I have put another 10" of insulation in my loft. It already had 8" with paper on the bottom of each batt. The new R30 batts also have paper on one side, this I put on top of the 8" with paper facing down. I have since found out the paper on the new batts will need cutting/holes made for venting. What should be the length of the cuts/holes ?

Don't think that's going to be your solution. Cutting vent holes is not going to allow for proper moisture movement. You can pull it out and try pulling the paper face off then reinstall. Pull it and go buy new attic insulation - unfaced. Pull it and rent a blown insulation machine and blow new in on top.. making sure you have baffles in place for the soffit vents

Sticky Sam follow Rivethead instructions 100% on either install!!
Good job Rivet head I tried to give you a AGREE but it said pass more around perfect solution to the problem!
Side note: Sticky I hope the second 9" "R" 30 wasn't on long. If it was take it off and let it air out some. You have a double vapor barrier that may have already dampened thee original and 5% of moisture in glass insul looses 95% of its properties. Just a heads up



Signed 21 Boat

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21 boat & Rivithead, ta for the advice. I have spent about $500 on the batts so I am not throwing them away. I guess I have to rip the paper off, I will put it down to experience.

21boat

I put the insulation in the loft last week, is that too long ?

Hard to say, How does it feel to the touch. If you wanted to be sure call an insulation company or someone that test for the moisture and has a meter reader. On the cheap end meters start around $200.00 of the better end $600.00 Delmhorst which is what we use. O would get it checked for piece of mind. 5% of moisture or more is a basic equivalent of putting an 18"X" of plastic on concrete and taping the sides and in 16hrs getting water droplets inside the plastic. It can dry out I'm not there feel is with your hand. The consolation in your case would be at the exposed surface. A simple test would be have a new piece of insul. Just laying loose and let that accumulate and touch that and then feel the insul that's already down and see if its different in dampness. Of course that would show up on the more extreme. A meter would be quick and accurate.
You should be all right if it is let to dry but the time is the question.
I'm just used to using the meter and its quick.
Signed 21 Boat

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The paper is coming off the batts easily without loosing much fiberglass insulation. I plan to insulate the loft walls with reflective ( on one side ) board. Can I use all this paper on the new board, if so which side ?

No - throw the paper out. Read the directions on whatever board you buy: the reflective foil is usually a vapour barrier, and you'll have to use special tape at the seams. If the board still needs vapour barrier, then I would still not reuse the kraft paper - there will just be too many seams.

This seems like a lot of effort for a loft. 18" ceiling and foam walls are far more than most would consider. Why so much insulation?

rtw-travel
According to local Government guidelines, R49 is required here. The 12" batts are R38 and 10" batts are R30. I am not sure what the original 8" R rating is? However the total of the two must be near R49 ? I also plan to fill the walls with spray in insulation. These American houses are nailed together by muppets, everything is cheap and nasty. They would be illegal in England ( where I am originally from ) I am just trying to make the house a decent place.