The Insulation Doctor

 QUESTION FROM RON IN HOWELL, MICHIGAN: 

I have some blown in insulation already and would like to add to it.  I believe it is paper type.  I had ridge vents installed when I had the roof done, there are gables openings at both the north and south ends of the house. I 'm not sure if I need any type of duct system from the eave vents to the ridge vents. The house is 1800 sq feet and the living room has a cathedral celling The house is sided with foam board about 1 inch thick. 

CONTINUED QUESTION:
Yes it is a ranch.  How much additional insulation would you recommend?
There is about 300 sq. ft. of cathedral ceiling.  Yes there are vents in the overhang.  What advantage would it be to do the cathedral part of the ceiling?  Would the proper vents help to reduce ice build up in the gutters?

 ANSWER FROM THE INSULATION DOCTOR:
 I have a few questions for you about your home:
1.  Is your house a ranch?  I'm asking to find out if the 1800 sq. ft. is all attic space.
2.  How much of the sq. ft. is cathedral ceiling?
3.  Do you have overhangs on your home and, if you do, do they have vents in them?

CONTINUED ANSWER FROM THE INSULATION DOCTOR:
Assuming the insulation that is presently in your attic is blown-in cellulose (paper-type) and the original R-value was R-19, I would recommend adding an additional R-30 cellulose.  This will bring your attic insulation to the maximum of R-49 which is presently the point of diminishing return.
 
The primary factor in determining whether to do or not to do the cathedral ceiling is the accessibility, which cannot be determined until the crew is there.  If it is at all possible it would be very beneficial to insulate your cathedral ceiling.
 
Adding proper vents to your attic would alleviate to a very great degree the ice build-up in your gutters.  Depending on weather conditions, ice dams cannot ALWAYS be prevented such as freezing rain after or before a snow storm.  This is uncommon but does happen.