Why Jaali Screens Are Making a Comeback on New Town Facades

Somewhere between 2018 and now, we started getting client briefs that used to be rare in New Town, requests for "something like the old Kolkata mansions had on the windows" or "that perforated pattern we saw on a hotel facade in Rajarhat," and what clients are really describing, whether they know the term or not, is a jaali, the perforated screen that has shaded Bengal facades for well over a century and is now returning to plots that face due west across Action Area I, II and III. We have specified jaali screens on a good number of west and southwest facing homes over the past few years, and what we want to lay out here is not the history of the form but the actual physics of it, because a jaali that looks right in a reference photo can perform very differently depending on three variables that most clients never think to ask about: the size of each perforation, the depth of the screen from front face to back face, and the material it is cast or cut from.

Why West Facing New Town Plots Need This More Than Most

New Town's grid was laid out along road alignments that put a disproportionate number of plots on west or southwest orientations, and a west facing facade in Kolkata takes the harshest possible sun exposure because the afternoon sun sits low in the sky from roughly 2pm to 5pm during the pre-monsoon months of April and May, throwing direct, low-angle light straight into windows rather than down onto a roof where it is easier to manage. A plain glazed window on a west wall in New Town can push interior surface temperatures up by 6 to 8 degrees Celsius above ambient during that window, and conventional curtains or blinds block the glare but also block the breeze, which in a city where cross ventilation matters as much as it does here, defeats half the purpose of having an opening at all. A jaali solves both problems in the same gesture, because it is neither a solid wall nor an open window, it is a filter, and getting the filter ratio right is the entire design exercise.

Hole Size Is Where Most Off-the-Shelf Jaalis Get It Wrong

The single biggest mistake we see in catalog-sourced jaali panels, the kind sold as a standard product rather than designed for a specific facade, is a perforation size that is either too large, which lets direct sun punch straight through at low afternoon angles and defeats the shading purpose entirely, or too small, which chokes airflow to the point where the room behind it feels stuffier than if there were no screen at all. Our rule of thumb, refined project by project since around 2016, is that for a screen mounted flush or near flush to a window opening on a west facing New Town facade, perforations in the 40 to 65 millimetre range, arranged in a repeating geometric or floral motif, give you roughly 35 to 45 percent open area, which is the sweet spot where you cut usable daylight glare by something in the range of 50 to 60 percent while still allowing enough open area for a genuine breeze to move through rather than just eddy against the surface. Go below 25 percent open area and you are effectively building a partial wall that happens to have a pattern on it, and clients who choose those dense, intricate laser cut patterns purely for how they photograph often end up asking us within a year why the room behind still needs the AC running all afternoon.

Depth Changes the Shadow Angle More Than People Expect

The second variable, and the one almost nobody asks about at the design stage, is how deep the jaali sits, meaning the distance between its outer face and the glazing or wall behind it. A jaali cast flush against the window opening, with only 50 to 75 millimetres of air gap, gives you a filtering effect but very little true shading, because at a low afternoon sun angle the light still travels almost straight through the holes onto the glass. Push that gap out to 300 to 450 millimetres, which we typically achieve by hanging the screen on a separate steel or RCC sub-frame projecting off the main facade, and the same size perforation now casts a much longer, more angled shadow onto the wall behind it during the critical 2pm to 5pm window, because the screen is effectively acting like a brise-soleil rather than a simple filter. On a recent Rajarhat home where the primary bedroom faced west onto an open plot with no neighbouring shade, we moved the jaali out to a 400 millimetre standoff specifically so the perforated shadow pattern would sweep fully across the window by 3:30pm rather than sitting as a static dapple near the top of the glass, and the client reported the room stopped needing daytime AC on all but the hottest days of May.

Terracotta, Concrete or Metal: Picking the Right Material for the Job

Material changes three things at once: thermal mass, weight, and how forgiving the design is of fine detail. Terracotta jaali blocks, the traditional Bengal choice and still made by potters working out of areas like Panihati and parts of North 24 Parganas, have real thermal mass, meaning they absorb heat through the day and release it slowly, which sounds appealing until you realise that on a west wall, that stored heat re-radiates into the evening exactly when you want the house to be cooling down, so we tend to reserve terracotta jaali for east and north facades, courtyards, and boundary walls rather than west facing habitable rooms. RCC or precast concrete jaali panels, cast in-situ or brought in as prefabricated tiles, carry almost no thermal lag problem by comparison because they are usually thinner in section, and they allow finer, more architectural perforation patterns since the formwork can be milled with real precision, but they are heavy, typically needing proper structural support rather than being hung off a light frame, which adds cost when retrofitting an existing balcony or window. Perforated metal, usually laser cut mild steel or aluminium sheet finished in a powder coat, is what we now specify most often for west facing New Town facades specifically because it has almost no thermal mass of its own, so it heats up and cools down with the ambient air rather than storing solar gain, it is light enough to hang on a slim standoff frame without extra structural work, and laser cutting lets us tune the perforation pattern, size and density down to the millimetre for a specific window's sun angle, something that is much harder to achieve consistently with cast concrete or hand pressed terracotta.

Privacy Is a Side Effect Worth Designing For Deliberately

Because New Town plots sit close enough to their neighbours that direct sightlines into bedrooms and bathrooms are a real concern on many streets, we treat the privacy function of a jaali as a design input rather than a happy accident, and the geometry that gives you the best glare and breeze performance, roughly 40 percent open area at a moderate standoff depth, also happens to be close to the geometry that gives you strong obstructed-view privacy from a normal standing or seated eye height on the street or an adjacent balcony, because the human eye needs a much larger, more direct sightline through a perforation pattern to resolve a recognisable image than a breeze needs to pass through the same opening. Where a client has specifically asked for maximum privacy on a ground or first floor facade facing a shared lane, we will sometimes tighten the pattern to 30 percent open area and compensate for the reduced airflow by adding a taller vertical proportion to each opening, since a narrow tall slot moves as much air as a wide short one of the same area but reads as far more private from an oblique street angle.

This kind of layered thinking, where a single facade element is doing shading, ventilation and privacy work simultaneously, is really a subset of a much bigger question about how a home handles Kolkata's climate before the mechanical systems ever switch on, and we have written more broadly about that whole toolkit in Passive Cooling Design: Beating Kolkata's Summer Without Cranking the AC, which is worth reading alongside this piece if a jaali is one part of a wider renovation or new build. A jaali also works best when it is not fighting the rest of the plan for airflow, and homes that pair a west facing screened facade with an internal courtyard tend to see the biggest comfort gains of any layout we have built, something we go into in detail in The Courtyard Comeback: How an Internal Open-to-Sky Space Cools a New Town Home. And if you are weighing up a jaali screen for a commercial frontage rather than a home, it is worth noting that the same glare and heat problems show up on office facades too, often compounding the layout mistakes we cover in 7 Office Layout Mistakes Kolkata Startups Make When Leasing Their First Space.

Bring Us Your Facade and Your Sun Angle

Every jaali we have ever specified started with the same site visit: standing on the actual plot at 3pm in April or May, watching where the sun actually falls rather than where a floor plan says it should, and only then choosing hole size, depth and material. If you have a west facing wall in New Town, Rajarhat or anywhere in greater Kolkata that turns your living room or bedroom into an oven every afternoon, we would rather walk the site with you than guess from a drawing, so get in touch with our team and we will bring a light meter, a tape measure and about a decade of trial and error on exactly this problem.