-
Also, I’ve seen air bricks shaped like a periscope. The outside grille brick is higher that the inside vent, with a bent tube linking them.
They are used when the outside ground level is too high/has been raised higher than is should be, so let air down into the subfloor but doesn’t let the outside rainwater water in. It doesn’t solve the problem of a higher water table, but may buy you some ventilation. The subfloor must be ventilated, you can’t make it airtight, it will rot!