Add Blown in Insulation to roof replacement

[yachi]

I'm having our roof re-shingled.  It's got so many valleys and transitions to flat roof sections that I don't dare DIY it.  But I thought it'd be a good time to insulate the attic from the rooftop, as it's only accessible from a bedroom closet, and the space under the flat roof sections might not be accessible at all.  The areas of the attic I can see have about 4" of loose Rockwool insulation, and out house is about 1650 square feet.  I got a quote for $6,200 to add 12" of blown in insulation.
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But I'm not sure we stand to save very much in heating costs.  I just looked and the last two years we've only spent $650 per year to heat it.  I the summer we spend about $66 to cool it.  We have a very efficient natural gas furnace we installed in 2011.

I'd do it if I thought we'd save $250 or more per year, but I don't see it happening.  What do you guys think?

[bacchi]

That's a crazy amount to put in only 12" of insulation.

How were they going to do it anyway? Pull up sheathing? Can you do it yourself a few days before the roofing crew arrives?

[nereo]

What climate zone are you in?
https://basc.pnnl.gov/images/iecc-climate-zone-map

In general I always recommend insulating the attic as much as possible after air-sealing as much as practical, and 4" of rockwool is woefully under insulated in almost all climates.  But I also agree with bacchi that $6200 is an insanely high quote for 12" of blown cellulose. Not sure what the square footage of your attic is (your home is 1650 ft2, but not sure if that's a single story).  I'd certainly get another quote, as the total cost to DIY would be under $2k in materials.



Also: you may qualify for the maximum Federal insulation tax credit of $1,200 for installing insulation (30% of the total cost up to $1,200).