Calculating the ROI of polyiso under siding vs. just doing PV instead
My pre-war Cape is getting more and more livable and less expensive to heat (I am about 1/4th the cost from when we dumped oil and got heatpumps). I got airsealing and attic blown in with cellulose last year by MassSave. They did dense pack rafters behind knee-walls and brought them into house thermal envelope, thought those areas of the roof are now unvented, so there is that.
In a couple of weeks, I am getting MassSave contractor again to densepack all empty walls with cellulose, so we are looking at what R1 walls turning into R12 or so? 2/3 of walls are empty in 3K sq ft house, so this should make a dent in my bills. Most windows are new too.
So now I am getting to the point where I am looking at my bevel cedar siding (likely original to the house) that has 4-5 coats of paint by now and peeling everywhere. I am wondering how many years I got left in it and at which point and what I want to do about it. I am also looking into PV, since I have ditched single-pipe steam and happily enjoy our heatpump minisplits.
Knowing I will have ~R12 in my walls, I want to figure out is it worth spending $$$ on 3″-4″ of PolyISO to triple the R value, when I redo the siding. Underlayment right now is T&G boards with felt paper over it.
For house like mine would be what about ~$20K in additional materials and labor, which is what 7kW PV system would cost after tax credits etc.
P.S. Is there easy to use energy modeling software for Mac out there fairly nerdy person, like me, can use without being building scientist?
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