According to Vastu Shastra, the Site slope affects the design of the house and the flow of the run-off around the house. Vaastu lays down guidelines to aid you in the Selection of a Site with the ideal ‘Slope’.
Since Vastu is a science, every guideline is based on logic and reasoning. As an Architect, I have attempted to explain these guidelines rationally and scientifically, so that you can decide what you want to follow and what you don’t, instead of blindly following them like a superstition.
The North-East corner should be the lowest and the South-West corner should be the highest: The Logic- This ensures the unobstructed flow of light and solar energy from the North-East corner (morning light and constant light) into the house. Also, when the South-West corner is higher than the North-East corner, it serves as a buffer (to the West and South-West sunrays) and prevents the heating up of the rest of the house.
Avoid plots with a depressed or raised centre: Avoid plots humped at the center and sloping on all sides. Similarly avoid plots that are depressed at the center. The Logic- If the center is either too depressed or humped, it is difficult and expensive to level the site as it may even have rock below, which will have to be blasted out.
The road level should be lower than the Site: The Logic- Normally there is a storm water drain between the Site and the road, so when there is heavy rainfall, even if the drain overflows, the excess water will flow onto the road instead of the site. Also, all the excess water from the site will flow out into the drain and road instead of vice-versa.
In cities, it is difficult to get sites that meet the requirements of Vastu. However, there are ways of correcting sites that are not in accordance with Vastu.
Plot sloping down from the North-East: The Solution- If the North-East corner is at a higher elevation than other sides of the property, you can dig soil from that corner and dump it in the South and West portions. This way the land will slope down from the South-West toward the North-East.
Plot with a raised/humped centre: The Solution- If the plot is raised in the centre then, the earth can be dug out and dumped towards the South-West of the plot.
Plot with a depressed centre: The Solution- If the plot is depressed in the centre, then earth can be dug out from the rest of the Site and filled in the centre to balance out the levels.