Can I place fiberglass batts over attic flooring?
Hi. I’m in the process of adding and replacing badly needed insulation to my un-conditioned attic. The floor joists are 2×4 16″ o.c. and there is existing 1/2″ ply on the floor in most of the attic (with just a few screws here and there) loosely laid down by the previous homeowner. I’m placing R15 batts between the joists and then R30 perpendicularly on top of those. Do I need to remove the existing plywood floor? Or can I just lay the R30 on top of the plywood that’s there? If I do that, will the plywood affect the effectiveness of the R30?
I’d like to keep the plywood there because if in case I need to walk around up there in the future it would be nice to have that there.
BTW, I’m also air sealing any holes or gaps I find while I’m at this.
Thanks to all in advance.
Replies
The plywood simply adds a tiny bit more insulation and an air barrier of sorts. It is perfectly fine to leave it there.
Yep, nothing at all wrong with leaving the plywood there, so long as you don't let it get in the way of a reasonably even application.
Air space = waste of space, heat and money.
For insulation to work, there must be no spaces for the heat to escape through.
If, the spaces between the joists and between the ceiling and the plywood are completely filled with insulation and there is no way that the wind can blow through the insulation, then yes, place the extra insulation above the plywood. If there are spaces, then your heat will escape; and will make the whole process a waste of time and money.
Keep in mind that the passing wind creates a very strong suction, pulling the air from your attic, and from your home. This warm air is replaced with cold air from outside. To make the proposed insulation work, it must be enclosed, holes let the warm air escape.
air sealing...
...how are you achieving the air sealing in your attic?
are you pulling up the plywood to access the ceiling penetrations that exist ?
i would suggest blowing cellulose over that plywood floor when your air sealing is completed.
it is a better insulation then fiberglass rolls and batts and really helps out with air sealing.
its also easier to install in an attic than fiberglass rolls and batts.