Re: Attic kneewall insulation
To add to jkirk's post ...
First thing that comes to mind ---- what's under that flooring as far as insulation?
Originally Posted by kbaynes
Unless someone had previously filled the bays with suffient insulation before covering with the wood, there's a good chance there's not much insulation there to begin with.
As jkirk mentioned adding insulation on top of this floor with an air space underneath is not a good thing. There will be some benifit from the extra insulation though not as much without the air space underneath --- not giving you your biggest bang for the buck. If there is an air space between the 2 layers of insulation you will end up with moving air ( stack effect ) which reduces the performance of the insulation.
Secondly if there are pentrations from things like electrical ( ceiling fixtures in the rooms below ) and plumbing stack there will be warm humid air escaping into that void under the attic floor.
In order to achieve R40 you will need to have at least 12 inches thick of insulation , regardless of fiber glass or cellulose.
If it were me I would pull up the wood flooring in the attic space -- cover any electrial boxes for lights below with vapour barrier , seal any other penetrations , then fill the attic space with the insulation of choice.
If you need the space for storage then closed spray foam in the joist bays would provide the R value needed and still allow you to apply a floor covering --- if you have the $$$$ budget.
Forget about using faced batts all together since they will have potential for creating mold/mildew issues in the attic space --- use the unfaced batts.
If I go fiberglass, is R-49 appropriate, should it be paper backed and does the paper go on the floor or on top? I also assume I would not want to put a vapor barrier in, right, since that might create a mildew situation?
The issue with a vapour barrier in your case isn't much of a concern. Chances are there is are several coats of paint on the ceilings below that will retard pretty much any diffusion.
The issue would be more from air infiltration from below --- seal any and all pentrations to stop the warm moist air from below reaching the colder attic which will condensate. This one of the most important steps before adding insulation.
Hopefully this helps.
"" an ounce of perception -- a pound of obscure "