9 Things to Know When Buying a prefab extension

Do you feel you have insufficient space in your home? Maybe you’re looking for an extended living space or need some area for extra storage? Well, this is the time to acquaint yourself with the concept of ‘prefabricated extension’ or ‘prefab extension’, also called ‘accessory dwelling unit’. These units are basically, the home extensions that are built off-site in a factory with complete finishes like lighting, flooring, fixtures, paint, and other pieces of equipments. After the completion of the furnishes, these units are then simply assembled and attached to your homes as per your desired location.

However, there are a few things you need to consider when buying these prefab extensions. Whether you’re looking for a specific structural material or a typical design style, or if you’re digging more into the costs and site logistics, these following considerations should be on the table from day one. So, here is a list that you need to sign-off and prepare for your checklist as soon as you consider buying an extension.

Be Open-Minded

First and foremost, when you’re planning to approach the idea of buying a prefab extension for your existing home, it is important to have an open mindset towards design and construction system. Don’t shop for the extension with a fixed idea as it may lead to dissatisfaction and disappointment later. You need to be open to ideas and solutions that might better fit the existing conditions of your home in amalgamation with the newly assembled unit.

Determine the Details

After analyzing the site conditions, local climate, and the given zone that requires the extension, it is important to keep a note of the materials, R-values, or insulation, loads, sizes, and scale of the newly assembled unit. Now, this is also the time to set your design goals, financial budgets, and a typical planning and circulation diagram of the new unit.

If the extension and existing dwelling vary in their structural materials, it is important to incorporate a movement gap that allows the potential expansion and contraction of the two materials under specified conditions. Typically, a stainless-steel channel is used to set up the two materials.

Note the Measurements

When buying a prefab extension, you should exactly know where it has to go in your home, the directions, the circulation as well as the dimensions. If you are planning to attach a new unit to the existing one, make sure you have the precise measurements as that will help fit in the new structure accurately.

Quality needs to be Rechecked

Since these units are built and manufactured in the factory at a very rapid speed, it is important to keep a check on the quality of the materials used. If you have certain requirements regarding the interior finishes, it is important to place them very early in the design stage. Also to create a seamless environment, you need to blend in the two different units in terms of materials and planning to foster a cohesive outlook.

Now here is another major drawback of the prefab extension. Many manufacturers have believed to compromise on the quality of these units. Hence, it is important to take an action before it gets too late.

Finances and Paperwork

If you have a set budget, it is always a better idea to buy an extension than move into a new space considering the high real estate fees and other contingency charges. Hence, you can easily finance the extension without any paperwork or hassle. Depending on the type of home extension and the interior finishes you choose, the price may vary somewhere between $1,000 per square meter to $1,600 per square meter for a single-story extension. Meanwhile, for a double-story, expect to pay almost 50% of the cost of a single-story prefab extension.

A-Pro tip: Don’t forget to double-check the guarantee you receive on your new prefab extension. It will usually be for a number of years and dedicated to only specific services.


Whether you want the base material of your prefab extension in timber, metal, or concrete – this all needs to be considered when buying your prefab home extension. All the interior and exterior finishes as well need to be chosen by the homeowner itself. Although, it is highly recommended to pick the same materials as the existing unit.  

Types of Extensions

Before purchasing an extension, it is important to know the exact type you’re looking for and how the cost may vary depending on their typologies. Hence, some of the prefab extension types that exist, and you may want to consider are:


This type of extension provides extra living space in the form of glass roofs, attachments, and windows. The main idea is to welcomes tons of natural light so you could enjoy the feel of the outdoors while you are indoors. However, glass is just a placeholder and you can use any material you prefer. Prices may vary between $3,800 to $24,000.

Basement Conversion:

If you don’t have enough land around, the best way to incorporate extra space is by adding a basement. This requires extra excavation of the land to protect the property’s superstructure. However, these extensions could get risky in some situations and are equally very expensive. The prices here may vary somewhere between $20,000 to $40,000.

Garage Conversion:

One of the most affordable options, space here has four walls, a roof, solid slab, and foundation to make the space more livable and comfortable. However, these spaces need to be made more comfortable by furnishing them. These extensions cost around $15,000.

Granny Flat:

One of the most creative and flexible prefab extensions, these units can be added to the backyard or the front yard and can later be altered as renting units in the home. Thus, later down the road, you could use or re-use these and flexibly change the layouts and design styles as desired.

Hence, depending on these types – you could choose the most appropriate extension for your homes.

Additional Costs

Apart from the basic retail or wholesale and labor prices, there are some additional costs to the prefab extensions. These are hidden costs, so be prepared to invest an extra amount in the following listed utilities.


Additional heating, ventilation, and air-conditioning might be required to keep your space cozy and comfortable. At this point, do remember to check with the insulation values provided by the manufacturer.

Water and Gas:

If you are planning to add a kitchen or bathroom in the extended space, you might need to install the ducts and pipelines to add the utility services.

Planning and Building:

Depending on your local government and norms, the prefab extension may require additional work like permits, taxes, insurance, construction labor, interior finishes, and structural design which are possible added costs to your extension unit.

Access to Site

One of the other main things to consider which often gets ignored is the ‘access’ to the home. Look around the home and land – do you see a clear pathway for a truck to transport your prefab extension? Remember, transportation of these modules requires careful planning and approvals. If a crane is required to move around the modules, you might need permission from the local authorities, or the associations concerned. Thus, it should definitely make a point on your checklist.

So, What’s the Takeaway?

Prefab extension very generously remind us of the constant change that life is unexpected, and the circumstances might change over and over again. After all, why do we need home extensions? We need them to fulfill our future needs and requirements. Thus, this for all makes it square one as to why prefab extensions are important and why need them. Here, the list of the 9 most important things to consider further helps track down the checklist. Also, let us know in the comments below if you want to add more points to consider when buying a prefab extension home or if you have questions or stories to share.