Do I need plastic under drywall and/or wood panelling on walls with wood joists and wood exterior panels?

Question

I have a small room built against a trailer so not airtight (Exterior wall of trailer is part of the wall of the room). Want to put drywall and/or wood panelling on walls, ceiling will remain open to joists with a tarred roof. Used in BC summer only, no heat in winter. I wasn't planning on insulating so do I need the plastic barrier? What is the impact of not insulating and/or no plastic?

Answer 1

Don't use plastic, it can trap condensation moisture. Also it is a plus to glue the drywall to the studs and ceiling joists. You should insulate the ceiling even for summer only use. The space above the ceiling may get very hot from the sun.

Answer 2

If this is going to be a liveable space, then not so certain about not using plastic or leaving the ceiling open.  When you have an exterior wall, you should insulate and use plastic meant to serve as a "MOISTURE BARRIER".  You can find the proper stuff at your local home improvement store.  Insulation is really good especially in the summer as you will lose cool air if you have an air conditioner.  No insulation means miserable heat in that room.  When you insulate the ceiling you have to make sure you are not insulating up to the roof as there has to be air circulation.  Otherwise you could start a fire spontaneously.  The moisture barrier should be sealed completely around the room using "Tuck tape"  not duct tape.  The tape will seal all the edges and this includes the ceiling which should also have the barrier and slice the plastic and tape it back around the electrical outlets. Don't cut a hole as you will defeat the purpose of the moisture barrier.   For the floors, glue the plastic to the floor with an acoustical sealant which will expand and contract with the temperature.   The moisture barrier will prevent mold from growing due to the humidity and dampness of the spring and summer.  If this is just storage then put OSB panels on the walls and leave it at that.  OSB is cheaper than plywood and will serve the same purpose.

Answer 3

Whether you insulate (highly recommended) or not, without heat and cooling inside the room a vapor barrier on the inside would not be good. I would insulate with a faced insulation (the paper is a vapor barrier and would go to the inside). You should use a house wrap on the outside with or without insulation. The house wrap allows the wall to breathe. The moisture is expelled out and not allowed in from outside. If not insulating, and not heating and cooling you should NOT use drywall or finished paneling as the weather will cause expansion and contraction and will look like a garden rows, and drywall will absorb moisture and come apart and also mold will thrive in it.