Floor joist insulation

[Unregistered]

When it comes to insulating floor joist, do i have to use faced insulation or can i use unfaced? I ask because I got a good deal on some R-30 unfaced insulation and would like to use it to make my hardwood floors a little warmer.
Thanks

[Wgoodrich]

Better way to insulate under floor crawl space areas is to wrap the perimeter of the crawl space walls with 2" styrofoam pressed against the outside walls tight to each other cutting out for crawl space venting. Keep the cut outs for packing those crawl space vents in the winter time for added warmth.

If your crawl perimeter is already insulated as above then you also insulate your floors you are inviting your plumbing to freeze in the crawl space. Not really a good idea to insulate perimeter and floors.

Installing insulation in the floor is recognized by the Code. However the vapor barrier [that is what the paper backing on fiberglass insulation is] must be installed on the warm side against the floor decking not on the bottom side facing the crawl area. To install paper back insulation with the paper down traps moisture in teh insulation thus pulling the insulation down from teh floor joists making a real mess in the crawl with hanging insulation.

I suggest the perimeter styrofoam insulation on crawl walls as a better choice.

Good Luck

Wg

[Unregistered]

The house has a full basement not a crawl space. I was just wanting to know if unfaced insulation (no paper backing) can be used.

[Wgoodrich]

Basement requires insulation in one of three places but only with one vapor barrier if more than one place is with vapor barrier as required per Code.

Be aware if your basement was built per Code it was probably water proofed on the walls by a purging of tar or plastic being a vapor barrier. Then there was supposed to be plastic sheet installed under the basement floor also as a vapor barrier.

If those were installed then you should not install paper back in the floor of your home being ceiling of that basement or you trapped moisture again.

If insulation is being installed on the floor joists they should be nonpaper back style with a webbing holding the insulation in place allowing moisture to escape and not be trapped.

If your basement walls have been insulated then it would do little good to insulate the floor also. Most likely will make little difference with the basement already having an insulation envelope around it from outside elements.

If you have an older basement not insulated with no vapor barrier on the basement walls or under the floor then you are fine other than the paper must be on the warm side of that stud space not toward the basement. All vapor barrier is required to be on the warm side of an insulation envelope. If the basement is older and no insulation then insulating the floors will help. Either way I would install no paper or other form of vapor barrier rather install the friction nonvapor barrier fiberglass insulation using the webbing to help hold the insulation in teh floor joists stapling the webbing to the bottom of the floor joist edges like a netting holding in the nonpaper pack non vapor barrier type insulation in the floor joists.

Just my opnion

Wg

[Unregistered]

Yeah, you can use unfaced insulation. If it is cold in your basement then you may want to put a layer of plastic up too. That would serve as your vapor barrier.

[Wgoodrich]

If the basement was installed with a purging on the outside of the basement wall as required in wet locations then you DO NOT want to install a second vapor barrier inside or you are trapping moisture between the waterproofing on the ouside of the basement wall and the plastic on the inside of that basement wall. This would not be a good thing but an invite for hidden mold.

Good Luck

Wg

[Unregistered]

The original post talks about insulating floor joists not the basement wall. So, I dont think that applies.

[Wgoodrich]

Everything matters. Where there is an action there is a reaction. Concerning a basement if you install a vapor barrier on the walls per waterproofing material as IRC rules call for and under the slab floor as IRC calls for then in the floor joists also you just made a swimming pool of moisture trapped with no means of escape from that basement. Talking about mold!

The IRC concerning basements require the walls of that basement to be insulated either inside or outside on the walls. The IRC in wet locations required the basement walls to be with vapor barrier aka waterproofing. The IRC requires a vapor barrier to be installed under the floor of the basement concrete slab floor.

The above rules requires the entire sides and bottom of that basement to be with vapor barrier. If you install a vapor barrier on the bottom of that basement floor joist then you just made a nice plastic bag to store moisture with no means of escape. That was my concern.

Then again if you read the rules an insulation when insulating a floor joist for a crawl space the vapor barrier is to be installed on the warm side of that floor top not the cold side bottom. If it were a crawl space you have a choice to insulate the basement perimeter or floor joist installing the vapor barrier on the bottom of that crawl space but not on the sides per IRC rules. This does not apply here with a basment but trying to avoid confusion for others reading along with crawl spaces.

You may insulate the basement floor but no vapor barrier should be installed because the rest of that cubic area is with vapor barrier effectively trapping moisture in the entire area.

In a basement you do not have that choice under slab floor and walls require vapor barrier and waterproofing serving as vapor barrier. Basement rules differ from crawl rules.

You may insulate your floor over a basement but do not install vapor barrier if built to meet codes over the last 10 years. If this is an older basement without vapor barriers then it is different. Many older basements have no vapor barrier or insulation when originally built.