Can You Build A Basement Under An Existing House?

Last Updated on April 30, 2021 by

Yes, you can build a basement under an existing house by increasing the depth of the existing foundation to allow the safe removal of soil under the building. The construction of basements underneath existing homes has become popular since the late 1990s due to the demand for more living spaces in cities. If well designed and executed, basements can create unique and valuable spaces.

If you’ve been considering building a basement under your house and want to know how much it would cost, you are at the right place. This article takes you through all you need to know about building basements. Please stick with us to the end.

What Is A Basement?

A basement is a building that is partly or entirely below the ground floor, either built as one or more floors. Basements can be used for residential purposes or as storage and parking spaces. Before you embark on creating a basement under your house, it is essential to contact an architect or engineer to determine if your property is ideal. Depending on the ground circumstances and site, sometimes it might be impossible to have a basement. 

Types Of Constructions When Building A Basement Underneath An Existing House:

The type of construction you choose for your basement will significantly impact your budget. After figuring out the need for a basement and setting aside the finances, the next step should be to choose the construction material. Working with a professional will make your work much more manageable. 

There are four main types of basement constructions. Let’s have a look at each of them in detail;

Type Of Construction:Description:
Masonry or block wallsMade from cinder blocks, this is the least expensive method of basement construction. Compared to other means, masonry walls take less time. A steel bar is sometimes used to strengthen the wall and increase durability. The only disadvantage of block walls is that water can sometimes seep through the mortar that holds the individual blocks together, in addition to the potential leaks along the floor and wall joints.
Precast panelsIn this method, the walls are molded at a different location, then placed on footers, and transported to the building site for installation. They are water-resistant and surprisingly strong in the long run. If water damage occurs between the floor and the walls, the effects will be seen along the joints.
Clay tile or stone wallsYou may find the basement foundation constructed with this type of wall if you buy an older or historic home. They were generally selected when other materials were not readily available and were common in the past decades. Despite being more rudimentary, they can be very strong. Groundwater can seep through relatively quickly, and this is their most considerable potential risk.
Poured concreteIt starts by pouring the footing for the basement foundation and is frequently preferred by people, making it the most common type of construction. Forms are then used to hold the poured concrete wall in place as they dry after set. This type of construction tends to be stronger compared to the other types.

Factors To Consider When Building A Basement Under An Existing House:

Below are some factors you need to consider before setting out to create a basement. These factors will help you mitigate the risk of building without prior knowledge of what is below the surface. 

1. Soil Type – Confirm the type of soil and the condition of the ground. For instance, clay-based soil will retain water better than the chalky type. Ensure you conduct soil investigations before you proceed with your building.

2. Water Levels– dig inspection pits to check the level of the water table. Before confirming the type and room of works

3. Design Works– Expect your designers to advise on what tests they would anticipate seeing for the scheme to assist in the design work., all of these factors help designers with the structure for the effective building. The design can be priced and worked up.

4. Basement Route – The type of construction used will be determined by the choice of the basement route. Be sure to identify any cables or service pipes as you go below the ground. Searches for assets owned by service providers like rail networks and utility providers will be included, as this is where land searches come in handy

How Much Does It Cost To Build A Basement?

The cost is determined by ease of access or how easy it is to remove the soil after excavation. Some other site-specific factors, such as the need to dissuade rain, can also increase the cost. The project will cost around $10, 000 and above under the best circumstances for an entirely below-the-ground basement. You might also incur extra charges for cleaning the perimeter drainage channels and pumps. Always ensure your design is easily accessible and maintainable.

There are four stages, according to a contractor, that will impact the price of basement work. 

1. The fit-out

2. Maintenance – If a pump and sump have been used.

3. Waterproofing – Determined by the number of pumps needed and the sump chambers, and the size of the basement space. 

4. The structure – Core and shell

How To Make A Basement Waterproof:

Waterproofing a basement is required for any structure below the ground used as a residential space and is very vital when creating a new basement.  Waterproofing ensures you have a dry environment that ventilation air conditioning installations can control, and domestic heating is provided. The building of slabs and mass concrete underpinnings are generally constructed below the ground.

This can be done by; Mixing the concrete with a batching plant and transporting it to the site in a lorry where the mixing is done. It is then pumped into the site according to structural underpinning schedules.

Unless treated by applying additives, the concrete is not waterproof, as many people tend to think. Monitored and certified to the designed specification to provide the required protection level for the application, these additives must be mixed at the batching plant. Registered or qualified installers of the waterproofing systems and products are required to carry out the entire process. 

What Are The Various Ways A Finished Basement Can Add Value To Your Property?

You can significantly increase the value of your property by adding a finished basement. You can add efficient living space to your property by considering this, and who knows, you can even attract a good source of income from it. Take a look at the following advantages;

1. An increased storage space, guest house, or an added recreation:

Prospective buyers love seeing a finished basement, and if they are transformed into a kid’s play area or a recreation area, this is an unexpected bonus to them.

2. Excellent return on investment:

They offer a great return, although they may not be considered livable square footage. A return of 70 – 75% of your investment if provided in the United States on average.

3. Income property:

You can add a rental unit in the basement after finishing up the building. This can significantly help lighten up the load of your mortgage or even increase your cash flow from a space that you’d have disregarded.

4. Additional bedroom and bathroom:

You can add more bedrooms and have more than one bathroom as this increases the size of your home. How convincing, right?

5. Additional space if zonal codes do not allow other additions:

There may be zoning restrictions prohibiting you from making certain additions to the property based on the lot size. Basements come in handy to create additional spaces in such instances.


It is possible to build a basement under an already existing house and get more space in your home. Basements can be great storage spaces and can also be used as living spaces. We hope that this post gives you the insight you need to start on that project you’ve been postponing. Best of luck!

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