A solid wall blocks the sun and the breeze together. A glass wall lets in both. A jaali wall sits between the two, and that in-between position is why jaali walls reduce heat without shutting out air.
A jaali is a perforated screen, traditionally cut from stone or built in brick, with the pattern formed by geometry, calligraphy or natural motifs. The word means “net”. Today the same idea is built in concrete, metal and even bio-based materials.
The short answer: a jaali shades the surface behind it and keeps air moving through the building. Both effects are real and measurable. Neither is as large as popular articles suggest, so the details matter.
How a jaali wall reduces heat
Most of the heat that enters a building in summer comes through the walls and windows facing the sun. A jaali stops a large share of that radiation before it reaches the glass or the inner wall.
The screen also breaks direct sun into small patches and diffuse light. That keeps the daylight and drops the glare.
What do the studies say? A 2026 simulation study by Bay-Sahin and Shah, published in Megaron, retrofitted a jaali-style screen onto a building in a hot, dry climate. Indoor temperatures dropped by up to 2°C during the cooling season when natural ventilation was available. A parametric DesignBuilder study of an office building found cooling demand reductions of up to 8.71% on the east facade, depending on the screen’s thickness, perforation ratio and cavity depth. A literature review inside the 2026 Energy and Buildings paper on bio-jaali puts the range for optimised perforated screens at 6 to 26% energy savings.
Notice the pattern. These are simulations, and the savings change a lot with design. Treat them as a direction, not a guarantee.
The BBC reported on one more comparison: a 2018 assessment of three shading systems by researcher Batool found jaali outperformed both a fully glazed facade and a brise-soleil facade.
How a jaali wall improves natural ventilation
A jaali lets you keep openings that stay cool in the shade. Instead of closing a window against the afternoon sun, you place the screen outside it, and the air still flows.
Three things happen:
- Air passes through the perforations, so cross-ventilation continues even when the sun is harsh.
- Wind is slowed and spread by the pattern, which can make it gentler and more evenly distributed inside.
- With a gap between the screen and the window, or a double-height space behind it, warm air can rise and leave. That is the stack effect.
You will often read that air “gets cooler” when it squeezes through the holes because of the Venturi effect. Be careful with that claim. The Venturi effect does speed up the air through small openings. Faster air feels cooler on skin, which matters for comfort. It does not by itself lower the air temperature. The measurable cooling comes from shade first, and air movement second.
Also be honest about one thing: any screen adds resistance, so a jaali always lets through less air than a fully open window. The Megaron study found that open windows behind the screen were needed to keep indoor temperatures below outdoor levels. The screen helps. The openings do the ventilating.
Design variables that decide performance
| Variable | What it does | What the research suggests |
| Perforation ratio | Balances shade against airflow and daylight | In the DesignBuilder study, 20% worked best on south and west facades and 50% on the east |
| Screen thickness | Deeper holes cut more low-angle sun | 100 mm on south, 150 mm on west and east in the same study |
| Cavity depth | Gap between screen and wall lets heat escape | 1.0 to 1.5 m performed best in that study |
| Orientation | Sun angle changes the shading needed | East and west need the most attention |
| Material | Affects heat absorbed and stored | Sandstone, brick, concrete and mycelium composites perform differently |
These values come from one office building simulation. Use them as a starting point and test your own geometry.
Hot-dry and warm-humid climates need different jaalis
Traditional builders already knew this. Architect Yatin Pandya has observed that jaalis in humid regions such as Kerala and the Konkan have larger openings and lower opacity than those in dry Gujarat and Rajasthan. Dry regions want more shade and less glare. Humid regions want as much air movement as possible.
So a Jaipur jaali and a Kochi jaali should not look the same.
Where it has been used
The Tomb of Salim Chishti at Fatehpur Sikri and Hawa Mahal in Jaipur are the classic examples, both studied in recent academic work on jaali performance. Modern buildings use the idea too. Pearl Academy in Jaipur uses jaali alongside other Rajasthani cooling strategies. The Punjab Kesari headquarters in Delhi, by Studio Symbiosis, wraps the building in a perforated white concrete facade. At a student residence in Gurugram, architect Sachin Rastogi told the BBC that the jaali cut air-conditioning needs by 35%. That figure is the architect’s own claim, so check it before quoting it as a benchmark.
Limitations
- Dust collects in fine patterns and cleaning is harder.
- A jaali does not stop rain, so it needs a window or glazing line behind it.
- Dense patterns reduce daylight, which can push up lighting use.
- Most published numbers are from simulations, not measured buildings.
Researcher Batool warns against romanticising traditional performance. Learn from it, but verify it.
Heat is also getting worse. The bio-jaali study reports a 60% rise in danger-level heat-stress hours in New Delhi over 28 years, a trend that is pushing architects to design for 45°C summers. In its simulations, a mycelium-based jaali cut annual cooling energy demand by 50.4% compared with a sandstone jaali. That is a lab-stage prototype, so it is not ready to specify yet. But it shows where the research is heading.
What to do with this
If you are designing for a hot Indian city, put the jaali on the east and west facades first, since the sun is low there and plain glass suffers most. Keep an openable window behind the screen. Leave a gap between the two if the plan allows it. And before you fix the perforation ratio, run a quick simulation with your own orientation and climate file. A pattern that looks good in a render can still block the breeze.
FAQs
Does a jaali wall really reduce indoor temperature?
Yes, mainly by shading. Simulation studies report reductions of up to about 2°C in indoor temperature and cooling energy savings from roughly 6% to 26% for well-designed screens. Results depend on climate, orientation and geometry.
What perforation percentage is best for a jaali?
There is no single best value. One office simulation found 20% best for south and west facades and 50% for the east. Humid climates usually need more open area than dry ones.
Does a jaali block ventilation?
It reduces airflow compared with an open window, but it allows far more air than a solid wall. Pair it with openable windows behind it to keep ventilation effective.
Can a jaali replace air conditioning?
Not on its own in most Indian cities. It lowers the cooling load. Treat it as one part of a passive design strategy with orientation, insulation and shading.