Cold tile floor over unconditioned space

[Lee Kinser]

Our master bathroom is built directly over an unconditioned space, the back porch, and gets absolutely freezing in the winter with huge deltas between ambient interior temps and the floor temps. The builder originally did not insulate the space below the floor at all, but upon request they added R-30 insulation between the bottom of the floor and the PVC soffit ceiling of the porch.

Since this is still an issue, I'd like to take it a step farther and I'm looking for suggestions on how to best insulate this space. From looking around online, it would seem R-30 to completely fill the space and 2" foam board / sheathing under the joists to prevent bridging. Does this sound right? Is a moisture barrier also needed? Should the insulation be faced or unfaced? Should we use spray foam around the seams between foam boards, edges, and where the boards meet the joists?

And assuming all of that is accurate, any advice on how to reinstall soffit or switch to a wooden ceiling after this extra 2" of foam board is added?

Sorry for the bevvy of questions, just trying to fill in the gaps.

 

[Snoonyb]

Welcome.
Functionally, and architecturally, were it I, I would enclose and marginally condition the back porch so that merely opening and closing glazing creates an all-season space.

 

[Lee Kinser]

Welcome.
Functionally, and architecturally, were it I, I would enclose and marginally condition the back porch so that merely opening and closing glazing creates an all-season space.

I mean I certainly wouldn't mind doing that in the future, but that's a bit out of scope for the current effort.

 

[Snoonyb]

Actually, the least costly solution would be rugs or washable mats.

 

[bud16415]

Our master bathroom is built directly over an unconditioned space, the back porch, and gets absolutely freezing in the winter with huge deltas between ambient interior temps and the floor temps. The builder originally did not insulate the space below the floor at all, but upon request they added R-30 insulation between the bottom of the floor and the PVC soffit ceiling of the porch.

Since this is still an issue, I'd like to take it a step farther and I'm looking for suggestions on how to best insulate this space. From looking around online, it would seem R-30 to completely fill the space and 2" foam board / sheathing under the joists to prevent bridging. Does this sound right? Is a moisture barrier also needed? Should the insulation be faced or unfaced? Should we use spray foam around the seams between foam boards, edges, and where the boards meet the joists?

And assuming all of that is accurate, any advice on how to reinstall soffit or switch to a wooden ceiling after this extra 2" of foam board is added?

Sorry for the bevvy of questions, just trying to fill in the gaps.

A few more questions. I don’t think you mentioned where you live, and what is an expected winter day temp might be. Where I live in NW PA it is not uncommon to hit –30f or even a bit colder. Being a bathroom where are the pressure and drain piping located, and has anything been done to heat them as required? What is the headroom on the porch below, is 2” the max you can add?



I am not a pro, but believe the vapor barrier should be against the bathroom subfloor and is likely in place with the first insulation job. I think I would remove the ceiling below and cover it with a layer of plywood first to make surface for attaching the foam and later the new porch ceiling. Two inches of foam will help but I would add a second layer reversing or overlapping the joints. I would also can spray the joints to get the best air seal I could. After I had that up I would strap the area with 1x3 furring strips with long screws into the plywood then put the original ceiling back up.



I bought an old place about 10 years ago that had a second floor bathroom over the kitchen so the floor was fine. It had two exterior walls that were pretty cold and a ceiling that had nothing and was oddly pitched in both direction. I had the whole house to redo and needed to do something with the ceiling to get going. I screwed up a layer of 2” insulating foam and it would take the contour bending both directions. I used the long screws with the 2” plastic washers that set themselves below flush. It took two sheets and foamed the joint. I skimmed the big screw holes with drywall mud and taped the joint like it was drywall, then painted it. It worked fantastic at warming the small room and looked good enough I still haven’t covered it with anything. I would have done two layers but the ceiling isn’t that high. So I stuck to one.