, you don't want that, it is a sign of hidden mold.

Bud
 
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Old 06-09-16, 05:22 PM
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Thank you so much Bud for your time and recommendations.
I probably misled you a bit with my previous explanation. They put a Zinsser Watertite waterproofing product on the inside basement cinder block walls and on the existing studs. After researching this myself, the best I can expect is 5 years from this product and the application on the studs will have little or no effect. As a result of your recommendations, I have already started removing the existing studs and will apply a 1/2 inch rigid board wall insulation on the cinder block walls. I will then restud with 2x4"s and add 3inches of unfaced fiberglass wall insulation. I assume the rigid board will act a the vapor retarder and therefore not need the faced fiberglass insulation. I will complete the effort by installing 1/2 inch drywall.
I think that is pretty much what you are suggesting. Thanks again for your time and assistance.
 
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Old 06-10-16, 07:09 AM
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Bud knows better than I do what the minimum thickness of foam required is to prevent condensation but I know 1/2" is not enough. Please stop and wait for Bud to respond again.
 
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Old 06-10-16, 09:23 AM
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Guidance for basement walls is limited, but the link below suggests 1/2" rigid for a 2x4 wall in climate zone 4 marine, central and southern coastal areas for NJ. But tat recommendation is for exposed walls above grade which is far more severe than most of your basement will be. Link below.
Calculating the Minimum Thickness of Rigid Foam Sheathing | GreenBuildingAdvisor.com

In my area the 1/2 inch rigid is not half of the one inch in price so I prefer the full 1" rigid. The objective is to keep the inside surface of the rigid above the dew point. Ironically, that means not installing too much extra insulation inside of the rigid. Note, when they go up to 2x6 walls they require more rigid.

Be sure to seal off all points where inside air can seep into those walls. Also air seal and insulate the rim joist area.

Bud
 
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Old 06-16-16, 07:25 PM
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Thanks Bud,
I dont think I have ever researched a topic of insulating a cinder block wall in a basement and got so many different and divergent views. It is almost mindboggling. I have decided to go with your approach since it seems to be the most prevalent of all the views and it makes the most sense to me. If I could just borrow your expertise one more time and answer a couple of relevant questions:1) it seems to me that xps is the better rigid wall board for my application. Do you have any preference between xps, eps, and polyiso? 2) Is the Lowes product-Kingspan Insulation unfaced polystyrene foamboard ok to use? Or Home Depots Super TUFF-R Foam Insulation any bettter? and finally3) believe it or not I am having a hard time finding unfaced fiberglass isulation in my area. Is it ok to buy the faced R11 fiberglass and remove the paper backing. Thanks in advance for all your help and recommendations in getting me thru this job.
 
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