# Insulating a Basement Question



## Fallen (Feb 25, 2009)

Was hoping I could get some tips / suggestions on the right type of insulation to use in finishing a basement. I live in a 6 year old 2400 SF home in the south suburbs of Chicago. Watching some of these home improvement shows, I see some contractors glue what looks like 4 x 8 foot sheets of foam (pink colored) insulation right to the concrete walls. And then, once the studs are up they also use fiberglass insulation as well. Not sure if the foam insulation is more for dampness than anything else. Is it overkill to do both? Any thoughts on this.

Thanks.


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## Tom Struble (Mar 2, 2007)

yea those home improvement shows are great:thumbsup:which ones do you watch?I like them all:thumbup:ill never know how they get all that work done in a 1/2 hour:no:i think Norms the best but my friend thinks Tommy is


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## SLSTech (Sep 13, 2008)

Oh come on Tom there can be no question - Silva, Silva, Silva

Norm gets the nod for woodworking - overall though Tom hands down

That Mike guy though - if has was back east, he could probably give them a run for their money....

Oh that's right, the question the stamp collector asked - I have plenty of thoughts on this, feel free to call me after paying for the consultation


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## Tom Struble (Mar 2, 2007)

but Norm used to work for the best of them all,my man Bobby V:notworthy


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## katoman (Apr 26, 2009)

This has been discussed in more detail. Do a search.

Here's the short answer - 2" foam, no VB needed. Pink in the stud cavity has been shown to be a waste.

Foam board in the ribbon space, all seams taped, you want an air tight system. This is called a thermal break.


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## Fallen (Feb 25, 2009)

Thanks Katoman. That's helpful.


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## RMcBride (Dec 21, 2009)

I have to say that I was very unimpressed with the entire TOH crew when I met them - sans Norm of course.

When we do basements here we pursue it in one of two ways. We either cover the wall in foam board and then put up a stud wall without any batt insulation. Or we build our wall slightly away from the foundation wall and have closed cell foam sprayed in. Most important part is not to let the wood touch the concrete or masonry as it will wick moisture in. We have all of our rehabs foam sprayed so it's affordable for us to have it done - otherwise use foam board. Depending on your market it can actually be cost effective to put up 1/2 foam board and R13.


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## Fallen (Feb 25, 2009)

Thanks RMMcBride!

I've been doing a lot of reading and also speaking with some folks at the big box stores. The more research you do, the more confused you become. Seems like everyone has a different opinion / approach.

Some of the local basement remodelers have told me they don't bother with foam board, but just put bat insulation between the studs, being sure to keep the studs an inch or so away from the concrete, and that's it. I was wanting to do both foam board and bat insulation. In the Chicago climate I have been told I can use 1" to 1 1/2" foam board, that 2" is prob overkill. You glue the foam board on with special adhesive and tape the seams. But my primary fear is that foam board can get moisture behind it from condensation and mold will develop. I do not plan on insulating the floor. I have begun applying waterproofing sealant to the concrete walls and will have to decide which route I'm going to take with insulating....


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## Morning Wood (Jan 12, 2008)

Putting closed cell foam on the inside of a foundation is risky. A foundation never dries to the outside. It can only dry to the inside. By putting closed cell on the inside you prevent the foundation from drying out. That is ok in a sense, but any excessive moisture in the foundation will not be able to get out. It will however go up and into the mudsill. If the house has PT sills and a capillary break (sill seal) then it might be able to handle it. If it is an older home with solid wood sills that aren't PT than it can invite rot. If you have foam over the outside of your foundation that helps keep it drier. Best approach is foam over the inside of foundation with 2" of extruded polystyrene or 4" of expanded polystyrene then stud up walls and blow cellulose or install formaldehyde free batts. My two cents.


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## We Fix Houses (Aug 15, 2007)

http://www.buildingscience.com/resources/homeowner_resources


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## s.kelly (Mar 20, 2009)

SLSTech said:


> Oh come on Tom there can be no question - Silva, Silva, Silva
> 
> Norm gets the nod for woodworking - overall though Tom hands down
> 
> ...


All that is fine and all,but how about whatzisname the wheelwright guy:thumbsup: love to drink coffee and watch how they used to do it (and he still does!)


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## katoman (Apr 26, 2009)

When closed cell foam is applied to the inside of the bsmt. walls, including the ribbon space, then any dampness/moisture will exit throught the above grade portion of the foundation.

This has been studied and proven extensively. In fact a builder in Minnisota built 10 homes and finished each bsmt. differently, the best was foam on the exterior, but how to finish the exposed foam is a problem.

The above method of 2" foam on the inside is now the standard in Energy Star rated homes here in Ontario, and will very soon be required in our building code. 

Like I said this has been extensively investigated and studied. I myself spent in excess of 50hrs. investigating known data on this for a new home builder, who was the first Energy Star builder in Ontario.

I have also installed this in bsmt. finishing, and can assure you of it's effectiveness, and no interior condensation/moisture problems.

I mention again though, it is important to tape all seams and foam all cracks/gaps. You want to create and air tight seal. As stated this is termed a thermal break. Then the only place left for moisture to escape is through the foundation that is above grade.

Hope this helps put your mind at ease. :thumbsup:


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## concretemasonry (Dec 1, 2006)

Just keep fiberglass out of a basement where there is any possibility of leakage, wicking, condensation or moisture.

It will never dry out and will hold moisture that can promote growth on wood, drywall or even dust. The correction cost is way beyond the initial construction cost when you consider the demolition involved.


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## Fallen (Feb 25, 2009)

Thanks Guys! 

Katoman...not familiar with the term "ribbon space" can you clarify what that means?

Thanks.


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## ryanh (May 30, 2008)

Thats the way I do basements now. 2" rigid foam with tuck taped seams and then a 2x4 wall with R12 built about a 1/4" out from the wall. No VB and real warm


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## katoman (Apr 26, 2009)

Fallen said:


> Thanks Guys!
> 
> Katoman...not familiar with the term "ribbon space" can you clarify what that means?
> 
> Thanks.


Also called the rim joist. This is the area between the bottom of the floor joists and the sub-floor running around the perimeter of the house.

You need to cut pieces to fit into these areas and foam seal any little gaps. 2" foam does not need a VB, I would not use anything thinner. And yes, keep your studs off the foam board 1/2 - 1"

Foam board does not mildew. Check with Dow Corning. Spray foam is also and excellent choice if the budget alows it.


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## luxbuildsmall (Jan 11, 2006)

katoman said:


> When closed cell foam is applied to the inside of the bsmt. walls, including the ribbon space, then any dampness/moisture will exit throught the above grade portion of the foundation.
> 
> This has been studied and proven extensively. In fact a builder in Minnisota built 10 homes and finished each bsmt. differently, the best was foam on the exterior, but how to finish the exposed foam is a problem.
> 
> ...


Katoman. So far this is the best explanation but I am still having a hard time wrapping my head around this. Are you saying that if the exterior does not have foam board, there isn't an effective method of keeping moisture out? 

I know that Spray foam is a vapor barrier but not a moisture barrier so I am concerned once the foundation is insulated with foam (board or spray) the moisture has to go somewhere.

Secondly, typically we seal the rim joists (ribbons) because in building science you want to eliminate any cold air entering the building envelope. So if the ribbon (rim joist) is sealed the moisture has to settle on the floor, no?

Katoma, would like to PM you if you don't mind. Or could you direct me with your Minneapolis study? I am doing an energy retrofit for an attic for a customer and they are asking my opinion for a previous mold basement. I recommended 2" ISO board, followed by cellulose in the framing. I think I need to rethink. Thanks for your help


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## greg24k (May 19, 2007)

luxbuildsmall said:


> Katoman. So far this is the best explanation but I am still having a hard time wrapping my head around this. Are you saying that if the exterior does not have foam board, there isn't an effective method of keeping moisture out?
> 
> I know that Spray foam is a vapor barrier but not a moisture barrier so I am concerned once the foundation is insulated with foam (board or spray) the moisture has to go somewhere.
> 
> ...


Try this stuff :thumbsup:


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## Morning Wood (Jan 12, 2008)

katoman said:


> When closed cell foam is applied to the inside of the bsmt. walls, including the ribbon space, then any dampness/moisture will exit throught the above grade portion of the foundation.
> 
> This has been studied and proven extensively. In fact a builder in Minnisota built 10 homes and finished each bsmt. differently, the best was foam on the exterior, but how to finish the exposed foam is a problem.
> 
> ...


Ok. I've read your argument and agree. I try very hard to foam the outside of the foundation whenever possible. Of course it is cheaper in labor to insulate the interior of the foundation.


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## katoman (Apr 26, 2009)

luxbuild- I said the most effective way is to insulate the exterior of the foundation. 

But that is impractical in a lot of situations, so second best is to insulate the interior.

If you either use foam board (2") or spray foam, you will be sealing the wall system. Therefore any moisture that is either present in the foundation, or that occurs due to the dew point, will have no where left to escape except out of the remaining 8" of foundation wall above grade.

Next is the issue of warm, moist air in the home. It can no longer pass through the wall system, into the foundation, so it will be necessary to install an HRV system. This must be done by a professional - sized correctly and installed correctly. I've seen many improperly installed.

For mold to grow you need both moisture and something for the mold to eat. Mold spores are present in all our homes, all the time. High density foam board will not mold. (in that the mold spores cannot eat it ) So the moisture that may occur behind the foam, or in the concrete, will not mold, it will simply exit to the exterior.

This is a slow process, but does happen. 

I would have to find that research paper. Been about 5yrs now, not too sure where it's at.

Your pm is off.


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## seifconst (Oct 14, 2008)

I even started foaming the storm shelter walls (under the front porch concrete cap) to deter condensation. I was told by the rep that if you leave closed cell foam uncovered (as we plan to do) you should paint it cause it will break down over time in UV light. seif
Here's a couple of pics from the house we're currently building







Common foundation wall is not foamed.


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## peterjames (Mar 11, 2010)

The insulation strategy of a building needs to be based on a careful consideration of the mode of energy transfer and the direction and intensity in which it moves. This may alter throughout the day and from season to season. It is important to choose an appropriate design, the correct combination of materials and building techniques to suit the particular situation.


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## peterjames (Mar 11, 2010)

Insulation a house should have depends on building design, climate, energy costs, budget, and personal preference. Regional climates make for different requirements.


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