HyPar Thin Shell Concrete Roof
George Nez and Albert Knott
The HyPar Thin Shell Concrete roof is a roofing system made from a mixture of cement, sand, water and acrylic latex on a mesh base forming a thin shell.
The HyPar Thin Shell Concrete Roof is a roofing system developed by George Nez and Albert Knott of [TSC Global] who trained groups in several developing countries in how to construct them. One of the groups they trained is Technology for Tomorrow (T4T) who is offering the roofs as a building product in Uganda.
The roofs are 1 cm thick and made from a mixture of cement, sand, water and acrylic latex on a fibreglass mesh or cloth and light wire mesh base. The shell layer is supported on a four sided pyramid framework of timber that creates a hyperbolic parabola shape.
Africa, Latin America & the Caribbean, Asia, North America, Uganda, Tanzania, Kenya, Sudan, South Sudan, Haiti, Thailand. TSC Global has a webpage that shows the locations of their projects or collaborations.
There is no similar product that is as lightweight. It competes with whatever roofing is typical for small buildings in each region such as corrugated metal roofs, thatch roofs, or standard concrete roofs.
Goal 1 and 11: Aims to provide affordable shelter that is better for the environment.
Implementing organizations, households, public sector, private sector.
Made on site with materials including latex, mesh, and wood members ordered from elsewhere and brought to site.
No patent for this particular method, though George Nez and Albert Knott developed and refined the original concept patented by Joseph Kersavage in 1975.
Users can build the Hypar roof themselves based on published instructions (see Product Schematics section) or else hire a company that has been trained such as T4T or EMI.
An average of the maximum compressive strength a typical structure could withstand with this building material. Units: σ (N/mm2)
An average of the maximum loads/forces perpendicular to the compressive forces that a typical structure could withstand with this building material. Units: σ (N/mm2)
A seismic design category expresses an area’s likelihood of experiencing damaging effects of an earthquake (A(low), B, C, D0, D1, D2, E(high)). This parameter denotes the highest acceptable SDC for the material.
Climatic zones appropriate for construction based on a material’s availability/feasibility in each climatic zone.
R value associated with material/product
The basic form is made as follows but can be adjusted to suit any building design. These specifications were taken from the book Latex Concrete Habitat by Dr. Albert Knott and Dr. George Nez. Other researchers and builders propose slight differences to the framing details and mix design, but the general process is the same.
The Edge Members: four poles with two slightly longer than the other two, and fastened so that the two longer poles meet at one corner. That corner can be lifted and propped on a post.
The Screen Surface: Posts are marked in 1′ (30cm) segments and then 1′ wide strips of fibreglass fly-screen are wrapped from one side of the frame to the other in both directions, layering them on so that they overlap by 6″ and stapling down to the frame.
Coating and Surface: The first coat is a latex slurry mixture of latex liquid and portland cement and water and brushed on to the surface using long handled brushes. The next layer is a latex mortar mixture made of latex slurry and sand and applied until the surface is about 1cm thick.
Other Considerations: The surface can be used for roofs, arched shelters, and walls, and additional strength provided by adding additional layers of fabric and mortar. The surface can also be perforated for smoke stacks and skylights. Only hand tools are required to build the structure and electricity is not essential. It is possible to construct the roof first before the walls and the roof structure is so light that it can be lifted onto the walls afterwards or can have separate columns supporting it.
Technical support may be provided by the trained builder of the system.
The system is not modular and therefore the whole roof would have to be replaced. The materials used are available in most countries that have a construction industry and can therefore be easily obtained for any additional construction.
The complete lifecycle is unknown, but there are HyPar structures that have been standing for over 20 years. Tests have shown that quality assurance is important in the construction of HyPar roofs because deterioration can happen if details or the mix is done poorly.
Designer specified performance targets include the system being light weight, strong, durable, portable, low cost, and minimum training required.
Testing of the system is being performed separately and does not relate to the projects that have or are currently being completed by implementers of the system. Research has been performed for the material science of the HyPar shell to determine the optimal mix design and structural performance during an earthquake.
The roof is lightweight and would therefore not be fatal to occupants if damaged by an earthquake. Workers would be subject to general dangers of a construction site including working with sharp tools. Construction does not require the use of large machinery.
Carlton, W. S. 2013. Material Behaviour of Latex-Modified Concrete in Thin Hyperbolic Paraboloid Shells: A Thesis Submitted to the Graduate Faculty in partial fulgent of the requirements for the Degree of Master of Science Civil Engineering.
There are many videos available about HyPar roof construction.
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