House foundations types
Foundations are one of the most critical parts of a house or a building that supports and holds the weight of whole structure. In most of the cases foundations are in depth and concealed in soil where load of whole structure is transferred to earth. House foundations are designed according to the terrain, quality and hardness of soil of a particular area and can be of following types:
- Brick foundations
- Strip foundations
- Piles and raft foundations
In areas such as Lahore, lower and central Punjab or where the terrain is plain and soil is hard, brick foundations are most commonly used as shown in picture below. House foundations are designed and drafted by the architect under the supervision of a structural engineer who recommends depth, width and other technical specifications. However despite of all these recommendations, responsibility lies on the shoulders of on site in-charge, builder or contractor to take care of all required technicalities during implementation of drawings provided by the architect.
There are certain precautionary measures that must be taken during construction of brick foundations. Very first step of brick foundations after getting the demarcation of plot is marking and layout. As it is a famous saying “You never get a second chance to make a first impression”, in case of construction of a house or a building, marking is the first impression on a clean chunk of plot/land. If it is imperfect and faulty, whole house or the building will be same. If measurements, straight lines, set squares and levels are not checked during marking, all walls will be out of lines. Hence marking should be carried out very carefully under the supervision of expert and technical individuals.
Once marking is complete, excavation is started width of which is advised by the structural engineer in form of excavation drawings. Another important decision upon which the strength of whole building or a house depends upon is the depth of excavations, it should be made very much sure that excavation is not stopped until hard surface is reached. In areas such as Lahore, lower Punjab and other areas of central Punjab, because of the land being used for agricultural purposes in past, soil has become very hard and hard surfaces can be found at normal depths provided that plot is not located in area which falls in the category of landfills. Landfills are areas where soil from external sources is used to fill the deep pits in order to make it look like a level plot as in its surroundings. Constructing a house on such lands without soil tests and recommendations of soil engineer can be a risky task. Such lands might require raft and piles foundations to bear the load of building
After completing excavation, soil is compacted using level compactor and anti-termite spray is carried out using a renowned medicine. Base of floor is prepared in form of PCC or PCC with RCC as recommended in foundation drawings by the structural engineer. A typical house foundation drawing for brick structures is shown in picture below.
Before starting brickwork, measurements are carefully checked and layout for brickwork is marked. As shown in drawing above, a centre line or a point for 9″ thick wall is marked that works as a reference point too. Brickwork is started with A quality bricks also known as “Awwal bricks” and 1:6 cement to sand mortar. Some people might recommend over burnt bricks called “khingar” however it is wise to use only best quality bricks in house foundations. Though over burnt bricks have maximum load bearing capacity but due to its irregular and uneven shape, it kills the aesthetic and appealing look of brickwork and might eat up more cement.
Initial layers of brickwork in house foundations consists of wider layers as compared to standard thickness of walls i-e 9″, these layers are prepared strictly as designed by the structural engineer in foundation drawings. However straights lines, set square and plumb line of each wall and room should be continuously monitored at each layer. Before reaching the first damp proof course (DPC), whole brickwork must be in one level which should be checked using water level pipe i-e if DPC at front of house is at the height of 1 feet from road level, it should be same at rear and sides. Brickwork should be properly cured however extra ordinary or more than required water curing should be refrained from. Once foundations are complete in all respects, sufficient time should be given for walls to gain strength before starting backfill.
DPC, damp proof course, is another very important part of brick foundations that protects the house from earth dampness and seepage. A typical brick foundations drawing as shown in picture above consists of two horizontal DPCs and a vertical DPC. Horizontal DPCs are made with M15 1:2:4 (Cement, Sand & Crush) concrete whereas vertical DPC is done in terrazzo plaster. Some walls that are main outer walls of house consist of two horizontal DPCs and a vertical DPC. Since porch and side passages of a house are mostly at a lower level as compared to internal finish floor level, hence these walls need to have a double DPC and vertical DPC in between both for complete protection from dampness and seepage, rest all internal walls of house have a single DPC.
As per experience and recommendation of Team Overc’s, though vertical DPC that a structural engineer designs and shows between two horizontal DPCs is enough to stop the dampness from travelling through, however extra measure and protection can be carried out by applying vertical DPC throughout the 9″ wall internally for walls with double DPCs only. Secondly plumbers should be asked to place the required drain pipes before terrazzo plaster as shown in picture below. In most of the cases when labor makes way for placing drain pipes, vertical DPC is damaged hence making that portion vulnerable against seepage and dampness.
An alternate to DPCs and more substantial approach is plinth beam. A plinth beam is must in cases where houses and buildings are constructed as frame structures, however in brick structure, DPCs can be replaced by plinth beam too for more durability and an extra R.C.C pad can also be provided above the P.C.C base. However this quality and more durability can only be obtained at a higher cost.