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Old 11-01-2019, 06:39 PM   #1
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Continuous questions on insulation


So I once again have more questions dealing with insulation. I am working on my basement and I have started putting up the first step of insulation which is XPS foam board. While in my basement I saw my run joist currently has batt insulation just stuffed in there. When I was googling before I saw a lot of people putting XPS foam in there and spray foaming around it to make it better. I asked a contractor about it before and told me 1 I will see minimum effects and 2 he doesn’t recommend it because the house needs some breathing.

Now what are everyone’s thought on redoing the rim joist this way?

Next question is, I saw before a video on “ask this old house” where they insulated a guys basement just with 2” XPS and then use wooden fir strips going both horizontal and vertical to allow 1 for drywall and 2 to run wire. How would you determine if you can go this route instead of framing the basement? Or is that just a old school way that isn’t recommended?

My last question actually doesn’t deal with insulation, but I had a company come out and they scanned my basement and measured my humidity to be at a 83% which mold grows at 60%. They recommended a dehumidifier, obviously theirs at $1,800. I’m sure I can go to these big box stores to get one. Anyone recommend any brand?
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Old 11-01-2019, 07:05 PM   #2
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Re: Continuous questions on insulation


Houses do breath even the tight ones they breath in and out thru or around tar paper or house wrap. You do not want any breathing from inside to outside. So insulate and seal the rim. If you have a nice smooth foundation like a block wall you might do a foam board, the inside of our concrete foundations are not smooth enough to get a good contact and a smooth wall for drywall, so it is not an option.
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Old 11-01-2019, 10:14 PM   #3
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Re: Continuous questions on insulation


Here is a good article about insulating the rim joist in crawl spaces.

https://www.buildingscience.com/docu...and-codes/view

Just as an aside, my crawl space would get close to freezing and it always had me concerned because I have water lines running through it. I sealed off the two outside vents, one on each side, and used Owens Corning Foamular R10 foam insulation to seal the rim joists. Since I had a remote temperature probe down there before I did this, I knew that the temperatures were in the upper 30's / lower 40's for most of the winter, even with the vents closed. After the rim joist insulation job, the temps down there now stay around 62 degrees all year, summer and winter. The best part is that the hardwood floors above in the living room, dining room, and kitchen are no longer ice cold during the winter.
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Old 11-02-2019, 07:28 AM   #4
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Re: Continuous questions on insulation


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While in my basement I saw my run joist currently has batt insulation just stuffed in there. ?
Might not be best, but if it is done well, its probably not worth the trouble to change. Unfortunately, its not always done well, with a functional vapor barrier (such as my place).

Where I did some renovations, I put in 2 layers of XPS with a snug fit and acrylic caulk to air seal. Spray foam in a can is a total mess. Over the length of your wall, you possibly have at least one joint in the rim board --- that can be a real big air leaker.

Best practice that I have seen is to put rockwool insulation in front of the XPS, as a fire retarder. I didn't do it, but code normally requires an XX minute fire retarder over any XPS.

.
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Old 11-03-2019, 10:38 AM   #5
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Yea my batts were just stuff there and that’s it, no VB or anything. I think I’ll go out and get some 2” XPS caulk it, foam can (have a lot anyway) and put the rock wool up.

Now my focus is this humidity and finding a good unit at big box stores because idk if I want to cough up the 1,800 for commercial unit.
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Old 11-03-2019, 10:42 AM   #6
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Dave Sal: I like what you did with crawl space. My crawl space as well has two vents, now the one is covered because of outside paved steps but the other is wide open. I too was nervous about water lines so I installed those pipe heaters to each one and when winter comes I just flick the switch on to make sure no freezing. BUT I think I’m going to the XPS Route with rim joist in there as well. The insulation in my crawl space is horrible because the house was vacant for a little time and that’s where the mice and snakes came in. That issue got handled but the insulation do destroyed so the plain is to rip it down, do rim joist and then see if I should put insulation up as well.
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Old 11-03-2019, 12:33 PM   #7
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Re: Continuous questions on insulation


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Dave Sal: I like what you did with crawl space. My crawl space as well has two vents, now the one is covered because of outside paved steps but the other is wide open. I too was nervous about water lines so I installed those pipe heaters to each one and when winter comes I just flick the switch on to make sure no freezing. BUT I think Iím going to the XPS Route with rim joist in there as well. The insulation in my crawl space is horrible because the house was vacant for a little time and thatís where the mice and snakes came in. That issue got handled but the insulation do destroyed so the plain is to rip it down, do rim joist and then see if I should put insulation up as well.

My initial plan was to install fiberglass insulation between the crawl space and the living area. My crawl space has a concrete floor. I bought a bunch of rolls of fiberglass insulation and had them delivered, all ready to go. Then I started reading up on insulating crawl spaces and found the article from Building Science, among others, that addressed crawl space insulation. I went ahead and did the rim joists and found that it was unnecessary (and not advised) to add insulation above the crawl space. Glad I found that out before I went through the trouble of installing all that insulation. I decided to use it up in the attics instead, and brought the R values up there to about R60.
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Old 11-03-2019, 01:46 PM   #8
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Yea I just read that article so I’m going do rim joist and call it.

Let me ask one more dumb question (maybe dumb). I see a lot of post online of people putting insulation up then building the wall on that, I’m putting the insulation batts in between each stud for the wall, which is preceded? Or doesn’t matter?
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Old 11-03-2019, 03:40 PM   #9
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Re: Continuous questions on insulation


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Yea my batts were just stuff there and thatís it, no VB or anything. I think Iíll go out and get some 2Ē XPS caulk it, foam can (have a lot anyway) and put the rock wool up.

Now my focus is this humidity and finding a good unit at big box stores because idk if I want to cough up the 1,800 for commercial unit.
There are no "good" ones at big box stores. if you look at the performance curves on any compressor based dehumidifier, they are all huge energy hogs under 70F operation. best bet is to eliminate as much moisture infiltration as possible and get a decent dehumidifier. if you want a dehumidifier that is "worth it" energy wise, look at the energy star website. the best ones are rated at 4.2L/kWh I believe.
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