Basement Finishing Insulation Question(s)

[cornfedkiller]

Partially finishing my basement - about 2/3 will be finished, the rest will be left unfinished for a gym and storage. House is 5 years old, exterior of concrete has waterproof tar. Rim joist was spray-foamed when the main story of the house was done. I've researched this ad nauseam and the only thing I'm sure of is that everyone has different opinions (even codes often contradict each other)..

The basement is currently framed and wired. Framing was held off the concrete 1". Was planning on using faced fiberglass batt insulation, but starting to wonder if that's the best idea. If I stick with batt insulation, should I use faced or unfaced? Manufacturer says faced for basement exterior walls. Poly vapor barrier or no? Tyvek behind the studs to keep the insulation away from the concrete?

I read/see a lot that foam board on the concrete and then framing against it is the best option, but most of the time at least 1.5" is suggested/required to be a proper air barrier. If foam board behind the studs is the best option, the studs could be taken down and foam slipped behind them, but 1" would be the only option since the top and bottom plates can't be moved (I know anything is possible, but it would basically be like starting over). I wasn't sure if 1" was even worth the time/cost.

They also mention how important it is to get a proper air seal, so I'm unsure what happens where my unfinished portion meets the finished portion?

Not interested in spray-foaming it due to the off-gassing inside our residence.

Climate zone 5, no local codes here. I'm less worried about R-value than I am about keeping it dry/mold-free.

 

[ben h]

https://buildingscience.com/sites/default/files/migrate/pdf/BSCInfo_511_Basement_Insulation.pdf

Building Science Corporation is probably the authority on this subject.

 

[huntinfool84]

When I finished my basement about 5-6 years ago, they made us remove the vapor barrier so the framing would not rot. Also we used faced insulation. I am in no way someone who knows anything about this, I just did what the inspector told us we needed to do.

 

[TaperPin]

As you are sorting out what to do, just keep in mind minimum code is not necessarily a best practice. Many techniques beyond minimum seem contradictory, but are actually better in some way. It can be confusing, even for contractors, to figure out what works well.

The principles to remember with basement finishing are to keep mice out, all basement walls no matter how well sealed outside will be giving off moisture, preventing moisture from condensing on cool surfaces is important, mold can only happen if organic material is in contact with high air moisture or liquid water, and folks from contractors, to inspectors, to architects, to well meaning organizations all have assumptions that limit how applicable what they are saying is to your unique house.

No small gaps in the wood can be left that would let a mouse enter behind the wall, from the sides, top, bottom or even through penetrations in the rim, or gaps between concrete and pressure treated plates. I’ve torn out many wall systems done by home owners and even contractors because mice started living and dying in the walls and there is no way to get the stink out short of starting over.

Best practices are often a rigid foam, or encapsulated batts. 1” of foam is usually all that’s needed to prevent condensation in region 5 and the rest can be fiberglass or whatever.

1” of foam on the concrete and no vapor barriers of any kind on the actual insulated wall or Sheetrock keeps moisture from condensing and allows the wall to breath and not buildup any damp spots. Earlier this year I tore into a basement with a mold problem on the surface of the sheet rock and 1” foam against concrete, and the foam in this 40 year old house had zero mold or evidence of condensation forming and dripping down on either side. All the moisture that caused the surface mold came from another source when the floor had standing water on it for a month or more. Even after that, there was no need to even replace the foam boards. That says a lot about how trouble free and durable that 1” of foam insulation is.

 

[Gseith]

I’m currently remodeling my family’s cabin. It’s all cinder block, similar to a basement. 35 years ago my father put up wood framing, using faced batt insulation, and a vapor barrier. Then covered it all with paneling.
I ripped it out this year and it was like a rain forest under the vapor barrier. There was a bunch of mold and rot.
I put styrofoam boards against the block and covered the walls with pine boards. I’m hoping it will allow it to breathe and allow the moisture out since there isn’t a vapor barrier. It sounded good in my mind.

 

[rogerdoger]

As stated, don’t use vapor barrier. If you are questioning the performance of fiberglass insulation on exterior basement wall then I would use rock wool, this does not mold and performs when wet (some use on exterior). You could use rigid but it’s a pane too cut for each bay, rigid r value is roughly 5 for every inch, but it’s expensive. Since your house is new you may have rigid on the exterior of the foundation. As a builder I have always used unfaced batts.