Rammed earth on the roof
There is no dearth of ideas in construction, only of implementation.
How many materials may we find in a typical urban home today from foundation to parapet walls, leaving out the interior finish? It could be half-a-dozen at the least, thanks to the manufacturing and supply chain. However, in the past, buildings would have had fewer materials, often with single material like the complete wood houses in Meghalaya, all stone houses of lower Himalayas or mud houses of Rajasthan.
Single material as an approach to building has been a major theory of architecture; as such, Taj Mahal in Agra or havelis in Jaisalmer are not freak cases, but specifically designed to evoke public perception, meaning and image. Today we mix and match everything available, creating hybrid designs never seen before, creating an urban aesthetics which can be debatable.
We may reason the architecture of the past to limited opportunities, and praise current times for multiple materials available, each appropriate in its context of use. However, multiplying options has also led to increased consumption, energy use and wastage, demanding a more greener living today. From the sustainability perspective, it makes sense to relook at the past practice where people lived with the materials they could get in their locale.
Rammed earth in roofs can be cited as an example, where stabilised soil cement block or rammed earth walls are already a part of the building. Having proved the benefits of mud in the making of the wall, organisations such as Hunnarshala at Kutch and Gram Vidya in Bangalore tried it out like a flat slab. After all, the wall can be visualised as a slab kept vertical and if so, these slabs can be kept horizontal also as floor or roof.
Domes and vaults in mud have proved to be stable, but flat slabs would need means of strengthening them, being weak in tension. Hence, nominal wire mesh reinforcement is placed during ramming. Besides, larger the dimension the weaker could be the slab, hence a safe size of 2 x 2 ft. has been adapted. These slabs were initially produced under lab conditions and only after testing, were applied to construction sites. As such, it needs engineering inputs and technical supervision before any site implementation.
For floors, the rammed earth slabs can be simply placed on a hard sub-floor, to be top finished as desired. In case of roofs, pre-cast concrete beams can be placed at two ft. spans to support the slabs on top, just the way stone slabs and wooden rafters were used in the past. Nominal roof concrete with minimal reinforcement can be cast atop the slabs to get a homogenous floor with choice of flooring or water-proofing layer if it’s the final terrace. The bottom of the roof can be left exposed to showcase mud or painted to emulate the looks of a false ceiling.
It’s often said that there is no dearth of ideas around, only of implementation. Rammed earth proves this point beyond doubt.