Detailed guide for double storey extensions

Property extensions are the ideal solution if you’re thinking of acquiring additional space or improving your home. Having a double storey extension is one of the many options that you can consider. Ideally because it is more cost-effective than choosing to move out or purchase new property.

Also, most property types are compatible with double storey extensions. In this detailed guide, we’ll explore some of the important things you should know before embarking on a double storey extension project.

double storey extension interior

Is my property suitable for a double storey extension?

As mentioned earlier, most properties in the UK are compatible with the double storey extension. Whether you have a detached, semi-detached, or terraced property, maisonette or flat, a two storey extension will be ideal.

But first you need to check with the local planning authority to be sure that you can have a two-storey extension. Your local authorities will let you know if you’ll need any planning permission or if your house extension in London falls under permitted development rights.

You also need to hire qualified builders with the right architectural team so that they can advise you accordingly with regard to the suitable design and other requirements for the project. Here are some of the properties that you can have a double storey extension:

A semi-detached house

With a semi-detached house you can either have a rear or side double storey extension. Considering the extension can be intrusive, you need to consider how your neighbours will be affected.

You’ll need to consult with the local planning authorities to determine whether converting your semi-detached home will need any planning permission. In a situation where the neighbours are likely to be affected, you might need to consider party wall agreements.

A detached house

Having a double storey extension on a detached home is the least complicated option. Aside from being easy to achieve it causes the least disruption to the neighbours and you also have the option of having either a rear or side two storey extension.

Unlike other property types where you may have to compromise on your design, you get what you want with a detached home.

A terraced house

Having a two storey extension on a terraced house can be pretty complicated. But with a qualified builder and structural engineer, it will be easier to determine a suitable design for your property.

rear extension

Two story extension vs. single storey extension

A two storey extension is more preferred because it gives you more value for your investment compared to having a single storey extension. Whether you need to accommodate your growing family or acquire more living space, a double extension guarantees you more space. It is also a cost-effective loft conversion option unlike the latter.

Types of double storey extensions you can opt for

Just like there are different types of house extensions that you can opt for, the narrative is no different for double storey extensions. Here are some of the options that you can consider, depending on the type of property you have.

A double storey rear extension

Suitable for both detached, semi-detached and sometimes terraced houses, a two storey rear extension involves having an extension at the back of the house.

Double storey side return extension

With this extension type you can easily preserve your garden space because it uses the space at the side of your house. It’s an ideal option for detached and semi-detached properties. You have to consider how the project will impact any neighbouring properties since they can limit its construction.

A wrap around double story extension

This extension type guarantees you the most additional space to the existing home because it involves having both the rear and side extensions. It is also suitable for either a detached or semi detached property.

Front two storey extension

A two storey front extension tends to have the most impact on how your home will look. Although it’s not such a common option for many homeowners, it is well suited for detached properties, especially if they have a significantly sizable front garden.

If you're wondering which direction you should extend, the rear of the home would be an ideal option especially if you have a large garden space. It will also cause less disturbance to your neighbours.

two storey house

How much does a double storey extension cost

This question, ‘How much does an extension cost?’ is one many people tend to ask depending on the project they’re about to embark on. Double storey extension costs range between £1,500 to £2,500 per square meters without including the finishes cost.

The finishes can cost you around £1,800 to £2,800 per square metre. Double storey extension add a significant value to your property because you get at least a £4,000 increase in value per square metre.

Of course there are other factors you should consider that are most likely to impact the overall cost of the project like:

  • The size of your extension
  • The legal fees you’ll be required to pay
  • The extension builder you hire
  • Your location
  • The type of roof for the existing property

Apart from the construction cost, some of the other fees you’ll need to consider while coming up with a budget for your project include the following:

Consultants fees

There are several circumstances that may warrant the need for consultants fees. Some of these situations include the need for survey of the existing building, flood risk assessment and historic building report(If your property is in a conservation area), among others. The fees charged will depend on the consultation firm you choose to work with.

Planning fees

Although there are situations where you don’t need planning permission for two storey extensions, there are some where it will be necessary. The planning permission application will cost you between £200 to £400 and if there are any other planning conditions to be met, you’ll pay an additional £34 for discharge.

If the project falls under permitted development rights, then you’ll need to pay a fee of around £100 for a certificate of lawfulness.

Party wall agreement fees

If you’re sharing a boundary with your neighbours and they are likely to be affected in any way when you build a double storey extension, you’ll need to sign a party wall agreement with them.

Depending on whether either of you will see the need for a party wall surveyor then it will cost you between £700 to £1500 for each neighbour.If your neighbour agrees to the proposed work, then you won’t need to appoint a surveyor.

Design fees

Design fees range between £3,000 to £5,500. You’ll also have to pay for the architectural fees( usually around 3% to 7% of the construction cost) and for the structural design. These costs will vary depending on whoever you’re working with. If you hire a company with a design and build team then this might be a more cost-effective option.

Building control fees

Upon completion of the project, you’ll be required to have a building control certificate showing that the construction is in compliance with the building regulations. Depending on the size of the double storey extension and the nature of the work being done, this might cost you around £750.

Apart from the above listed costs, you need to include the fitting costs for your two storey extension in your also need to consider the cost for the interior and exterior materials used for the finishing touches.

wrap around extension

Is planning permission necessary for a double storey extension

In situations where the project falls under permitted development rights, acquiring planning approval isn’t necessary. Where permission is needed, you can always choose to work with a design and build company because this will make the cost more affordable.

You’ll find most such companies include the cost of acquiring planning approval in their quote. It is important to note that projects in designated areas or conservation areas have more strict planning rules.

Restrictions for permitted development rights

If your project falls under permitted development rights, it needs to adhere to the following requirements:

  • The appearance of the new extension should blend with the existing house and neighbourhood.
  • The extensions width should be less than 50% of the width of the existing house.
  • Balconies and terraces aren’t allowed.
  • The area of the new addition must be less than 50%of the free area surrounding the house.
  • The height of the two storey extension shouldn’t exceed the eaves for the original house.

Certificate of lawful development

This certificate shows that the extension was built in adherence to the permitted development rights requirements. Therefore, you will need to acquire one once the project is done.

Do I need building regulations compliance

To ensure compliance with the health and safety requirements, all builds must comply with the building regulations. You will need to acquire a building regulations approval upon completion of the project. Your builder can also work closely with the local building control officers to provide you with a building regulation certificate upon completion.

From the above, we can see that there are several things you can learn about double storey extensions. There are also several house extension ideas that you can implement depending on your needs, taste and even preference. We’ve also established the need to adhere to any legal requirements and that hiring a qualified and reliable builder is one way to ensure that you have less to worry about.

Frank Binoshi

About Author

Frank Binoshi
Building Homes at the Highest Standard.

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