When the dry season peaks, a two-storey cluster house in North Bekasi easily turns into a small oven by late afternoon. Heat pools on the upper floor, gets stuck under the ceiling, and the AC works overtime until the electricity bill climbs with it. Yet before rushing to add AC capacity, there's a far cheaper approach tropical architects have leaned on for ages: roster blocks and cross-ventilation.
The two work together. Cross-ventilation handles the airflow path; roster blocks give a permanent opening so air and heat still have a way out even when the windows are locked. For the long, narrow footprint typical of Bekasi clusters, this combination is what keeps rooms breezy without running the AC all day.
The Cross-Ventilation Rule: Air Needs a Way In and a Way Out
The rule is simple. Air only flows when there are two openings facing each other, one on the side the wind comes from, one across to let it out. With just a single window, the air inside a room sits still even if that window is wide. That's why a house with plenty of windows all bunched on one side still feels stuffy.
This is where the cluster footprint becomes a challenge. Take the Emerald 70 House at Kingspoint Residence: its dimensions are 4.5 × 10.5 metres, long front to back, with the left and right sides sharing walls with the neighbours. Practical openings only sit at the front and rear. So that front-to-back air path is the one to keep clear: cut down solid partitions in the middle, or swap some of them for perforated dividers so air travels from the front all the way to the back kitchen. For why two-storey houses take the heat worse, we cover it separately in our look at extreme heat for 2-storey houses in Bekasi.
Where Should Roster Blocks Go?
A roster block is a permanent air vent. Unlike a window, it keeps working in the rain or when you're out of the house with every window locked. A few spots make the biggest difference:
- The front facade. Placed as a second layer (secondary skin) in front of a wall or window, roster blocks soften direct sun while keeping privacy from the street.
- Stairwell and void walls. Hot air always rises. Roster blocks high on a stairwell wall or in the void give an exit for the heat that piles up on the second floor — the chimney effect.
- The bathroom. Damp air needs a way out. A small roster block high on the bathroom wall helps clear the vapour that breeds mould.
- The kitchen. Smoke and stove heat need somewhere to go. A roster block above the cooking area keeps the kitchen from holding onto smells and stuffiness.
Heat in a two-storey house moves vertically: it rises from below and hits the ceiling above. A void in the middle of the house plus a roster block or skylight above it gives that heat an exit upward instead of circling around inside the rooms. That pairing of void and high opening is the core of passive design done right.
Types of Roster Blocks and Their Trade-offs
Roster blocks aren't a single thing. The material varies, and each type has its own character in price, look, and upkeep. Here's the general picture. Prices are deliberately left open because they differ from shop to shop — check your nearest building-materials store for the current price per block.
| Type of roster | Strengths | Weaknesses | Best used on |
|---|---|---|---|
| Concrete | Strong, durable, most affordable, many patterns | Heavy; plain colour often needs painting | Fences, facades, garden walls |
| Ceramic / terracotta | Warm look, relatively light, pores help soften heat | More fragile under a hard knock | Facades, interior partitions |
| GRC (fibre cement) | Light, precise, modern patterns, weather-resistant | Higher price per block | Upper-floor facades, partitions |
| Exposed brick | Industrial feel, strong, easy to find | Needs a tidy mason, plus anti-moss coating | Facades, fences, dry gardens |
For an upper floor out of arm's reach, lightweight GRC is a common pick so the structural load stays low. For fences and garden walls that get rained on daily, concrete roster blocks take the beating better. That's why many houses mix two or three types at once, matched to the position and the load.
What People Often Forget: Privacy, Rain, and Dust
A roster block is a see-through opening, so there's a catch. Three things trip people up most if left unplanned: the view from outside can get in, rain can blow through, and street dust slips in easily. The fix isn't to skip roster blocks, but to combine them:
- Fit fixed glass or a window leaf behind the roster block for rooms that need full privacy, such as bedrooms.
- Choose a tighter hole pattern for private areas, and a more open pattern for service areas like the kitchen and stairwell.
- Add an overhang or canopy above facade roster blocks so slanting rain doesn't come straight in.
A house with a west-facing facade has extra homework, since Bekasi's afternoon heat really stings. Here the roster block as a secondary skin earns its keep most: it becomes a shield that breaks up the sun before it hits the main wall, while still letting air through. Add a climbing plant in front of it and the inner wall temperature can drop noticeably without a single watt of power spent.
Note: this piece is technical and educational. Price ranges, material types, and how much cooling effect you get depend on the house orientation, the design, and the mason doing the work — all of it illustrative, not a promise of results. Before tearing down a wall or adding openings, consult an architect or a builder who understands structure first, especially where a load-bearing wall is involved.
Back to the House You're After
Passive design like this is easiest to apply when the house shape supports it from the start. The Emerald 70 House on Jl. Raya Perjuangan, North Bekasi, for instance, is two storeys with 70 m² of building on a 4.5 × 10.5 metre plot — long and narrow, so a front-to-back cross-ventilation path plus a central void can be pushed to cut the reliance on AC. If you still plan to run AC in certain rooms, pairing passive design with an energy-efficient unit usually strikes the best balance; on picking the unit, we compare options in our look at inverter vs conventional AC for a 2-storey cluster house.
For wet areas, airflow also decides whether a house stays mould-free or not. The technical detail on exhaust and bathroom ventilation is laid out in our guide to exhaust and bathroom ventilation in a 2-storey house.
The point is that coolness can be designed, not only bought through AC. Roster blocks and cross-ventilation just need planning up front. After that they work for free every day, including when Bekasi's dry season is at its fiercest.
Want to see the Emerald 70 ventilation design?
The Kingspoint team can walk you through the opening layout, the void, and roster block placement in the ready-stock Emerald 70 unit in North Bekasi, so you can picture how the house stays cool without heavy AC before you decide.
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