Prefabrication experiments - 120 - material innovations - 1 - prefab rammed earth panels

Environmental priorities, the pursuit of high performance materials and new production techniques are combining to stimulate imaginative, resourceful and extraordinary building materials and methods. From super lightweight carbon reinforced concrete to glue-laminated timber produced from undersized reclaimed branches, material hybrids are, as was the case in the early twentieth century, reforming production and altering the way we build and perceive the limits of traditional building materials. This union of tradition and technology is behind a fresh look into rammed earth as a prefabricated mega-building-block for buildings. 

Rammed earth is a traditional building material made of a dampened mixture of clay, straw, lime, gravel and stabilizers such as cement or asphalt emulsions. The mixture is compressed with a flat-headed rammer, a type of large mallet or sledgehammer, into timber formwork. Austrian company Lehm Ton Erde transferred this labour intensive process into a factory setting for an ornithological visitors centre in Sempach Switzerland. Designed by architectural firm MLZD the building was the first to use prefabricated rammed earth panels. The panels were produced in climate-controlled conditions using techniques similar to precast concrete. The fundamental difference is that the rammed earth formwork is vertical whereas concrete panels are usually cast horizontally.

Each panel consists of equivalent layers of compressed dampened loam. The earth mixture is transported and dumped into the vertical formwork by an automated loader. A linear pneumatic rammer followed by steel rollers then moves across each thickness ensuring an identical quality and constitution for each subsequent layer of loam. The production of large rammed earth blocks in the factory reduces construction time and also allows for greater quality control. Each mega block is bound on site by a loam mortar, similar to standard brick construction. The loam binder is also used for repairing any damage from shipping or handling.

The ornithological visitors centre in Sempach Switzerland is a hybrid system of vertical rammed earth building blocks which support simple timber framed floors and roofs. The on-site version of the same technology is as old as civic building culture and outdates more standardized mud brick building. The certified «MInergie-P-Eco» (eco-label) the rammed earth massive panels participate in creating a low-energy building and a low-energy embodied building material.

Delivery and stacking of rammed earth panels

Prefabrication experiments - 119 - Structures - 10 - Open Frame Steel Skeletons

"The architecture of steel is a skeleton". Gio Ponti's take on steel construction in In Praise of Architecture identifies the resilient relationship between the manufacturing of steel from iron ore, the continuous rolling of assorted profiles and their assembly into grid-based structures. The steel producer and its capacity to efficiently manufacture infinite material variations is the emblem of the second industrial revolution. Steel elements can be laminated and rolled to any specified thickness, shape or alloy and are the basis of steel construction.

Posts, beams, girders, joists or hollow structural sections are the linear edges of platform frames, balloon frames, or any variant of post and beam construction from rectangular organisations to rounded skeletal compositions. Based on the basic principles of box frame construction, the vertical, horizontal or diagonal members are connected by simple means, nuts and bolts or rivets, to form interrelated planes and their edges. Steel relates to the essence of dry construction: It can be disassembled as easily as it is assembled making it both durable and sustainable. Properly maintained, steel frames can outlast a building’s functional service life and be economically reused for other purposes

Open spans up to nine meters characterize the basic advantage of steel frame construction: flexibility and adaptability of light bearing systems relying on repetitive elements to transfer loads. This type of frame construction requires special attention to the capacity of its connections to resist lateral loads.  This resistance is often achieved by diagonal steel rods or cables, which stiffen and brace building planes.

Today’s steel frame construction involves the complete combination of the design and manufacturing processes. Eco steel in the United States and Bone structure in Canada are two companies that propose an engineered to order building kit.  Both companies offer an integrated design, manufacturing and construction process. Their Building systems are custom designed kits of steel components. Data management and building information modeling are used to directly link design and production. The contemporary modeling and information management tools employed by these companies allow a totally customizable architecture produced as required. This budding business model challenges the long lasting paradigm of prefab companies producing repetitive architecture. 

(Left) Eco Steel website - (Right) Bone Structure website

Prefabrication experiments - 118 - Structures - 9 - Frank Lloyd Wright's textile block building system

Prefabrication has evolved to signify manufacturing large chunks of buildings or parts in a factory. However prefabrication can also refer to any building component that is mass-produced to simplify the on-site construction process. Although not normally associated to prefabricated building systems, masonry walls are in a sense the simplest result of prefabrication: a continuous production of identically dimensioned modular units. The units are easily stacked and bonded to develop infinitely variable designs based on purely compressive building systems such as walls or arches. Exemplifying the ideas of  "materia povera", masonry construction is founded on earthen materials, craftsmanship and is conceptually different from the skeletal frame structures that are synonymous with modern architecture and industrialization.

Inspired by both simple materials, workmanship and an idealized «do-it-yourself» construction from prefabricated ornamental blocks, Frank Lloyd Wright's Usonian automatic homes related to masonry’s simplicity and sought to fill the need for authentic, aesthetic, affordable, and potentially mass produced homes for the “modern” family. Designed in a period of fertile exploration for industrialized building systems, the Usonians were sequels to Wright's textile block houses designed in the early twentieth century. These houses employed the same simple stacking to achieve a global patterned textile like composition and design. Although the designs maintained Wright’s ornate Aztec inspired intention, each block was recognizable as a basic building unit. The inexpensive repetitive blocks could be assembled and even produced by prospective owners. Established on a two-foot square grid the envelope's blocks were of modular dimensions: four inches thick by twelve inches high and twenty-four inches wide. The brickwork bond involved an inlaid reinforcing steel grid of rods encased in a semi-circular grove filled with mortar. The resulting monolithic load bearing walls habitually supported a simple wood framed roof. 

Wright's simple construction system did not revolutionize America's domestic building as the timber balloon frame remained the go to system for housing. The simple modular blocks did however relate to many do-it-yourself building systems from mass timber blocks to compressed earth blocks or even today’s 3d printed building units. As architecture moved to renew its building systems based on technology, Wright imagined the simplest form of handcraft assembly from prefabricated elemental building components.

Prototype design and building block system

Prefabrication experiments - 117 - Structures - 8 - Reinforced Concrete waffle slabs

Reinforced concrete embodies architectural variability. Concrete structures can be cast in any shape or size, on or off-site, through precise engineering and manufacturing processes. Concrete surfaces are quick to produce, durable and require minimal maintenance. Furthermore concrete construction simplifies the building process as the shaped surfaces provide exposed flooring or ceilings without any other structural components such as girders or joists as for lightweight steel or timber framing. Curing time and weight are reinforced concrete’s main downsides. Reducing weight while providing interesting architectural expression has been a recurring theme for the quest for greater efficiency in concrete building systems.

Thin shell concrete construction or pleated plate construction makes use of form resistant shapes to decrease concrete’s weight to span ratio. In simpler floor slab construction, ribbing has been explored to provide stiffness and optimal mass distribution to reduce overall weight. Pier-Luigi Nervi's Gatti wool factory's ribbed slab is perhaps one of the most famous ribbed slabs which uses stress-lines to produce a waffle like expressive structural ceiling pattern.  Used in more simple orthogonal compositions, ribs are moulded and the concrete cast into a waffle type formwork such as Louis Kahn’s triangular pattern at the Yale Art Gallery. A matrix of interconnected beam-like elements, the resulting waffle slabs can span larger spaces while using less material. Analogous to a massive cast-in-place space frame, the waffles vertical ribs carry stresses through short beam like planes. Although not common in small domestic architecture the Aldeia da Serra house by MMBB architects stages space beneath a remarkable waffle slab element which covers and expresses limitless modern architectural space.

The waffle elements can be cast on site or waffle panels can be produced in the factory. The resulting two directional structural slabs are ideally composed in symmetrical square patterns varying from small spans to relatively large spans up to 15 metres. Combining waffle slab with beam principles, the Holedeck (holedeck.com) formwork, further reduces weight as openings are cast in each vertical rib. The central openings are positioned in the plates’ neutral axis where compressive stresses cancel tensile stresses to develop a network of voids which can be used as mechanical spaces for ducts, piping or electrical wiring.

Gatti wool factory - Yale Art Gallery - Aldeia da Serra house - Holedeck

Prefabrication experiments - 116 - Structures - 7 - Planar construction from monolithic panels to structural insulated panels

A load bearing organization of vertical and horizontal thick flat surfaces is the simplest form of planar construction. Prefabricated panels can be manufactured in any material from lightweight steel or wood to more heavyweight reinforced concrete. Panels can be dry fastened and bolted to transfer vertical and horizontal stresses through the panels' thickness.  Architectural concrete panels, steel stressed skin panels or the contemporary cross-laminated timber panels are the most common manufactured elements used in this type of moderately spanning structures. Habitually flat packed, panels are easily transported and produce an easy to assemble construction kit, where floor panels span from one wall panel to another.

Whether timber, steel or concrete, exposed joinery connects overlaid panel edges in simple "T" or "L" patterns. Once the bearing walls are anchored to a foundation, the floors and walls are continuously stacked in a platform arrangement to reach varying heights. If simplicity is a major advantage, planning flexibility is one of the drawbacks, as the vertical planes impede free flowing open plans. The 9 m x 6 m prism like spans offer less overall building adaptability as compared to open skeletal frame structures.

Concrete and mass timber panels have the additional drawback of weight and make sense for large multi-story buildings. For smaller scale structures, commercial or residential, structural insulated panels (SIPs) are a variant of this type of planar construction, with a much lighter panel.  A SIP is a type of stressed skin lightweight panel composed of en external sheathing of plywood or other material with a high density polyurethane foam core. This type of structural panel can be manufactured to varying thicknesses and manufactured with windows, doors or wiring networks being milled by numerically controlled cutters in the factory. 

Architects Ian Hsu and Gabriel Rudolphy explored SIPs in their recent project for the Casa SIP m3 prototype. The casa SIP showcases the modular panels as walls, floors and roofs and reproduces a simple type of cardboard model like building system using rectangular flat surfaces. The casa SIP project employs this simple construction method to produce dynamic volumes and spaces as well as a clear tectonic expression planar construction.

Mass timber planar construction (left) Casa SIP by Ian Hsu and Gabriel Rudolphy (right)