The Giant Oven Movement: A Building Should Be More Than a Glass Box

It is crazy to see how often beautiful buildings are considered to be buildings full of glass.

If a building is not fully glazed, it is sometimes seen as less appealing, less elegant, less contemporary, less expensive, or simply less beautiful.

What is even more interesting is how quickly this idea of beauty is becoming common across African cities, many of which are located in warm and humid climates.

I have observed this trend across major cities from West to East Africa, and I am sure many people will recognize it.

But before we examine the problem, let’s first ask: where did this obsession with glass come from?

My probably biased answer is that it has been imported from the West and the Middle East, where fully glazed buildings have become associated with luxury, strong selling points, and contemporary architecture.

Let’s assume this is partly true and put it into context.

Many countries in the West have historically been heating-dominated. In those climates, glazing can provide useful solar heat during cold periods for passive heating, although it can also create overheating during warmer periods.

In the Middle East, the story is different. These are predominantly cooling-dominated climates, but they also have access to highly developed technologies, materials, and energy infrastructure that make it possible to cool heavily glazed buildings - at a cost.

Now let’s bring this copy-and-paste approach into a warm African city.

Warm climates are generally hot and sunny for much of the year. And these two conditions are not necessarily friends with glass.

Unless carefully designed and shaded, large areas of glazing can turn buildings into giant ovens.

And there is another problem: we cannot always assume that electricity will be available 24/7 to run air conditioning. Many African cities continue to face challenges with energy reliability and affordability.

Someone might say: “So what? If I can afford the air conditioning, generators and maintenance, why is a fully glazed façade a problem?”

Fair question.

More glass should not necessarily mean better buildings

Glass is useful. It brings daylight into buildings and connects people with the outside.

But somewhere along the way, more glass became synonymous with better views and better architecture.

We hear things like:

"My office has full-height glazing and the views are amazing."

But do we really need a fully glazed façade to connect with the outside?

Probably not.

We need enough glazing to provide useful daylight and meaningful visual connection with the outdoors - not necessarily as much glazing as the façade can physically accommodate.

This is where building physics becomes interesting.

The right amount of glass depends on climate, orientation, shading, room depth, window size, daylight requirements, and how the space is used. It is a performance question, not simply an aesthetic one.

And then there is the sun.

Glass needs shade

Large areas of glazing can introduce significant solar heat and glare. That heat eventually has to go somewhere.

Have you ever walked into a beautiful fully glazed office or apartment and noticed that all the blinds are down because the sun is simply too intense?

If we need to keep the blinds closed throughout the day, what was the point of installing all that glass?

To enjoy the views at night?

And what exactly are we seeing at night?

One of the simplest ways to address solar heat and glare is to shade the glass externally.

Deep balconies, roof overhangs, awnings, horizontal and vertical fins, and other external shading devices can dramatically reduce direct solar exposure before the heat reaches the glass.

This sounds simple until someone says:

"I don't like those things on the façade."

Or:

"I don't want to hide the building."

I understand. Beauty is subjective, and I am certainly not an expert in aesthetics.

So I will leave the question of beauty to architects and designers.

I want to talk about what I know:

building performance.

Let's run some numbers

Glass absorbs and transmits solar energy into a building. But the interesting question is not whether this happens.

We already know it does.

The interesting question is:

How bad is it?

That is where building performance simulation becomes useful.

For example, 1 m² of unshaded glass in Kigali, Rwanda can receive up to 5 kWh of solar energy over a day. If we assume this translates into 5 kWh of additional cooling demand, a 2.5 kW room AC would need to operate for approximately 2 additional hours to remove that heat.

And this is not just an energy problem.

It is a thermal comfort problem

This additional solar heat gain can raise indoor temperatures and increase the risk of overheating.

It is also a cost problem.

Large areas of high-performance glazing can also be significantly more expensive than conventional opaque wall construction. As an indicative comparison, 1 m² of single glazing in Rwanda can cost roughly 2 times as much as 1 m² of concrete wall and around 3 times as much as 1 m² of earth-brick wall, depending on the specification, supplier and construction system.

But there is another cost we should be talking about.

What about embodied carbon?

We often talk about the energy a building consumes once it is occupied. But what about the carbon that goes into making the building in the first place?

Every material has an environmental footprint associated with extracting raw materials, processing and manufacturing, transportation, construction, maintenance and eventually replacement or disposal.

For example, the embodied carbon (A1-A3) of 1 m² of single glazing curtain wall is roughly 2 times as much as 1 m² of Concrete Masonry Unit(CMU) wall and around 5 times as much as 1 m² of Compressed Stabilised Earth Block (CSEB) wall.

So when we replace a simpler wall system with a highly glazed façade, we are also increasing the embodied carbon associated with the building.

In other words, the most sustainable material is sometimes the material we did not need to add in the first place.

This brings us back to the same question:

So why follow a design trend that increases construction cost, operational costs, maintenance requirements and environmental impact?

Less glass should not mean less architecture

The answer is not to eliminate glass.

The answer is to use the right amount of glass, in the right place, with the right shading and the right performance.

A building can have daylight.

It can have views.

It can feel open and connected to its surroundings.

It can still be contemporary (if you are into this!) and beautiful.

But it does not need to become a glass box to achieve these things.

At Habindi, we believe in sufficiency before efficiency.

That principle applies here too.

Before asking how efficiently we can cool a fully glazed building, perhaps we should first ask whether we need so much glass in the first place.

Before adding more technology, reduce the problem.

Before adding more air conditioning, reduce the heat.

A building should do more than look good.

It should work.