House Extension Costs You Don’t Think About

When budgeting for your house extension there may be costs that you haven’t envisaged but which will impact the overall price. We take a look at some of the house extension costs that many people don’t think about. 

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Building Regulations

Every extension whether it is a side return, rear extension or loft conversion will need to meet various Building Regulations. Due to the technical nature of the process involved, you will need to factor in the cost of an architect, structural engineer and the cost of inspections by Building Control at various stages of the build. 

Architects charge around 5-10% of the cost of the build but it may be more. A structural engineer will likely charge by the hour or day and can vary according to the type of extension you are building. The cost of Building Control approval for various stages of construction will depend on the local authority or the independent company that you use for this service but should be approximately £800-£1,000. 

Party Wall Agreements

Any extension that involves a shared wall or boundary will be subject to a Party Wall Notice. This means formally advising your adjoining neighbour of your extension plans and allowing them to raise any concerns. If they object a Party Wall Surveyor can be appointed. 

The Party Wall Surveyor will attend the neighbour’s property and assess the other side of the wall, often taking pictures and providing a report. The cost will vary but should be between £900-£1,500 if your neighbour agrees to share a surveyor, who is bound to neutrality. If your neighbour refuses to share a surveyor you’ll have to pay for your own as well as theirs which will double the cost. 

Skip and Scaffolding

The least glamorous part of your house extension will be the scaffolding wrapped around the building and the big metal skip sitting on your driveway. But these are vital parts of the construction and the work would be impossible without them. Many builders will include the cost of scaffolding and skip hire in their quote to you but make sure that you understand what that involves. 

In some areas, you may need to pay a skip licence if you don’t have off-street parking or a front garden large enough to accommodate it. It means that the skip has to go on the public road and you need to pay for a permit for this. These permit fees vary from one local authority to another. 

Interior Fit

Unless your extension quote included the cost of fitting out the interior you will need to budget for this. Of course, the cost will depend on the purpose of your extension. If you’re adding a kitchen then the cost of all the appliances, cabinets, and countertops will need to be added. 

If you are adding a loft conversion to your home then things like staircase prices, roof windows and a Juliet balcony may be expenses you may not have thought about. Bespoke joinery is another way that your costs will be increased if you are not keen on off-the-shelf internal fittings. 

External Finish

You should also think about what kind of finish you want on the exterior of your new house extension. The external finish protects the outside of the building but is also an important aesthetic feature of the extension. There are various options including brick, render, stone or timber cladding, zinc or a mixture of materials. 

The choice will depend on your desired look, whether you want to complement or contrast the existing building and any limitations imposed on you by the local authority. Budget, of course, will also play a part and you should also consider the ongoing maintenance of each option. 

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