Calculating value of insulation

[BlueCollar]

All,

I'm having trouble understanding this process. Between R "factors" and "ratings" it's enough to drive one to drink.

I've had fiberglass insulation added to my existing insulation in an effort to reduce the electric costs of heating my home during the winter and cooling it in the summer.

The original insulation in the attic was less than 3" of white blown fiberglass, so I had 17" added to bring it up to a uniform depth of 20". Additionally, I invested in having a radiant barrier coating sprayed on the inside of the attic ceiling.

Based upon what I have been able to deduce, 1" of blown fiberglass is worth a "value" of 2.3 - 2.7. If I average this at 2.5 per inch and multiply by 20 I come to a "value" of 50 which appears to be what is recommended by the various websites (D.O.E.).

Am I on the right track?

Thanks in advance.

[ConcernedCanuk]

1. Are you on the right track? - yup

.
.
.

regular bat insulation is approx r3 per inch - ergo 4" bats have a rating of r12

I DO hope you have a proper vapor barrier underneath all that insulation.

Vapor barrier was not used not all that long ago - makes a big difference on the effectiveness of the insulation.

[BlueCollar]

2. Thankyou...no vapor barrier

It isn't a standard practice here in Texas to put a vapor barrier on the ceiling itself.

The insulation is just blown in across the sheetrock.

The Radiant Barrier is a product called solashield that is sprayed on the inside of the attic designed to reduce heat in the attic itself.

The blown fibreglass insulation hopefully will reduce heat loss from inside the house during the winter, and reduce heat transfer into the house through the attic in the summer.

I'm keeping my fingers crossed...