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Three-seasons room floor insulation

Osborn_Cox | Posted in General Questions on

I have searched the Q & A’s and read several different articles and the more I read, the more confused I seem to be getting.    Here is my situation:   I live in zone 6 and have an existing 12’x12’ section of my raised deck that has a roof over it.   The deck is 8-9’ above ground level and the covered section has a concrete patio below it and is constructed with 2×10’s.     I am having the covered section converted to a 3 seasons room, with insulated walls and glass.  In preparation for the room addition I will be removing the existing deck boards and replacing it with 3/4” plywood subfloor and insulating the floor.     At this point it is not my intention to heat/cool this room but I want to leave that as possible phase 2 as well as extending the spring and fall season as much as possible.    My plan for insulating the floor is as follows, starting from the 3/4” plywood, then 1.5” rigid foam between joists with canned foam to fill any gaps around that, followed by batt insulation, followed by 1” of 4’x8’ sheets of rigid foam across the bottom of the joists, and then capped off with 3/8” LP smart soffit, to make a nice ceiling appearance for the patio below.     Does this plan sound reasonable?     Some of the things I’ve read have suggested that the foam board against the subfloor would be unnecessary.    Thanks for any input you can offer.

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Replies

  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Osborn,

    You don't need rigid foam insulation against the subfloor, but whatever insulation you install in the joist cavities does need to be in contact with the subfloor to be effective. The continuous insulation attached to the bottom of the joists will give you a good opportunity to air seal the assembly, which is also very important. Check out this FHB article for more info: How to Insulate a Cold Floor

    1. Osborn_Cox | | #2

      Thanks, that is the article that I used as the model for my plan, specifically the cantilevered floor detail, which I felt was closest to my situation. If I were to use just batt insulation between the joists, understanding that I am supposed to avoid compressing it, what is the best method for keeping it tight to the subfloor, or is it acceptable to use 10” thick insulation in a 9 1/4” cavity to provide some upward pressure on the batts?

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