Cellulose, when installed properly, doesn't settle either.
that depends on how leaky it is now. but if there are leaks, and there usually is. sealing will make a LARGE difference. probably not so much in the comfort of the spaces. but in the comfort of the money in your wallet.How important is it to seal the attic? Another company suggested I seal the attic for $1700 in addition to blowing insulation. As a landlord, I'm not sure if this is going to be cost effective for me.