vapor barrier?

[doug barr]

Turning my garage to a workshop. It has been tyvek wrapped and a layer of 3/4 pink insulation put on and then the siding. I want to insulate the walls, ceiling and floor. It will be heated and a/c. I will be putting down a wood floor with PT sleepers, pink insulation in between and 3/4 ply on top. I have heard so many stories about vapor barriers and where to put them. Do I lay 6mm plastic on cement floor and then sleepers,insulation and then ply or do I lay down the sleepers and insulation then plastic then ply? I have seen both ways talked about. What about the walls? I will be using fiberglass batt (can not afford spray foam so not an option) do I buy faced fiberglass insulation or not? Do I put faced/unfaced in the walls and ceiling and then cover with 6mm plastic before sheetrock. I want to do this so there will not be any moisture problems. Thanks for your help. Doug

[Dave Wagner]

I believe the vapor barrier is always towards the living area, you don't want the conditioned air (moisture) getting into the insulation.

I use the paper faced batting on my walls, and I do have Tyvek on the outside. Just make sure you have good ventilation in the attic part of the garage to help pull any moisture that may migrate up.

AS for the floor, I have heard both ways also. I would also paint it for a moisture proof barrier. I would think putting the plastic down first would help keep the moisture from the concrete from migrating anywhere.

Is your garage floor insulated on the sides to the outside? Block/Slab construction or floating slab? There are certain installations if the space was going to be heated, so you don't get the coldness migrating into the slab.

[Bruce Wrenn]

You didn't post where you are located, and that could make a difference. Vapor barrier is to prevent the transmission of vapor. On the floor, you don't want moisture from below coming up through insl. and floor, so vapor barrier goes on the bottom. Because the floor in your garage most likely slopes towards the door, you may want to build a "floor system" ( joists and plywood) that is level. This will be your only chance. Anything you attach to the floor (sleepers, or bottom plates) should be treated.I strongly recommend the use of screws, rather than powder actuated nails. You won't leave a crater when removing screws. On the walls, VB goes on the inside, and same for ceiling. But if you live in south Florida, the rules are different. VB goes on the outside on walls.

[Rob Fisher]

You didn't post where you are located, and that could make a difference...On the walls, VB goes on the inside, and same for ceiling. But if you live in south Florida, the rules are different. VB goes on the outside on walls.

Location, location, location. As Bruce is alluding to, where you live will play the biggest part on where your vapor barrier goes.

On walls the vapor barrier typically goes on the warm side. The gray area occurs where you heat for a good portion of the year and then cool for a good portion of the year, which side is the hot side? Well in those locations (typically somewhere in VA to somewhere in PA, for the east coast at least) vapor permeable barriers (tyvek is an example) are typically installed on the outside of the wall, just beneath the finish (ie between the siding and exterior sheathing).

On the floor you are trying to prevent any water and/or water vapor from coming up through the slab so I would place the vapor barrier directly on the slab. Then build up the floor accordingly. Remember that any fasteners you put into the slab after the vapor barrier is down will put a hole in it and reduce its effectiveness.

If you have any further ??? feel free to ask.

Rob

[doug barr]

Thanks guys I live in new youk city

[Rob Fisher]

Thanks guys I live in new youk city

The existing Tyvek and 3/4" pink insulation board ( I assume its XPS) are acting as a vapor barrier (and air barrier if the insulation board joints are taped). In light of that I would not add a poly barrier on the inside as your vapor barrier is already covered. You could use faced or unfaced batts in the walls. I would use faced on the ceiling as I assume there is no other vapor barrier on the ceiling, and typically the vapor barrier should be continious from walls to ceiling.

This is unfortunately not an easy subject.

Rob