Home Improvement → Re: R-30 to R-38 in attic

Without seeing the Manual J for the house and $/BTUH for the OP, it is hard to put an exact $ number on the savings.

Generally, in a tight house, the conduction losses through the ceiling can be 30% of the energy budget for the house. So If he took the ceiling from an R 30 to R 45, he would save 10% of his total heating AND cooling cost for the house.

This could be worth $200/year. I would take a 40% return on my investment any day.

These are just typical/assumed numbers, your results will depend on the construction, energy costs and climate.

Most favorable (for savings) scenario: 8ft walls assume a 30x45ft house (1350sqft), that gives 1200sqft of R-13 walls and 1365sqft of ceiling with R-30.
Disregarding the higher losses of doors, windows, air leaks and even floor, the ceiling would represent 33% of losses. Increasing from R-30 to R-38 would save 7%.
However OP has stated the presence of cathedral ceilings and uninsulated floors - which means the actual savings would be significantly lower -> waste of money (at least for now). No need to patch a pinhole leak in a strainer...