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Add blowen insulation no vapor barrier 115yr old house

I have a 115 yr + 2 story old house. As a spring project I took up some of the double floor boards in the attic thinking I would check and if needed, add more insulation. I have joist 3x5, 24in space between the joists. The depth is 7” total, to the lathes and plaster with 1” of rock wool insulation all ready there.
1 My question is do I need to clean out the old insulations, then place a vapor barrier down in the cavities then blow in the new insulation ?
2 Do I need the vapor barrier? Or can I blow more insulation in what is all ready there?
3 I’m going to place 2x8 on its end on top of the existing joist to add heights to 14” thick of insulation. These 2x8 r going to be integrated into the existing timbers to add strength
Hoping that I don’t bow the 3x5 joist and knocking the plaster off the ceiling.

4 As well could I use vapor barrier paint in the rooms below on the ceilings instead of the vapor barrier in the attic?
Then place the double floor boards back over so I don’t lose the storage space.
Thanks for any info . Hamm8 , Nova Scotia

Timothy Miller
Re: Add blowen insulation no vapor barrier 115yr old house

Howdy, i would simply add blown in insullation on top of the rock wool. Since blown fiberglass tends not to compact what you add it to would be my first choice. Cellous would be # 2.

If your ceiling are plaster or drywall and painted you already have a good vapor barrier. There are paints that you can apply that are made to increase the vapor barrier aspect too.

Be sure not to cover any attic vents when adding additional insullation. You can baffel to isolate the vent space too.

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