Insulating/moisture above living room

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Agduod22

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Hey all, new home buyer, so I am new to this forum. Sorry if I missed a similar article, but I am stumped. Half of my living room is under other living space like the master bedroom, the other half is not (exposed to outside air). A steel beam supports the floor above one side below living space, one side not. I will be insulating above the exposed ceiling with fiberglass, and adding a Durovent rafter vent between sheathing and insulation. My question is, what is the best way to insulate so the other side doesn't get cold air in the ceiling, and how to keep the air flowing as to not allow moisture to build, and mold to set in. I am thinking about putting foam board as a block from side to side with some holes in the board as to allow a bit of air to flow, but not to much.

Sorry, it's confusing, but any help would be great. Thanks
 
I would think blocking the gap with unfaced fiberglass would work if I'm understanding the situation right, but I'm not sure I am. Do you have photos of the area you're talking about?
 
If I have it right, you have a transition from floor to attic, it should have solid blocking with out any air movement.
 
Thanks for the quick reply.

I have done a little more research and you're right, I will definitely seal it off between sides. The ceiling joists above the side without living space above is only 5.5" (2x6's). It is unvented, and that same side is only about 180 square feet..maybe I'm worrying to much about it?

The picture shows the living room. The right side of the beam is below the master bedroom..left side is below walk out balcony that is off the bedroom (still has ceiling up in picture)

image.jpg
 
So above the beam all the space between floor joists should be filled with 2x6 sealed and insulated.
The deck today would be built a little different. It would have been built with the floor joists and then 2x4s on the flat going the other way for venting and some playing with the trim around the deck to look good but also allow air movement above the insulation. We also build them so they have a six inch step down from the door upstairs. Or in a house like yours we would raise the door and have a 6" step over.
 
Thanks for the input. Sounds like the best way to do it is to NOT leave space between the insulation and the sheathing..I'm just worried about condensation, moisture, mold, etc. if I had room above the sheathing, I'd lay down some foam board but unfortunately I don't.
 
The real fix would be to lower the ceiling under the deck to allow for everything you need. But if it has been that way for a long time with out a problem, may be you should leave well enough alone.
 
I thought about lowering the ceiling, but I'd have to lower it quite a bit, and with it being a living room, I'd rather not. There isn't any mold or wood rot on the sheathing or the joists, which lead me to think it will be ok. The previous owners had blown in insulation with paneling for the ceiling, no moisture barrier..
 
It is tar right now but come spring it is getting replaced, not sure what the contractor will use, I'm waiting to here back from him.
 
I’m no expert on insulation. What if you filled the bottom of the bays with strips cut from 4” thick foam board and sealed them in with can spray foam?

I had a similar situation in our second floor bath and the ceiling was curved and sloped in two directions with wood lath and plaster. I screwed up a 2 inch layer of the blue foam board and re-plastered it and the room is staying nice and warm.

I gather any foam board 2” or thicker is viewed as a vapor barrier.
 
We did one where the homeowner finished a bedroom under a cover deck, we removed the deck applied 2x4s across the joists, and raised the the glass slider door 1 1/2" and a raised box against the house for venting.
 
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