Sign In to join the community | Help
Install & Replace

Home addition, choosing the correct insulation (faced/unfaced) width for R-38 in cieling

I have had an addition added to the house over the garage.  It is a bedroom.  The floor joists are 12 inches on center, and are 2x10's and require R-30.  So I plan to use fiberglass 9 1/2 inch R-30 insulation... but Home Depot only offers R-30 in 24 inch widths.  Understand I may need to cut the 24 inch product to fit, can you confirm.


Also I believe I would use faced insulation, and install the insulation from underneath with the facing faced into the room.  Correct?  So, the facing is put in first and abutts the bottom side of the floor.


Next I am struggling with the cieling/attic.  The framing is 2x8 on 16" OC.  The code requires R-38.  The only R-38 HD offers is 24/23 inches wide... This will also be "faced" insulation, correct?  With the facing faced down into the room.  I really do not want to cut all this insulation... and wouldnot have the staple tab on one side due to having to cut it off to fit the 24 " into the 16 OC space. 


Alternatively I thought I would install R-30 which I can purchase faced for 16 OC framing... and then install R-13 perpendicular to the cieling joist/R/30 insulation to reduce the spaces where heat could escape. 


I believe the R-13 laid on top of the R-30 perpendicular should be unfaced.  Can you confirm that.


I am unable to find unfaced R-13 in the online choices... my preference would be for a "roll" verses batts... and I would like in in 23/24" widths as I do not have to be between any framing it would be less work to roll out wider pieces... and fewer potential gaps for heat to leak. 


I can only find unfaced R19 insulationn in rolls...


Can you verify that I would use faced insulation for the R-30 in the attic, facinf faced down into the room or do I use unfaced?


Can you verify that I use unfaced to lay over the R-30 in the attic and the additoion of the R-30 and the R-13 or R-19 is R-43 or R-49 respectively?


Thanks... I would like to purchase the insulation this afternoon... so I would appreciate a quick response if possible.



Not what you were looking for ? Try posting a question
Posted 2010-11-18T14:36:40+0000  by baustin56 baustin56

Hey Baustin56,

I am Gregg from The Home Depot in Chicago and we love our insulation here. These are all really good questions. Just to make sure we are on the same page you have a garage with a room above it and that room has an attic above it, correct? You are going to insulate the ceiling of the garage and you are going to insulate the attic floor, correct?


The paper on the kraft-faced insulation acts as a vapor barrier and vapor barriers should always be installed on the warm side of the wall. If you want to use a faced insulation then you would put the paper toward the room, but it won’t be extremely beneficial in your case. Is your garage heated? Are you going to put drywall up on the ceiling of the garage, or leave it open? I would use an un-faced insulation on the ceiling in the garage. This way you would just stick the insulation into place and drywall over it. You will have to cut the insulation to fit in between the joists, around pipes, and ducts, but try not to leave any gaps. If you don’t plan on putting up drywall on the garage ceiling then you can use 1”x2” furring strips perpendicular to the joists to ensure the un-faced insulation is held in place.   


The insulation for the attic floor should be un-faced insulation. The way you were planning on installing the attic insulation is the correct way. Fill in between the joists and then the second layer will be laid perpendicular over the joists using un-faced insulation for both layers.  

Let me know if this answers all your questions, and don’t forget to wear long sleeves, gloves, hat, and safety glasses.

Posted 2010-11-18T15:41:49+0000  by gotogregg
Not what you were looking for ? Try posting a question