As a corollary to my other question on insulating existing walls, I am also interested in insulating my floors. Right now, only about half of the 300 sq. ft. has its "final" flooring completed. We installed tongue-and-groove laminate over a light foam underlayment on top of the existing subfloor. Unfortunately, the floor is pretty cold. It's probably close to ambient + 10°F. Because we got a ridiculous quote on a mini-split, we plan to install either electric or hydronic (above subfloor) radiant heating, and I'd like to minimize heat loss to the crawlspace.

Things to know:

  1. There is currently no insulation at all, other than the underlayment we added (and that's not very insulative)
  2. The crawlspace is about 6" deep, making access nearly impossible
  3. The subfloor is made of 1x2 (actual dimension, this is old construction) planks, nailed into the floor joists
  4. I don't want to add too much on top of the existing subfloor because a hydronic radiant system will add ~1" to the floors already

I'm willing to consider ripping up the current floor, installing rigid insulation between joists, installing a new subfloor with radiant channels already underneath, etc. but I would really rather see if there is a better way.

EDIT: I just asked another question about radiant ceilings instead of floors, so I can also consider insulation above my subfloor, provided it doesn't add more than 1-2" maximum.

  • If you add insulation, do have crawl space vents or can you add them? If not, you'll have moisture and eventually rot.
    – Lee Sam
    Feb 23, 2017 at 6:42
  • My crawlspace is ventilated, or at least can easily be ventilated. The only problem with the crawlspace is that it only has ~6" of clearance.
    – Hari
    Feb 23, 2017 at 20:20
  • I understand, but if you insulate the floor, then moisture can build up without CROSS ventilation.
    – Lee Sam
    Feb 23, 2017 at 20:44
  • I get that. If necessary, we will add ventilation. I was simply mentioning that the only concern we have with the crawlspace is its size, not its ventilation or anything else.
    – Hari
    Feb 23, 2017 at 20:53

1 Answer 1


I'd have to go with #5 as the better way and only right way. If the partial new floor has to come up for radiant heating anyway, and it does, then I'd strip everything to the joists and do it right with screws. You'll be eternally quiet, solid and comfortable with the heating protected by the subfloor and reflected up by foil-faced insulation for maximum efficiency. Make it all pay you back.

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