Insulation, Radiant and Vapor Barriers - Vapor Barriers

I had a second floor addition built recently and put insulation between the second floor; floor joists with a vapor barrier up toward the second floor to assist with radiant floor heating. Now the first floor insulation was never removed so I have R19 insulation with the vapor barrier down toward the first floor and R30 insulation above that with the vapor barrier up toward the second floor. Am I in for future problems because of this? In researching this topic it appears as if i'm ok because the vapor barriers are toward the living spaces and not between the insulation. Is this correct?

Thanks
Gary

If I understand the ceiling of the 1st floor had insulation in it then you took the roof off and added a 2nd floor. The floor of the 2nd floor is just above the old 1st floor ceiling. If that is correct then it will not matter. For what it matters the insulation between the floors will not give you any benefit.

Vapor barriers are not an absolute value and there are also many different degrees. That is the reason you can legally have two barriers in the same wall/floor if the vapor transmission rates are sufficiently different.

As an example you can have a piece of plastic that is not classified as a "vapor barrier", but if it is one mil thicker it magically becomes a vapor barrier, but is still not as good a vapor barrier as one 5 or 10 mils thicker. That is an example of arbitratry classifying to put things in cute little "bins" to make the code enforcement easier (not better), but the code is just the worst you can build to and still be legal, but it is not necessarily the best way to do it.

Most materials are tested in labs using idealized samples. An example is the backed fiberglass where the backing material is legally a vapor barrier, but if not installed to prevent any air leakage around the seams, it can be worthless. The "pink panther" like to sell with mirrors because it is an easy gimmick and can be a false sense of security.

Similarly, a 10 mil poly vapor can be destroyed with a surface flaw, a couple of holes by accident or a purposeful slash.

Dick

The amount of moisture an object can hold before that moisture will condensate is influenced by temperature and is represented by Relative Humidity (RH%). Since the first and second floor are conditioned areas (heated) it is highly unlikely that "Dew Point Temperature" will ever be reached inside the insulation.

For your information, radiant heat moves in all directions the insulation is there to direct the heat towards the area it was designed for.

Vapour barriers are placed on the warm side of a wall or ceiling in areas where it is cold and on the outside where areas are hot and the inside of the home is cold.
The principal is that we create water vapour and that it will naturally migrate towards the nearest cold surface or area.
When that cold object is made of wood, paper, leather etc; the resulting condensation then tends to lead to mould and sometimes wood rot.
Having the vapour barrier inside the home will do little, except restrict the movement of water vapour upwards, its natural journey.
I do hope that you installed another vapour barrier under your new upstairs ceiling.

Airman you are correct, thats exactly the way it went. Perry I have not yet but will.
Thanks you all for your input.

Gary