Re: Insulate under exposed floor
Never Never put plastic on the bottom side of the insulation.
To add to jkirk's post ............ you can also apply rigid foam sheets to the underside of the joists to cover the insulation ..... this will increase the insulation performance by also preventing thermol bridging.
If varmits are an issue then nail or screw plywood or OSB over the foam.
There are particular construction adhesives that can be used for foam boards like the PL300 foam board adhesive....... whicever brand used just make sure it's safe for foam board.
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