Hello As time and money allows, I am replacing some really worn out 1962 windows with New Anderson 400series window! I mean new with the nailing flange! (I do not like more expensive Replacement Windows) No old sill left in and all the area between the house studs and window case is filled with ROXUL. The best Rock Wool for around windows and doors! Yes it is more tedious to push in Roxul with a putty knife than to spray that great stuff but the results are better!! Also more flexible and will NOT pull away from the old wood causing a crack for cold air to come in! See pics below So at 10 PM at night with the temperature inside at 71 Deg F and the Temp outside is at 32 Deg F. We did not turn the heat on yet! See the difference below between an old window and the new window on the same back side of the house!!