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Adding insulation to a plywood floor attic

Posted on 10/26/25 at 8:39 pm
Posted by armsdealer
Member since Feb 2016
12280 posts
Posted on 10/26/25 at 8:39 pm
The previous owner lined the attic wall to wall with plywood or 2X material, it is nice to have all the space but lets be honest, I don't want to fill up basically the entirety of the house footprint with junk, what I do want to do is add some insulation, because everyone knows enough to fit in between the rafters is just not enough.

Everything is nailed down, I really don't want to undo any of it. I was considering just rolling fiberglass batt insulation over the harder to reach areas and then foamboard on top of the areas I still want to use for storage, which might be 25% of the space I have.

It is pretty wide open up there, I can get to every corner and insulating the attic ceiling would be easy, but I am not sure that is how things are done.
Posted by 9rocket
Member since Sep 2020
1657 posts
Posted on 10/26/25 at 10:46 pm to
I would use a blown-in insulation. Cut small holes in the decking where you need to.



Edit : anyone downvoting this either didn’t read the OP or lacks real-world experience. This is the way.
This post was edited on 10/27/25 at 6:35 pm
Posted by Tadey
Baton Rouge
Member since Aug 2012
662 posts
Posted on 10/27/25 at 8:57 am to
If you know for a fact that the cavities are full up to the plywood board i would thing this would be fine; otherwise, blowing in to fill would be first priority.
Posted by armsdealer
Member since Feb 2016
12280 posts
Posted on 10/27/25 at 9:06 pm to
quote:

If you know for a fact that the cavities are full up to the plywood board i would thing this would be fine; otherwise, blowing in to fill would be first priority.


It has batting rolled everywhere I can see.

I was thinking to blow half to 2/3's of the attic with blow insulation and then use foamboard over the rest with the reflective side up. I just don't want to cause any issues with moisture where it shouldn't be
Posted by Tadey
Baton Rouge
Member since Aug 2012
662 posts
Posted on 10/28/25 at 6:59 am to
I don't think you would cause moisture doing that at all. I think the moisture issues come up when you try to insulate the ceiling in the attic, but I digress. I am not an insulation expert.
Posted by Tadey
Baton Rouge
Member since Aug 2012
662 posts
Posted on 10/28/25 at 6:59 am to
delete
This post was edited on 10/28/25 at 7:00 am
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