Totally open should be selected when the floor is high above the ground and there is very little to impede air movement under the floor. The modelling assumes outside air temperature under the floor. High set houses and upper floors of houses that protrude beyond the floor should use this option.
Very open and open assume little in the way of sides but require knowledge of height above ground. Very open would be used for a floor with an average height of 1.2 metres or less above the ground with no sides at all. Open is used where 1 or 2 sides are enclosed.
Enclosed requires the wall material and insulation level to be identified as well as the ventilation area. All sides must be enclosed with only small openings provided to maintain dry conditions under the house. The area of these openings must be entered.