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Discussion Starter · #1 · (Edited)
I have a few questions regarding insulation:

#1) I plan to put 1" XPS board insulation directly against a cinder block foundation/wall before studding out a finished basement. Is there any reason to glue/fasten it to the cinder block if it stays up just fine on its own?(as I said walls will be going up right after)

#2) In that same finished basement, I was planning to put Rockwool's safe and sound in the ceiling, however, it is cheaper to actually buy 2x6 R23 Rockwool. Is it OK to insulate the heated basement ceiling that is connect to the heated living area upstairs? Any downsides?

#3) The garage ceiling will also be insulated with Rockwool. Above the unheated garage are bedrooms. Should any type of barrier be used here, or will it just trap moisture?

#4) Our attic has full sheets of plywood down the middle. Pictures: ..and right now there is just 2x4 fiberglass insulation which is VERY under insulated for PA weather. I was think of switching this over to rockwool, but what is the best way to do it with the massive plywood there.


Thanks!
 

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Answers:

  1. If you are framing right away and it will stay up, not necessarily. You just need to make sure that it is totally air sealed at the seams so that air doesn't bypass it and condense on the block wall.
    1. Be sure to air seal the bandjoist areas before you frame everything up and close it off. Plenty of threads on here about that.
  2. No issues with insulation, but largely unnecessary unless you are going for some additional sound attenuation. That said, cavity insulation only gets to a small part of what is the sound attenuation mitigation strategy.
  3. You should have drywall or an otherwise thermal barrier here on that ceiling. Insulation is great, but you need drywall (fire rated at that).
  4. Are you using that for storage in the future? If not, loose fill and blow over it. Be sure to air seal first. Loose fill (cellulose) will be easier and work better.
 

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Discussion Starter · #3 ·
Answers:

  1. If you are framing right away and it will stay up, not necessarily. You just need to make sure that it is totally air sealed at the seams so that air doesn't bypass it and condense on the block wall.
    1. Be sure to air seal the bandjoist areas before you frame everything up and close it off. Plenty of threads on here about that.
  2. No issues with insulation, but largely unnecessary unless you are going for some additional sound attenuation. That said, cavity insulation only gets to a small part of what is the sound attenuation mitigation strategy.
  3. You should have drywall or an otherwise thermal barrier here on that ceiling. Insulation is great, but you need drywall (fire rated at that).
  4. Are you using that for storage in the future? If not, loose fill and blow over it. Be sure to air seal first. Loose fill (cellulose) will be easier and work better.

#1) Yep, will be taping all XPS seams. Do you tape the top and bottom as well?, does not seem like it would adhere well to concrete/block.

#2) Yeah the whole point was sound reduction. It will be a drop ceiling as well, so figured that was the best I could do.

#3) I really do not want to do drywall on the garage ceiling. What are some other products you recommend.

#4) Doubt it would ever be used for storage, temp fluctuates drastically. It is nice to have easy access. I avoided the cellulose because if it gets wet, its done.


Thanks for your help
 

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1. before you put of foam board put a 2x6 against the floor joist up tight to the sill that is on top of the block wall. That will give you fire stop between the wall and the floor system

Seal the top and bottom of the foam board with caulk or spray foam
Put sill gasket under your walls bottom plate even if you are using treated wood.

3. The subfloor above the garage is the VB but code says you need 5/8 fire rated drywall with some amount of tape and fill. So it i fire rated and sealed for auto off gasses.



4. before you add insulation to the attic the ceiling of the house needs to be sealed from above, Pipes wire and light fixtures all leak air and need to be sealed.

Then assess the air chutes, high and low vents so you will have a system that works.
 

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Discussion Starter · #5 ·
Put sill gasket under your walls bottom plate even if you are using treated wood.

3. The subfloor above the garage is the VB but code says you need 5/8 fire rated drywall with some amount of tape and fill. So it i fire rated and sealed for auto off gasses.

Then assess the air chutes, high and low vents so you will have a system that works.

I was not going to use a sill gasket, just treated lumber, good call, ill buy this: https://www.homedepot.com/p/Owens-C...ERCH=REC-_-pipsem-_-202080947-_-202084452-_-N

Well the garage hasnt been up to code for 40 years, not too concerned with it honestly, maybe if we actually used it to store our vehicles..haha

The attic has a lot of work, after removing the existing fiberglass, i need to seal, as you said and install roof vent/baffles to replace the fallen down cardboard ones.. still not 100% sure how i want to insulate it yet
 

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I was not going to use a sill gasket, just treated lumber, good call, ill buy this: https://www.homedepot.com/p/Owens-C...ERCH=REC-_-pipsem-_-202080947-_-202084452-_-N

Well the garage hasnt been up to code for 40 years, not too concerned with it honestly, maybe if we actually used it to store our vehicles..haha

The attic has a lot of work, after removing the existing fiberglass, i need to seal, as you said and install roof vent/baffles to replace the fallen down cardboard ones.. still not 100% sure how i want to insulate it yet

There isn't much you can do about leaks in the roof, that will be a problem for any insulation other than keeping the roofing in good shape.

We have a member here that we talked into sealing the ceiling and he did that before winter and he came back to say, he saved a pile on his heat bill and was now not sure he needed more insulation. So that is the best place to start. He just sealed and replaced the old until budget would allow more insulation.
You use treated lumber because water will wick to it thru concrete,
Sill gasket or sheet poly will just stop the water.
 

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#1) Yep, will be taping all XPS seams. Do you tape the top and bottom as well?, does not seem like it would adhere well to concrete/block.

#2) Yeah the whole point was sound reduction. It will be a drop ceiling as well, so figured that was the best I could do.

#3) I really do not want to do drywall on the garage ceiling. What are some other products you recommend.

#4) Doubt it would ever be used for storage, temp fluctuates drastically. It is nice to have easy access. I avoided the cellulose because if it gets wet, its done.


Thanks for your help
  1. You can foam it or seal it. Be sure to air seal the rims.
  2. Drop ceilings work well for noise.
  3. Gotta have it. Plywood would suffice if it meets the rating as well, but would cost you more.
  4. I would never pick an insulation on the basis of a roof leak. Cellulose is fine if it gets wet. It dries out just like anything else. it will be cheaper...and easier. Be sure to air seal like @Nealtw and I mentioned.
 

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Discussion Starter · #8 ·
@Nealtw
@Windows on Wash


Thanks for all your help so far.

If I dont want to use spray foam for air infiltration, are there any other viable options?

If I use spray foam, should I spring for the 2 component over just using the cans? If so, do you recommend any 200-600sqft kits?
 
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