This may be a bit theoretical, but I am trying to figure out if the additional cost of foam board insulation and higher R value compared to fiberglass is economical and provides a good return on investment over time, ie by figuring savings in heating cost into the equation.
here the facts:
- I am looking to put new insulation into my attic roof
- The attice room will be used as liveable space
- I live in zone 1 as defined by the DOE - recommending R49
- 1 sq foot of R38 in fiberglass cost about 80 cents (before tax)
- the same insulation using foam Boards is about 3$
- the total roof is about 600 Square foot
here is the situation - if I have enough depth in my rafters I would go for fiberglass as it is more economical, however my rafters are only 6 inch deep to the roof
so I am trying to figure out, if I spend more money on the more expensive foam boards, I can achieve an higher R value and insulation, which over the years should save on my heating bill
How can I calculate the savings I will get with each R I increase, ie how much heating bill savings can I expect when I increase insulation by 1 R (assuming the formular is linear, I can calculate my return on investment for different thickness of foam baord as options)
hope this makes sense, I am sure this is not an exact science, but I am looking for some rough estimates to help me with the decisions....