Fireplace - Insulation

[Nzemke]

I'm in the process of converting the attached garage into living space and I'm going through and replacing all of the 1950's insulation with new insulation. I'm now doing around the back side of the fireplace and I'm uncertain as to if I can insulate certain portions of it. In the image below I have two inches between the fireplace and the stud designated with a '1'. From what I gather I don't want to insulate between that. Between '1' and '2' can I insulate and if so what kind of insulation is ok to use? Between '2' and '3' there was existing insulation that I will fill in.



Thanks ahead of time to anyone who takes the time to answer what may seem like a very simple question.

[hearthman]

Actually, you need a 4" clearance to combustibles off the rear of the masonry fireplace (IRC). This clearance cannot be packed with any kind of insulation but must be fireblocked vertically and firestopped at the ceiling per your building code. Typically, this is sheetmetal secured with masonry anchors and caulked with high temp. silicone.

Not sure I understand exactly what is happening with that masonry at #2&3. If that is the rear of the firebox then that is where your 4" clearance should be.

All that insulation must be sheathed over with drywall or similar wall sheathing per your code. In some areas, you may have to use 5/8" type 'x' fire rated drywall. Regardless, it must be sheathed. The vapor barrier does go towards the warm side of the room.

HTH

[Nzemke]

Thank you that makes a lot of sense and yes I will be putting up the drywall today but needed to find out if I could insulate that empty portion which you cleared up for me. Thanks again for the assistance.