Seepage from soil/earth into the walls of house is a major issue that many people face. In newly constructed houses it causes much more distress & worry as compared to old houses which already require renovation and maintenance. Almost 90% of houses that are constructed as brick structures witness seepage in minor to major form. There are various reasons due to which seepage becomes visible in walls of house that we have already discussed in detail in one of our blogs related to house foundations. In this article we will discuss effectiveness of plinth beam & DPC in protecting seepage and cost comparison of both.
House construction method that is adapted in lower, central and upper Punjab is known as Brick structure. In brick structure foundations are made completely in bricks and no concrete is involved. Now as we already know that bricks absorb water, hence this method becomes really sensitive for seepage. Bricks absorb water from surrounding soil and start travelling upwards towards open air. To stop this water from travelling above a certain level, a water barrier is required which is called Damp proof course DPC or a Plinth beam PB.
Damp proof course DPC
DPC is a thin layer(1.5 inches – 3 inches) of concrete that is laid on bricks in width with accordance to the size of bricks. Concrete is a normal mix of cement, fine aggregate(sand) and course aggregate (crush). Water proofing chemicals and plasticizers are also available in market that can be added for a better mixture. DPC is provided on two levels, first one is at porch level of house and second one is at finish floor level, in between both levels, a vertical DPC is also applied from internal side that is a thick terrazo plaster (mixture of cement and marble chips powder).
Though DPC is meant to act as water barrier and provide protection from seepage, but it is never 100% safe. Even during construction, if it gets minor damaged from any point, travel path for seepage is created.
Plinth Beam PB
Plinth beam is an alternate water barrier and true scientific and engineering method for protection from seepage. Unfortunately due to the higher cost of this method, it is rarely used in brick structure constructions. In frame structure houses or buildings, it becomes necessity. A plinth beam as its name suggests is reinforced cement concrete which is made with concrete mix along with the mesh of reinforcement/steel. Once foundations are at the first level of water barrier, instead of first DPC, plinth beam is directly placed which is 12 inches of 1 ft in height and width in accordance with the size of foundations. Before pouring the concrete, steel mesh is prepared and placed as per the instructions of structural engineer, formwork (shuttering) is done along the path of plinth beam in required sizes and concrete is poured. Addition of water proofing chemicals and plasticizers is recommended.
Plinth beam provides 100% protection from seepage unlike the DPC. Other than providing best protection as water barrier and from seepage, it also provides unmatched strength to house as compared to normal DPC and acts as a binding/tie beam too for foundations.
Plinth beam construction cost & DPC cost
Quality in protection from seepage and the extra strength for foundations in case of plinth beam comes at a higher cost. Plinth beam construction cost is much higher and to make it easy to understand for laymen we will calculate per running feet cost for both DPC and plinth beam.
Lower & Upper DPC with 3 layers of bricks to achieve 1 ft (12 inches) height
2 DPC’c 1.5 inches each in height i-e 3 inches total
1 running ft of DPC with 3 inches in height = 3/12 = .25 cubic ft
Dry volume of DPC = .25 x 1.54 = .385 cubic ft
Sum of ratio = 1+1.5+3 = 5.5
Cement = .385/5.5 = .07 cubic ft
Cement in bags = .07/1.25 = .056 x 540 Rs/bag = 30.24 Rs/running ft
Sand = .07 x 1.5 = .105 x 32 Rs /cft = 3.36 Rs/running ft
Crush = .07 x 3 = .21 x 75 Rs/cft = 15.75 Rs/running ft
Bricks required to complete 1 cubic ft = 9 x 10.5/brick = 94.5 Rs/running ft
Total cost of DPC per running ft = 143.85 Rs/running ft
Plinth Beam 1 ft (12 inches) in height
1 running ft of PB with 12 inches in height = 12/12 = 1 cubic ft
Dry volume of PB = 1 x 1.54 = 1.54 cubic ft
Sum of ratio = 1+2+4 = 7
Cement = 1.54/7 = .22 cubic ft
Cement in bags = .22/1.25 = .176 x 540 Rs/bag = 95.04 Rs/running ft
Sand = .22 x 2 = .44 x 32 Rs /cft = 14.08 Rs/running ft
Crush = .22 x 4 = .88 x 75 Rs/cft = 66 Rs/running ft
Steel reinforcement approximately 2 kg/rft = 2 x 115 Rs/kg = 230 Rs/running ft
Shuttering/formwork cost = 75 Rs/running ft
Total cost of PB per running ft = 480.1 Rs/running ft
Point to be noted is that labour cost (masonry) has not been considered in both the cases as that will remain same. As we can see in above calculations that Plinth beam construction cost is significantly high as that of DPC cost. But in our experience this price difference is worth spending due to the positive outcome. Most of the people can afford only once in lifetime to construct their houses so any step that will ensure the strength of your house and prolong the life must be taken specially during the grey structure house construction. For making it further simpler for laymen to understand the approximate plinth beam construction cost, average running feet required of DPC or plinth beam in 10 marla houses is in the range of 275 ft to 300 ft.
300 ft damp proof course (DPC) cost = 300 x 143.85 Rs = 43155 Rs
300 ft plinth beam construction cost (PB) = 300 x 480.1 Rs = 144030 Rs