do i need to insulate basement?

Old 09-08-22, 08:45 AM
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do i need to insulate basement?

Live in NJ so it can get cold in winter. Framed out basement with 2x4's - The walls are a few inches away from the concrete. There was existing 1.5" foam insulation already glued to the walls. Do I need to put fiberglass insulation on the outside walls? I've read pros and cons regarding moisture. Thoughts?
Old 09-08-22, 10:36 AM
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The foam should provide a thermal break to inhibit condensation. A few inch gap to the studs is excessive but only causes your living space to be smaller. You can insulate between the studs if you like - fiberglass or mineral wool are fine.
Old 02-23-23, 12:31 PM
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I would but you don't have to. It will help with the climate down there and in New Jersey, like Mass, I assume it's going to get pretty cold down there in the winter so insulations would help. Maybe not much but it will help.
Old 02-23-23, 08:25 PM
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Be sure to airseal and insulate the rim joist area and house to foundation. Air leakage in that area is common.

Old 02-24-23, 02:36 AM
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Moisture issues in a basement are really rare. Basements are consistent 60 degrees, for moisture issues you would need very warm humid air which in a conditioned space really isn't going to happen.

Comfort is the key, if your using the basement then yes more insulation is needed. If just for storage, them maybe not but you already have framing done so why skip an easy step.
Old 02-24-23, 06:51 AM
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100% what Marq1 said. Insulation is a 1 to 2 hour job tops and not hard to do.
Old 02-24-23, 03:45 PM
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Basements may average 60F but basement walls are not, at least not in the winter in much of the USA. So the foam on your walls is good. 2" would be better, but it is what it is. Add insulation if you intend to finish the basement walls. You need to meet current codes requirements for R value, and your 1.5" is not enough.

Additionally, you could have fireblocked the perimeter prior to framing. If it wasn't done, fire blocking should now be installed to seal the space between the back of your top plate and your concrete wall. The top of the foam should usually be covered by the fire blocking... (easiest to do if the fireblocking is installed first, prior to installing the foam.)

You have local codes that can help you make good decisions on how you proceed so you might want to look into them.

Some general code requirements from the IRC are N 1101 - N1102. See table 1102.1.2 for minimum basement wall u values for your climate zone and table 1102.1.3 for minimum basement wall r values. See also N1102.4.1.1 regarding no use of class 1 vapor retarders below grade. (Kraft facing is a class ii vapor retarder.)

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