# Basement Insulation Questions



## mklein49 (Dec 31, 2012)

Hi Folks,

I'm a novice DIY'er in the process of finishing my basement. I've just passed my rough-in electrical and framing inspections and I'm ready for insulation. 

I live in St. Louis, MO. The foundation walls are 9 feet tall. The house is built into a hill and two of the four foundation walls are above grade. In addition the garage is essentially in the basement. I'm interested and insulating the following areas: in ceiling for sound, interior walls between garage and to-be finished basement area, interior walls surround the HVAC room, rim joist area, and finally the framed walls around the foundation walls.

I have a number of questions: 
1.What type of insulation should I use for the garage walls? Regular faced fiberglass batts?
2.In the ceiling, should I use fiberglass or a product mineral wool type product?
3.How is unfaced fiberglass batts held up in a wall?
4.For the rim joist, would sealing the seams with caulk and filling with fiberglass be acceptable? I'm concerned about the effort required to place rigid foam in the cavity with engineered floor joists.
5.Finally the tricky one...What to do for the exterior walls?
For the exterior walls, I strongly considered putting up the rigid foam board, but did not. I did leave an air gap of 1" +/- 1/2" between the framed and foundation wall. I also have areas unfished storage areas that will have foundation walls as a perimeter?

Long post I know, it could probably be simplified to asking what insulation type should I use for each part of my basement.


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## From a Buick 8 (Mar 3, 2014)

Very new to this and also starting a basement remodel. From what I have read (and this May be based on where you live) but it should be foam board against the basement wall, then the framing wall with fiberglass insulation in between the studs, then the drywall.


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## joecaption (Nov 30, 2011)

If you go to the search function there's at least 2, thousand post on just basements in the insulation forum.


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## Windows on Wash (Aug 30, 2011)

Joe made a funny.

But in all seriousness, there are a ton of posts with copious amounts of information from Gary, Joe, and others with everything you will need.


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## mklein49 (Dec 31, 2012)

Thanks guys. I've read so much and know the information is out there. I think I was looking for a shortcut. 

In any case, I think I've made a decision. I started adding Roxul ComfortBatt in the garage walls. That work is nearly complete. I plan to seal the sill plates with caulk as well as there was no sill sealer added when the wall was constructed. I'll use my left over Roxul Safe n'Sound from my fireblocking to stick in the HVAC walls and bathroom plumbing wall.

I plan to have spray foam added on the foundation walls and in the rim joist area. We'll add unfaced fiberglass batts to get up to the code required r13 for our area. Finally, fiberglass in the ceiling for sound dampening.

Hopefully, it all works out.


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## Windows on Wash (Aug 30, 2011)

Keep us posted on the progress.

I would look at rigid foam on the basement walls. Cheaper than SPF and will net better performance.

For sound isolation, you are going to need to uncouple the framing from the ceiling to make it work.


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## Gary in WA (Mar 11, 2009)

http://www.diychatroom.com/f103/seeking-suitability-dryright-insulation-basement-167895/

I hope you acquire a permit for this project. Cannot leave the 1" gap unblocked more than 10'; 

I would have used FB and left the wall cavities empty; http://energycode.pnl.gov/EnergyCodeReqs/index.jsp?state=Missouri

Or R-5 and cavity FG to stop all condensation you may now get with just Roxul (air permeable); http://www.homedepot.com/p/Owens-Co...sulating-Sheathing-36L/100320356?N=5yc1vZbaxx

Gary


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## mklein49 (Dec 31, 2012)

Gary in WA said:


> http://www.diychatroom.com/f103/seeking-suitability-dryright-insulation-basement-167895/
> 
> I hope you acquire a permit for this project. Cannot leave the 1" gap unblocked more than 10';
> 
> ...


So, I did acquire a permit and I have passed the framing inspection. He only required me to provide vertical fireblocking. I had no knowledge of fireblocking prior to the inspection. In any case, as the basement stands right now the air is free to move horizontally behind the walls for well more than 10'.

Would you recommend adding the additional blocking every 10'?

The airgap is not 1" in all places. It drops to around 1/4" in some places. Our foundation wall was being pushed in.

Is the spray foam approach a bad idea for what I have now?


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## Gary in WA (Mar 11, 2009)

SPF will fill any holes behind the wood studs. Some AHJ require fire-stopping per letter of the code, not allowing a flammable material (as fire-stop) behind the wood as the burn rate may be much faster, check locally.

SPF on the concrete wall now? I missed that.... which is why I said use R-5, actually R-2.5 is enough for your Zone 4 to prevent condensation in cavity- use cavity insulation to meet code minimum R-value (minus SPF R-value).
OR, if you meant SPF the rims, yes, go for it; http://www.buildingscience.com/documents/information-sheets/critical-seal-spray-foam-at-rim-joist

Gary
PS. FG fills the stud bay and stays supported by friction fit.


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## mklein49 (Dec 31, 2012)

Gary in WA said:


> SPF will fill any holes behind the wood studs. Some AHJ require fire-stopping per letter of the code, not allowing a flammable material (as fire-stop) behind the wood as the burn rate may be much faster, check locally.
> 
> SPF on the concrete wall now? I missed that.... which is why I said use R-5, actually R-2.5 is enough for your Zone 4 to prevent condensation in cavity- use cavity insulation to meet code minimum R-value (minus SPF R-value).
> OR, if you meant SPF the rims, yes, go for it; http://www.buildingscience.com/documents/information-sheets/critical-seal-spray-foam-at-rim-joist
> ...


It probably wasn't clear, because I changed plans throughout this thread. I've actually contracted a local insulation company to add SPF on the concrete wall and the rims. Finally, I'll add unfaced batts in the wall cavity to meet the code required r-13.


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## Chewbacka (Feb 27, 2014)

Meeting code is the MINIMUM requirement. If it were me and I had the space I'd use the best quality insulation and highest R value that I could fit in any space. Foamboard or similar, sprayfoam, for the rim joist area. It is it's own vapor barrier if closed cell. There's also the spray 2" then fill rest of a cavity with rockwool or similar, (flash & Batt).
I'm not a fan of fiberglass batt- it's old school and suffers from allowing air to pass through it which defeats much of the insulation quality other product shave over it. I wouldn't put fiberglass above the ceiling panels to deaden sound. It's likely not going to work, as mentioned to create sound deadening you have to isolate each material from the next with none touching each other.
High quality ceiling tiles like Owens Corning uses for it's Basement Finishing System would be a lot better, IMHO. I have a 1K sq' basement with their system in place. It works great for me.:yes::thumbsup:


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## Gary in WA (Mar 11, 2009)

Keep in mind; the more cavity insulation you add in front of the SPF/FB, the colder the inside face will be- making the FB less effective at controlling condensation by lowering the dew-point;Figs. 3,4; http://www.buildingscience.com/docu...ld-weather-condensation-using-insulation/view

Basements require about 1/2 the insulation above-grade areas do, due to the thermal/air buffering from the concrete wall. Code minimum below grade is fine- IMO, with surface temps the same as a couple of feet below grade (climate dependent) and 6' down 10-11*F warmer. The FB (code min. thickness) will slow the water vapor inbound, the cavity doesn't need/require filling with any insulation to allow the HVAC control the temp/moisture more effectively; http://www2.dupont.com/Tyvek_Weathe...rior Insulation Building Science Bulletin.pdf

Spend the saved money in the attic or other places that need it more than your basement... since code min. is R-10 SPF/XPS without additional cavity fill or mix-n-match as I said earlier. Remember to canned foam (fire-proof) the (wiring/plumbing) holes in all interior top plates and cover any plumbing stacks/holes around tubs, etc. 

Gary


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