May 4, 2012
Day 14: Foundation plan 

Excavation is more or less complete for load bearing walls now. Now that we know quality of the ground, I asked Ravi to explain plan to reach the plinth level. Plinth level is the base level above which ground floor walls come up.

At a high-level there are four main areas:

1. Foundation masonry - Cement building blocks that are about 38cm tall, 15cm wide and 15cm deep are the foundation of the building. They are "stuck" together with cement concrete masonry. It is recommended that anti-termite treatment be done twice - once before placing any cement blocks and next after placing all layers of cement blocks. As Ravi says, they make this mixture with 1 part of cement, 4 part of sand, and 8 part of aggregate. They do a number of "layers" of such building blocks which together provide load bearing support. In our case, ground level at living room side is about 6 to 12 inches higher than that on the guest bedroom side. Hence, they'd do more layers at latter so plinth beam will be at even level. 
2. Rain water tank - Bangalore outskirts have water shortages.. As you see from our plan we have decent size garden and we didn't want to feel guilty of over-burdening already acute supply of water. Hence, we decided to go with what seems like a good size rainwater (RWH) tank - 60,000 litres. My calculation for 60,000 was as follows:
• Our monthly usage for a family of four is about 25,000 litres each month (~200 litres per person per day). Out of this, my guess is about 10,000 litres is used for gardening and 5,000 for bathroom usage. Those are the obvious low-hanging applications for RWH water. 
• Bangalore gets about 1000mm rainfall each year with raingods showering in for all except four months (December to April) within a year. I wanted to have sufficient water to live through that period. Hence, we got the tank size to be about 60,000. For those interested, amount of rain that'd be accumulated is roughly calculated as - Accumulation area x Amount of rain. Our roof area is 180 square meter and September rainfall is 200mm. So, accumulation in September would be 180x200 = 36,000 litres. Chances are with this size RWH tank it may not overflow. But, in case, it does, there would be a recharge well to let overflown water seep back into the ground.
3. Columns - Four columns need a bit of special work to get set up. They would essentially setup iron columns in those areas and put concrete around them. Once columns come up to the plinth level, they would be connected to the rest of the house via plinth beam. 
4. Plinth beam - Foundation around load bearing walls will be done first followed by columns and finally by RWH tank structure. Once each component is built they will be joined together through plinth beam. Our expectation is plinth beam will be about 2.5 feet above the natural ground level. This so as to keep house safe from flooding as well as provide appropriate elevation. 

General expectation is foundation level will be reached within 6-8 weeks from start. However, this doesn't consider construction of RWH tank. With that, we should expect 10-12 weeks, first fortnight of July, to complete plinth level and start the ground floor construction.