What Is The Purpose of External Envelopes?

12.06.23

While older structures weren’t always constructed with the external envelope in mind, nowadays, a strong building envelope is always at the forefront of the design process. And for good reason.

The envelope is crucial for protecting the inside of a building and its inhabitants. But what exactly is a building envelope and what is its larger purpose?

Well, that’s exactly what we’re here to discover. In the guide below, we’re going to break down six key reasons an external envelope is so important.

What is an external envelope?

An external envelope, also called a building envelope, is the structure that seals the property and protects it from the external environment. There are two types of building envelopes, tight and loose.

A tight building envelope is one which doesn’t allow for air to flow so freely. This is achieved using insulation, sealant and energy-efficient windows and doors. This tight seal is created for better control of the indoor environment.

Then you have loose envelopes, which allow for more airflow and better natural ventilation. However, these structures need to be extremely carefully designed and built to ensure they don’t let in too much moisture and that poor-quality air does not affect inhabitants.

In any case, an external envelope is made up of several elements, including:

  • The roof
  • Doors and windows
  • Floors
  • Exterior walls

With this in mind, think of it like a protective shell, it acts as a barrier that keeps the outside world out of the building. But that’s not all it does. The external envelope has a number of key purposes and we’re now going to look at these in more detail below.

6 purposes of an external envelope

1. For structural support

The walls and floors make up an important part of a building’s structure, and since these are part of the envelope, this would mean that the envelope is crucial for structural support.

All of these are usually a combination of materials like slabs, footings and concrete. This helps to keep the building structurally sound and protected from the exterior environment.

The envelope also offers a way of attaching internal elements, such as cladding insulation and vapour barriers.

2. For durability

As part of offering structural support, the building envelope is also important for durability. When constructed correctly, the envelope will stand the test of time and ensure the building is durable and functional for years to come.

This includes adding cladding and barriers to stop moisture from getting in and damaging the property from the inside.

3. For aesthetics and finish

While all the elements that make up a building envelope are functional, they also play an aesthetic role, creating a visually pleasing exterior.

From the brickwork or building materials to the windows, doors and roofing, every aspect needs to be installed and placed carefully to look good and function as effectively as possible.

4. For controlling the climate

Climate control is arguably one of the biggest functions of an exterior envelope. A carefully constructed and sealed building envelope helps to ensure that conditioned air stays inside. That doesn’t matter whether it’s been cooled or heated, it helps to control the internal climate without letting the air escape.

That being said, in looser envelopes, more air can flow naturally through the envelope. This is OK if this is the desired effect but not so good if it is due to poor construction.

The exterior envelope ensures that humidity doesn’t build up and lead to moisture, which in turn, could lead to mould or mildew growing inside the building.

5. For energy efficiency

On a related note, the external envelope also affects energy consumption. If the building is unable to control the climate effectively, warm and or cold air can escape, making it less comfortable for those inside.

Not only this, but if air leaks in or out, the need to condition the air increases, using more energy. This is not cost-effective or good for the planet. Therefore, the purpose of a strong envelope is to make a building more energy efficient.

6. For controlling acoustics as well as climate

Finally, it’s not just about climate, it’s also about controlling the acoustics of the building. The envelope will be insulated to manage both internal and external sounds, this adds to the comfort of the occupants.

It’s important that sounds from outside don’t interfere with inhabitants, but also that any sound made inside doesn’t disturb those outdoors.