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Old 09-26-2014, 10:05 AM   #16
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One good thing a previous owner did was replace all plumbing with copper and pvc, so I'm good there.

Does it really matter what thickness foam board I use? Any reason I couldn't use 1/2"? I just know they say not to compress fiberglass batts too much, since it's the air that insulates, not the fiberglass itself.

Josh
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Old 09-26-2014, 12:23 PM   #17
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1/2" is fine.
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Old 09-28-2014, 06:27 AM   #18
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Quote:
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One good thing a previous owner did was replace all plumbing with copper and pvc, so I'm good there.


Josh

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Old 09-30-2014, 07:53 AM   #19
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Couple more questions...

What should I use for caulk to seal around my foam board? Also, what's the suggested/best way to secure the foam board in the stud bay? And finally, once I put up the new batts, do I need to put up a plastic vapor barrier before I put up my drywall?

I kind of feel like I'm asking too many questions here, but I'd like to do this right the first time...

Thanks again, Josh.
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Old 09-30-2014, 05:11 PM   #20
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Answers:

- Any caulking or foam that is foam compliant (i.e. no VOCs). Standard Latex or Urethanes will typically work. If you have questions, do a test spot and make sure it doesn't melt the foam.

- As far as spacing the foam, rip the 1/2" foam or whatever air gap you are going to leave into strips. Use those strips to maintain the air gap. The foam can be back caulked on the spacing strips and just tacked into place with small (shallow) staples.

- You don't want to form a vapor trap and depending on the foam used, you will have a Class I, II, or III vapor retarder level there.

Gotta know what kind of foam you are going to use but in most cases, you will not need a vapor barrier on the insulation.

Use roxul anyway. Better stuff.
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Old 10-02-2014, 10:02 AM   #21
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I've done some more research and made a decision on what I'm going to do. I decided to use foil backed 1/2" rigid foam and I'm going to leave a 1/4" gap between the exterior wall and the foil face by cutting some spacers from a couple of 2x4 scraps I have around. Then, as we discussed, seal everything up with caulk and spray foam. And finally put up Roxul R-15 batts and drywall over that.

I'll also take the opportunity to bring all my wiring up to date while I have the walls opened up as well.

Thanks for the help everyone, I'll try to post pics as I go along.

Josh
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Old 10-02-2014, 07:39 PM   #22
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so, you are saying that you are going to put all that in a 2x4 stud bay ?
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Old 10-02-2014, 11:32 PM   #23
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Yes, I'm only 3/16" over the 4" (actual) depth of the stud bay... My 1/4" spacer, plus my rigid foam (actual measurement of 7/16"), plus my insulation meant for 3 1/2" deep studs. Am I missing something here?

Josh
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Old 10-03-2014, 08:40 AM   #24
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Might as well not use the foil face then as 1/2" gap is really not enough.

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Old 10-03-2014, 01:13 PM   #25
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Okay...i hope don't come off sounding like a jerk, but I'm confused. I said 1/4" gap, and windows on wash, who's been guiding me on this whole thing, said 1/2"... If it needs to be more than that, why was it brought up to begin with? I mentioned I was trying to fit all of this into a 4" deep stud bay, so I assumed we were talking about the best way to do that.

Maybe it's best if someone can explain the point of he gap and the foil faced foam. I know the gap is for air flow, but how much is enough?

Thanks.
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Old 10-03-2014, 01:41 PM   #26
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The gap from foil faced radiant barrier is not for "air flow" it is to have a dead air gap (though flowing air is better if possible) so that the radiant energy will not radiate into the living space. 1-1/2" is considered minimum for this.

The foil (radiant barrier) is commonly recommended for locations that have a warm climate more than locations that are not considered worm so as to reflect the radiant heat energy back outside.

I have not read all previous posts from everyone and you do not sound like a jerk.

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Old 10-03-2014, 05:40 PM   #27
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So am I still okay doing what I said above, only not using foil faced?

I'm starting to feel like there's no good way for me to do what I want to do here...

Josh
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Old 10-04-2014, 07:49 AM   #28
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Quote:
Originally Posted by Radcon91 View Post
Yes, I'm only 3/16" over the 4" (actual) depth of the stud bay... My 1/4" spacer, plus my rigid foam (actual measurement of 7/16"), plus my insulation meant for 3 1/2" deep studs. Am I missing something here?

Josh
i just want to let you know = DO NOT over stuff a bay with roxul, must be pretty much flush with the stud. otherwise you are going to have bulging drywall.
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Old 10-12-2014, 04:18 PM   #29
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So even my 3/16" over is going to cause a problem? At this point, it's either I go back to using fiberglass batts, (which I don't really want to do as everything I've read about Roxul sounds waaay better than fiberglass) and keep my air gap. Or, I get rid of the air gap and just put my rigid foam directly onto the exterior sheathing and seal it up. It sounds like what little air gap I can get is going to be pretty much useless anyway?

I'm right at the prime point to start this project since it's not too cold, but not too hot out to not have insulation for a couple of days while I do the demo work.

Any input is appreciated.

Josh
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Old 10-12-2014, 06:57 PM   #30
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Quote:
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So even my 3/16" over is going to cause a problem?
Josh
it doesn't need to be absolutely flush. but pretty close.
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