> My electric bill used to average $220/month on the level payment plan.
>> In the summer my AC would run constantly from 10:00 in the morning
>> until 8:00 in the evening without cutting off once. My AC wouldn?t
>> hold the temperature in the house (set at 74 in the summer 68/winter).
>> I had an open cell spray foam put in my attic in 2019 and my level
>> payment amount is now at $152/month and my AC not only holds the temp
>> I set it at, even in the hottest or coldest days the unit will cut
>> on/off in contrast to running all day. Open cell is well worth the
>> investment. My attic used to read as high as 130 in the summer, now it
>> doesn?t get more than 85 degrees in the summer and 65 in the winter. >>
A typical homemoanershub post on a 14 year old thread.
> A foot of properly installed fiberglass will do even better.
The base question is whether to add insulation under the roof deck when the attic floor is insulated and attic is ventilated. Well established principle is you add insulation to the floor, like "a foot of properly installed fiberglass". Original problem was ducts went through the attic that were allegedly not insulated. Obvious fix is to insulate the ducts.
Poster's attic may not be well ventilated.
> "Showing results for open cell foam insulation
> Search instead for open cell foan insulation
>
> Open Cell vs Closed Cell Foam: Which Should I Choose?
>
> Open cell foam is full of cells that aren't completely encapsulated. In
> other words, the cells are deliberatly left open. This makes the foam a >
> Is open cell foam a good insulator?
> R-Value. A foams R-value is its resistance to heat flow or, in other
> words, how well they insulate. ... Open cell foams have an R-value of
> around 3.5 per inch. This is significantly lower than closed cell foams,
> which can limit open cell insulations usefulness in extreme temperature
> conditions."
>
Don't know why the poster is pushing open cell foam.
Closed cell is also a vapor barrier. Open cell probably not.