Insulating floor of former deck

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Old 10-11-18, 01:31 PM
J
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Insulating floor of former deck

I just moved into a home on the N.C. Coast about one mile from the ocean. There is a room that was a former covered deck. It is under the the main house roof trusses with an insulated ceiling. The previous owner had it closed in with insulated windows and a door. The floor was formerly a deck and now has outdoor carpet glued to the old deck boards with styrofoam insulation tucked between the floor joists. I have added a heat pump AC unit and intend to keep it open year around. Should I add another layer of styrofoam insulation in 4x8 sheets underneath, covering the joists as well? Today is windy and the carpet floats up as the wind blows indicating the poor floor insulation. I donít want to waste money but obviously this was not designed to be a four season room.
 
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Old 10-11-18, 02:32 PM
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I would start with air sealing, as you clearly do not have such at the moment.
 
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Old 10-12-18, 04:06 AM
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Addressing the high humidity

I am new to dealing with the excessive humidity in construction. My thought is to staple a plastic or Tyvek sheet to the bottom of the joists then add a 3-4Ē layer of rigid insulation to the bottom of the joists. Would this work or would it encourage mold to grow between the plastic and the rigid? Do I skip the plastic or just put it on last?
 
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Old 10-12-18, 06:58 AM
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Any vapor barrier should go to the warm side of the room, which I'm guessing would be the inside with as cold as it can get there in the winter. That said, I'm not sure what you're talking about when you say, "excessive humidity in construction" so I'm not exactly sure what problem you're trying to solve.

As I mentioned, my first thought is the wind you talk about lifting the carpet, which tells me airflow is the biggest current issue.
 
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Old 10-12-18, 07:14 AM
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Understanding how to deal with excessive humidity and build properly so as to not trap moisture within the wall or floor cavity. In dry and mostly cold environments like Colorado we put the vapor barrier in the inside. I understand in wet and hot environments like the N.C. coast I believe it is the reverse. So a foil backed polyisosyanurate foam may be my answer.
 
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Old 10-12-18, 09:16 AM
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Humidity of the climate has nothing to do with the vapor barrier. If - and I repeat - if you use a vapor barrier, it goes to the warm side.
 
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Old 10-12-18, 11:42 AM
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I have been reading about people putting the vapor barrier on the wrong side and trapping condensation in resulting in mold or rot. I understand in hot humid areas the barrier goes on the outside. Or warm side as you so succinctly put it. As usual, I have been overthinking it. Thanks
 
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