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Introduction
Each year, cyclones destroy several thousands of houses. This website aims to be a guide for all who wish to design and build cyclone resistant houses in foam concrete. The Foam & Form building system is a very fast and efficient building system for mass construction of very strong, safe and comfortable houses at low cost.

For more information on the Foam & Form building system please refer to website: www.foamconcretehousing.com
I would appreciate to receive remarks, corrections, additions and questions at my email address: ahmandemaker@gmail.com
Albert Mandemaker

Disclaimer
Please note that all information in this website has been compiled with utmost care. No rights can be derived from any mistake or incorrect data.

Tropical cyclones
Tropical Cyclones are wind systems with a warm core that form over warm tropical waters (Pacific Ocean) when the water temperature is a minimum of 27 degrees C.
High speed winds blow spirally inward from all sides to form a roughly circular core or eye which can range from about 16km to 50km in diameter. The total system can have a diameter as large as 650km.
The spiraling action is a result of the rotation of the earth: clockwise in the southern hemisphere and anti-clockwise in the northern hemisphere.
Air drawn into the eye of a cyclone is carried vertically by convection and a pumping action generated by high altitude winds. This eye activity extends up to 12km above the sea.
The air rising in the eye carries substantial quantity of water vapor which condenses to form heavy cloud and rain in the area of maximum wind force around the core.
The condensing water vapor releases large amounts of heat energy which is enlarging the system.
Cyclones extract their energy from warm water, over land they dissipate rather quickly but often not before doing enormous damage.
Cyclones normally move at speeds between 8 and 60km/hr, and because of their size, high speed winds can last for many hours. These winds are subjecting buildings and other structures to great dynamic forces and are bringing very heavy rain that can cause serious flooding.
Because of the rotation of the cyclone, wind may come from any direction, depending on the position of the eye.

Classification of Cyclones (Asia)
Tropical cyclones are classified in 5 categories, as follows:

1

Below is my simplyfied formulae to calculate the wind force based on windspeed, drag and windcoefficient.  (indicative only)

Force (kg/m2) = Speed (km/hr) ^2 x 0.0048 x Cd x K2

2

The effect of wind on buildings
The high wind speeds of cyclones have a very heavy impact on building structures. The force can be positive as well as negative (suction). The drag effect will increase the force at certain areas of the building significantly. The areas where drag has the largest effect are the edges and corners. At the corners and edges of buildings and roofs, the force can be increased by 40%.  Roofs will mainly be subject to huge suction, depending on the design and pitch of the roof.
Cyclonic winds may come from any direction, so buildings have to be designed and calculated on this basis.

Guidelines for design and construction of cyclone resistant houses
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Cyclone resistant beach house in Reunion

  1. Location, orientation
    The location is an important factor in the structural and architectural design of houses in cyclone prone areas. Houses near the sea in an open area will be fully exposed and will get maximum impact from a cyclone. Houses in sheltered areas, built up area or further away from the seaside will be less impacted. Most countries that are prone to cyclones will have Regulations  in place with rules for the design and structural calculation for all affected areas.
    Houses on a higher elevation are generally more exposed, but will have better protection against flooding. Sheltered locations are preferred, but these may have increased danger of flooding and landslides. 
  1. Foam Concrete
    Foam concrete is a mixture of sand, Portland cement and water to which a stable pre-formed foam is added. The foam is in most cases made on site from a protein or synthetic foaming agent. By varying the material quantities, densities from 200kg/m3 to 1,600kg/m3 can be made.
    Foam concrete is the main material for cyclone resistant houses as all walls and in some cases even the foundations are cast in this material. Foam concrete in higher densities of 1,400 – 1,600kg/m2 has sufficient weight, is strong, lasting and is reinforced with steel bars. Foam concrete is very liquid and is cast in a formwork system that is used in a daily cycle.
  1. Simple layout and elevations
    Houses in foam concrete have the great advantage that all walls can be tied to the foundation and that the walls are made as a solid, fully interlocking grid-like structure. This means that each wall will act as strong support for the joining walls. External walls, that take the brunt of the storm, must be supported at corners and at regular intervals so that the unsupported sections of the walls are limited to maximum of about four meters. If no internal walls are planned, abutments can take over the support role.
  1. Weight and Structure of the house
    There are two essential factors for a house to be able to withstand the direct effects of a cyclone or tropical storm.
    Weight : The total weight of a house must be sufficient to keep it in its position and to maintain its integrity.
    Structure: All walls are securely tied to the foundation and tied to each other with steel reinforcement bars,  so that a very strong and resilient structure is achieved. The top of all walls is made with extra reinforcement bars and forms a continuous and strong ring beam. A number of walls are cast up to the roofline so that the roof itself can be simple, but very strong and deeply anchored into the walls.The proposed houses will be designed with the Marulin Form & Foam construction method. With this method, all walls are reinforced and firmly connected with each other. In additions, all walls are anchored to the (raft) foundation so that a very strong and stiff structure is achieved. The top of the walls have more reinforcement to form a continuous ring beam for additional strength.
    External walls are designed to withstand cyclonic forces and have a limited span as they are supported by perpendicular walls and beams. These walls are made in 10cm, 15cm or 20cm thickness, depending on the wind-load and span.
    Internal walls are all 10cm thick.
  1. Foundation
    Raft foundation in dense concrete is recommended. Floor level should be more elevated than usual because of extensive rainfall and risk of flooding. Edges should be dug in deeper than normal for additional stability. Starter bars to all external and internal walls.
  1. Walls
    4
    Foam concrete house in progress

All external and main internal walls will be made of foam concrete with a density of 1,400 or 1,600kg/m3. Since strength is of paramount importance, a density of 1,600kg/m3 is recommended. All walls are reinforced with steel bars, with additional reinforcement such as starter bars, top of the walls and in areas of increased stress. The structural engineer is responsible for the structural design of the house.
External walls are designed to withstand cyclonic forces and have a limited span as they are supported by perpendicular walls and beams. These walls are made in 10cm, 15cm or 20cm thickness, depending on the wind-load and span.
A 10cm thickness should be sufficient for almost all internal walls.

  1. Roof
    The roof structure and roof panels need to be designed to withstand all wind forces, positive and negative. Along the edges of the roof the wind forces are extreme. The structural members such as purlins need to be anchored securely into the walls, with long anchor length. The roof panels must be suitable for cyclonic conditions and must be fixed firmly to the purlins are other structural components. Large washers are needed to prevent the roof panels from ripping off the roof structure.
    Special attention is required for waterproofing the capping and flashing. During rainfall, the water will be blown towards the ridges and leakage is not unlikely.
    The eaves must be small as large eaves are particularly vulnerable during storm.
    The forces to a roof depend for a large part on the pitch (preferably 25 – 40 degrees pitch) and the design of the roof.
    Pitch and orientation might be dictated by other factors such as the installation of solar panels.
    Terrace-  and walkway covers must be anchored separately from the roof of the main building so that storm damage does not effect the main building.
  1. Windows, doors, shutters
    Windows and doors are parts of the house that, after the roof, are most frequently damaged: windows by flying debris and failure of hardware such as hinges, latches and bolts.
    Windows and doors
    It is very important that the wind has no impact on the inside of the house. Wind force that can enter the house will lead to increased pressure build-up inside the house. This increased pressure will work in concert with the suction on the outside of the walls and roof and so may far exceed the structural capacity of the roof. The danger of the roof blowing off is very substantial.
    The external doors must be able to withstand both pressure and suction. The door itself must be very strong and of suitable design and be fixed securely inside the doorframe with 3-point lock and special hinges. The doorframe itself must be securely tied to the wall.
    The windows must be fitted with a fixed or loose shutter to protect the windows from flying debris.
    As mentioned above, the roof must be water- and air tight to prevent build up of pressure inside the house.
    As corners of the house are more heavily impacted by the storm, it is prudent to place windows and doors not too close to these corners.
    In normal weather conditions, (natural) cross ventilation is very important and should be promoted by the correct positioning of doors and windows with opening leaves are louvers.
    Ventilation in roof space is recommended with closeable openings in the gable walls.
    An opening in the windward side of the house may lead to internal built-up of high pressure. This high pressure build-up must be prevented as it will work together with suction on the roof and lead to blowing up the house. The increased air pressure inside the house can be prevented by having an opening on the leeward side to allow the air to escape.
  1. Rain, flooding
    Cyclones bring incredible strong winds, but also huge quantities of rain that may cause flooding and landslides. Measures to counter these hazards must be incorporated in the design of the house.
  • Town planning
    Town planning in cyclone prone areas can make an important contribution in making the houses cyclone resistant. Placing houses in rows may lead to extra wind load, an irregular positioning of houses will reduce the impact of the wind.
    Elevated level for floor above land
    Storm drains to divert water stream and drain the land
    Positioning of units not too close
    Trees as windbreak , strong trees at least 10m away from houses. 
    Make use of sheltered areas if available such as hills and trees. 

Climate Change mitigation
Over time, the effects of Climate Change are expected to become more extreme. Since houses are designed to be durable and lasting, it is strongly recommended to incorporate the foreseen effects in the architectural and structural design of the house.
These effects can be:
•Increased wind speed – must be taken into consideration with the design and structural calculation of the house.
•More frequent and torrential rain – provision of drains, limiting of hardened area, extra attention to roof design.
•Possible flooding – storm drains, elevated floor levels etc.
•Possible landslides – trees, secure slopes;
More extreme temperatures – trees to provide shade, better insulation value for roof and external walls, natural ventilation.

Remarks:
•For detailed information for the construction of foam concrete houses please refer to my website foamconcretehousing.com
•For questions and clarification email: ahmandemaker@gmail.com
•Consultancy available on request.