# Insulating my basement...Foam or fiber or both?



## cleveman (Dec 17, 2011)

I'm a proponent of XPS on the exterior. What is the current state of affairs regarding your basement? Insulation on exterior, waterproofing, condition of walls, perimeter drainage? What type of siding do you have on the house? How is the grade? How much bsmt wall showing? What do you want to use the space for?


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## jdtox (Jan 9, 2012)

The house was built in '62 and is made of brick. I doubt there is any insulation on the exterior basement walls. The walls are poured cement as best I can tell since I dont see any cinder blocks. However I don't see any rod holes or such either

There was some type of waterproofing done at some point (according to the home inspector), possibly where there were leakage issues. I have these large, plastic panels which are riveted to the walls in 6 different spots along the basement walls. There are some discolored spots on the concrete at the bottom in a few different places as well. However It does not feel moist down there, only cold.

Basically I have all of the concrete walls showing, they have been painted at some point with I'm guessing a waterproofing paint, but have no way of knowing. We plan on using the space for entertaining. Pool Table/Bar/TV, etc. I plan on putting up outer stud walls/drywall and some type of vinyl flooring.


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## cleveman (Dec 17, 2011)

If that were my house, I would dig out a piece on the exterior and see what I'm dealing with.

You didn't mention any drainage problems.

I think you have an excellent candidate to dig out around the perimeter, wash the walls, do any minor repairs, apply some water/dampproofing, address any drainage problems, and install 2" extruded polystyrene.

With your brick veneer, you can just bring this up to the top of the basement wall and grade a bit above it, burying it.

Then you can observe your walls for some time and decide if you want to finish the interior. That finish would simply be studded walls with r-13 in them and sheetrock or whatever wall finish.

I think everyone needs to understand that there will always be the need for some conditioned air down there as well. The floor will still want to sweat.

You'll still have to address the rim joist area as well. I think the best way to do that is with xps on the exterior as well, but you won't be able to do that. If you have some scrap xps left over, I usually rip some pieces to the width of the floor joists, then crosscut each piece individually and jam it in the space as tight as possible. You can use r-20 in this area. You can caulk around the edges of the xps. You are trying to keep warm air from passing through the cracks and condensating on the exterior surface. You have to seal where the sill plate meets the concrete wall as well.


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## Beepster (Oct 19, 2009)

OP, you did not say where you were located.

I am in Minneapolis, and for my built in 1957 home, I am glueing 1" XPS to the wall and 2x4 framing over with unfaced insulation. I could have went 2" XPS, but chose to go 1" and keep the humidity levels down in the summer months.

I also know my drainage on the outside is not an issue. I only need to control the condensation from the inside.

If I could snap my fingers and have 2" on the outside I would, but I am not that magical.

B


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## cleveman (Dec 17, 2011)

a realtor friend of mine was telling me about a recently built house that went into foreclosure and sat for months. There was no flood damage, but the amount of condensation that happened in the basement was enough to get mold growing throughout the house.

That is what bothers me. We are building things which rely on mechanical systems to keep from falling apart. I want to have something which will take care of itself as much as possible. 

Sure, if we rely on a sump pump to keep the basement dry, that is fine. But don't expect to finish the basement and not have a power outage during a high water table episode and ruin all the finish.

Likewise, I would like to turn off the A/C and go on vacation during the summer and not come home to a fuzzy house.


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## jdtox (Jan 9, 2012)

I am located in Michigan.

Not really concerned with exterior insulation. More concerned with insulating the interior of the basement walls for warmth and comfort.

Beepster, thats what I was thinking of doing as well. 1" XPS with batts in between the studs...I'm thinking the XPS (pink/blue) foam might help with any moisture from the cement walls, but I don't know if its needed. 

I've looked on owens corning and other sites and they suggest just using their basement insulation in between studs. They don't say anything about using the foam first. In fact from what I understand they recommend using the foam for unfinished non studded basement walls. 

I don't have any major water issues in my basement, but I do know that if that insulation got wet for some reason it would cause mold to grow in those batts of insulation. 

So if I do both, I use XPS between the stud wall and the basement wall, then unfaced insulation? If I do only the insulation between the stud walls, I use kraft faced insulation with the paper facing me? is that correct?

Trying to keep this project somewhat inexpensive, but will do the XPS foam as well if its necessary.


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## Beepster (Oct 19, 2009)

I don't have time to find the links, but GBR in WA has links to Building Sciences studies.

The foamboard isn't to keep water from leaking in from the outside. It is to keep moist interior air from condensing on the cooler concrete walls in the summer and collecting in the insulation.

No insulation against the concrete - bad idea.

B


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## Gary in WA (Mar 11, 2009)

" Do I need to do foam insulation on the outer walls before putting up the stud walls? Or can I just put up the stud walls and then insulate with standard basement insulation."------ The worst to the best; http://www.buildingscience.com/docu...merica-high-r-foundations-case-study-analysis

Notice the problems with each one until the foam board is thick enough to warm the wall cavity offsetting the the cold side from concrete wall. This will prevent condensation. Here are some guides on foam board thickness; Page #9: http://www.eere.energy.gov/buildings/building_america/pdfs/db/35017.pdf

Page #10: http://www.buildingscience.com/documents/reports/rr-0202-basement-insulation-systems

Read this and click on the links: http://www.buildingfoundation.umn.edu/FinalReportWWW/Chapter-5/5-optimum-main.htm

The heat savings; http://www.quadlock.com/technical_library/bulletins/R-ETRO_Value_of_Basement_Insulation.pdf

Lastly, you can/should figure your location requirements on design for "dew point": follow the links/charts: http://www.greenbuildingadvisor.com/blogs/dept/musings/are-dew-point-calculations-really-necessary

Gary


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## jdtox (Jan 9, 2012)

THanks for the Links. Very useful.

So best I can tell, my best/cost effective option is installing XPS on the walls first, then framing with fiberglass between the studs, then drywall.

I see that 1" XPS is good 2" is better. But see no reference to 1/2". Wouldn't the 1/2 be better than nothing at all? or just wasting money?

One last question is in the graphic for CASE 4 : 1” XPS, 2X4 WOOD FRAMED WALL WITH FIBREGLASS BATT in the building science document which is most likely what I will be doing....they show a polyethylene barrier on top of the fiberglass. 

Wouldn't just using fiberglass with a kraft faced moisture barrier be sufficient for between the studs instead of covering it all with plastic?


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## Windows on Wash (Aug 30, 2011)

jdtox said:


> THanks for the Links. Very useful.
> 
> So best I can tell, my best/cost effective option is installing XPS on the walls first, then framing with fiberglass between the studs, then drywall.
> 
> ...


see above.


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## eurovw89 (Feb 12, 2011)

sorry to highjack this thread...but I can not find the answer I am looking for.

I am doing this method http://www.buildingscience.com/docu...=resources/high-r-value-foundation-assemblies

But my problem is that I had to start my framing my studded wall 5'' away from concrete wall due to plumbing. So after installing the XPS insulation I will have a 3'' gap between the XPS and studs. What can I do to to fill that void. I have been looking all over and can not find anything.


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## Windows on Wash (Aug 30, 2011)

Batts or a blown in fiberglass or cellulose will be fine.

If you wet spray, it needs plenty of time to dry because it will not dry towards the block with the XPS.


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## Beepster (Oct 19, 2009)

eurovw89 said:


> sorry to highjack this thread...but I can not find the answer I am looking for.
> 
> I am doing this method http://www.buildingscience.com/docu...=resources/high-r-value-foundation-assemblies
> 
> But my problem is that I had to start my framing my studded wall 5'' away from concrete wall due to plumbing. So after installing the XPS insulation I will have a 3'' gap between the XPS and studs. What can I do to to fill that void. I have been looking all over and can not find anything.


What do you mean "due to plumbing"? Plumbing can be within the framed wall and put the insulation in around it.

B


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## eurovw89 (Feb 12, 2011)

Windows on Wash said:


> Batts or a blown in fiberglass or cellulose will be fine.
> 
> If you wet spray, it needs plenty of time to dry because it will not dry towards the block with the XPS.


What about the 3" void between the studs and xps


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## eurovw89 (Feb 12, 2011)

Beepster said:


> What do you mean "due to plumbing"? Plumbing can be within the framed wall and put the insulation in around it.
> 
> B


My plumbing is right against the concrete wall....2 - 3/4 copper lines spaced 2" on center. I didn't want to built a 2" bulkhead around the pipes so just framed straight down


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## Windows on Wash (Aug 30, 2011)

Fill it.

You might be a good candidate for something like a JM spider insulation. Filling voids like that with batts is a real PITB


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