Code of practice for drainage of building basements
1987 Edition

IS 12251 recommends several approaches to stop subsoil water ingress: first, install perimeter drainage systems around footings or beneath basement slabs, directing water to open outlets, storm sewers, or sumps with pumps; second, manage surface runoff with humps and grated channels before ramps (minimum 600 mm width), parapet walls at least 750 mm high alongside ramps, and catch drains (minimum 200 mm by 200 mm) draining into sumps with pumps; third, design basement walls to withstand water pressure assuming the water table is at one-third the basement depth above the floor, even if actual groundwater levels are lower. These combined measures effectively control water intrusion.

The standard specifies that sumps must be constructed watertight to collect basement wastewater with an appropriate capacity based on expected volume. Pumping systems should use non-clog permanent pumps equipped with automatic start and stop features in areas with frequent rainfall, while portable pumps may be employed in less rainy regions, connected via heavy-duty GI pipes as per IS 1239 Part 1. Non-return valves are mandatory immediately downstream of pumps to prevent backflow. Drainage channels surrounding basement walls and floors should slope towards sumps with minimum slopes of 1:800 near walls and 1:200 on floors, and appropriate channel dimensions must be provided.

Basement sewage lines from toilets must connect directly to external or municipal sewer systems at levels below the WC to prevent backflow. All such connections are required to be made through manholes for inspection and maintenance access. The connecting sewers should have a minimum slope of 1:100 (1%) to assure gravity drainage. Crossings over potable water lines are to be avoided, or if unavoidable, adequately protected. Municipal authority permission must be obtained prior to installation, and pipe materials must comply with IS 1536:1976. Additionally, sump and pumping arrangements must incorporate silt and sand traps and non-return valves to ensure hygienic disposal.

Stormwater runoff management entails installing at least two humps spaced 6 meters apart before ramp entries, paired with grated channels of a minimum 600 mm width to intercept runoff and channel it safely to municipal or building drains while preventing backflow. Parapet walls at least 750 mm tall should be constructed alongside ramps to block runoff from adjacent areas. Catch drains with minimum dimensions of 200 mm by 200 mm, fitted with gratings, collect ramp runoff and discharge into sumps equipped with pumps. Basement floor channels of minimum 150 mm by 150 mm with slopes of at least 1:800 collect wash water, all directing to sumps from which water is pumped out to ground-level drainage points.

The code recommends several waterproofing measures: all construction joints in basement walls and floors must be sealed using approved sealants, and expansion joints must be equipped with water stops to block water ingress. Reinforced concrete used in basements should include waterproofing compounds blended into the mix. Exterior basement walls require two coats of bituminous paint applied after thorough crack inspection and necessary repairs. Additionally, proper drainage systems should be installed around footings and beneath slabs to channel water away, while structural design must consider water pressure assuming groundwater at a certain level to ensure durability and watertightness.