Chapter-5 Construction Details

5.1 Construction Detail

5.1.1 Ferrocement Structures

Ferrocement is a system of construction using reinforced mortar or plaster (lime or cement, sand, and water) applied over an "armature" of metal mesh, woven, expanded metal, or metalfibers, and closely spaced thin steel rods such as rebar. The metal commonly used is iron or some type of steel, and the mesh is made with wire with a diameter between 0.5 mm and 1 mm. The cement is typically a very rich mix of sand and cement in a 3:1 ratio; when used for making boards, no gravel is used, so that the material is not concrete.

Ferrocement is used to construct relatively thin, hard, strong surfaces and structures in many shapes such as hulls for boats, shell roofs, and water tanks. Ferrocement originated in the 1840s in France and the Netherlands and is the origin of reinforced concrete. It has a wide range of other uses, including sculpture and prefabricated building components.

Example of Ferrocement Structure:

Candela’s hyperbolic paraboloid Los Manatiales restaurant in Xochimilco under construction and the incredible open space inside. The formwork was straight wooden boards, with wire reinforcement laboriously laid down on top before the concrete pour. The concrete was only 4 cm thick.

Fig. 124: Ferrocement Construction Fig. 125: Ferrocement Construction

Fig. 126: Ferrocement Parabolic Roof Structure

5.1.2 North Light Truss

North light trusses are traditionally used for short spans in industrial workshop-type buildings. They allow maximum benefit to be gained from natural lighting by the use of glazing on the steeper pitch which generally faces north or north-east to reduce solar gain. On the steeper sloping portion of the truss, it is typical to have a truss running perpendicular to the plane of the North Light truss, to provide large column-free spaces.

The use of north lights to increase natural day lighting can reduce the operational carbon emissions of buildings although their impact should be explored using dynamic thermal modelling. Although north lights reduce the requirement for artificial lighting and can reduce the risk of overheating, by increasing the volume of the building they can also increase the demand for space heating.

Method of Construction:

1. The whole of the south slope is covered with profiled sheets and the whole of the north facing slope with glass or clear or translucent plastic sheet. 2. North light truss has an asymmetrical profile with a south facing slope at 17º or more to horizontal and the north facing slope at from 60º to vertical. 3. Because of the steel pitch of the north facing slope the space inside the roof trusses of a north light roof is considerably greater than that of a symmetrical pitch roof of the same span. Fig. 127: North Light Truss Design

Fig. 128: North Light Truss Examples

5.1.3 Light-Well

A light well is an architectural feature that can be used to take natural light into the interior spaces of a building. It takes the form of a vertical shaft within the volume of a building that typically penetrates from roof level down to lower levels, allowing the transmission of natural light to areas that would otherwise require artificial lighting. Light wells can also be used to promote ventilation.

Light wells may be open to the elements at the top (i.e. without a roof), with internal windows around its perimeter, or it may be open internally with glazing at the top.

The advantages of light wells are that they can reduce the electric lighting requirements of a building, as well as providing an open space that can be used as an outdoor area or garden. A large light well may be referred to as an atrium.

Small, highly-reflective light wells that 'collect' light and transmit it to the interior of a building may be referred to as daylight systems or light tubes.

Fig. 129: Examples of Light-Well

Fig. 130: Garden Light-Well

5.1.4 Passive Cooling

1. Passive cooling systems are the least expensive means of cooling a building which maximizes the efficiency of the building envelope without any use of mechanical devices.

2. It rely on natural heat-sinks to remove heat from the building. They derive cooling directly from evaporation, convection, and radiation without using any intermediate electrical devices.

3. All passive cooling strategies rely on daily changes in temperature and relative humidity.

Fig. 131: Passive Cooling Techniques

List of Passive Cooling Techniques:

 Natural Ventilation

 Shading

 Wind Towers

 Courtyard Effect

 Earth Air Tunnels

 Evaporative Cooling

 Passive Down Draught Cooling

 Roof Sprays

Natural Ventilation:

Outdoor breezes create air movement through the house interior by the ‘push-pull’ effect of positive air pressure on the windward side and negative pressure (suction) on the leeward side. Windows play a dominant role in inducing indoor ventilation due to wind forces.

Firstly the rising air creates a low pressure zone on the cool mass floor, pulling air along the floor from other areas of the house as well as from any open doors. Secondly the rising and escaping air creates an interior low pressure that should pull in large volumes or exterior from the patio doors. Fig. 132: Natural Ventilation

Courtyard Effect:

Due to incident solar radiation in courtyard, the air gets warmer and rises. Cool air from the ground level flows through the louvered openings of rooms surrounding a courtyard, thus protecting air flow. At night, the warm roof surfaces gets cooled by convection and radiation.

If this heat exchange reduces roof surface temperature to wet bulb temperature of air, condensation of atmospheric moisture occurs on the roof and the gain due to condensation limits further cooling. If the roof surfaces are sloped towards the internal courtyard, the cooled air sinks into the court and enters the living space through lowlevel openings, gets warmed up, and leaves the room through higher level openings.

However, care should be taken that the courtyard does not receive intense solar radiation, which would lead to conduction and radiation heat gains into the building.

Fig. 133: Courtyard Effect