Plinth Area Calculation as per IS 3861-1966

The plinth area of a building is the total built-up area of all floors measured at the floor level including the thickness of the external walls. IS 3861-1966 is the Indian Standard Code for measurement of the plinth area of buildings. According to this code, certain areas should not be included while calculating the plinth area. Let's discuss each option and why option D is the correct answer.

a) Porches of non-cantilever type:
Porches are covered areas typically located at the entrance of a building. However, the porches of non-cantilever type should not be included in the calculation of the plinth area. This is because these areas are usually open from at least one side and are not considered as enclosed spaces. Therefore, they do not contribute to the built-up area of the building.

b) Area of barsati at terrace level:
Barsati refers to an additional floor or room constructed on the top of a building, usually at the terrace level. The area of barsati should be excluded while calculating the plinth area. This is because barsati is considered as an additional structure built on the terrace and is not included in the main built-up area of the building.

c) Area of walls at floor level:
The area of walls at floor level should be included in the calculation of the plinth area. Walls are an integral part of the building structure and contribute to the overall built-up area. Therefore, the area of walls at floor level should not be excluded.

d) Area of lofts:
Lofts are small elevated spaces within a room or building that are typically used for storage purposes. The area of lofts should not be included in the calculation of the plinth area. Lofts are not considered as habitable spaces and are usually not included in the built-up area of the building.

Conclusion:
Based on the guidelines provided by IS 3861-1966, the correct answer is option D - the area of lofts should not be included while calculating the plinth area of a building. The other options, including porches of non-cantilever type, area of barsati at terrace level, and area of walls at floor level, have different considerations and should be included or excluded based on the specific requirements and definitions provided by the code.