We have a room projecting above our front door, with a concrete floor and 0.24m below that wooden rafters (if that is the right term, horizontal, 7 cm × 5 cm) beneath which a wooden roof (2.3m × 1.7m) is fixed, forming a small covered but not enclosed area in front of the door. The room above gets cold, so I would like to insulate the floor1 and was thinking of filling the 0.24m gap with glass wool (in two layers of 0.12m). I see that small amounts of water have in the past penetrated this space2; do I need to take precautions against a build-up of moisture, or can I expect it to disperse naturally?
1 I make take other steps, but am here only concerned with how to insulate this space (which I have open anyway).
2 There is some staining of the wooden strips, but no significant damage.