Is the purpose of the 2x8s to make the floor an equal height to the
interior? I would be more concerned about the suitability of the slab to
support the structure. Is there a suitable footer? If there is I would leave
the step down. Put pressure treated sleepers on the slab, rigid insulation
between the sleepers. I would not vent it to basement. I would make sure
that the grade will take away all water.
"TP" wrote in message
...
We have back porch built on a 4” concrete slab. I would like to enclose
it and make it a storage room. It has a 7” step down from the house floor.
I was thinking of just covering it with plastic 6mil, putting 2x8 (and
shims) across. Put some fiberglass (Upstate NY) insulation and nail
sub-floor, done.
Then I got wondering if I should vent it to my basement. What would be
the recommended way of raising this floor and avoiding rot?

Thanks
TP