Use of loadbearing brickwork for three storey houses in Sri Lanka

Abstract

For residential buildings, brickwork out of hand moulded burnt bricks is widely used in Sri Lanka. The majority of these buildings are single storey construction. However, in recent times, two storey residential buildings have gained popularity due to advantages such as saving in land area required and the thermal comfort that can be offered on the ground floor during the day time.

When large houses are required on small blocks of land such as 6 perch in extent, three storey residential construction can be considered as an option. This also offers further advantages since both ground and first floor are now shaded. Thus, achieving a reasonable thermal comfort in a properly planned house would be easier despite the hot humid climatic conditions prevailing in Sri Lanka.

It was shown by Jayasinghe & Attalage (1999 b) that the reduction of external surface area and the roof area of a residential building is useful for reducing the external thermal gains. Reduced external thermal gains coupled with enhanced natural ventilation can be one of the possibilities for achieving a reasonable thermal comfort. It was shown by Jayasinghe & Attalage (1999 a) that Sri Lankans can be thermally comfortable even at elevated temperatures when sufficient ventilation is available.

When three storey houses are required, the structural form generally considered is reinforced concrete frames. However, load bearing brickwork can be a cost effective alternative when the residential buildings are planned with a considerable number of partition walls and with upper floors built on top of lower floor walls.

It is shown in this report with few examples that planning of such three storey houses is practically possible. Such houses can offer a number of advantages like reduced circulation space thus leading to better usage of space, bed rooms arranged around the courtyards, study rooms located at well shaded first floors etc.

When locally available hand moulded bricks are used for construction, it is possible to obtain a characteristic compressive strength of 1.5 N/mm2 when 1:6 cement sand mortar is used (Jayasinghe, 1988). It is also necessary to exercise certain quality controlling measures while selecting the bricks for construction and carrying out the actual construction.

Since the characteristic compressive strength is limited to 1.5 N/mm2, it is necessary to use walls of sufficient thickness for load bearing walls at lower levels. It is shown that a wall thickness of one and a half bricks is appropriate for the ground floor and one brick for the first floor walls. The second floor wall thicknesses should be selected with the aim of minimising the self weight, hence half a brick thick walls would be appropriate for partition walls. The external walls can be one brick thick for enhanced resistance to wind induced forces and rain water penetration. Since openings will act as a source of weakness in load bearing walls, guidelines that can be used for the initial layout planning stage are developed. These guidelines are also compared with those recommended for enhanced earthquake resistance, since when new concepts are introduced, the resistance to dynamic forces could be considered as important. The measures that can be taken to prevent cracking in such three storey buildings are also presented along with cost effective foundation improving methods.

The cost implications of using load bearing brickwork for three storey residential buildings were determined by carrying out a cost study. It is shown that the saving in a house of about 200 m2 of total area could be in the range of Rs 100,000/= when compared with the corresponding reinforced concrete framed building. Such cost savings are extremely important for middle income earners since the bank loans are often used for financing the house construction. Thus, it is shown that three storey residential building construction with load bearing brickwork can have many advantages such as cost effectiveness, thermal comfort, saving in land area and possibility of creating a comfortable micro climate around the house.