The Kolkata Architect's Monsoon Checklist, From Sumana Kumar

Every year, somewhere around the third week of June, our phone starts ringing with the same call. A homeowner in New Town or Salt Lake has water coming in somewhere it should not be, and it is never the dramatic thing they expected, it is almost always a small detail that got decided in a hurry two years ago and nobody thought about again. A parapet that was built without a proper drip, a terrace slope that runs the wrong way by half an inch across ten feet, a bathroom sunk slab that was filled with construction debris instead of clean sand, a window sill that sits flush instead of projecting. None of these are exotic engineering problems, they are just details that quietly stop mattering to everyone except the person who has to live in the house when it rains for eleven days straight.

Our studio has been working in and around this belt since 2014, and across 330 plus buildings in New Town, Salt Lake, Rajarhat and greater Kolkata, the pattern has been consistent enough that we now treat monsoon performance as a design decision rather than a maintenance problem. The monsoon here is not a mild inconvenience, it is roughly four months of sustained saturation combined with wind driven rain from a fairly predictable direction, and a building either respects that in its bones or it spends the next thirty years being patched.

So this is the checklist we actually run, written out plainly, because if you are a plot owner or a homeowner about to hire an architect in this city, the quality of the questions you ask during the design stage is worth more than any amount of repair budget later. Sumana Kumar, our principal architect, works out of New Town and takes these projects through sanction and construction herself, and her view has always been that the monsoon is the honest examiner, it finds every shortcut eventually.

Start with the roof, because the roof is a drainage system pretending to be a slab

A flat roof in Kolkata is not really a roof, it is a shallow tank that you are hoping empties fast enough. The first thing we set on any residential drawing is where the water goes and how quickly, and that decision comes before we decide anything about the terrace as a usable space. We want a minimum fall of about 1 in 100 across the whole terrace, we want the outlets sized generously and placed at the genuine low points rather than at the corners that happen to be near a downpipe, and we want the fall to be built into the structure through screed rather than achieved by tilting the slab, so that the ceiling below stays level.

The catch here is that outlets are the failure point, not the surface. A terrace with three properly sized, properly detailed outlets with removable gratings will outperform a terrace with perfect waterproofing and two outlets that clog with leaves in week two of the monsoon. We specify at least one more outlet than the calculation demands, because redundancy costs a few thousand rupees at construction and saves a ceiling replacement later, and we insist that every outlet is accessible for cleaning without a ladder and a prayer.

Then comes the actual waterproofing, and here our position is unfashionably conservative. We prefer a system that is tested with a genuine ponding test, water held on the terrace for at least 48 hours before any protective screed or tiling goes down, and we prefer the upturn at every parapet, every wall junction and every outlet to be taken up at least 300 mm and tucked into a groove rather than simply painted up the wall and left to peel. Most terrace leaks we are called to inspect are not surface failures at all, they are junction failures, and junctions are a design responsibility.

The facade is where wind driven rain actually gets in

People obsess over the roof and then leave the walls to chance, which is backwards for this city, because a large share of the damp we see on internal walls is not rising damp and it is not roof leakage, it is water being driven horizontally into a wall face and finding a path through an unfilled joint, a hairline crack at a lintel, or the gap around a window frame that was filled with mortar instead of a proper sealant.

Our standing rules on this are simple enough to hold an architect to. Every projecting element gets a drip groove on its underside, because water travelling along a soffit will keep travelling until something breaks its surface tension, and a 10 mm groove is the cheapest detail in the entire building. Every window sill projects and slopes outward, never inward, and never flush. Every frame to wall junction gets a backer rod and a flexible sealant rather than cement mortar, because mortar and aluminium expand at different rates and the crack is guaranteed, it is just a question of which summer. And on the south and south west faces, which take the brunt of the wind here, we push for deeper reveals, projecting bands and generous overhangs, which incidentally is also what makes those elevations look composed rather than flat.

This is the point where good residential architecture stops being a styling exercise and starts being a set of decisions with consequences, and it is also why we push clients towards deep overhangs and shaded openings even when the brief starts out asking for a minimal box. You can have the clean lines, you just cannot have them without the details underneath.

Ground level, plinth and the water that comes from below

New Town and Rajarhat sit on ground that was substantially reclaimed and filled, and drainage at plot level behaves differently here than it does in older parts of the city. We look at three things before finalising the plinth. Where does the water on this plot go when the surrounding roads are already carrying more than they can handle, how high does the plinth need to sit relative to the road level after future road resurfacing, and how is the setback strip around the building actually graded.

That last one gets ignored constantly. The setback strip is a regulatory requirement, so most people treat it purely as a compliance number and pave it flat, and then it holds water against the plinth for four months a year. We grade it away from the building, we put a shallow perimeter drain along the boundary side, and we keep the plinth protection sloped and sealed at the wall junction. If you want the underlying rules in plain language, our guide on setback and open space rules in New Town walks through what is required and what is merely convention.

Plinth height is worth arguing about, so argue about it early. We generally want a meaningful step above the finished road level with an allowance for the road being relaid higher later, and we would rather add two steps at the entrance than explain to a client in 2031 why their living room floor is level with the street.

Rainwater is not the enemy, standing water is

Once the drainage logic is sound, the same system can be turned into an asset rather than a nuisance. Rainwater harvesting on a plot in this belt is straightforward when it is planned with the plumbing layout rather than bolted on afterwards, and the honest reason to do it is not only recharge, it is that a building with a considered rainwater path tends to have a considered everything else path, so the downpipes are sized right, the first flush is handled, and the water is not simply discharged onto the neighbour's setback strip, which is how most boundary disputes in this city actually begin.

The design cost of doing this properly is close to zero if it is decided at the drawing stage. The retrofit cost is real, which is the same argument we make about most services, and it is the argument behind our renovation and remodelling work too, where a good half of the scope on older Salt Lake houses is undoing drainage and services decisions that were never designed at all.

What this means when you are choosing an architect

Here is the practical translation for a plot owner. When you meet an architect, ask them to walk you through the terrace drainage before they show you the elevation. Ask where the water goes when the outlet closest to the parapet clogs. Ask how the window frame meets the wall. If the answers are vague or the conversation keeps sliding back to renders and finishes, you have learned something useful about how the project will be run.

The second thing worth checking is process familiarity, because a design that cannot get sanctioned is not a design, it is a drawing. Our studio works through the NKDA, KMC and Bidhannagar Municipal Corporation building plan sanction routes regularly, and that repetition matters mostly because it removes surprises, you know which drawings will be questioned, which dimensions get scrutinised, and how the sequencing runs from submission to construction to completion. Our guide to the NKDA building plan sanction process lays out the sequence, and if you are earlier than that in your thinking, the broader guide to hiring an architect in New Town covers what to ask before you sign anything.

If you are building for the first time, our first time homeowner hiring guide is probably the most useful thing to read next, and if you are buying an older property to renovate rather than building fresh, why experience with NKDA buildings de risks a renovation explains what we look for during a pre purchase walkthrough. You can also see how these decisions land in a completed project at our DE Block residence in New Town, where the overhangs, the sill profiles and the terrace levels were all set for exactly this climate before a single finish was chosen.

The interiors have a monsoon checklist too

Interiors get treated as a separate, later, softer conversation, and that is where a lot of avoidable damage originates. Wardrobe backs pressed flat against an external wall on the weather face will develop mould, so we hold them off with a ventilated gap. Sunk slabs in bathrooms need to be filled with clean, well graded fill and given a drain of their own, because a sunk slab that traps water is a slow leak with a two year fuse. Skirting details need to allow for movement. Electrical points on external walls need proper back boxes and sealing at the conduit entry.

And lighting matters more than people expect during these months, because you lose a genuine amount of usable daylight for a third of the year, so the layered scheme we design under false ceiling and lighting design is not decorative, it is what keeps a house feeling alive in late July. Basically, the interiors and the shell have to be designed by people who are talking to each other, which is the entire argument for keeping architecture and interiors under one roof.

At the end of the day, none of this is clever. It is just a set of decisions that have to be taken by someone who has watched enough buildings go through enough monsoons to know which corners come back to bite, and taken early enough that they cost nothing but attention. That is really what you are hiring when you hire an architect in this city, not a style, but a body of accumulated judgement about what this specific climate and this specific approval system will do to a building over the next thirty years. If you have a plot in New Town, Salt Lake or Rajarhat and you would like to talk through your site before the drawings start, get in touch with the studio and we will walk your plot with you, look at where the water actually goes, and tell you honestly what the site will and will not allow.