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Old 03-10-2016, 08:32 PM   #1
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How Should I Insulate Basement Walls that Were Studded Out?


Hello everyone! I bought a house in Upstate New York. The basement was all studded out, ready to be finished. Unfortunately, the previous owner didn't put up foam board behind the 2x6 studs. Instead, he hung R-13 Batts between the studs. Since I have space to fill, I was going to pull the R-13 and replace it with R21 Batts. I recently excavated part of the foundation and waterproofed it with rubber membrane and a polyethelene protection course, with tile drain along the footer, running to a dry well with a sump pump. I also backfilled with gravel from top to bottom. I will waterproof the rest of foundation the same way, but the tile drains will be pitched away from the house, so I will no longer need the drywell/pump setup. So technically, the foundation will be as waterproof as it gets from the outside. In addition, I plan on running a dehumidifier, as I will be finishing the basement. I will also treat all walls with Concrobium prior to insulating to prevent mold growth. Is switching out the R-13 to R21 the right move? Or, should I cut foam board to fit between the studs, then put R-13 on top of the board to get more R-value. Any suggestions would be appreciated.
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Old 03-11-2016, 07:12 AM   #2
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Are the studs tight to the walls?

Are you opposed to Spray Foam or are you wanting a Homeowner/DIY application only?
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Old 03-11-2016, 07:23 AM   #3
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Half of the basement has the studs tight to the wall, the other side is about 4 inches out, due to plumbing. Never thought about spray foam. How expensive is it? I'm going to spend about $1500 on R21. What are the benefits of spray foam? Thanks for the advice!
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Old 03-11-2016, 08:48 AM   #4
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Spray foam will be more.

Benefits are that it will serve as an air barrier, typically performs better in harsher climates, and it easier to get it done behind a wall that is already there.

I am not typically a fan of the SPF, but in a case like this, it seems to make sense.
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Old 03-11-2016, 09:59 AM   #5
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Can you detach the walls and slide them forward enough to get rigid foam back there? Well, you definitely can, but are you willing to? Just knock out a stud or two to get the rigid foam in there depending on what size you can get and then slide it down the wall and repeat. Use tape and spray foam to seal seams and top/bottom.

If there's pipe or tight wiring in the wall already it might take a little extra effort, but still doable.

Last edited by mikegp; 03-11-2016 at 10:02 AM.
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Old 03-11-2016, 10:18 AM   #6
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XPS behind the studs and then unfaced batt between the studs will get you a good R rating, plus it's a great choice to reduce any moisture or mildew concerns. Make sure you don't put in any plastic sheeting behind the walls!
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Old 03-11-2016, 10:46 AM   #7
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There is subflooring up to the studs, and the previous owner/contractor bolted the base of the studs to the concrete slab, so if I move the studs, I am basically starting all over. There is zero space behind the studs in half the basement. What is XPS? Also, I should avoid faced insulation with a vapor barrier no matter what?

Do I want a gap between the insulation and the wall, or do I want to fill the entire space? keeping in mind how I waterproofed the foundation. Thanks everyone!
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Old 03-11-2016, 10:50 AM   #8
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Another question. Can I use faced batts without the vapor barrier, or is unfaced the only way to go?
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Old 03-11-2016, 11:04 AM   #9
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XPS is extruded polystyrene, a type of foam board insulation that's better suited for an environment like a basement. You can buy it at any of the big box stores.

You are probably okay with faced batt insulation, but I would recommend unfaced. Using a vapor barrier is a no-no. Moisture will always find a way in and out of your basement, there's no way to make it 100% waterproof. So the trick is to minimize moisture intrusion, which you did. But what moisture does get through you should allow it a way to migrate. If you put up a vapor barrier, that will trap the moisture, and trapped moisture is where mold and mildew grow. I suggested unfaced batt cuz mold grows on organic surfaces like the paper facing on the batt. I actually bought faced batt that was on sale and gently peeled off the paper.

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Old 03-12-2016, 08:26 AM   #10
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Re: How Should I Insulate Basement Walls that Were Studded Out?


lets see pics. perhaps you could use a recip saw to trim the studs back from the wall.
but that would be a bit of work.
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Old 03-15-2016, 07:03 AM   #11
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Re: How Should I Insulate Basement Walls that Were Studded Out?


Fix'nit, that sounds like a good idea. I might do that, since I'll still have 4 inch studs to support sheetrock... If I go that route, 2 inch xps and then unfaced R13 on top of it?
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Old 03-16-2016, 10:43 PM   #12
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Re: How Should I Insulate Basement Walls that Were Studded Out?


Welcome to the forums!

Seems like a LOT of work, since you have the membrane/drainage on the exterior to stop any water/moisture from going to the inside. That is why one uses XPS, most don't have the water stopped outside or CMU walls with a lot of area exposed above grade. Foam board is the safest way, but have you looked at other options?

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Old 03-31-2016, 10:45 AM   #13
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Re: How Should I Insulate Basement Walls that Were Studded Out?


Gary, what else would you recommend? Should I just go with R-21 unfaced batts?
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Old 03-31-2016, 12:02 PM   #14
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Re: How Should I Insulate Basement Walls that Were Studded Out?


Try PM'ing him directly. He will probably get notification of that communication more quickly.
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Old 04-23-2016, 12:32 AM   #15
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Spray foam would be the best option in my opinion but it is not cheap, you get what you pay for. No gaps, no leaks, great to seal up rim joists, and adds rigidity to studs along with moister barrier. Expect to pay at least a $1 per square board foot. That's 12"x12" by 1" thick and you want at least 2" thick so $2 per sq ft. That's cheap imo but that's what I paid, had quoted as high as $6. Best of you I didn't do anything but cut a check, was done in a few hours.
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