AFFORDABLE HOUSING IN SOUTH EAST ASIA

Purbasha M. Chakraborty

Debjani Bhattacharya

DEFINITION

Affordable housing is a term used to describe dwelling units whose total housing costs are deemed "affordable" to those that have a median income. Although the term is often applied to rental housing that is within the financial means of those in the lower income ranges of a geographical area, the concept is applicable to both renters and purchasers in all income ranges. This article focuses on the affordability of owner-occupied and private rental housing as social housing is a specialized tenure.

A roof is constructed to support the dead load of the structure and its covering, insulation and internal finishes, snow loads and pressure or suction due to wind and live load without undue deflection or distortion. In engineering parlance roof is termed as slab.

ROOF

FUNCTIONAL REQUIREMENTS OF A ROOF

Strength and stability Resistance to weather and ground moisture Durability and freedom from maintenance Fire safety Resistance to the passage of heat Resistance to the passage of sound

Strength

The strength of a roof/ floor/ slab depends on the characteristics of the materials used for the structure of the floor, such as timber, steel or concrete. The floor structure must be strong enough to safely support the dead load of the floor and its finishes, fixtures, partitions and services and the anticipated imposed loads. Dead loads are calculated from the unit weight of the materials set out in IS 875 : Part I and imposed loads from IS 875: Part II.

Stability

The slab should have adequate stiffness to remain reasonably stable and horizontal under the dead load of the floor structure and such partitions and other fixtures it supports and the anticipated static and live loads it is designed to support. The floor structure should also support and accommodate either in its depth, or below or above, electrical, water, heating and ventilating services without affecting its stability. For stability there should be adequate support for the floor structure and the floor should have adequate stiffness against gross deflection under load.

Resistance to weather and ground moisture

The slab should be able to protect the ingress of moisture

either from the ground from the top. The degree of penetration of moisture from the ground to a floor will depend on the nature of the subsoil, the water table and whether the site is level or sloping.

On a gravel or coarse grained sand base, where the water table throughout the year is well below the surface, there will be little penetration whereas on a clay base, the water table is close to the surface, there will be appreciable penetration of moisture from the ground to floors.

Durability and freedom from maintenance

Ground floors on a solid base protected against rising moisture from the ground, and suspended upper floors solidly supported and adequately constructed and protected inside a sound envelope of walls and roof, should be durable for the expected life of the building and require little maintenance or repair.

Fire safety

Suspended upper floors should be so constructed to provide resistance to fire for a period adequate for the escape of the occupants from the building. The notional periods of resistance to fire, from 2 to 4 hours, depending on the size and use of the building, are set out in different Building Regulations.

Resistance to the passage of heat

A floor should provide resistance to transfer of heat where there is normally a significant air temperature difference on the opposite sides of the floor, e.g., where a floor is exposed to outside air. A ground floor should be constructed to minimize transfer of heat from the building to the ground or the ground to the building. Both hardcore and a damp-proof membrane on, under or sandwiched in the over site concrete will assist in preventing the floor being damp and feeling cold and reduce heating required for comfort and reduce transfer of heat.

Resistance to the passage of sound

Upper floors that separate dwellings, or separate noisy from quiet activities, should act as a barrier to the transmission of airborne sound and reduce impact sound.

Types of Roof

The principal types of reinforced concrete floor

construction are:

Beam and slab, Waffle grid slab, Drop beam and slab and Flat slab .

(1) Beam and slab floor

It is generally the most economical and therefore most usual form of floor construction for reinforced concrete frames. A rectangular column grid supports beams and floor as shown in left-hand side sketch. The floor can be cast in-situ on shuttering and form work. The floor may be formed with pre cast reinforced concrete floor beams, planks, tee beams or beam and infill blocks that require little or no temporary support and on which a screed or structural concrete topping is spread. Pre cast beams and plank floors require no temporary support in the form of shuttering. The advantage of these pre cast floor systems is that there is a saving in site labour in erecting and striking the form work. The most commonly used pre cast floor are described below.

Beam and slab floor

Pre cast hollow floor units

These floors comprise of large pre cast reinforced

concrete, hollow floor units of different size. The purpose of the voids or hollows in the floor units is to reduce dead weight without affecting strength. The reinforcement is cast into the webs between hollows. The hollow floor units can be used by themselves as floor slab with a floor screed or they may be used with a structural reinforced concrete topping with tie bars over beams for composite action with the beams.

Pre cast hollow floor units

Pre cast concrete plank floor units

These are comparatively thin, reinforced solid plank, concrete floor units and are designed as permanent shuttering and for composite action with structural reinforced concrete topping. It may be necessary to provide some temporary propping to the underside of these planks until the concrete topping has gained sufficient strength. The popular concrete plank floor unit is known as pre cast reinforced concrete plank and joists system by Indian standards having 300mm wide planks, partially 30mm thick and partially 60mm thick with a maximum length of 1.5m.

Pre cast concrete plank floor units

Pre cast beam and filler block floor

This floor system consists of pre cast reinforced concrete planks or beams that support pre cast hollow concrete filler blocks. The planks or beams are laid between supports with the filler blocks between them and a concrete topping is spread over the planks and filler blocks. The reinforcement protruding from the top of the planks acts with the concrete topping to form a reinforced concrete beam.

The advantage of this system is that the lightweight planks or beams and filler blocks can be lifted much more easily and placed in position than the much larger hollow concrete floor units

Pre cast beam and filler block floor

(2) Waffle grid slab floor :

If the column grid is increased from about 6.0 to about 12.0 square or near square it becomes economical to use a floor with intermediate cross beams supporting thin floor slabs. The intermediate cross beams are cast on a regular square grid that gives the underside of the floor the appearance of a waffle, hence the name.

The advantage of the intermediate beams of the waffle is that they support a thin floor slab and so educe the dead weight of the floor as compared to a flush slab of similar span. This type of floor is used where a widely spaced square column grid is necessary.

Waffle grid slab floor

(3) Drop slab floor

This floor construction consists of a floor slab which is thickened between columns in the form of a shallow but wide beam. A drop slab floor is of about the same dead weight and cost as a comparable slab and beam floor and will have up to half the depth of floor construction from top of slab to sophist of beams. This difference would cause a significant reduction in overall height of construction of a multi- storey building with appreciable saving in cost.

Drop slab floor

(4) Flat slab (plate) floor

In this floor construction the slab is of uniform thickness throughout, without down stand beams and with the reinforcement more closely spaced between the points of support from columns. To provide sufficient resistance to shear at the junction of columns and floor, hunched or square headed columns are often formed.

The dead weight of this floor and its cost are greater than the floor Systems earlier explained but its depth is less and this latter advantage provides the least overall depth of construction in multi-storey buildings.

Flat slab (plate) floor

FOUNDATIONS

The foundations of buildings bear on and transmit loads to the ground. The foundation is that part of walls, piers and columns which is in direct contact with and transmit loads to the ground.

The Functional Requirements of foundation in general

Strength and stability

Resistance to ground moisture

Resistance to the passage of heat

Types Of Foundation

Strip foundation

Isolated foundation

Raft foundation

Pile foundation

Shot-bored piles

Strip foundation

Strip Foundations consist of a continuous strip, made

up of brick masonry/stone masonry/concrete formed centrally under load bearing walls. The continuous strip serves as a level base on which the wall is built and is of such a width as is necessary to spread the load on the foundations to an area of subsoil capable of supporting the load without undue compaction.

Isolated foundation

It is sometimes economical to construct a foundation of isolated piers or columns of brick or concrete supporting reinforced concrete ground beams in turn supporting walls, rather than excavating deep trenches and raising walls off strip foundations, some depth below ground. The isolated foundations are typical rectangular or trapezoidal block made up of reinforced concrete. In some places where burnt clay brick quality is good, these are made with burned bricks also.

Raft foundation

The Raft foundations consist of a raft of reinforced concrete under the whole of the building designated to transmit the load of the building to the subsoil below the raft. Raft foundations are used for buildings on compressible ground such as very soft clays, alluvial deposits and compressible fill material where strip foundations would not provide a stable foundation. A typical raft foundation comprises of beam column system along with huge slab below ground.

Pile foundation

Where the subsoil has poor or uncertain bearing capacity or where there is likely to be appreciable ground movement as with firm, shrinkable clay or where the foundation should be deeper than stay 2 m, it is often economical to use piles. A pile is a column of concrete either cast in or driven into the ground to transfer loads through the poor bearing soil to a more stable stratum. The piles support reinforced concrete beams off which load bearing wall are built.

Shot-bored piles

For small buildings, for example on shrinkable clays where adjacent trees or the felling of trees makes for appreciable volume change in the subsoil for some depth, it is often wise and economical to use a system of short-bored piles for foundations. Short-bored, that is short length, piles are cast in holes augured by hand or machine.

WALLING

A wall is a continuous, normally vertical structure of brick, stone, concrete, timber or metal, thin in proportion to its length and height, which encloses and protects a building or serves to divide buildings into rooms. Walls are defined as external or internal to differentiate functional requirements, and as load bearing or non-load bearing to differentiate structural requirements. Walls are of two types, Solid and Framed.

Functional Requirement of walls

Strength and stability Resistance to weather and ground moisture

Durability and freedom from maintenance

Fire safety

Resistance to the passage of heat

Solid Walls

A solid wall (sometimes called a masonry wall) is constructed either of brick, burnt clay or stone blocks or concrete blocks laid in mortar. The blocks are laid to overlap in some form of what is called bonding or as a monolith, that is, one solid uninterrupted material such as concrete which is poured wet and hardens into a solid monolith (one piece of stone). A solid wall of bricks or blocks may be termed as a block (or masonry) wall, and a continuous solid wall of concrete, as a monolithic wall.

Solid wall of blocks of brick, stone or concrete

Solid wall

Frame wall

A frame wall is constructed from a frame of small sections of timber, concrete or metal joined together to provide strength and rigidity, over both faces of which, or between the members of the frame are fixed thin panels of some material to fulfill the functional requirements of the particular wall. Another popular construction practice all over the world is Frame construction i.e. beam column construction. The walls required to fill the space between beam columns are termed as infill walls. They are also treated as non-load bearing wall.

Frame wall of small sections of timber, metal or concrete

Frame wall

Affordable Housing Techniques: Asia-Pacific Region

Concrete Footings, Slabs, Columns, Beams

Features of Concrete in Structures

Concrete is a mixture of Portland cement, sand, stone and water, which sets hard. It may include various other components which provide colour, increase strength, accelerate hardening, retard hardening, improve fluidity, lighten the structure and many other functions.

Characteristics

Concrete is strong in compression, but weak in tension. It may crack when pulled apart, but not when squeezed together. Tensile strength is provided to concrete structures by the incorporation of steel reinforcement.

Characteristics

Concrete shrinks and thus cracks. The inclusion of steel reinforcement (at close centers) will restrict the width of cracks that for in concrete as it shrinks.

Characteristics

Steel reinforcement rusts, expands and spills the concrete if it is placed too close to the concrete surface or if the concrete does not include sufficient cement to protect the steel.

General Behaviour of Concrete Structures

When a concrete slab is suspended, it will bend under the action of its self weight and any imposed gravity loads. This will cause cracks to form at the top of the slab over supports and at the bottom of the slab at the centre of the span. It is at these locations the main tensile reinforcement is placed.

General Behaviour of Concrete Structures

Masonry Veneer and Cavity Construction

Reactive clay foundations under a building may swell to form a dome or shrink form a dish. In both cases, the concrete footings or beams & slabs will bend, placing stresses on the superstructure. The design of buildings with conventional masonry veneer and cavity masonry walls involves

Increasing the stiffness of the footings or beams & slabs

Incorporating articulation joints in the masonry walls to “break up" the structure, thus pre-empting the formation of any cracks.

Diagrammatic Representation

Crack Formation in Masonry House Walls

As the foundations shrink or swell and the concrete footings (or beam & slab) respond, the following can occur:

Un reinforced Masonry Walls Un reinforced masonry walls of weak masonry may form

multiple small cracks. If un reinforced masonry walls have relatively high strength,

they will remain intact for small movements, but will eventually crack. Most likely, this will be a single large crack, the most undesirable outcome.

Diagrammatic Representation

Reinforced Masonry Walls Connected to Concrete Slab

1. Single leaf reinforced hollow concrete masonry superstructures built integrally with the concrete footings, incorporating steel starter bars, vertical “wide spaced" reinforcement and a continuous horizontal bond beam are capable of cantilevering and spanning large distances without cracking.

Thickness and Reinforcement in Concrete Slabs-on-Ground

Often concrete slabs-on-ground are only 50 mm thick and do not contain any steel reinforcement. This can lead to cracking and moisture penetration. The thickness of slabs-on-ground (that are bigger than 3.0 m x 3.0 m) should be at least 70 mm thick with at least SL42 steel reinforcement mesh (3.8 diameter at 200 mm centers) over compacted fill. If the thickness is increased, so should the reinforcement be increased.

Reinforcement Congestion

Congestion of reinforcement within beams, columns and the like reduces the cover and leads to difficulties in compacting the concrete around the reinforcement. This can cause both corrosion and loss of bond between reinforcement and concrete.

Vibration

The strength of concrete members (footings, slabs, beams, and columns) is dependent on the density of the concrete. Concrete density can be maximized by adequate mechanical vibration. Mechanical vibration is recommended for all concrete members. Although AS 2870 does not make mechanical vibration of residential footings and slab-on-ground construction mandatory, it is strongly recommended.

Concrete Finishing

Mechanical trowel ling is used to produce a fine surface. However, if the concrete has not achieved sufficient hardness, the mechanical trowel (helicopter) may “dig into" the surface. Excessive trowelling will lead to a concentration of bleed water at the surface and eventual dusting and/or abrasion of the surface.

Curing

Contractors often neglect the correct curing of slabs, resulting in excessive cracking and/or dusting and abrasion. It may be expedient for the Builder to assume responsibility for applying and maintaining the curing system. Sprayed curing compounds require less attention than moistening and covering the slab for an extended period. Curing compounds should comply with AS 3799 and shall be hydrocarbon, solvent-based acrylic, water-based acrylic or wax-based acrylic. However, wax-based compounds should not be used in areas requiring the subsequent application of curing adhesives.

Recesses in Concrete Slabs

In order to achieve falls in tiled floors in bathrooms and the like, it is preferable to recess the concrete slabs, otherwise there will be a lip at the tiled edge. This recess may be formed after the concrete has been screened level. The corner position of recesses can be marked by fixing temporary vertical reinforcing bars to the fabric. Such bars should not puncture the membrane. For large tiled areas, the slab should provide for uniform falsetto wastes and associated pipe work. If there is likely to be difficulty in achieving such uniform falls, it may be advisable to allow for a 40 to 50 mm screed laid subsequently by the tilerin

Control Joints

Control joints in concrete structures should be of a material and detail such that they can accommodate the movement that is expected.

Termite Barriers

Care must be taken to ensure that any termite barrier can be properly located on the finished concrete structure.

Cracking Due To Excessive Retardant

Overdosing premixed concrete with retardant will cause excessive cracking and surface defects consistent with the extremely slow hardening.

Affordable Housing In Mauritius

MAURITIUS – The island

Evolution of Key Economic Indicators

Population as at date: ~ Rs 1.24 million

Main Sectors

Housing Sector In Mauritius

Main Players In Housing Sector

Commercial banks (total = 19)

Insurance companies (total = 19)

Mauritius Housing Company Ltd – MHC

National Housing Development Company Ltd –NHDC

Ministry of Land and Housing

MHC Ltd

Creation:1963

Mission: To help as many families as possible to become owners of a house and to be at the forefront of housing development in the country.

Provider of finance

MHC Ltd -Services

Core business : housing finance facilities to both individuals & private property developers

In-house Ancillary facilities1. Administer Government Sponsored Loans (GSL)2. Housing Savings scheme3. Life & Building Insurance4. Architectural & technical services5. Preparation of fixed charge documents

6. Term Deposits facilities

GSL –6.5% p.a. (offered by MHC Ltd)

Maximum loan amount: Rs 325,000, i.e. US$ 10,150(including grant from Govt)

Govt Grant: 20% of loan amount, maximum Rs 33,000, i.e., US$ 1,030

Monthly income of couple: maximum Rs 8,500, i.e., US$ 265

Repayment term: maximum 25 years

NHDC Ltd

Developer of low cost housing units Delivers 500 units per year while there is a waiting

list of 20,000 units Provides grants for slab cast (up to Rs 60,000, i.e.,

US$ 1,800) Provides grants for slab cast (up to Rs 60,000, i.e., US$ 1,800)

Provides grants for purchase of construction materials (up to Rs 35,000, i.e., US$ 1,060)

Construction of apartments

NHDC FLAT

Main Players In Housing Sector

Commercial banks and insurance companies : Offer housing finance facilities apart from their usual core banking activities.

MHC Ltd – provides finance NHDC – provider of housing units and grants to

lower income groups Ministry of Lands and Housing–provides broad

policies/ guidelines

Challenges

Inculcate savings culture in low income group

Proper land administration:

Area of Mauritius: 1,860 sq km

Assessment of market segments

1. Very low, Low

2. Moderate and High income groups

Affordability Increasing development/ construction costs Financing - Mauritius unable to raise finance from certain donor

agencies being a middle income country.

High cost of finance – past few years trend has been increasing interest rate

Mismatch --Lend on long term basis

--borrow on shorter term

Challenges

Challenges

Improve loan recovery methods For MHC 25% arrears from low income groups Sale By Levy

“Borrower Protection Act”1. Prudential measures to safeguard interests of both

lender & borrower

2. Lesser finance for low income clients

3. Arrears worsen

Challenges

Most important challenges:1. Managing risks

2. Maintaining incentives

3. Affordability

Affordable Housing In THAILAND

Thailand : Demographics

• Population – 65 million

• Population growth – less than 0.5 % per year

• Migration increasing urban housing needs

• 36 per cent – urban population

• GDP per capita -$US4,072

National Housing Policies

NESDB : National Housing Policy Subcommittee 1. 1982-19972. GH Bank + NHA + NESDB + Private sector3. Annual National Housing Report

No comprehensive national housing policy

3 main government units implement 1. government middle and low-income housing programs2. Government Housing Bank (GH Bank), National Housing 3. Authority (NHA) and Community Development 4. Organization Institute (CODI)

Private sector provides housing from low-income to Multi-million baht homes

New Housing Policies

Cabinet approved National Housing Policy Committee – May 28, 2008

Major responsibility of NHPC – oversee formulation of comprehensive long-term national housing policy

NHA and CODI play major role in housing provision for lower income groups

Private housing developers play a leading role in housing development for low - middle – high income group

National Housing Authority (NHA)

Assuring shelter for all residents in Thailand Operates as state enterprise Rental apartments, condominium, government employee housing Currently, primarily acts as an enabler between government and private sector

NHA – Baan Eur-Arthorn Project

Project to build 600,000 homes -

2005 Scaled down – currently 200,000

under construction Government subsidies granted to

private sector developers Houses sold at affordable prices GH Bank and Government Savings

Bank – buyer financing

Community Organization Development Institute (CODI)

Finance slum-area communities Develops community-based savings programs and

organization through co-operatives Funded from Government budget Baan Mankong program – very successful Since 2003, CODI has funded more than 77,000

households in more than 245 districts throughout

Thailand

Private-sector developers and mortgage lenders

Well developed private-sector

housing industry Provide most homes from

low-income sector to

multi-million dollar homes Commercial banks financing

readily available – 55%

market share GH bank market share of home

loans – 36%

Keys to future growth – policy issues

Reducing housing costs (Construction Technology) Government incentive programs for the LIG (BOI) Further developing housing financing markets Developing resale housing markets (professional brokers +licensing law) Strengthening professional housing associations Statistical data and Information for a well- functioning housing market (REIC+ GH Bank journal) Housing and housing finance education for the public (Homeownership counseling services)

Affordable Housing In CHINA