Unit – 2

Building Components & Building Planning

1. Briefly describe Foundation and Superstructure?

Foundation

The lowest part of a structure which transmits the weight of the structure together with live loads, seismic and wind pressure to the ground surface on which the structure rests, ensuring its safe bearing capacity, is called foundation. To increase the stability of the structure, foundations are generally placed below the ground level.

The selection of the foundation type for a particular site depends on the following considerations:

1. Nature of subsoil.

2. Nature and extent of difficulties

3. Availability of expertise and equipment

Depending upon their nature and depth, foundations have been categorized as follows

• Open foundations or shallow foundations
• Deep foundations

Superstructure

Superstructure is the portion of a  building parts which is constructed  above the ground level and it serves the purposes of structure intended use . Such as column, beam, floor, wall and roof etc .

Materials used- timber, steel and concrete.

2.    What are the Functions of Foundation?

1. Reduction of load intensity

Foundations distribute the loads of the super-structure, to a larger area so that the intensity of the load at its base (i.e. total load divided by the total area) does not exceed the safe bearing capacity of the sub-soil. In the case of deep foundations, it transmits the super-imposed loads to the sub-soil both through side friction as well as through end bearing.

2.     Even distribution of load

Foundations distribute the non uniform load of the super-structure evenly to be sub-soil. For example, two columns carrying unequal loads can have a combined footing which may transmit the load to sub-soil evenly with uniform soil pressure. Due lo this, unequal or differential settlements are minimised.

3.     Provision of level surface

Foundations provide levelled and hard surface over which the super-structure can be built.

4.     Lateral stability

It anchors the super-structure to the ground, thus imparting lateral stability to the super-structure. The stability of the building, against sliding and overturning, due to horizontal forces (such as wind, earthquake etc.) is increased due to foundations.

5.     Safety against undermining

It provides the structural safety against undermining or scouring due to burrowing animals and flood water.  

6.     Protection against soil movements

Special foundation measures prevents or minimises the distress (or cracks) in the super-structure, due to expansion or contraction of the sub-soil because of moisture movement .

3.    What are the different Types of Shallow and Deep Foundations? Briefly explain?

Depending upon their nature and depth, foundations have been categorized as follows

(i) Open foundations or shallow foundations

(ii) Deep foundations

SHALLOW FOUNDATIONS

This is the most common type of foundation and can be laid using open excavation by allowing natural slopes on both sides. This type of foundation is practicable for a depth up to 5m and is normally convenient above the water table. The base of the structure is enlarged or spread to provide individual support. Since spread foundations are constructed in open excavations, therefore they are termed as open foundations.

The various types of spread footings are:

1.Wall footings

2.Isolated footings

3.Combined footings

4.Inverted arch footings

5.Continuous footings

6.Cantilever footing

7.Grillage footing

1. Wall Footings:

These footings can either be simple or stepped. The base course of these footings can be concrete or of entirely one material. They have only one projection beyond the width of the wall on either side. The width of the concrete base should be at least equal to twice the width of the wall. The depth of the concrete bed is at least equal to the projection. Generally the projection provided in the footing is 15cm, on either side and the concrete mix comprises of cement, sand and aggregate in proportion of 1:3:6 or 1:4:8.

2. Isolated or Column Footings:

They are used to support individual columns. In case of heavy loaded columns, steel  reinforcements is provided. Generally, 15cm offset is provided on all sides of concrete bed. The footing of concrete columns may be slab, stepped or sloped type.

3. Combined Footings:

A combined footing supports two or more columns in a row. The combined footing can be rectangular in shape if both the columns carry equal loads or can be trapezoidal if both the loads are unequal. Generally they are constructed of reinforced concrete. The location of the center of the gravity of the column loads and centroid of the footing should coincide.

4. Inverted arch footing:

This type of footing is used on soft soils to reduce the depth of the foundation. Loads above an opening are transmitted from supporting walls through inverted arches to the soil. In this type of footings the end columns must be  stable enough to resist the outward pressure caused by the arch action.

5. Continuous footings:

In this type of footing a single continuous R.C. Slab is provided as foundation of two or three or more columns in a row. This type of footing is suitable at locations liable to earthquake activities. This also prevents differential settlements in structures.

6.     Strap or cantilever footings:

Strap footing consists of two or more individual footings connected by a beam called strap. This type of footing is used where the distance between the columns is so great that the trapezoidal footing becomes quite narrow with bending moments.

7. Grillage footings:

This type of footings is used to transmit heavy loads from steel columns to the soils having low bearing power. This type of arrangements prevents deep excavations and provides necessary area at base to reduce the intensity of the pressure.

DEEP FOUNDATIONS

These foundations carry loads from a structure through weak incompressible soils or fills on to the stronger and less compressible soils or rocks at depth. These foundations are in general used as basements, buoyancy rafts, caissons, cylinders, shaft and piles

1. Basements

They are constructed in place in an open excavations. They are hollow substructures designed to provide working space below ground level.

2.     Buoyancy Rafts

They are hollow substructures designed to provide a buoyant substructure beneath which reduce net loadings on the soil to the desired low density.

3.Caissons

They are hollow s8ubstructures designed to be constructed on or near the surface and then sunk as single units to their required level.

4.Cylinders

They are single small cell caissons.

5.Shaft Foundations

They are constructed within deep excavation supported by lining constructed in place and subsequently filled with concrete.

6.Pile Foundations

The pile foundation is a construction supported on piles. A pile is an element of construction composed of timber, concrete or steel or a combination of them. The piles may be placed separately or they may be placed in form of a cluster throughout the structure.

4.    Define Walls?

Walls

Wall is a structure defining an exact area and providing safety & shelter. There are various types of walls used in the construction of buildings given below.

1. Load Bearing Walls
   1. Precast Concrete Wall
   2. Retaining Wall
   3. Masonry Wall
   4. Pre Panelized Load Bearing Metal Stud Walls
   5. Engineering Brick Wall
   6. Stone Wall 
2. Non-Load Bearing Wall
   1. Hollow Concrete Block
   2. Facade Bricks
   3. Hollow Bricks
   4. Brick Walls
3. Cavity Walls
4. Shear Walls
5. Partition Walls
6. Panel Walls
7. Veneered Walls
8. Faced Walls

Load bearing wall is a structural element. It carries the weight of a house from the roof and upper floors, all the way to the foundation. It supports structural members like beams (sturdy pieces of wood or metal), slab and walls on above floors above. A wall directly above the beam is called load bearing wall. It is designed to carry the vertical load. In another way, if a wall doesn’t have any walls, posts or other supports directly above it, it is more likely to be a load-bearing wall. Load bearing walls also carry their own weight. This wall is typically over one another on each floor. Load bearing walls can be used as interior or exterior wall. This kind of wall will often be perpendicular to floor joists or ridge. Concrete is an ideal material to support these loads. The beams go directly into the concrete foundation. Load bearing walls inside the house tend to run the same direction as the ridge.

A wall which doesn’t help the structure to stand up and holds up only itself is known as a non-load bearing wall. It doesn’t support floor roof loads above. It is a framed structure. Most of the time, They are interior walls whose purpose is to divide the structure into rooms. They are built lighter. One can remove any non-load bearing walls without endangering the safety of the building. Non-load bearing walls can be identified by the joists and rafters. They are not responsible for gravitational support for the property. It is cost effective. This wall is referred to as “curtain wall”.

The cavity wall consists of two separate wythes. The wythes are made of masonry. Those two walls are known as internal leaf and external leaf. This wall is also known as a hollow wall. They reduce their weights on the foundation. They act as good as sound insulation. Cavity wall gives better thermal insulation than any other solid wall because space is full of air and reduces heat transmission. They have a heat flow rate that is 50 percent that of a solid wall. It is economically cheaper than other solid walls. It is fire resistant. Cavity wall helps to keep out from noise.

It is a framed wall. It is designed to resist lateral forces. This lateral force comes from exterior walls, floor, and roofs to ground foundation. The usage of the shear wall is important, especially in large and high-rise buildings. It is typically constructed from materials like concrete or masonry. It has an excellent structural system to resist earthquakes. It provides stiffness in the direction. The construction and implementation are easy in shear walls. It is located symmetrically to reduce the ill effects of a twist. The shear wall doesn’t exhibit any stability problem.

It is used in separating spaces from buildings. It can be solid, constructed from brick or stone. It is a framed construction. The partition wall is secured to the floor, ceiling, and walls. It is enough strong to carry its own load. It resists impact. It is stable and strong to support wall fixtures. The partition wall works as a sound barrier and it is fire resistant.

It is a non-bearing wall between columns or pillars that are supported. The panel is installed with both nails and adhesive. The paneling design choices include rustic, boards, frame. Paneling can be from hardwoods or inexpensive pine. One should paint the space before installing panel walls.

With a veneered wall, we are holding up the material. It can be made of brick or stone. The most famous veneered wall is made of brick. The wall is only one wythe thick. It became the norm when building codes began to require insulation in the interior walls. It is light weighted. The construction takes less time to complete in veneered walls.

It is a wall that masonry facing and backing are so bonded as to exert common action under load. It creates a streamlined look. The faced wall is easy to install.

5.    Define Lintels? And types of lintels?

A lintel is defined as a horizontal structural member which is placed across the opening. Hence, the structure remains in the position by the resistance from the support.

Classification of lintel

Lintels are classified into the following types, according to the materials of their construction: 

1. Timber lintels 
2. Stone lintels
3. Brick lintels
4. Reinforced Brick lintels
5. Steel lintels 
6. Reinforced cement concrete lintels

Timber lintels

• Easily available in hilly area. 
• Relatively costly, structurally weak and vulnerable to fire.
• Easily decay, if not properly taken care. 

Stone lintels 

• Used , where stones are easily available.
• Consists of a simple stone slab of greater thickness.
• Due to high cost and its inability to with stand the transverse stress load it is not commonly used.

Brick lintels 

• The brick are hard, well burnt , first class bricks .
• Suitable for small span.
• The bricks having frogs are more suitable. 

Reinforced Brick lintels 

• For large spans and heavy loads .  
• They are reinforced with mild steel bars.
• Very common due to durability, strength and fire resisting properties.
• Joints are filled with cement concrete. 

Steel lintels  

• Provided at large opening and where the super-imposed loads are heavy.
• It consists of rolled steel joists . 
• Either used singly or in combination of two or three units.
• Joint with Bolts.

Reinforced Cement Concrete Lintel

• Common in used
• They may be pre-cast
• For smaller span, the pre- cast concrete lintels are used
• Depth of lintel depend on span

6.    Define Beams, Columns, Slabs?

Beams

Horizontal member of a structure. It Carries transverse loads

It is classified into-

• SIMPLY SUPPORTED BEAM
• OVERHANGING BEAM
• CANTILEVER BEAM
• FIXED BEAM
• PROPPED
• CONTINUOUS BEAM

Columns

Column is a vertical structural member. It transmits the load from ceiling/roof slab and beam, including its self-weight to the foundation.

This is classified into three types-

• Long Column/ Slender
• Short Column
• Intermediate Column

Slabs

• It is a flat horizontal surface
• It is supported by beam and column
• It transfers load to the beam

This is classified into-

1. GRANAIT
2. MARBEL
3. CONCRETE

• ONE WAY
• TWO WAY
• FLAT
• BEAM

4.     RIBBED WOODEN

7.    Explain Staircases and its types?

The means of communication between various floors is offered by various structures such as stairs, lifts, ramps, ladders, escalators.

STAIR: A stair is a series of steps arranged in a manner as to connect different floors of a building. Stairs are designed to provide an easy and quick access to different floors.

• A staircase is an enclosure which contains the complete stairway.
• In a residential house stairs may be provided near the entrance.
• In a public building, stairs must be from main entrance and located centrally.

STAIRCASE: Room of a building where stair is located.

STAIRWAY: Space occupied by the stair.

Requirement Of Good Staircase

Stairs should be so located that it is easily accessible from the different rooms of a building.

It should have adequate light and proper ventilation.

It should have sufficient stair width to accommodate no. Of persons in peak hour/emergency.

Generally for interior stairs, clear width may be

• At least 50cm in one/two family dwellings
• At least 90cm in hotels, motels, apartment and industrial building
• At least 1.1m for other types like hospitals, temples etc.

No. Of steps in a flight should be restricted to a maximum of 12, minimum of 3.

Ample head room should be provided for tall people to give feeling of spaciousness. It should be minimum of 2.15m.

Risers and treads sizes should be provided from common point view.

TYPES OF STAIRS

1. Straight stair
2. Turning stairs
3. Circular stair
4. Spiral stairs
5. Curved stair
6. Geometric stair
7. Bifurcated stair

Classification Of Stairs Based On Materials Of Construction

• Wooden
• Stone 
• Brick 
• Metals/steel
• Plane concrete
• RCC

8.    Define floor and its types?

Floors

A floor is the bottom surface of a room or vehicle. Flooring is the general term for a permanent covering of a floor, or for the work of installing such a floor covering. A lot of variety exists in flooring and there are different types of floors due to the fact that it is the first thing that catches your eye when you walk into a house, as it spans across the length and breadth of the house. It is also the surface that goes through the most wear and tear, and that's why choosing the right material is of utmost importance.

Types of Floors

1. MUD FLOOR:

Earthen Flooring also commonly known as Adobe flooring is made  up of dirt, raw earth or other unworked ground materials. In modern times, it is usually constructed with mixture of sand, clay and finely chopped straw.

Mud flooring is commonly constructed in villages where by using stabilizers the properties of the soil are enhanced by manipulating its composition by adding suitable stabilizers. The tensile and shear strength of the soil is increased and  shrinkage is reduced.

2. BRICK FLOOR:

Brick flooring is one of the types of floors whose topping is of brick. These are easy to construct and repair but the surface resulting from these is not smooth and is rough, hence, easily absorbs and retains moisture which may cause dampness in the building.

3. TILE FLOOR:

The floor whose topping is of tiles is called tile floor. The tiles used may be of any desired quality, color, shape or thickness.

4. FLAGSTONE FLOOR:

The floors whose topping consists of stone slabs is called flagstone floor. The stone slabs used here may not be of the same size but should not be more than 75 cm length and not less than 35 cm in width and 3.8 cm in thickness.

5. CEMENT CONCRETE FLOOR:

The types of floors whose topping consists of cement concrete is called cement concrete floor or conglomerate floor. These floors consists of 2.5 cm to 5cm thick concrete layer laid over 10 cm thick base concrete and 10 cm thick clean sand over ground whose compaction and consolidation is done. These floors are commonly used these days.

6.TERRAZZO FLOOR:

Terrazzo is a composite material, poured in place or precast, which is used for floor and wall treatments. It consists of chips of marble, quartz, granite, glass, or other suitable material, poured with a cementations binder (for chemical binding), polymeric (for physical binding), or a combination of both.

9.    What is Doors and windows ? also list and explain the different types of doors and windows?

A door is a movable barrier provided in the opening of a wall, to provide access to various spaces of a building. A door is a frame work of wood, steel etc. secured in the wall opening for the purpose of providing access to the users of the building.

Types of Doors 

1. Type of doors based on material 
2. Types of doors based on placing of components 
3. Types of doors based on working functional

Type of doors based on material 

WOODEN DOOR

• Wooden doors are classic choice for many Indians.
• This door material does not go out of fashion even if by passing long generations.
• They are like first preference of home owners without any hesitation.
• There are certain reasons due to which wooden doors are quite famous.

GLASS DOORS

• Glass doors makes an excellent choice for business houses as well as home owners.
• For the doors open towards outwards will provide great natural view .
• Glass doors provide great aesthetic look to business houses , hospitals.
• Easy to clean with liquid detergent available in market.
• Glass doors are not damaged by any insects , termites , or rain or sun.

STEEL DOORS

• Steel doors are mostly preferred outside or main doors of the house. They are not preferred for interior door of the house.
• Even though steel doors are used for institutional purposes ,but it can be used for residential purposes.
• Steel doors are mainly used for garages, Storage rooms and for commercial and institutional buildings.
• But still many home owners use it for residential homes.

PVC DOORS

• PVC doors are appreciated for their benefits as an affordable and durable material.
• Vinyl doors have superior durability and not damaged by termites.
• They are self extinguishing making the house fire resistant.
• They are very good insulators.

FIBER GLASS DOORS

• Wooden doors require a lot of maintenance. • If not maintained properly they can wrap, rot or corroded.
• But there are other materials available which door is more better. Fiber glass doors is one of them.
• They have a very good range of designs .
• Fiber glass doors are fairly modern providing great benefits.
• Fiber glass doors are very durable as they are moisture resistant, whether resistant.
• They provide good security as they are heavy in nature.

ALUMINIUM DOORS

• Aluminium doors are widely used in commercial building.
• But now people are also using it in residential buildings for modernizing purpose.
• They are very durable and have high strength .
• Aluminium resist rust , therefore they are good for coastal areas.
• They are having high cost.

Types of Doors based on Placing of Components:

BATTENED AND LEDGED DOORS

• These doors are wooden or timber doors in which battens are vertical wood slabs joined together horizontally with the help of wooden ledges.
• To make more durable doors wooden strips are joined diagonally which are called braces. 
• For simple battened and ledged doors framework is provided through 2 vertical slabs.

BATTENED, LEDGED AND BRACED DOORS

• To make more durable doors wooden strips are joined diagonally which are called braces.

BATTENED, LEDGED AND FRAMED DOORS

• For simple battened and ledged doors framework is provided through 2 vertical slabs.

FRAMED AND PANELLED DOORS

• These doors look very elegant and are most preferred Indian doors. They are widely used.
• In this doors frame is prepared in which the timbers are grooved along with inner edges of frame and the jointed together.

GLAZED DOORS

• Glazed doors are generally transparent.
• They are mostly preferred in Institutional buildings.

FLUSHED DOORS

• Flushed doors have two parts.
• Inner part is made with either hard strips of timber or hollow cardboard materials.
• Then outer side is glued with plywood sheet or veneer finish under high pressure.

Types of doors based on working functions:

REVOLVING DOORS

• Revolving doors are one of the fascinating doors.
• They are mainly used in institutional buildings like hospitals, hotels, museums, offices.
• Revolving doors revolves in 360 degree angle.
• Only limited people can enter at a single time.

SLIDING DOOR

• Sliding door is one of the most essential requirement of modern buildings now a days.
• Due to lack of space and easy functionality they are most preferred.
• Also for natural view glass sliding doors are mostly preferred.

SWING DOORS

• Swing doors swings in 180 degree angle.
• Swing door is the style which is mostly used in Indian homes.
• They are the oldest form of doors.
• Due to it’s look, strength and security purpose it is used mostly.

COLLAPSIBLE STEEL DOOR

• They are mainly used for outside door of home . Then can collapse horizontally saving space.
• They are very strong.
• Very long lasting

SHUTTER DOORS

• These doors are mainly used for garage purposes. But many people are using for security purpose on front doors.

Windows

A window may be defined as an opening made in the wall for the purpose of providing day light, vision and ventilation. Windows are also made of frame work of wood, steel, aluminium etc., provided with shutters.

TYPES OF WINDOWS

Depending upon the manner of fixing, materials used for construction, nature of the operational movements of shutters , etc.,

The common varieties of windows used in the building can be grouped as follows:

1. Casement windows

2. Sliding windows

3. Metal windows 

4. Corner windows

5. Gable windows bay windows

6. Lantern or lantern lights

7. Skylights

CASEMENT WINDOWS:    

These are the windows, the shutters of which open like doors. The construction of a casement window is similar to the door construction.

SLIDING WINDOWS:

These windows are similar to the sliding doors and the shutters moves on the roller bearings, either horizontally or vertically. Such windows are provided in trains, buses, bank counter, shops etc.

METAL WINDOWS:

These are now a days widely used, especially for public building. The metal used in construction may be mild steel, bronze, or other alloys. The metal frame may be fixed direct to the wall or it may be fixed on a wooden frame.

CORNER WINDOWS:

These windows are provided at the corner of a room .They are placed at the corner of the room and thus they have two faces in two perpendicular direction. Due to such situation, there is entry of light and air from two direction and in many cases , the elevation of building is also improved.

GABLE WINDOWS:

These  are the windows which are provided in the gable ends of a roof.

BAY WINDOWS:

These windows project outside the external wall of a room. They maybe square , splayed, circular, polygonal or of any shape. The projection of bay windows may start from floor level or sill level. These windows admit more lights, increase opening area , provide ventilation and improve the appearance of building.

LANTERNS:

These are the windows which are fixed on flat roofs to provide light to the inner portion of building where light coming from external windows are insufficient. They maybe square or rectangular or curved.

SKYLIGHTS:

These are the windows which are provided on the sloping surface of a pitched roof. The common rafter are suitably trimmed and the skylight is erected on a curb frame. As skylight are mainly meant for light, they are usually provided with the fixed glass panel.

10.                       What are Principles of building planning ?

The factors or principles which govern the theory of planning are given below:
1. Aspect
2. Prospect
3. Privacy
4. Furniture requirements
5. Roominess
6. Grouping
7. Circulation
8. Sanitation
9. Flexibility
10. Elegance
11. Economy
12. Practical considerations

ASPECT

• Placement of different rooms of house in accordance with our activities at different hours of day.
• Rooms should get enough sunlight and air, which gives,
• Great environment
• Comfort  etc
• A room which receives light & air from particular direction is said to have ‘aspect’ of that direction.

PROSPECT

• Prospect is the view from outside of a house.
• The house should have a proper prospect so that it can give a feeling of cheerfulness to the people living in it.
• It should create a good impression on a person who views it from outside.
• It must also possess good qualities like comfort, cheerfulness, security, labour saving and modern outlook.
• For e.g. Small Projections or bay window can have a good out-look as well as helps in providing breeze, light and sunlight to the room.

PRIVACY

It is an important principle while planning a residential building.

Privacy can be maintained in ways:

1. External

2. Internal

External Privacy : The privacy from sides can be secured by providing planned entrance and pathways. This can achieved by screening the front and rear entrance

Internal Privacy : Privacy in internal rooms can be easily obtain by proper planning of diff. Areas and location of doors and windows.  The shutter when opened should give the minimum view of room for an entering persons.

CIRCULATION

• Circulation is movement within the premises and includes both horizontal and vertical circulation.
• Horizontal circulation ( room to room)
• Passage
• Corridors
• Lobbies etc.
• Vertical circulation (floor to floor)
• Stairs
• Roominess
• Roominess means getting maximum advantage from the minimum dimension of the room.
• The effect of roominess depend on the relative dimension of length, width and height of room.
• The shape and size of the room are also very important for roominess. A rectangular room has more roominess then square room in same area.

GROUPING

• Grouping means the arrangement of various rooms in the building for the convenience of user.
• It minimizes the circulation and at the same time improves the comfort.
• A dinning room should be close to kitchen ,while sanitary be away from kitchen, but convenient to bed rooms.

ELEGANCE

• Elegance is grand appearance of a building attained mainly owing to the elevation which in turn depends on the plan.

It depends upon proper positioning/selection of doors, windows, balcony, roofs, staircase etc.

For better elegance

• Selecting superior building material for facing as polished stone- granite, marble or mosaic.
• Providing projection like sunshades, balconies, porch with or without pergola opening.
• Providing bay window, corner window, etc.

SANITATION

• It includes providing light ,ventilation, cleanliness, water supply and sanitary amenities.
• For residential building window area should not less then 1/10th of floor area.
• In school not less than 1/5th of the floor area.

FLEXIBILITY

• Flexibility means that a room which is planned for one function be used for other, if required.
• Like study room may be planned for using guest room. Etc..

ECONOMY

• The building should have minimum floor area with maximum utility. It will reduce cost of the building .hence, it will be economical.
• Economy can achieved by-
• Providing simple elevation.
• Reducing the storey height.
• Dispensing of porches, lobbies and balconies.

PRACTICAL CONSIDERATION

• After the all fundamental some practical points should be additionally considered:
• Provision for future extensions without dismantling should be made while planning.
• Strength, stability, convenience and comfort of occupants, should be the first consideration while planning.
• As far as possible sizes of rooms should be kept large. Large room can be shortened by providing movable partition but smaller room cannot be enlarge easily.
• The number of door and window should be minimum provisions for built in furniture at proper places are useful from point of view of utility.

11.                       Explain different types of ventilation?

1.Natural ventilation

2.Mechanical Ventilation 

NATURAL VENTILATION

Is ventilation that occurs primarily through open windows and doors and by infiltration through cracks in the building envelope, such as walls, around windows and any penetration through the walls. Natural ventilation is driven by wind or pressure and/or temperature differences between inside and outside a building. One of the biggest advantages of natural ventilation is that it does not cost any money to run. Mechanical ventilation and electronic climate control can be quite costly, and may contribute significantly to the overall energy costs involved with running a building. No use of energy also makes natural ventilation an environmentally friendly choice.

Three forms of natural ventilation are:

• Through ventilation
• Cross ventilation
• Back to back ventilation

Through ventilation: In this method the windows are opposite to each other, so that a current of air may pass straight through the room.

Cross ventilation: In this method the windows are so placed that a current of air may pass diagonally across the room. Cross ventilation is obtained by having windows in both sides of the room, causing airflow across the space. Positive pressure on the windward and/or a vacuum on the lee side of the building causes air movement across the rooms from the windward to the lee side, provided the windows on both sides of the room are open.

Back to back ventilation: Neither through ventilation nor cross ventilation takes place. It is considered to be unhygienic type of ventilation, since the same air tends to be repeatedly used without being replaced. 

MECHANICAL VENTILATION OR FORCED VENTILATION 

Outside air is delivered indoors typically with a fans, which draws air from outside and forces it through ducts to the place where occupants are located. Mechanical ventilation can exacerbate infiltration and/or ex filtration.

Three forms of artificial/mechanical ventilation are:- 

• Exhaust (extractor/vacuum) system
• Pressure (plenum/propulsion) system
• Balanced system 

Exhaust (extractor/vacuum) system: Fans draw air out of the building in openings high up in the outside walls. The air thus drawn out is replaced by fresh air through windows and other inlets.

Pressure system: Unlike the exhaust system, this forces the air into a building and therefore control of entering air is possible, the fresh entering air displaces the used up air. The advantage of this method is that the source of air-entry can be controlled and its purity thereby ensured.

Balanced system: This is a combination of the exhaust and plenum system. Air is drawn in through ducts by means of a centrifugal fan and extracted at suitable points by exhaust fan. When this system of ventilation is employed there should be no natural inlets or outlets.

• It includes providing light ,ventilation, cleanliness, water supply and sanitary amenities.
• For residential building window area should not less then 1/10th of floor area.
• In school not less than 1/5th of the floor area.