# Rigid Foam? Moisture



## Amitabh (Oct 21, 2010)

Hi All,

I am running through the plans of my basement and am thinking through a insulation and a vapour barrier.

I dont want to have moisture problems (also plan on installing mold resistance drywall) and i think that having a plastic vapour barrier might create a barrier that traps moisture. Right now, the tail end of winter, humidity is roughly 36. But we are no where near summer and we dont plan on running the AC soon. So, I plan on buying a dehumidifier for the basement as well.

So in terms of insulation right now, we have a fiberglass blanket going across the top half of all the poured concrete walls and then the FG blanket is wrapped with plastic. i dont see any moisture build up within the plastic and this past winter and last summer we had record snow, heat and rain.

I also bought an air purifier, but doesnt run that often because the sensors are not picking up much.

So instead of installing a plastic vapour barrier after framing, i am thinking about rigid foam insulation against the walls (including the FG blanket). thoughts? worth it? 

also, does it just rest against the concrete? or does it need to be fastened in?


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## Amitabh (Oct 21, 2010)

anyone?

would a pix help?


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## monsterbash (Apr 7, 2009)

Check out this thread...pretty much the exact question.

http://www.diychatroom.com/f19/yet-another-basement-insulation-question-193138/

What I ended up doing is what Gary recommended. Glued 2" foam XPS to the bottom..spray foamed the seams...and taped. What gave me confidence to do it this way was the recent weather. In the beginning of December the water table was at a record high in my area..and there was major flooding less than a mile North of our house. We had no moisture of any kind in the basement. Our 2 neighbors didn't have the same results.

The general jest I got out of my research and the links Gary provided was...if you're confident that you have no water issues and control the humidity in the basement..you 'can' get away with this method. 

Of course if I had an unlimited budget..and time..I would have used 2" XPS on the entire wall. Hell...I would have spray foam the entire basement if that was the case


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## Amitabh (Oct 21, 2010)

thanx for pointing me here. it was helpful.

What did you end up doing?

personally, i want to save a few bucks and keep the blanket. But is it really that bad?


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## GreenFoamFan (Jan 25, 2014)

Great advice from monsterbash. I would also recommend adhering 2” XPS board to the walls, and then applying 1” of closed cell foam on top. 

This method will give you a high R-Value, will stop air leakage, and resist moisture penetration. Our company’s foam also prevents mold growth, which is a big plus in basements.

I totally get wanting to stay within a budget. What I would do is move the fiberglass from the basement to the floor of your attic. That way you will get to use the fiberglass you already have, and bulk up on R-Value in an area which can always use it. 

When are you planning to finish the basement?


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## Gary in WA (Mar 11, 2009)

You won't see any build-up of moisture until you cover it with drywall; Photo 3, 7; http://www.google.com/url?sa=t&rct=...5YCwBw&usg=AFQjCNGYl3LafAv-Hjm7Gq3ToLZQruI9mg

2" XPS was enough to stop condensation in a test in Kitchener, fairly close to you; http://www.buildingscience.com/docu...Hygrothermal_Modeling_Basement_Insulation.pdf

IMHO, save your money and DIY (part of the forum title- not "hire it out"), we can help you. You don't need 3" and if careful can air-seal the rigid board just fine. Enough chemicals in FB without adding more to stop mold... especially since FB is not organic in the first place. http://www.trustgreenguard.com/faq.aspx#insects

Gary
PS. Welcome to the forums, GFF!


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## Amitabh (Oct 21, 2010)

thank you 

i am starting today with removing the FG blanket - one section at a time... and then installing 1.5" XPS FB. Then frame (with a foam sill gasket on the under the bottom 2x4) and then install FG Batts between the stubs. to get the r value close to R21

i have roughly 120 linear ft to cover.


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## mikegp (Jul 17, 2011)

I would go with Roxul or another rock wool product.


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## Amitabh (Oct 21, 2010)

hi all

thanx 

i am going to start a new thread call my basement project.... dont wantto hijack my own thread with another thread.


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