In my 1960's house, the attic has most of the original 3.5" thick rock wool insulation. It is double faced (so on top of the ceiling panel and facing outwards towards the attic). The ceiling joists are 2x8's and the roof has 2x6's. Why? It was built for a flat roof but it seems the roof was a modification to the original plans. We get a bit of snow each year, but right now, either because of the lack of good insulation or because of our high altitude sun, the snow melts fairly quickly off the roof (only about 15 deg pitched roof). It is a fairly dry environment here.
We are looking to improve the insulation in the house for comfort and reduced energy use consumption. ROI is not a huge concern though it certainly helps. My choices are:
1) R30 unfaced rolled out on top of the existing double faced original rock wool insulation
2) R38 faced down after pulling up existing rock wool insulation
3) Blow in foam
4) Insulate bottom of roof and close of ventilation
I listed this in my order of preference. Does anyone have their own recommendations? My thoughts/questions:
-Is it okay to roll out unfaced insulation on top of existing upward faced insulation or would I be better off pulling out the old insulation entirely? I am concerned about the double vapor barrier in between the ceiling and the attic.
-Is there any reason why blow in foam is better than rolling out some insulation? It seems blow in insulation requires a lot of prep work for ventilation, etc.
-I assume closing off the attic and insulating underneath the roof is probably not needed. We have no plans to open up the attic for anything.