Asked on Aug 12, 2018

How to insulate my plywood shed floor?

Magi Tomasic
by Magi Tomasic

I'm turning my 130 square foot tool shed into a small livable room and the floor is plywood on floor joists. It is on a hill, so the back is very close to the ground (too low to get under to insulate from the outside). I'd love some suggestions on how to insulate the floor from the inside. I have about 4 inches before the door won't close! Thanks to all ideas.



The walls have since been insulated and drywalled. But the floor is the same; plywood!

This pic shows the pitch of the yard under the shed. Even the front is only about 12 inches, then it gets lower from there back.

  5 answers
  • Patti Nicholas Patti Nicholas on Aug 12, 2018

    It’s difficult to imagine without a photo but simply using a wall to wall carpet (I’d use indoor/outdoor) would provide some insulation. The key is to use very good padding, even a double layer (one solid, one more open weave) of padding would provide a decent insulation. I’m curious though, could you not use a spray foam insulation on the exterior under the floor? Or even take up the plywood, lay insulation and put the plywood back in place.

  • Zard Pocleeb Zard Pocleeb on Aug 12, 2018

    There are insulation panels that you can buy. They are about an inch thick, but I don’t know what the ‘R’ value would be. Additionally, you would need to put another floor over the top of the insulation. Another possibility would be to pull up the plywood flooring and put in regular batt insulation. Since you are dealing with a small space the job wouldn’t be too bad.

  • Jeremy Hoffpauir Jeremy Hoffpauir on Aug 12, 2018

    Hi Magi, You can remove the plywood and use standard floor insulation batts. If this isn't an option, you can make a small hole in the plywood between the floor joists and use slow expanding spray foam. The foam expands to fill the space and there are many DIY kits and instructional videos on how to do this.

  • Pbl33829081 Pbl33829081 on Aug 13, 2018

    If you've got 4" of height clearance, I would consider creating another floor on top of the existing one. You can purchase foamboard insulation panels to insulate. 2" foamboard has an R10 insulating value. 1 1/2" foamboard is R7.5. The advantage of foamboard is that if you cut it to fit as tightly as you can, you can caulk it and it becomes it's own vapour barrier also. It is also impervious to moisture. Cheers.

  • Hope Williams Hope Williams on Aug 13, 2018

    Hi! We just did this to a deck turned sunroom. I’ll try to explain this the best I can.

    We removed all the top decking boards.

    The we rigged 4X8 treated plywood from the top and underneath, I went under and screwed the plywood into the floor joists. (2X8’s)

    the I ran 1X1 strips the circumference of each opening and used caulk and screws.

    Then I used block batting and laid it each cavity.

    Then we put 3/4 untreated plywood down as a subfloor.

    If this doesn’t make sense, I’ll help you in more detail if you need me to.

    o will say this, it is not complicated but some steps are a two person job.