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International Symposia on Low Cost Housing Problems

Civil, Architectural and Environmental Engineering Conferences

09 Oct 1970

Construction Methods For Low-Cost Housing Construction Methods For Low-Cost Housing

V. Malakonda Reddy

A. S. Sarma

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Recommended Citation Recommended Citation Reddy, V. Malakonda and Sarma, A. S., "Construction Methods For Low-Cost Housing" (1970). International Symposia on Low Cost Housing Problems. 9. https://scholarsmine.mst.edu/islchp/9

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CONSTRUCTION METHODS FOR LOW-COST HOUSINGBy

V. Malakonda Reddy*

andA. S. Sarma**

1. INTRODUCTION

Housing is one of the major problems which India has to solve in a satisfactory manner. The main reasons for this problem being acute at present are population increase and rapid urbanization. Also the cost of housing, as compared to the limited financial resources of the community in India remains very high, on account of the high cost of building materials such as steel, cement and timber. The two prin­cipal components of housing cost are cost of labor and cost of materials. The cost of labor in India is only about 30 to *+0 percent ’ of the total cost of construction, the cost of materials being 60 to 70 percent. In some developed coun­tries, the ratio is just the reverse. So it is all the more important in India to introduce such housing concepts as would assure reduction in the consumption of structural materials. Any reduction in the consumption of materials will directly reduce the cost of labor and this can be achieved by intro­ducing better design concepts and new construction techniques.

2. LOW-COST DESIGN CONCEPTS

The general economy in the construction of a house can be achieved by:

a) Proper layoutb) Proper selection of materialsc) Better structural designs andd) Speedier and economical construction methods.

Before presenting the new techniques in building construction, it may not be out of place here to give a brief account of the conventional methods of construction adopted in this country.3. CONVENTIONAL METHODS OF CONSTRUCTION

A house, basically, consists of two major structural elements-walls and floors of roofs. These two items including doors and windows, in a conventional house, account for more than 70% of the total expenditure on it.3.1. The conventional types of walls.

i) Mud walls with or without bamboo reinforcement,ii) Brick masonry walls,

iii) Stone masonry walls.3.2. The conventional types of floors or roofs,

i) Thatched roof.

ii) Tiled, Asbestos cement, or Galvanised Iron sheet roof,iii) Madras terrace and the allied floors or roofs,iv) Reinforced concrete floor or roof.

‘Department of Civil Engineering, Regional Engineering College, Warangal-4, A.P., INDIA.‘•Lecturer in Civil Engineering, Regional Engineering College, Warangal-4, A.P., INDIA.

The above types of walls and floors or roofs are not very advantageous on account of one or more of the following reasons:

i) Heavy increase in the price of building materials,ii) Lack of economy in structural design,

iii) Slow and laborious process of construction,iv) Short span of life.v) Expensive maintenance.Various attempts are now being made to devise new methods

of construction, which can reduce building costs and also speed up construction, without affecting either the strength or the durability of the building.4. NEW METHODS OF CONSTRUCTION FOR LOW-COST HOUSING

In recent years, prefabrication of components of houses or complete houses has proved to be the most satisfactory method for reducing the consumption of structural and center­ing materials, construction time and skilled labor required at the site of work. Prefabrication does not necessarily mean mass-production, mechanization or installation of ex­pensive equipment.

Large scale mechanized prefabrication industry will be premature at the present stage of housing efforts in India because India does not have a strong industrial base and the great majority of the people live in rural areas which lack good transport facilities. A simple style of prefabrication, without the use of expensive equipment or mechanization is the need of the day. It would be possible to effect overall

economy in low-cost housing if prefabrication is adopted for the components which are light enough to be handled by a few men or a small mobile crane. The manufacture of the com­ponents should be located near the site of the housing pro­ject to reduce the transport charges. Also the locally available materials such as soil, stone, lime, fly ash, coal ash etc. should be used as freely as possible without sac­rificing the quality and the strength of the products.4.1. New forms of walls:

Some of the recent methods of construction of walls using the locally available materials and prefabrication techniques are illustrated below:

Oi) Rammed stabilized mud .Vide Fig.l.

For a single-storey house, the cheapest wall one can think of is a rammed in-situ stabilized mud wall. It can be built by laying mixture of mud with water and crushed straw into a sliding form and ramming it. Next layer is done after hardening of the previous one. For stabilization it is ad­visable to add cement or clay. Sliding form is made of timber as a unit about 10' long. The usual thickness of wall is 10". The wall can be improved by plastering or white washing.

ii) Soil-cement blocks3 .Vide Fig.2.

These blocks are used in walls varying in thickness from 6" to 12" upto a height of 12'. Soil-cement blocks are made by hand or power-operated machines in a standard unit size of 4" x 8" x 12" and also in three-quarter unit and half unit

sizes. Soil-cement mixtures with optimum moisture content are selected to give a minimum compressive strength of 250 lbs/in2 and a flexural strength of 50 lb/in2 after 28 days, n i ) Concrete hollow blocks * Vide Fig,3.

Prefabricated concrete hollow blocks are made from heavy or light-weight concrete can can be used for one or two- storyed houses as bearing walls or for multi-storyed houses as partitions. Blocks of nominal size 8" x 8" x 16", also three-quarter and half length blocks are produced using wooden or steel moulds by hand or machine. The walls are laid in the conventional way using composite cement lime mortar (1:1:10).iv) Pillars and panels** Vide Fig.4.

The pillar units can be of any suitable size but the most convenient one is 8" x 8" x 12". Such units can be solid or hollow and are provided with a groove on the sides to receive the panel slabs. They are made in cement mortar (1:6) in the same manner as concrete hollow blocks.

The panel slabs are 1 1/2" to 2" thick and 12" wide.The length varies with the spacing of "he pillars. The con­crete mix used is (1:2 1/2: 3 1/2) and the reinforcement is 1/4" bars longitudinally and 1/8" bars transversely at 8" centers. These units are made in simple wooden or steel moulds.v) Precast panels (UCOPAN)2 *^.Vide Fig.5.

These panels have been designed and standardized by the Calcutta Metropolitan Planning Organization. The panels are 1 1/2" thick and have two sizes 3' x 9' for walls and 3' x 10'

for floors and roofs. Different types of wall panels with

voids for doors, windows, ventilators or solid ones can be manufactured in a single-type universal form by using re­placeable inserts wherever necessary. The panels have a mesh reinforcement consisting of steel bars of diameters 1/8",3/16", 1/4" and 5/16". They have ribs 8" in depth which serve to provide the rigidity needed.v) Precast panels and cost-in-situ columns Vide Fig.6.

The panels are 1 1/2" thick and are lightly reinforced by steel mesh. They vary in size from 3*-2" x 3'-0" to 3'-4" to 2'-6". A set of two panels is placed together with an air gap of 4" to form the wall of 7" thickness. The sets of panels are keyed by cast-in-situ reinforced columns of 4" x 4" size. The columns are made continuous from foundation slab

to roof slab, thus making the walls and roof act in a mono­lithic way.

n4.2. New forms of floors and roofs 4.2.1.Floors

During the last 30 or 40 years the conventional types of floors have gradually given way to reinforced concrete floors which are being adopted on account of many advantages inherent in them. Although in-situ reinforced concrete construction

39

is still predominant, recent attempts to bring down the cost of house construction have evolved a number of new systems of precast floors. The new systems can be broadly classified into two categories, one category using entirely precast units for structural action and providing 1" to 2" topping of in-situ

concrete only as a finish and the other using composite con­struction of precast units and in-situ concrete for structural action. The chief draw back of the former is the loss of

monolithy compared to cast-in-situ construction. The latter combines, to a large extent, the advantages of both forms of construction. The types of floors that are going to be described are for relatively light loads, say, a live load of 40 lbs/sq.ft. and are ideal for low-cost houses.i) Precast T-beam type,Vide Fig.7 and 21b

This floor system is very simple and easy to construct and has been successfully used on a number of constructions in India. It is of two types - ordinary and hollow. For all spans, these units have a uniform flange width of 12". The depth of the rib and the reinforcement are adjusted to suit the span. After units are set in position, the joints are grouted to make them water-proof, with cement mortar (1:2), mixed with 10 percent of (by weight of cement) crude oil.

The hollow type of floor, although more expensive, pro­vides better heat insulation and also has the added advan­tage of better appearance due to flat ceiling. The T-beam units are cast in simple moulds either of wood or steel. If the number of units required is small, an adjustable mould can be made to make T-beams of different depths.ii) Composite T-beam type. Vide Fig.8

This floor consists of precast rectangular ribs support­ing precast slabs of 6* span and a layer of 1 1/2" thick in-situ concrete laid over them. The in-situ concrete when

poured, bonds with the precast rib and slabs so that the

rib together with portions of precast and in-situ slabs, acts as a T-beam; this action is further aided by the provision of stirrups protruding from the rib. For all spans, propping of beams at mid span is essential until in-situ concrete has hardened sufficiently.iii) Composite I-joist-slab type. Vide Fig.9

This floor is similar to the composite T-beam type ex­cept that I-joists are used instead of rectangular ribs and the ciling tiles are supported by the bottom Flanges of I-joists. The maximum spacing of the joists is usually limited to 3'-0" to facilitate the provision of flat ceiling.

Joists exceeding 12' span require propping.iv) Composite Joist-Filler block type. Vide Fig.10 S 21c.

In this floor, the depth and spacing of joists are governed by the dimensions of the filler block. The filler blocks can be assumed to assist the cast-in-situ slab in re­sisting the bending moment. For the purpose of calculation, the thickness of the shell of the filler block may be added to the slab. As the span of the slab is small, reinforce­ment for shrinkage and temperature stresses only is provided.

Work that is being carried out on this floor is described in para 5.

v) Precast Cellular slab-beam type.

This floor system was developed by the Central BuildingDResearch Institute, Roorkee, India. It is similar to the

composite Joist-Filler block type (Fig.10) except that the

filler blocks are replaced by 4" thick cellular slabs of size 20" x 40" allowing a larger spacing of 40" for the joists. The floor can be made of entirely precast units or composite in construction.

vi) Precast Hollow beam type.Vide Fig.11.

The units for such floors are manufactured in one piece to the required span and therefore are restricted to a max­imum span of 14' as beyond this limit the individual units become too heavy for easy handling. The beams are usually made 12" wide and their depth is varied to suit the span.The hollow cores are made by means of pneumatic tubes, which are inflated to the necessary pressure and fixed in position. About 12 hours after the concrete is laid the tubes are de­flated and removed.

vii) Precast Joist-brick type.Vide Fig.12.

The floor system consists of precast trapezoidal joists with bevelled bricks on edge placed between them. The bricks can be bevelled at edges by masons during construction or they can be specially manufactured. This system is recommended where bricks of good quality are available at a reasonable rate. The depth and spacing of joists are governed by the dimensions of the brick.viii) Precast panel type. Vide Fig.13.

The special feature of this floor is that a standard panel of size 8" x 24" x 168" has been developed by the Cal- cutta Metropolitan Planning Organization for the purpose of using it for low-cost housing in rural areas. The use of this

standard panel eliminates completely the forms and scaffoldings and the need for plastering the concrete surfaces. The amount of concrete and steel required for this panel is found to be considerably less than that required under conventional cast- in-situ flooring.

ix) Precast doubly curved tile type.9Vide Fig.21a.This floor system consists of 3/4" to 1" thick plain

concrete doubly curved tiles square or rectangular in plan supported on partially precast concrete joists. The method of making tiles and joists and construction of the floor is so devised that it can easily be adopted by unskilled workers, even at the village level. By adopting a smaller size of the tile (shell) units, even the normally required R.C.C. edge beams can be omitted.4.2.2.Roofs:

The construction of precast roofs is similar to that of floors except that the roofs require improved insulation through a ceiling or by an additional insulation course. The special requirements for roofs are given below:

Water Proofing: In order that a roof is leak-proof against heavy rains, it is adequately sloped to drain away water

and a water proof course is laid over the structural slab.The slope required is generally 1 in 50 and is provided either

in the structural roof or in the insulation layer.Several methods of water proofing are available in­

cluding .

i) Lime terracing - an indigeneous method popular in the Eastern and Northern parts of the country,

and ii) Laying a bitumen compound or felt.A simple method of water proofing is to place a layer

of paper or bitumen and cover it with another layer of 1 1/2" thick flat tiles set in cement mortar.Thermal insulation: Due to the prevalence of high tempera­tures in India, thermal insulation of roofs is very essential for comfortable living.

A number of proprietory insulating materials, which are costly, are available but equally effective results can be obtained with a 3" layer of earth preferably mixed with rice husk and covered with 3/4" flat tiles set in cement mortar

or a 2" insulating concrete layer made with rice husk, cin­der or other light weight aggregates.

As air is a good insulating medium, the adoption of such roof systems as Hollow beam, Cellular slab-beam or composite joist-filler block type in which air spaces are preformed in the structural portion of the roof itself is advantageous. In such roofs, the insulation layer may be dispersed with or its thickness can be considerably reduced.4.3. New forms of door and window frames.

Since good seasoned wood is not easily available ex­

cept at exorbitant prices, substantial savings in cost can be affected by replacing the timber frames of doors and win­

dows by those of reinforced concrete. They cost about half

the price of country teakwood and are becoming increasingly popular, especially for low-cost houses. The details of doors and windows with R.C.C. frames are given in Fig.17.4.4. New forms of lintels.

For low cost houses, dressed stone lintels upto a clear span of 3'-0" are used. Even stone sunshades are used when they are locally available. Also present R.C.C. lintels with or without sunshades are widely used. The details of a pre­cast lintel with sunshade are given in Fig.18.4.5. Erection.

A simple device of lifting precast roof units is ill­

ustrated in Fig.19. In this device, no special mechanical lifting tackle is used. The units are tied with ropes and dragged up along the inclined rafters by two unskilled laborers.5. WORK BEING CARRIED OUT BY THE AUTHORS.

The authors are now investigating the various aspects of the composite joist-filler block system (Fig.10) with a view to effecting further economy. This system, because of its flat ceiling, has better appearance. It also has better insulating properties due te the presence of hollow spaces in

it. The cast-in-situ concrete while acting as a compression

40

flange of the joist, makes the system monolithic. It uses less quantity of steel for the same covered area and virtually eliminates the costly forms and scaffoldings. It is about 25% cheaper than the conventional R.C.C. roof. The units (Filler blocks and joists) are manufactured using simple wooden moulds shown in Fig.14 and 15 respectively.

In some of the filler blocks, cement is partly replaced by fly ash to reduce their cost and sand is replaced by coal ash to reduce their weight. Also short pieces of binding wire are mixed in the cement mortar on the tension side of some of the filler blocks to see whether they will improve the ten­sile strength. In order to study the short and long time be­havior of this roof, a demonstration room is constructed and it is now under observation. The photographs showing the filler blocks as they are manufactured and the wooden mould used to manufacture the same are given in Fig. 16a and 16b respectively. The photograph showing the arrangement of the filler blocks on joists is given in Fig. 16c.6. TYPICAL LOW-COST HOUSES.

In India, according to a recent estimate, there is a dearth of about 12 million houses in urban areas and 72 million houses in rural areas. Most of these houses are generally needed for slum clearance schemes in big and small cities and for accommodating the growing number of industrial workers, whose needs can be met by low-cost houses. A low- cost house is generally meant for a small family with low- income and consists of one or two living rooms in addition to a kitchen with dining room, bath and lavatory. The bath and the lavatory rooms may not always be roofed. The area of such houses varies from 150 to 400 sq.ft, and the cost is about Rs. 25/-per sq.ft, of plinth area, if the conventional type of construction is adopted. The typical layout of a low cost house with conventional type of construction is given in Fig. 20. The sections of three units of low cost-houses with load bearing walls using new forms of construction are shown in Fig. 21.

Also the plan, section and elevation of a typical low- cost house with non-load bearing walls and candella type hyperbolic paraboloid roof10 are shown in Fig. 22. The photographs showing the form work for the shell and the partition walls of the house are given in Fig. 23a and 23b

respectively.The houses, the details of which are given in Fig. 21

and 22 are actually constructed at Visakhapatnam by Town- Planning Trust^ for demonstration. A statement of compa­rative costs based on the type of construction is given in

Table. I.

TABLE.I.Statement of comparative costs.

SIJJo* Type of construction.Plinth Plintharea of area Remarks.one unit, cost/sq.ft. sq.ft.

Rs.Ps.1. Conventional brick masonry

(load-bearing) for walls with R.C.C.roofing and cement or stone slab flooring (Fig. 20).

2. Precast concrete hollow block masonry for walls with D.C.shell roofing and Hessian flooring(Fig.21)

3. Precast concrete hollow block masonry for walls with precast T-beam roofing and precast slab flooring (Fig.21)

4. Precast concrete hollow block masonry with composite joist-filler block roofing and brick on-edge flooring (Fig.21)

5. 9" and 6" brick masonry for partition walls with Cande­lla type H.P.shell roofing and brick-on-edge flooring (Fig.22)

340 25.00

170 14.64 This cost isbased on the existing rates of materials and labor in

170 15.04 Andhra PradeshSouth India.

170 14.15

264 11.50 Bath and W.C.not roofed.

ACKNOWLEDGEMENTS:The authors are thankful to Prof. M. J. Kirpalani, Princi­

pal, Regional Engineering College, Warangal, India for his en­couragement in preparing this paper. They are also thankful to the authors of the various references from which the material is freely drawn.

REFERENCES

1. "Low-cost Concrete Houses"-1963. The Concrete Associationof India, Cement House, 121, Queen's Road, Bombay.

2. "Papers on Housing" - 1969. Calcutta Metropolitan PlanningOrganization, Development and Planning (T S CP) Dept.Govt, of West Bengal, Calcutta.

3. "Low cost-Soil Cement Houses" 1966. The concrete Associa­tion of India, Bombay.

4. "Elementary Hand book of Concrete House Construction" - 1963The Concrete Association of India, Bombay.

5. "Low cost Housing-designs for North Bengal-Siliguri Plan­ning Organization, Development and Planning (T S CP)Dept., Govt, of West Bengal, Calcutta.

6. "Low cost Integral House" - S.K.Iyer, Architecture andBuilding Industry, May 1969, 87/88, New Market, Begam Bridge, Meerut, U.P.

7. "Precast Concrete Floors and Roofs" - 1958, The ConcreteAssociation of India, Bombay.

8. "Building Digest 45" Sept., 1966, Central Building ResearchInstitute, Roorkee, U.P., India.

9. "Building Digest-43" July, 1966, Central Building ResearchInstitute, Roorkee, India.

10. A Private communication dt. 1-8-1970 from the Chairman,T o m Planning Trust, Visakhapatnam, Andhra Pradesh, India.

41

FIG- I. RAMMED STABILISED MUD WALL -

TIG- 2 A WOODEN MOULD FOR MAKING S O IL. CEMENT BLOCKS

FIG. 3 ( a j WOODEN MOULD FOR MAKING ONE HOLLOW CONCRETE BLOCKAT A T IM E

42

Stole - <J)

WPl 9XSUD

WPiftKU)

«Pl X 5LW

(S>W A L L P A N E L T Y P E S

Nofe -All fxinelt should be produced m H** Same

f o r m * 70<*e o.<<ord<n§ Am **+ t*n>pfa.te f< * &<• Fmrm mmd supplem ented w »M inserts

P J G 5 P R E C A S T P A N E L S ( u c O P A N j

F I S 6 P R E C A S T P A N E L S A U O C A S T - IN —S I T U C O L U M N S .

43

o-CBLiNa m i

S P E C IF IC A TIO N S :i . f i l l e r s l o c k . . c m - r <a. j o i s t ................. 11 a : a n i x .s. c a s t >h t m i c m c u r a i . a > 4 M iK .

INDEX.@ . SPACINB OF JO ST C .C C . 2 4 - 'L : L X N fiT I OF F IL L M BLOCK • 2 1 Jjg." T . TNICNMISS OF PILLSR BLOCK. 5 ^ " D : DKFTM OF F lL L C I BLOCK . 10"J l WIPTN OF JoK T* t : TMICKKKSS OF FOIST-

4 * 4

FILLER BLOCK FLOOR/ROOFI NO. 10 MM ^ BAR a V lA N S KXTKMDIMO r - | 'O N l m U * «D « OF MID SFAM-

S MM 4 BTIKRUPB------AT B IN . INTBRRMD SU AK TE K V M S AKO SK A O U A LLV m cR IA S IPTo 10 IN a t MID S f a n

1o m m d b a r *CHNTRALA ORB CRANRIS UP

d e t a i l s o f j o i s t ." ' rPO * T * EFFRCTIVB SPAM * 1 0 -0

Mo t i ..-JOISTS A R B TO B E T S M F O B A R IL y SUFFORTBD a t m i © s p a m ■

ISOM ETRIC VIEW O F FILLER BLOCKS C A L E : O N E IN C H lg IN C H E S.

FigJQDETAILS OF A COMPOSITE JOIST-FILLERBLOCK FLOOR/ROOF.

44

PRECAST HOLLOW BEAM FLOOR FIG.11

A” PRECAST JOIST-REINFORCED DEPEND IMG UPON THE SPAM S -B R IC K . C -C A S T IN SITU CONCRETE

PRECAST JOIST- BRICK TYPE FLOOR F IG .12

F IG . 13

WOODEN MOULD FOR FILLER B LO C K.FIG : 14-.

WOODEN MOULD FOR JOIST.F IG - rS f .

S E C T I O N A T A - A .

46

F IL L E R B L O C K S A T T H E

S IT E O F M A N U F A C T U R E

F IG . 16 0

A R R A N G E M E N T O F F IL L E R B L O C K S

O VER THE J O IS T S

F I G . 16 C

46

—

2 KOS. 1/4 () n r TOP

3 «OS 'M * ♦ A t BOTTOM

3̂ 16 $ STIRRUPS AT 6” CBSi*

i l l t + AT V c BS

V l « ' > AT a ‘ c «S

FIG. 10. DETAILS OF PRECAST LINTEL. CUM SUNSHADE.

F I G - 19 - S K E T C H SHOWING AR RANG EM ENT F O R LIFTING PRECAST R E IN FO RCE D CONCRETE T E E . B E A M S .

47

PL AM

T O T A L P L IN T H A R I A . . . 3 4 0 S 8 F T . (E X C L U D IN G OPEN P LA C E . )

T O T A L C A R P E T A R E A - - - 2 6 1 - 9 3 S O F T .O P E N P L A C E ......................... 6 1 - 3 0 S Q .F T -

INDEXD. . POORS........ 3 o"x 6 l 6 “D, d o o r s 2 ,. s ‘ x 4 ' . e "

W . WINDOWS - - 3'. o " x 4 - o “ V .VENTILATORS-2-o"x l ' .6" O . OPENING . . 2 . < " X 6 - 6 "

N O T E - - A L L P A R T IT IO N W A L L S

ARE 4 ’ T H IC K .

S P E C I F I C A T I O N S

F O U N D A T IO N S - R R M A S O N R y IN CM ( l - 'g j

O VER l ' - o " L IM E C O N C R E T E B E D | N ( | : 5 l o )

B A S E M E N T - C .R S - M A S O N R y IN C M ( t : * ) S U P E R S TR U C TU R E _ l 3 ' / a “ B R IC K M ASO N R y W A L L S IN L-MROOF _ R E IN F O R C E D C O N C R E T E S L A B D O O R S . W IN D O W S k V E N T IL A T O R S -COUNTRY

TEAK W O O D -F L O O R IN G - R O U G H S N A H B A D S TO N E .

TYPICAL LAYOUT OF A LOW COST HOUSE(C O N V E N T IO N A L T Y P E O F C O N S T R U C T IO N )

FIG. 20

S E C T IO N S O F THREE UN ITS O F LOW C O S T HOUSES W ITH LO A D -B E A R IN G W ALLS U S IN G N E W FO R M S OF C O N S TR U C TIO N .

FIG - 21

48

ELEVATION.

F O R M W O R K F O R C A N D E L L A TYPE

H Y P E R B O L IC P A R A B O L O ID S H E L L R O O F

F IG . 2 3 0

C A N D E L L A T Y P E H .P - S H E L L R O O F

A N D P A R T IT IO N W A L L S

F I G . 2 3 b

49