How Thick Are Exterior & Interior Walls? (Explained)

If you are building yourself a new house or any other building, you must have encountered a few questions regarding the exterior and interior walls. One common confusion that people face during building is the thickness of the walls both inside and outside the building.

As exterior walls and interior walls have different purposes, they have different thickness requirements. Now the question remains how thick are exterior and interior walls. Let’s take a look and find out.

How thick are exterior walls?

When it comes to the thickness of the walls, exterior walls are thicker than interior walls. Because they often need to support the pillars in bearing loads. Furthermore, exterior walls are more exposed to outside weather conditions also. That is why exterior walls are always 8 to 10 inches thick.

Exterior walls on a residential house:

Exterior walls, in general, are thicker than the interior walls in any building. It is not different in the case of residential houses as well.

The thickness of residential houses is also a crucial factor as it signifies the overall structural strength of the house.

Commonly, the exterior walls in residential houses are about 10-inches to 12-inches thick. Sometimes this thickness increases depending on the type of plaster or panels over them.

Exterior walls on a building:

The thickness of the exterior walls of a building depends on multiple different factors. These factors include the climatic conditions, the material of the wall and its height, and many other things.

However, on average most buildings have exterior walls that are at least 12-inches thick. If the building carries big loads, then this thickness needs adjustment accordingly.

Commercial exterior walls:

As the thickness of the wall majorly depends on its materials, commercial exterior walls are not very thick. Because commercial buildings usually have high-quality materials. They are pretty strong and can bear loads to a great extent.

The average thickness of exterior walls in commercial buildings ranges between 7.5-inches to around 10-inches. This thickness is capable enough to hold the high loads in such buildings.

Exterior brick walls:

When it comes to building materials, brick is a very popular choice. These are pretty cheap in comparison to many other building alternatives. Brick walls are also very good at bearing a high amount of loads.

While the minimum thickness for brick walls is 9-inches, there is no upper limit for the thickness. Based on the designs, a brick wall can get around 12-inches.

Exterior concrete walls:

Concrete walls are very strong when it comes to the structural strength of walls. As a result, concrete walls do not need to be very thick to perform at their best.

However, if additional beams or pillars do not support the wall, it needs to be thick enough to bear the loads.

Typical concrete foundation walls are usually 6, 8, or 10 inches in thickness. The thickness of the wall will be decided based on the type of support the wall has.

Exterior glass walls:

In different builds nowadays, glass walls are reportedly being used. These walls are mostly for aesthetic purposes as they are not the best option for bearing heavy loads.

As glass walls are not for bearing loads they are usually much thinner than usual wall thicknesses. Commercial glass walls are typically 1/4-inch to 1-inch thick.

Exterior wall with vinyl siding:

Exterior walls are in general 8 to 10 inches thick. However, when these walls are covered with additional vinyl siding, the total thickness of the walls increases a bit.

Good quality vinyl wall sidings are, in general, 0.4-inches thick. This thickness increases as the quality and durability of the sidings increase.

As a result, exterior walls with vinyl sidings become around 10-inches thick where the wall alone is 8 or 9 inches thick and the vinyl siding is 1-inches or 1.5-inches thick.

How thick are interior walls?

Typically interior walls are thinner in terms of thickness. Interior walls do not bear any loads or face any harsh weather conditions. That is why interior walls are usually 4-inches to 6-inches thick. Furthermore, if they have any plumbing in them, then they are around 8-inches thick.

Interior walls in a residential house:

Interior walls in most residential houses usually do not bear any of the building’s loads. That is why to save extra cost many people choose to let them remain thin. However, a minimum thickness is essential for interior walls as well.

In residential buildings, the interior walls are primarily around 4-inches thick. But this thickness can increase depending on the material and plaster as well.

Interior walls with plumbing:

Making too thick walls is a waste of your budget. But, extra spacing for plumbing in your walls is not a bad expense. Instead, it is a clever way to manage your space.

Interior walls with plumbing are thicker than regular walls. The thickness of such walls is around 6-inches to 8-inches. It even sometimes stretches to 12-inches.

Interior walls with drywall:

Drywalls, also known as plasterboards, are made of gypsum put in between thick paper. They are strong and durable. That is why they are very thin in terms of thickness.

Drywalls are usually 0.5-inches thick. So when an interior wall contains drywall paneling over them, the overall thickness of the interior wall goes around 4.5-inches to 5-inches.

Commercial interior walls:

Commercial buildings serves multiple purposes based on the need of the clients. That is why the interior walls in the commercial spaces vary. However, they are usually thicker than regular residential interior walls.

Commercial interior walls are around 5.5-inches to 7.5-inches thick. This thickness helps to maintain a quiet professional environment inside the rooms.

What is the minimum and maximum thickness of the interior wall?

Internal walls are usually less thick than their exterior counterpart. Because interior walls, in most cases, do not need to bear the load of the building, so they are usually less thick.

Internal walls that do not bear any load need to be at least 4.5-inches thick. Additionally, if they have any internal plumbing cavity, this thickness will increase to 6-inches. However, if they are load-bearing walls, then the minimum thickness needs to be at least 8-inches.

On the other hand, including plumbing and added plasters, internal walls can usually be about a maximum of 8-inches thick. Anything more than this thickness will be a waste.

The thickness of a wall, be it an exterior or an interior wall, is crucial. The safety of the building depends on it. That is why while building walls, make sure to build them with proper thickness according to their purpose. However, also try to avoid building unnecessarily thick walls.

What is the minimum & maximum thickness of the external wall?

External walls, in comparison to internal walls, usually face all the harsh weather conditions. They are the ones to bear the load of the building. That’s why external walls, in general, need to be thicker than internal walls.

The minimum thickness for external walls needs to be around 10-inches. This thickness is good enough to withstand almost all harsh weather conditions.

However, if the exterior wall has some cavity for additional insulation or plumbing, this thickness can increase to around 11-inches.

In addition to the 10-inches of minimum thickness, there will be plaster and additional protective layers on the external walls. As a result, the wall thickens even further. The maximum thickness of an exterior wall varies from around 11.5-inches to 12-inches.

Note that if your wall has extra insulation materials between them or a plumbing cavity, then the maximum thickness of your external wall will stretch further.

How thick should exterior wall insulation be?

The thickness of the insulation of walls depends on the desired R-value. The standard R-value acceptable is R-38. Based on this value of R, you need to set the thickness of your exterior walls.

The insulation of exterior walls is more important than the interior walls to some extent. It is because the exterior walls are exposed to hot summer and outside weather all the time. That is why naturally, exterior walls need thicker insulation.

 To achieve the industry standard R-value of R-38, you will need insulation that is 12-inches thick. This amount of thickness will insulate almost most of the heat of the outside weather.

Note that if you want a higher R-value, such as R-49, you will need to thicken the exterior walls even further.

Final thoughts:

Exterior and interior walls differ in terms of their purpose and vary in thickness. While exterior walls are 10 or 12 inches thick to bear heavy loads, interior walls are 4 or 6 inches thick. Furthermore, thick walls come in thick load-bearing materials, while interior walls are thin.