Looking for some insight on proper insulation methods. We will be building a raised wood framed floor above an existing concrete slab garage floor. Converting the garage into a bedroom. The heat will be hydronic in floor radiant, we will have 9-10" from concrete to the top of sub floor.Current thoughts are EPS on the floor sealing all seams and perimeter W/ Roxul bats in the joist cavity then a layer of radiant under the sub floor.

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Matthew, if you use 2 lb EPS or 25psi in two layers staggered layers 4" overall then you can put a 2x4 flat for bearing. This allows for smaller joist while giving you R20 minimum. Then between the joist I would put any batt insulation but put a foil bubble foil product to reflect the heat upward with pex tubing. This will be the most efficient for least cost. The inability to staple upward to the subfloor is why I recommend the foil bubble foil. Also tape the seams. THE CLOSER to the subfloor with the foil the better.

I have done this before. We did not use hydronic heat or radiant barrier. We used all EPS foam leaving a small half inch gap between foam and wood framing to foam in w a can. Yes we cut and filled the whole framed cavity as well as a 2" EPS continuous taped under everything. 

Just make sure the EPS is highest PSI rated possible. Usually the 2" comes in the highest PSI rating. 

Pay attention to a vapor barrier. You will have one'ish the bottom so make sure the cavity can breath into conditioned space. So put the radiant barrier reflecting upward on top of the EPS. Like what Dave Taylor said. Dont sandwich the cavity w 2 vapor barriers.

Roxul is amazing stuff?

I ment Roxul is amazing stuff!

Thank you for your insight.

Proper insulation methods:

Blanket: Batt and Roll Insulation
Fiberglass Batt Insulation Characteristics
Concrete Block Insulation
Foam Board or Rigid Foam
Insulating Concrete Forms
Concrete Form Association.
Loose-Fill and Blown-In Insulation


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