Basement ceiling insulation
I am interested in insulating my unfinished basement ceiling. The primary reason I would like to do this is so that I can have separate conditioned zones since the temperatures between floors are not consistent. The main floor is about 2200 sqft, as is the basement. Currently there are only 2 registers feeding the basement and no returns. I calculated that the heat loss between the main floor and basement via conduction is around 9,000 btu/hr (R-value of floor is 1) when the temperature difference between the main floor and basement is only about 4 degrees F which it is usually at least that. The heat pump for my main floor is only a 3-ton and has difficulties keeping up when the indoor/outdoor temperature is more than 45 degrees. Eventually I would like to add a separate conditioning system to the basement once I finish the basement, but for now I was thinking about using some Roxul safe-n-sound in the ceiling and that should significantly reduce the heat transfer from the main floor to the basement.
Please give me advice on whether or not this would work or where I am wrong.
Thanks
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Their is already R-10 insulation on the walls that are unfinished without any framing. The basement is a walkout with a bunch of full sized windows and two doors. Like I said, there is typically at least a 4 degree temp difference between the two floors and I would rather not heat 4400+ sq ft with a 3 ton unit b/c it does not seem to be able to handle it when it gets cold outside and I would rather it not use the aux heat. I just want to know the downsides of insulating the ceiling (like if there will be water vapor issues) or if my math is wrong and I really am not losing at least 30% of my heating load trying to heat the basement that is currently only used for storage and mechanicals.
Thanks
For zone isolation "contractor roll" R11s or R13s snugged up to the subfloor is enough. Even if adding the insulation turned it into a 20F difference between the basement and first floor (it probably won't be that much), it's hard to rationalize more than R13.
R10 continuous insulation only meets IRC2015 code minimum in zones 4A/B and lower. Zone 4C and up calls for R15.
https://up.codes/viewer/utah/irc-2015/chapter/11/re-energy-efficiency#N1102.1.2
Would you use faced or unfaced fiberglass as opposed to Roxul. How do they compare to each other for noise isolation as well. Any concerns with fire safety if I don't plan on sheetrocking anytime soon. Also, any concerns with vapor build up between the insulation and subfloor above it?
Thanks
Think cheap. Kraft faced fiberglass in long rolls is cheap, and will do the trick.
There's no "vapor buildup" when using insulation between two insulated spaces. If the basement is so cold that condensation would form on a true vapor barrier it means either your indoor humidity is ridiculously high, or your basement is so leaky that it's a freeze-risk.
For noise abatement you need to air seal the subfloor first, and install the batts as close as possible to the subfloor without compressing them or leaving large gaps (an 1/8" gap is fine.) A hard and air tight ceiling is also required (sheet rock.)
The better option is to insulate the walls. See this article for details: https://www.greenbuildingadvisor.com/blogs/dept/musings/how-insulate-basement-wall