Thanks, TB... here it is usually a non-liveable space as well, but I was somewhat confused (not unusual) by the reference to an "attic floor", since, here at least, there isn't actually a floor in the attic, rather the insulation is layed on the cieling of the room below. The joists, in other words, are exposed in the attic and the insulation is layed between and over those from the top.
Thanks, heathfield... I did mean the asphalt type "shingles" rather than any wood product like cedar...