Raised Floor- Insulation- Garage conversion

I have searched but do not see a best case answer for my application.

I have used pt lumber in contact with the concrete slab.
I am now at the insulation stage.

The floor was raised 18" above concrete, this created roughly 9" of open space between bottom of joist and concrete slab. And when its finished this area will have very little air flow. My question now is how to insulate install vapor barrier.

Should I put poly directly on the floor and than plastic wrapped insulation between the floor joists?

Should I try to get air movement by cutting in vent?

Floor sheathing will be 3/4 osb.

What is recommended?

 

Basically this space is just a crawl space under a living space. Choices are to make that space part of the conditioned space inside the house or make part of the outside. In VA you probably get a lot of humidity in the summer which eliminates venting it to the outside.

First you want to insulate the perimeter foundation wall with one or two inch rigid insulation and air seal and insulate the rim joist all the way around just like a basement house to foundation. Then install the plastic vapor barrier and lap up a foot or so and tape to the rigid insulation. Check local codes to see if the rigid insulation will need a fire rated covering. Then add a supply and return air vent to this space and possible passive vents to allow air movement when the fan is not running.

Read up on radon risks and test if needed. Attached is a link on crawlspaces.
BSI-009: New Light In Crawlspaces — Building Science Information

Bud

 

Thanks Bud that actually make perfect logical sense. .....and it never crossed my mind.