There is much information that you need before you embark on adding an extension to your home, and this might relate to any stage of the build, from design issues and potential problems with logistics, to the various nuances of the law.
So here we have 24 pieces of advice that should be – but not always are – needed. Make sure you take this advice on board before you do anything towards building your extension!
1. Living on site might hinder progress
The problem with living in a property during building work, apart from the inevitable noise and dirt of a building site, is that your presence might just slow the project’s progress.
So it might be a good idea to vacate the premises whole work is going on.
2. Choose the right designer
An important early decision concerns the choice of designer you are going to work with.
You may work with a design specialist, with an architect or architectural technician, or you might decide to procure the services of a Design & Build company and use their in-house design team.
But, whatever you decide, take the time research the industry and find people who have the type of experience that you require, and be guided by the views and recommendations of others.
3. Consider any site access issues
An important consideration is access to your site, as there may be physical restrictions on the materials and equipment that can be delivered to your property.
This is a particular issue for terraced properties, for example.
It might also be necessary for your neighbours to move any trees or fences that might cause an access obstacle during your build, and such issues need to be addressed before any plans are made.
4. You must be insured!
It is essential that you take out insurance for the duration of the build, and you should also seek the advice of your existing insurer.
Insurance is needed for both your exiting property and any new structures that are erected, and your policy needs to be taken out with an A-rated insurance company.
It may not be sufficient to rely on contractor’s insurance, as such policies might not cover eventualities such as fire and flooding, and might only protect the contractor in the event of that company being proven liable for any costs or damages.
A legal dispute with your builder might prove costly. If you take the option of not living on site during the build, then Unoccupied Buildings Insurance, probably for at least six months, might be needed.
5. Harmonising the extension with the existing building
An important design consideration concerns how the new structure sits with what you have already.
Your preference might be for an extension that exactly matches, and blends in with, the original building, but this carries with it the considerable challenge of using matching materials throughout.
An alternative is to deliberately design the additional structure so that it contrasts with the existing building.
6. Consider a complete rebuild
Before beginning a project to extend, it is important to ask yourself whether this is really what you want to do.
This is because you might be able to achieve all of your objectives by completely rebuilding a house on your plot, or by selling the property and buying a new one.
If your motive is profit, then you should consider the maximum that your house can be worth, regardless of any improvements you make, given the price of properties in the area.
It is important to realise that there is a ‘ceiling’ value for every property.
7. Consider issues relating to kitchen appliances
If the project includes extending your kitchen, then there are additional considerations relating to kitchen appliances and equipment.
It is important to think through how appliances are to be plumbed in, wired in and ventilated.
Careful plans need to be made for how cookers and fridges etc, need to be positioned in relation to all your cabinets and units.
8. You might need to upgrade your hot water system
Similarly, thought must be given to whether your existing boiler will be able to manage the additional workload involved with providing hot water and heating for an enlarged property.
This entails getting to grips with the size of your boiler, the amount of heat output it is capable of, the size and number of radiators you will have, the time that it will take for the water in the boiler to be heated and distributed, etc.
9. Building Regulations still apply
When carrying out a project under Permitted Development Rights, although planning permission will not be needed, this is not the case with Building Regulations, which still apply.
The regulations will generally cover any extension to a building, whether it be a kitchen extension or an addition to the general living space of a home.
This includes loft conversions, the addition of a new chimney or changes to window openings. In terms of internal alterations, Building Regs will be required for any changes to load-bearing walls, the refitting of bathrooms and toilets (due to any plumbing and drainage changes), the addition of new heating equipment, or even the installation of a new flue. This is because the Building Regs are important for ensuring a number of safety issues, including fire precautions and structural integrity throughout the build.
These regulations also cover issues such as energy efficiency, ventilation and damp proofing. They apply to all work which entails alteration to a building, as well as to new-build projects.
The only exceptions to Building Regulations are projects involving outbuildings such as sheds, and some conservatories and orangeries.
Repairs are generally exempt from Building Regs, unless they involve structural work such as underpinning, or rewiring or the replacement of windows.
10. Off-site construction is an option
One possibility for saving time and money is to have components of your build manufactured off-site, in a specialist factory.
Such components might include oak frames, or maybe SIPs (Structural Insulated Panels) or CLT (Cross-Laminated Timber).
11. Sewerage issues
One issue that should not be overlooked is consideration of whether your build affects the sewerage system.
If an extension is to encroach within 3 metres of a sewer that serves one or more other properties, apart from your own, then you should get in touch with the relevant Water Authority.
It is possible that the Authority will require you to enter into a Build-over Agreement, and it may even be necessary to change the location of a manhole, or to create a new one.
12. Project Management
The role of the Project Manager is very important, and one option is to employ a specialist professional to fulfil this task.
Alternatively, some people like to manage a project themselves, and this does have the advantage that they are the experts in their own needs and aspirations, they will have unique insights into the site and will also be extremely motivated to get things right.
However, managing a build is not a good idea if you are not highly organised, a good decision-maker and capable of solving the type of problems that will inevitably arise on site.
You should also be sure that you will have the time to devote to such a demanding task.
13. Extending upwards
A common type of build is the upwards extension, entailing building on an existing structure.
It is important, however, to give careful consideration to whether it might be necessary to strengthen current foundations, or to provide a new steel framework, in order to ensure that the weight of the new structure can be supported.
In such cases, it may be less costly to simply remove what is currently on the ground floor and build a fresh, 2-storey extension.
14. Community Infrastructure Levy
There is a possibility that an extension that exceeds an internal area of 100 square metres may be subject to an additional charge from the Local Authority, known as the Community Infrastructure Levy (CIL).
This is an additional charge that you might be able to avoid through securing Self-builder’s Relief, for which you will need to have the intention to live in the extended property for at least the subsequent three years.
The situation with both the CIL and the related Relief needs to be checked with your Local Authority before you embark on a project.
15. Thermal efficiency
The Building Regulations specify certain standards relating to construction materials and airtightness levels that relate to the thermal efficiency of your property.
This is expressed in terms of a ‘U value’ describing the amount of heat that is lost from the building.
However, it is possible to go beyond the minimum requirements of the Building Regs, and a good time to do this is when you are in the process of designing and building your extension.
16. Party wall issues
All matters relating to the party wall between adjacent properties are covered by The Party Wall etc. Act 1996, which covers properties in England & Wales, and deals with the rights and responsibilities of both parties when building work is undertaken.
The Act empowers a property owner to carry out work as far as, and on, the party wall between properties, provided that any necessary planning permission for the work has been obtained.
This might include one party gaining access to the neighbour’s land.
There are specific provisions under the Act relating to the laying of foundations, if these foundations are to be within 6 metres of a boundary or 3 metres of a party wall, and these provisions may make it necessary to procure the services of a surveyor.
17. Privacy issues
One important consideration at the design stage is that of privacy for you and your family, and this can be dealt with through the careful selection of glazing, or by designing in various screening measures.
But take care that any such measures do not compromise the views from your property.
18. Tree Preservation Orders (TPOs)
Even though a building project might come within Permitted Development Rights, this might not be true of the trees on a property.
Any tree with a diameter that is greater than 7.5cm, and which stands within a Conservation Area, will be the subject of a Tree Preservation Order (TPO) – and a TPO might also apply to trees elsewhere.
It is a criminal offence to even make alterations to a tree that is covered by such an Order, without first securing planning permission to do so.
19. Value Added Tax (VAT)
Regulations The cost of building your extension will normally be subject to VAT.
Even if you employ the services of a contractor who is not registered for VAT, it is only that contractor’s labour that is exempt, meaning that you will still need to pay the 20% VAT on any materials that are used.
Exceptions to this include projects carried out on a listed building, which are not subject to VAT, and work on a building that has been vacant for two years or more, for which 5% VAT is payable.
The reduced rate of 5% is also available for a project that converts an existing property to a different number of units.
However, the VAT on eligible projects can only be claimed back on a project if a VAT-registered contractor is carrying out the work on behalf of a client.
20. Don’t forget a contingency budget!
It is extremely important to build in a contingency budget with your cost calculations, for any unforeseen additional spending.
This should be 10% to 20% of the main project budget.
21. Building Control
It is important for you to notify your local Building Control department at the start of the process.
You can do this by sending in your full plans, which, if Building Control signs them off, will enable you to ‘go full steam ahead’ with your project.
Alternatively, if you want a quick start, then you can just submit a Building Notice, but you will need to do remedial work on any aspect of your build that is subsequently found to not meet Building Regulations.
22. Beware of letting in too much light
Whilst it is nice to have plenty of light coming into your property, it is important to avoid too much light coming in, as this will create problems of ‘solar gain’.
This is sometimes an issue with conservatories, which are only comfortable to be in at certain times of the year.
Issues with solar gain can be mitigated by the use of screen fabrics which are designed to soften incoming light and so reduce glare.
23. Carefully consider the scale of your extension
Extending your property is not simply a case of adding cubic metres of floor space. With clever and thoughtful design, it is quite possible to create a feeling of space and airiness, without necessarily increasing the dimensions of what you have.
24. Restrictions on the use of glass
There is a limit to the amount of glass that can be used in an extension, with the maximum being set at 25% of the total floor area created. This is laid down in Part L of the Building Regulations. This means that much care must be taken with the inclusion of, say, French doors in a design, as these will take up much of the permitted quota of glazing.
If large, bi-fold doors are a priority, then the design should include the discarding of unwanted existing windows, so as to minimise the extra glass that the extension will create. If it proves impossible to avoid exceeding the 25% limit, then one course of action might be to demonstrate that the extension’s glazing has high energy performance levels that are at least equivalent to those of other materials.
Alternatively, your plans might be passed by Building Control if you can show, with a SAP assessment, that your extension’s CO2 emissions will not exceed those of an extension that would conform to Part L of the Building Regs.