In my chart no planet is exalted or debilitated. How should I understand this for choosing a door?
There is nothing to read into it; not everyone has exalted or debilitated planets, and it is neither good nor bad. In such cases the door is chosen towards the direction in which the benefic planets sit, which was taken up in the evening astro-vastu class.
Related questions
In the example of the Sun in the 8th house, would an East entrance have suited if the Sun had been retrograde?
Possibly, but then its degree and the aspects on it, such as a benefic planet's aspect, would have to be checked. A house is built only once, so such a risk should not be taken. Retrograde (vakri) planets are taught later in the course.
Is choosing the door related to astrology?
Yes. With the person's astrology as the base, the door is chosen according to whom it will suit. The class covers three ways, by rashi, by exalted and debilitated planets in the birth chart, and by mulank, and the birth chart carries the most weight.
My Jupiter is exalted and my door is on N6-N7, towards the North-East, yet we have had no problems. Why?
The Ishaan (North-East) corner belongs to Jupiter, so people whose Jupiter is exalted can keep their door there. This shows how the birth chart decides which door suits a person.
My new flat's entry is on N4, but Mercury sits in the 8th house of my Mesh lagna chart, though not debilitated. Will using this door activate the 8th house?
Such a case has to be judged from the birth chart, so it was taken up as a special case study in the evening astro-vastu class. For this analysis only the lagna chart is used, not the navamsha, so only the lagna chart needs to be sent.
Saturn and Venus are in my 8th house in sign 8 (Scorpio); can I open a West door?
Saturn in the 8th is not bad. Here Saturn sits in a sign of Mars, and Mars with Saturn forbids the South, but the West door can be opened. Send the kundli for a closer look before opening it.
The kundli chart was shown with directions. How are those directions used, and what can a kundli tell about a house?
Go by the houses, not the numbers written in them: the top house is the 1st house (East) and the 4th house is North. If the planets on the North side are strong, the North direction is very good for the person. A kundli can even reveal where a person's house is, where its door is, how many windows it has and where a nearby river, pond or temple lies, so a map of the house can be drawn without seeing it.