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Blog updates by Watershed Materials. Developments for sustainable new concrete block technology funded by the National Science Foundation.

Modular and Prefab Strategies Applied to Rammed Earth and Watershed Block to Lower Cost, Reduce Waste and Speed Construction Time

There is a lot of interest today in modular and pre-fab housing - it’s affordable, shortens on-site construction time, reduces construction materials, and cuts down on construction waste. The December/January 2015 issue of Dwell Magazine is entirely devoted to “The New Prefab”. Amanda Dameron, Editor-in-Chief, points out that one of the originators of the prefab movement - Frank Lloyd Wright - held the notion of affordable housing delivered by machine as a mainstay in his practice and a grounding element in his architectural philosophy.

Architectural model for a home designed using modularity principals and constructed from rammed earth Watershed Block. The dimensions of the structures were designed in multiples of the dimensions of the blocks to avoid waste from cutting blocks. The structure was designed with two primary structures connected by adjoining roofs to create a third living space between.

Architectural model for a home designed using modularity principals and constructed from rammed earth Watershed Block. The dimensions of the structures were designed in multiples of the dimensions of the blocks to avoid waste from cutting blocks. The structure was designed with two primary structures connected by adjoining roofs to create a third living space between.

Although not built in a factory and trucked to the site, rammed earth and the new rammed earth Watershed Block from Watershed Materials have the potential to capture many of the same benefits as prefab - affordability, shortened construction time, reduced materials, and less waste. How so you ask? By going modular.

The new prefab (think haute shipping containers) combines the speed and efficiency of building structural elements on an assembly line with an architect’s cleverness at coupling those structural elements into a group of exciting spaces. Lake|Flato’s Porch Houses are fully assembled units, trucked to the site, sometimes coupled together into larger modules, and placed in such a way as to create additional living spaces, most often outdoor spaces. Blu Homes builds frames with hinged walls trucked to the site and “unfolded” into living spaces. Multiple frames create additional rooms.

What these and dozens of other prefab housing companies have in common is modularity. Modularity is the degree to which a system's components may be separated and recombined. Rammed earth walls can leverage modularity by re-using a forming system to build repeating volumes that are placed in such a way as to create additional living spaces between volumes. Watershed Blocks can leverage modularity by capturing the same value of repeating volumes, and doing so with an assembly of small modular units designed carefully as to require no cutting of blocks and no waste.

The principle is simple: build two boxes, space them a dozen or more feet apart, and drop roofs onto and between the boxes - two boxes, three spaces. Build three boxes and a remote support and drop on roofs - three boxes six spaces. The architect’s cleverness keeps the boxes from being boring.

The repeating formwork used to construct this rammed earth vacation home in Hawaii decreased construction time while the modular design joins three structures together to form five spaces.

The repeating formwork used to construct this rammed earth vacation home in Hawaii decreased construction time while the modular design joins three structures together to form five spaces.

We’ve been working on this idea of modularity for a dozen years. It started with our beach house in Hana. Three volumes (pavilions we call them over there), three dropped on roofs, and three outdoor rooms. The formwork was small and reusable, the pavilions each a different dimension. Rammed earth wall panels, like the ones we used in Hana, were simply big blocks - 9 feet long by 8 feet high. The key is that everything repeats. Repetition increases speed and reduces cost.

Our next modular building project was for my daughter, Terra. Her new rammed earth house was built on a hundred acres in Calaveras County and marked the first iteration of repeating, identical volumes. The walls for her modular home are comprised of a series of repeating rammed earth panels. The plan for the new house was to build three 20’ x 24’ rectangles - one kitchen and two bedrooms - and then use the spaces between the rammed earth volumes to create an entry hall, a library hall, a shed-roofed bathing suite, and a large window-walled living room.

A rammed earth home in the mountains of California that uses repeating modular formwork and three identical 20x24 foot structures with adjoining roofs to create additional living spaces between. 

A rammed earth home in the mountains of California that uses repeating modular formwork and three identical 20x24 foot structures with adjoining roofs to create additional living spaces between. 

We built one set of formwork that coupled together to create the large rectangles. Fill the forms, re-set them, and fill again - set, fill, set. The beauty to this system is that the formwork is used multiple times without being modified. At Terra’s we even created the closets, niches, bookshelves, and pantry within the formwork. To do this, the carpenters build collapsible boxes set into the formwork. Whether it’s more efficient to build these boxes into the walls or to frame the closets and pantry afterwards is a question we haven’t answered yet, but the effect of them being “carved” out of the walls adds to the sense of being surrounded by earth.

Back to the construction site: after we completed the third of three volumes, along with the single rammed earth column at the living room corner, we dropped the heavy timber support beams into their respective niches and set the SIP roof panels. Voila - finished wall surfaces and a structural roof. I’d be fibbing (and cause Terra a fit) if I claimed the house itself was finished at this stage, but the bones were there, set quickly and efficiently using principles of modularity.

The repeating formwork has been hoisted up to build the rammed earth walls for the second story of this modular rammed earth home in Mountain View.

The repeating formwork has been hoisted up to build the rammed earth walls for the second story of this modular rammed earth home in Mountain View.

Our third modular building project was for my daughter-in-law, Juliet. Her new rammed earth house was built on a 60 x 140 foot lot in old town Mountain View. We used the same three 20’ x 24’ modules as Terra’s, but arranged them differently to fit the lot. We built one volume on the street side for the kitchen and pantry and stacked two volumes on top of one another for the bedrooms. The twenty-four feet separating the front and back volumes became the high-ceiling living room with a glass wall to the south and a framed wall to the north. Bathrooms were built into a shed hanging off the back of the bedrooms.

At Juliet’s we did not build the closets and pantry into the wall forms, but framed and drywalled them. Switching strategies between the two projects gave us a good point of comparison, but we still don’t feel we’ve answered the question yet on whether it’s more efficient to build displacement boxes into the wall forms or frame afterwards.

We started with the kitchen volume, then moved the forms to the lower bedroom - set, fill, set, fill. We left the lower bedroom forms in place while we poured the concrete slab floor of the upper bedroom, then re-set the forms ten feet in the air and completed the third volume. The beauty of the modular system is that the formwork gets used multiple times without modification. Re-using the formwork saves tons of time and materials.

We used steel I-beams at Juliet’s rather than timber, dropped them into their respective niches and set the SIP roof panels. For the living room we used a steel compression truss landing on steel posts on the low side and a steel I-beam spanning from kitchen to bedroom. Voila - finished wall surfaces and a structural roof. But like Terra’s I’d be fibbing if I claimed the house itself was finished. Carpenters, drywallers, glaziers, tile setters filed through one after another, often times working on top of one another. The house is cool, but too many weeks of finish work if you ask me. We can do better next time.

Modular building principles were continues for this modern home in Napa built with pre-fabricated rammed earth Watershed Block. Two building structures are separated by a third space that, when roofed, becomes a third living space.

Modular building principles were continues for this modern home in Napa built with pre-fabricated rammed earth Watershed Block. Two building structures are separated by a third space that, when roofed, becomes a third living space.

Our fourth and most recent modular building project offered the chance to try a new version of the modular house, this time using rammed earth Watershed Block while still employing the key modularity principle from Terra’s and Juliet’s - repeating volumes spaced far enough apart to create a third room. Two volumes, three roofs, three rooms. One of the big differences to the Watershed Block version, is that the volumes were much bigger, 22’ - 8” x 34’ -8”, an exact multiplier of the dimension of the blocks. In keeping with the principle of modularity, no blocks were cut or wasted to build this house.

If I have any complaints about traditional prefab housing, it’s that they lack grounding. They come in on a truck and are “placed” onto the site. Admittedly, I am a compulsive advocate for mass walls, and for that reason, I want a house “attached” to the site - grounded. Let’s take all of the creativity and engineering that has gone into the success of modern prefab and overlay it onto the beauty, permanence, resiliency, and just plain weight of earth wall architecture.