The concrete frame would be produced in local precasting yards. Concrete frame houses are widely used in the developing world, but these concrete frames can be manufactured more efficiently and with higher levels of quality in "mass" production yards. A simple yard could produce one frame a day, allowing each frame to cure to its maximum strength over thirty days in the yard, and then the completed precast frame would be transported to the building site.
The encouragement of local entrepreneurs to build local casting yards that both produce and sell products has been demonstrated to be an effective way to build sustainable local markets for basic necessities by NGOs like IDE. The role of the NGO is to provide training and the designs.
The floor, central wall and posts would be cast as a single piece. This piece of concrete would be 8' wide, 16' long and 9' high, and weigh 5,500 lb (2.44 x 4.88 x 2.74 m - 2,400 kg). Although this appears large, this is road transportable on any standard medium duty truck that is widely available in the developing world (this compares to a standard shipping container at 8' x 20' x 10'). The truck would have to be equipped with a hydraulic lifting system. The roof of the structure would be cast from bagged concrete on the construction site. The form for the roof would be installed at the precast yard, and it would provide horizontal stability during shipping (material for the form is TBD, but it would likely be made from fiberglass or galvanized steel).
The concrete frame is strong, durable, weather resistant and made from materials that are widely available in all markets. Cost calculations are based on using steel for reinforcement within the concrete, but the steel may be replaced with local materials like bamboo.
The central concrete wall within the structure provides support, and strength, and more. The wall and roof are think enough that they can contain separate piping and outlets for both electrical and water systems. The roof has been designed to collect water, that can then be piped through the central wall to a rain water collection vessel. The electrical piping in the central wall and ceiling allows for the installation of lighting, electrical outlets, solar panels, batteries or an electrical service at any time.
The frame, roof, non-reusable concrete forms, and electrical and water systems could be provided for $100.
The exterior sheathing of the house would be completed by the final homeowner. The choice of sheathing would be based on the climate, culture, security requirements and the financial capabilities of the home owner.
All of the potential sheathing options considered were lightweight, and could be installed by one person. Most sheathing options require limited skills.
As the strength of the structure is independent from the walls, the sheathing can easily be replaced as the financial capabilities of the owner changes. The house could initially be built with bamboo walls, these could be replaced with corrugated steel, and the later replaced once again with bricks or masonry that could eventually be covered with stucco.
Option 1 - Local Vegetation
The home owner may be able to gather or buy bamboo or grasses to build bamboo or thatched walls. There is virtually no costs associated with this type of materials, but access to these materials is mostly limited to rural tropical areas. This material does offer a low level of security and it is a fire risk.
Cost ~ $0
Option 2 - Corrugated Steel
Corrugated steel is available in all urban markets. It may be purchased of scavenged. Metal walls do offer improved security and reduced fire risk, but they are noisy and not comfortable in extreme temperatures.
Option 3 - Brick or masonry walls
Plain brick or masonry walls would be a luxury in most poor neighborhoods. The material would have to be purchased, and may require skilled labor. At this level, home owners would also want to consider purchased doors and windows.
Cost ~$140 (excluding labor)
Flexibility and Stackability
The Precast Frame House is specifically designed to address many of the issue facing poor communities - high land costs, flooding, and room for expansion. The precast frame structure was designed to be stackable - both one on top of the other, and cross stacked. The roof design has two functions, when exposed to rain, it catches and funnels water, but when stacked, it interlocks with cut-outs in the base, something only achievable with precast concrete - creating a securely stacked structure.
Stilt houses are extremely common in the developing world, the improved air circulation helps with cooling and humidity, and the height off of the ground provides protection during flooding. By stacking two precast frames, and only sheathing the upper houses, the benefits of a stilt house can be replicated, enabling the increased use of flood prone lands for housing.
Land costs are a significant concern in many urban areas, and the structures commonly built in slums make poor use of expensive land. By stacking multiple precast frames, and adding an external staircase, a multi floor dwelling can be built that makes efficient use of the land. The stacking of shipping containers demonstrate how secure a tall stack can be.
Through the use of a standard design, new floors can be added to existing dwellings long into the future, allowing the home to expand with the family and its financial capability - a practice that is culturally normal in many parts of the world.
In many parts of the world, the home and the business are one. The Precast Frame Home continues this tradition. The clear division of the structure into two zones, with a solid dividing wall allows for the use of the front room as a business, and the back room as a home. As the business expands, and additional units are stacked, the home can move to a higher floor, and the business is expanded across the main level.
167 bags of concrete, $4.00 each $668
256 ft2 wire mesh, $12.00 per 4x8 sheet $96
16 pieces of rebar, $3.75 each $60
Roof form $120
(estimated 8 pieces of 8'x26" corrugates steel)
Electrical & Plumbing Pipe and Fitting $50
Total $994 - converts to $100
24 Sheets of 8'x26" corrugates steel, $15.00 each $360 - converts to $36
432 pieces 8"x16"x4" concrete blocks, $1.50 each $648
36 bags of mortar, $6.00 each $216
9 bags of block ties, $4.00 per bag $36
6 steel lintels, $30.00 each $180
Glass Block for windows $135
Steel Door $150
Total $1365 - converts to $140