BMKG has already flagged it: the peak heat for Greater Jakarta is expected to land in August 2026, with daytime temperatures touching 35–36 degrees across parts of Bekasi. In a two-storey home, the upper floor that takes direct sun can feel 4–5 degrees hotter than the ground floor. Most people reach straight for an AC. But getting the airflow right lowers that stuffy feeling before the cooling unit even joins in.
Three layers usually work together against heat: roof insulation (glasswool, foil, or PU foam), active cooling (AC), and passive airflow. The first two we cover separately. This one stays on the third layer — free, no electricity bill, working 24 hours as long as the windows are set up right. Air only needs a path, not power.
Why a Narrow, Deep House Stays Hot
The Emerald 70 footprint — 4.5 m × 10.5 m, two storeys — is a plan that runs long toward the back. Light and wind only have two open sides: the front and the rear. The left and right sides share walls with the neighbours. If windows sit only at the front, air comes in, loses its push in the middle of the house, and stops. The living area in the centre becomes the stuffiest spot.
The fix rests on two simple bits of physics. First, cross ventilation — wind needs an inlet and an outlet facing each other to flow through, not just a single opening. Second, the stack effect — hot air is lighter, so it rises. Give it a way out up top and the heat escapes on its own, pulling fresh air in from below. A two-storey house has an advantage here: there's a height difference to put to work.
Cross Ventilation: Set Openings Face to Face
The base rule: the inlet and the outlet should sit on two different walls, ideally opposite ones. In the Emerald 70, that means the front window in the living room paired with a door or window at the kitchen-rear. Wind coming in off Jl. Raya Perjuangan through the front gets drawn across the full depth of the house toward the rear opening.
A few technical points people often miss:
- The outlet should be slightly larger than the inlet. That size gap makes the air flow faster inside the room, like a hose you pinch at the end.
- Place the inlet lower, the outlet higher. Cool air creeps along the floor, hot air gathers up top — follow the natural direction.
- Avoid solid barriers in the air path. A tall wardrobe or a brick partition mid-room blocks the flow outright. Use a rooster partition or open shelving if you really need a divider.
- Use the prevailing wind. In North Bekasi the breeze often arrives from the east-southeast in the late afternoon. Openings facing that way catch the most air.
The Void and the Stairs: A Path for Rising Heat
This is where a two-storey house wins. A void — an empty vertical space cutting through both floors — acts as a chimney. Heat from the ground floor rises through the void, and if the top of the void has a window or vent that opens, that heat leaves the house. An open staircase does something similar: it becomes a vertical tunnel for hot air to climb.
On a plan only 4.5 metres wide, a big void is expensive in land terms. But a small void above the stairs, plus one louvred glass window on the second floor facing it, is enough to get the stack effect running. Open that upper window morning and evening — the heat trapped overnight suddenly has a way out.
A simple test: light a stick of incense in the centre of the ground floor, then open the front window and the upper void window. If the smoke leans and gets pulled up toward the void, the stack effect in your house is working. If the smoke just hangs there, a path is still blocked somewhere.
Opening Types, Function, and Cost Range
Not every opening does the same job. Some pull air in, some dump heat out, some run 24 hours without ever being opened or closed. Here's the comparison builders in Bekasi use as of mid-2026:
| Opening Type | Main Function | Cost Range |
|---|---|---|
| Louvred (nako) glass window | Directs incoming air, opens fully | Rp 350–600 k/unit |
| Concrete / terracotta rooster block | Permanent 24-hour vent, stays shaded | Rp 15–45 k/piece |
| Top pivot window (in the void) | Exhausts hot air via the stack effect | Rp 800 k–1.5 m/unit |
| Roof vent / turbine ventilator | Pulls heat from the second-floor ceiling | Rp 250–700 k/unit |
| Kitchen / bathroom exhaust fan | Forces humid, hot air out | Rp 150–450 k/unit |
| Rear insect-screen door | Keeps the outlet open but mosquito-safe | Rp 600 k–1.2 m/unit |
One note on price: the turbine ventilator gets asked about most because it spins on its own from the wind, so it costs nothing to run. For a house the size of the Emerald 70, one turbine on the rear porch roof plus rooster blocks on the stairwell wall make a cheap, effective combination.
Practical Steps: Make the Emerald 70 Cool Without AC
- Map the two open sides. On a 4.5 × 10.5 m plan, mark the front and rear walls as the main inlet-outlet path. Treat the left and right as closed.
- Pair a front opening with a rear opening. Living-room window at the front, door or window at the kitchen rear. Keep them roughly in line of sight so air runs straight through.
- Open a vertical path at the stairs. Add a window at the top of the void or above the second-floor landing. This is the exit for rising heat.
- Fit rooster blocks at dead spots. Stairwell walls, above bedroom doors, or a kitchen partition — rooster keeps air moving even when windows are shut.
- Put a turbine or vent on the second-floor roof. The top ceiling is the biggest heat pocket. A roof ventilator clears it before it seeps into the bedrooms.
- Back it up with exhausts in the kitchen and bathroom. Both rooms produce hot vapour. A small exhaust pushes it out so it doesn't spread to the rest of the house.
- Set a daily open-shut rhythm. Open wide in the morning and at night when the outside air is cooler; close the west-facing curtains at midday so radiant heat stays out.
That's why the order of work matters: airflow gets sorted first at the layout and opening stage, then roof insulation and AC follow as extra layers if it's still not enough. With the air path done right, plenty of homes in North Bekasi stay comfortable all day on open windows and a single turbine spinning on the roof.
The Emerald 70 and Where Its Openings Sit
The Emerald 70 by Mandiri Development stands on Jl. Raya Perjuangan, North Bekasi — an area that's flood-free and still catches the afternoon breeze from open ground. With a 47.25 m² land area, 70 m² building area, and bore-pile foundations, its two-storey frame leaves room for the stair void and upper openings the stack effect needs. Prices start from around Rp 700 million, with instalments from Rp 5 million a month.
If you're house-hunting in North Bekasi and want to know where the facing windows sit on the Emerald 70 plan, our team can send the full layout. So before you budget for AC, see how far free wind can take your home toward cool.
Want to see the Emerald 70 opening layout?
The Kingspoint team can send the Emerald 70 floor plan over WhatsApp — with window positions, the stair void, and the cross-ventilation path marked.
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