Laying the right foundation
Boulder-packed foundation is an easy and widely applicable solution
Crucial factor: Soil condition has its impact on the foundation
This is the third in the ‘Green Sense’ series focussing on topics that could help one follow some rules or get ideas for an eco-build. Getting ecologically conscious or bringing in sustainable architectural methodologies, the column speaks of green sensibilities and makes you contemplate on matters for your construction.
If you dig around the walls of your ancestral home, you may not see any foundation steps or size stones. If you enquire at most century-old villages of Karnataka, you may hear about foundations in laterite, bricks, stone slabs or even timber, with mud or lime mortars. If you check out Laurie Baker on websites, possibly you would come across the term ‘boulder-packed foundation’.
Foundation is the first action at site, but should be the last design decision. The first part we are aware of, but the latter part we never thought of. Surprised? We all know that the soil condition has its impact on the foundation, which the engineers attend to. Besides, the invisible foundation is influenced by all the visible parts of the building – if flat roofs behave one way, the sloping roofs demand a different approach. We may or may not need columns. How about curved roofs over large areas without any columns? When walls are not in one alignment, the foundation can be used to tie the walls. Foundations cannot be done only in one way, in standard sizes.
So, if we know what we are designing for, the foundation can be optimised. However, most Bangalore houses start with the standard trench 3’x3′ even before the design is finalised. We hope to save time by doing earth-work during designing, but waste resources by unwanted dimensions and avoidable locations. As such, most houses end up with over designed or the standard foundations, without considering the alternatives.
Boulder-packed foundation is an easy and widely applicable solution. It may not be safe to apply it in very loose soil or water-logged areas without expert advice, where boulder packing may have to be combined with soiling or plinth beam, as the case may demand. Once the foundation trench is dug as per size, place a levelling course of stone slabs or plain concrete at the bottom. Build up the foundation in courses of irregular stone boulders packed with sand and layers of only sand to the full width of trench up to the ground level. Then use undressed stone with external edge along the wall edge. Materials specific to the place can replace stone.
Most buildings built before the British stand on boulder-packed foundation, even today.