Seepage from soil into the walls of a house is a major issue that many people face. In newly constructed houses it causes far more distress and worry than in older houses that already require renovation and maintenance. Almost 90% of houses built as brick structures witness seepage in some minor to major form. There are various reasons seepage becomes visible in the walls of a house — reasons we have already discussed in detail in our blog on house foundations. In this article we discuss the effectiveness of the plinth beam and the DPC in protecting against seepage, and compare the cost of both.
Video guide accompanying this article.
The house construction method adopted across lower, central and upper Punjab is known as brick structure. In a brick structure, foundations are made completely in brick, with no concrete involved. Since bricks absorb water, this method becomes genuinely sensitive to seepage — bricks absorb water from the surrounding soil and begin travelling upwards towards open air. To stop this water from travelling above a certain level, a water barrier is required, which is called a damp proof course (DPC) or a plinth beam (PB).
Damp Proof Course (DPC)
DPC is a thin layer (1.5 inches to 3 inches) of concrete, laid on top of the brickwork at a width matching the size of the bricks. The concrete is a normal mix of cement, fine aggregate (sand) and coarse aggregate (crush). Water proofing chemicals and plasticizers are also available in the market and can be added for a better mixture. DPC is provided at two levels — one at porch level, and one at finish floor level — and in between the two, a vertical DPC is also applied from the internal side, in the form of a thick terrazzo plaster (a mixture of cement and marble chip powder).
Though the DPC is meant to act as a water barrier and provide protection from seepage, it is never 100% safe. Even during construction, if it gets minor damage at any point, a travel path for seepage is created.
Plinth Beam (PB)
The plinth beam is an alternate water barrier, and a truly scientific and engineering method of protection from seepage. Unfortunately, due to its higher cost, it is rarely used in brick structure construction — though in frame structure houses or buildings, it becomes a necessity. A plinth beam, as its name suggests, is reinforced cement concrete, made with a concrete mix along with a mesh of reinforcement/steel. Once the foundations reach the first level of water barrier, a plinth beam is placed directly in place of the first DPC — typically 12 inches (1 ft) in both height and width, in accordance with the size of the foundations. Before pouring the concrete, the steel mesh is prepared and placed as per the structural engineer's instructions, formwork (shuttering) is done along the path of the plinth beam at the required size, and the concrete is poured. Addition of water proofing chemicals and plasticizers is recommended.
The plinth beam provides 100% protection from seepage, unlike the DPC. Beyond providing the best protection as a water barrier, it also provides unmatched strength to the house compared to a normal DPC, and acts as a binding/tie beam for the foundations too.
Plinth Beam Construction Cost & DPC Cost
The quality of protection from seepage, and the extra strength for foundations that the plinth beam provides, comes at a higher cost. To make it easy for laymen to understand, we calculate the per-running-foot cost for both DPC and plinth beam below.
Lower & upper DPC — 3 layers of bricks to achieve 1 ft (12 inches) height
2 DPCs, 1.5 inches each in height, i.e. 3 inches total
1 running ft of DPC with 3 inches in height = 3/12 = 0.25 cubic ftDry volume of DPC = 0.25 x 1.54 = 0.385 cubic ftRatio 1:1.5:3 — sum of ratio = 5.5
Cement = 0.385/5.5 = 0.07 cubic ftCement in bags = 0.07/1.25 = 0.056 x 540 Rs/bag = 30.24 Rs/running ftSand = 0.07 x 1.5 = 0.105 x 32 Rs/cft = 3.36 Rs/running ftCrush = 0.07 x 3 = 0.21 x 75 Rs/cft = 15.75 Rs/running ftBricks required to complete 1 cubic ft = 9 x 10.5 Rs/brick = 94.5 Rs/running ftTotal 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 ftDry volume of PB = 1 x 1.54 = 1.54 cubic ftRatio 1:2:4 — sum of ratio = 7
Cement = 1.54/7 = 0.22 cubic ftCement in bags = 0.22/1.25 = 0.176 x 540 Rs/bag = 95.04 Rs/running ftSand = 0.22 x 2 = 0.44 x 32 Rs/cft = 14.08 Rs/running ftCrush = 0.22 x 4 = 0.88 x 75 Rs/cft = 66 Rs/running ftSteel reinforcement approx. 2 kg/rft = 2 x 115 Rs/kg = 230 Rs/running ftShuttering/formwork cost = 75 Rs/running ftTotal cost of PB per running ft = 480.1 Rs/running ft
| # | Method | Cost (Rs/running ft) |
|---|---|---|
| 1 | Damp Proof Course (DPC) | 143.85 |
| 2 | Plinth Beam (PB) | 480.1 |
It should be noted that labour cost (masonry) has not been considered in either case, as it remains roughly the same. As the calculations above show, plinth beam construction cost is significantly higher than DPC cost — but in our experience, this price difference is worth spending, given the positive outcome. Most people can only afford to build their house once in a lifetime, so any step that ensures the strength of the house and prolongs its life is worth taking, especially during grey structure construction. To make it further simpler for laymen to understand the approximate cost, the average running feet required of DPC or plinth beam in a 10 marla house is in the range of 275 ft to 300 ft.
300 ft damp proof course (DPC) cost = 300 x 143.85 Rs = 43,155 Rs300 ft plinth beam construction cost (PB) = 300 x 480.1 Rs = 144,030 Rs