Daylight, Heat & Wind: Building Science Beside the Texts
Some Vāstu rules can be checked against a measurement, and most cannot. This chapter is about the ones that can: where a rule of the texts has a building-science basis in heat gain, shade, drainage or ventilation, the reference says so and shows the figure. The rule corpus marks these class D. Everything else on these pages is what a text says or what a school practises, and is marked as such.
1. Heat and shade
Two rules of the texts meet a measured effect. In each, the text and the measurement are different statements: the text places a room, and the measurement says what heat a wall takes in.
Stores and utility rooms on the south-west and west
- What the text says
- Household stores and vessels in the south-west (Bṛhat Saṃhitā 52.116 in Kern's numbering, 53.118 in Sastri–Bhat; Matsya Purāṇa 256.34).
- What the measurement says
- In a warm or hot climate the south-west and west walls take among the most solar radiation (orientation factor 1.12 to 1.20), and the north walls the least (0.55 to 0.66). Eco-Niwas Samhita 2024, §9.8, Table 49.
- What follows for a plan
- A store, stair or utility room on a hot afternoon face keeps that heat from the rooms people live in. In a cold climate the same face is better given to a living room.
VASTU-STORE-001, class D
A verandah outside the house
- What the text says
- A verandah (vīthikā) a third as wide as the hall it fronts, in front, behind, at the sides or all round (Bṛhat Saṃhitā 52.20–21, Kern's numbering).
- What the measurement says
- A fixed projection lowers an opening's effective solar heat gain by its external shading factor. Eco-Niwas Samhita 2024, §9.9.
- What follows for a plan
- The verandah shades the wall and the openings behind it, and so cuts the heat they take in.
VASTU-VERANDAH-001, class D
2. Slope and drainage
- The Bṛhat Saṃhitā (52.113–115, Kern’s numbering; 53.115–117 in Sastri–Bhat) reads ground raised in the east or north as inauspicious. Whether its word vṛddhi means elevation or extension is itself disputed.
- The Mayamata (3.1 and 3.20) has the best site rise toward the south and west, with its water flowing east and north.
- The Bṛhat Saṃhitā’s slope by class of person (52.89) is inverted between Sastri–Bhat and Iyer, and the Kerala Manuṣyālaya Candrikā (1.19) names eight slope classes by the direction the land falls. The texts do not agree on a direction.
- What holds whichever direction a site falls: grade the ground so that rain runs away from the building and does not pool against it. That is drainage, and it is why the corpus records the slope rule as a located verse (class A) whose drainage consequence can be tested, not as building science.
3. Wind and the kitchen
The Bṛhat Saṃhitā (52.116), the Viśvakarma Prakāśa (2.94) and the Matsya Purāṇa (256.33–34) put the kitchen in the south-east; the corpus holds it as class A. Across much of India the summer monsoon blows from the south-west and the winter monsoon from the north-east, but the wind at a given site follows its terrain, and the engine does not read local wind. Where the prevailing wind allows, the sensible practice is to place high-temperature work so that flue gases and odours vent away from living spaces.
4. The direction of the head in sleep
The Bṛhat Saṃhitā (52.122 in Kern’s numbering; 53.124 in Sastri–Bhat) says not to sleep with the head to the north or the west, and traditional practice prefers the south or the east. The corpus holds this as class C: something measurement could test, and which has not been tested here. No mechanism is cited, and the reference claims no effect of sleeping one way or another on anyone’s health.
How every rule is graded is set out in the rule corpus. A statement about heat, light or air in a building is not medical advice, and none of this replaces it.