30 Things You Need to Know Before Starting House Extension

Extending your home can be a long and cost-intensive process, especially if you don’t know enough about design, planning, construction, and the relevant legal aspects.

Let’s take a look at 30 things you need to know before you start your home extension project.

1. Living on Site

Living in your home for the duration of the project may seem like a more convenient option than finding temporary accommodation. If you live on site, however, the accumulation of dirt and the presence of workers can have a negative impact on your lifestyle and privacy. Your daily program can also interfere with the builders’ activities, and delay the project completion time.

Arrange short-term accommodation, or ask friends if you can stay with them. You will be able to go about your routine as usual, and your absence will allow the builders to complete the project without disturbances.

2. Choose Your Designer Carefully

The design is an integral part of your room extension or attic conversion project. The designer should be able to understand the project outcomes that you want and find creative solutions to meet them. Working with a designer that has experience in projects that are similar to yours can save you a lot of time and money.

House Extension

Architects, architectural designers, and design consultants typically have their areas of specialisation. Choose a professional with skills that are congruent with your specific ideas. If the building company has an in-house designer, make an appointment with them to discuss your project requirements and to build a professional relationship with them.

3. Restricted Access

If access to the building site is limited, you may not be able to use certain building methods. Before you start the project, invite the builder and designer to the building site to determine if access is a potential problem.

In some cases, you may have to arrange with neighbours for access via their property. Removing security walls or fences may also be necessary to allow unrestricted access.

4. Site Insurance

When conducting an extension project, you need site insurance to protect you from damage to the existing structure as well as the extensions.

Home insurance companies typically don’t cover your house if you are making changes to the structure of the building. Although many building companies have an insurance option, chances are that this option is a liability cover, and you will have to prove fault to file a successful claim.

If you don’t live in your home during the renovation project, you will need unoccupied building insurance. Contact the existing home insurance provider to notify them of the extension, and to find out what site insurance policies they have available.

5. Design Style Compatibility

There are no rules when it comes to the style of an extension. The appearance of a modern addition can complement the classic look of the existing structure.

Before starting your house extension project, spend some time to make sure that the existing and new design styles will work well together. Look at examples of similar style combinations and discuss them with the designer. The visual compatibility of the old and new structures will go a long way to ensure a successful result.

6. Property Value

All houses in a neighbourhood typically have the same ceiling value. A mistake that many homeowners make is to think that an extensive renovation project will increase their property’s value beyond this ceiling price.

If the build costs are too high, and your home’s maximum market price is too low, rebuilding your entire home may be a better option. Selling your house and buying elsewhere may also make more financial sense.

It can be a challenge in determining if an extension project will add sufficient value to your home. Take a look at the selling prices of homes in your area. You can also ask a real estate professional to base an estimated market valuation on your plans and extension description.

7. Kitchen Layout

If your extension project involves your kitchen, plan its layout first. Changing the location of appliances, electric outlets, fixtures, and plumbing can be expensive and time-consuming.

House Extension

To save yourself from a lot of frustration, plan the entire extension build around an established kitchen layout. Ask the designer to help you draw up a kitchen plan to ensure complete practicality and proper ventilation.

8. Boiler Upgrade

Structural add-ons can often increase the need for hot water, especially if these additions consist of bathrooms and bedrooms.

Determine the size of the boiler upgrade you need by considering the daily requirement for hot water, your existing boiler output, and its reheating time.

An efficient boiler upgrade can reduce your utility bill and your home’s carbon footprint. If you can, go for modern, more energy efficient alternatives. Contrary to popular belief, the UK gets enough sunlight to power photovoltaic panels – around 60% of the solar radiation found in the Equator.

9. Building Regulations

Since you are using permitted development rights, you need Building Regulation approval before starting your house extension. Building Regulations are in place to ensure that a building is energy efficient and safe.

Adhering to the relevant Building Regulations ensures that your extension and existing structure meet the minimal requirements for damp proofing, ventilation, fire safety, and structural integrity. All new building work should meet the Building Regulations except for specific repair work and the construction of certain outbuildings.

Building Regulations apply to all home extensions, loft conversions, and internal structural alterations. You also need approval before installing plumbing fixtures and heating appliances. The architect or building company should be able to advise you on the Building Regulations that apply to your existing structure and extensions.

The aim of the building regulations is to provide for the safety and welfare of people in and about buildings.  The building regulations apply to the design and construction of a new building (including a dwelling) or an extension to an existing building.

Please, visit the Department of Housing, Planning and Local Government Website

10.  Off-site Component Construction

Off-site construction refers to the manufacture or assembly of building elements in a factory and not at your house. Since the work happens in a designated space, it lowers the input cost per unit of these elements and saves you money.

Additionally, off-site construction saves you a lot of time. Installing a building element to a permanent structure is simple and doesn’t take long.

11. Shared Sewer Location

If you are planning to build over or close to a sewer, you may need a Build Over Agreement (UK) with the local water board. Shared sewers service more than one property so construction defects can cause issues within the public sphere.

Before starting your house extension, make sure that you know exactly where all the sewers are.

If you plan on building within 3 meters of a drain, contact the local water board before you start construction.

In some cases, you may have to build or move a utility hole. Since this is expensive, consider changing your plans to accommodate the existing sewers.

12. Conservation Areas

Permitted Development rights allow you to make specific structural alterations without regulatory approval. If you live in a conservation area, however, this is not the case. Every local authority has regulations in place for conservation areas. Contact the local conservation officer before you extend an existing structure.

The objective of conservation regulations is to protect the character of the area. The architectural style of buildings in the region plays a key role here. Conservation regulations focus primarily on changes to the shape and height of roofs. You need approval if you, for example, want to add dormer windows.

13. Managing the Extension Project

Since the designer and builder are professionals, you may feel that they are more suited than you to manage the extension project.

As the owner, however, you may know the property more extensively than they do. You are also more motivated to see favourable results than anybody else.

To manage an extension effectively, you have to apply some creative problem solving, patience, and organisational skills. You also need time to make informed decisions and manage the day-to-day activities of the project. If you don’t feel that you have what it takes to oversee the extension, consider employing the services of a professional project manager.

14. Extra Storeys

Adding a second storey allows for beautiful views and economic use of property space. The existing structure has to be able to support the weight of a second storey, however. Foundations of buildings younger than 25 years may be deep enough to carry the weight of an extension above.

If your house is old, you have some options to increase its loadbearing capacity. You can either underpin the existing foundations, strengthen the current structure with a concrete embedded steel frame, or knock down the entire existing structure and build from scratch.

15. Community Infrastructure Levy

If you plan on extending the existing structure with a floor size of 100 square meters or more, you may be liable to pay the Community Infrastructure Levy (UK). Under certain circumstances, however, the CIL charges may not apply to you. For example, if your local council doesn’t operate under this scheme, or if a self-builders` relief applies to your project.

To be successful in your self-builders` relief application, you have to plan on living in the house as a resident for at least three years after completion of the extension project, and you don’t have to build the extension yourself physically. Find out about CIL charges before you start constructing the extension.

16. Thermal Efficiency

Since you will be using modern building techniques and materials, you can look forward to sufficient airtightness and thermal efficiency. If the existing structure has lacking insulation, however, an efficient extension will not lower the running cost of your HVAC system.

House Extension

During the extension project, use the resources and building services at your disposal to insulate the existing building as well. Thermal efficiency throughout your entire premise is critical to ensure you adhere to Building Regulations.

17. The Party Wall Act

A party wall is a wall that separates your property from your neighbour’s. The Party Wall Act (UK) is a guideline to prevent disputes that may arise about party walls. It sets out a procedure that you have to follow if you plan on making changes to an existing party wall as part of your extension project.

If you want to dig a foundation within three meters of a neighbour’s property, you have to comply with the Party Wall Act. A surveyor can act on your behalf and ensure that you remain within the provisions of the act, especially if you dig foundations that are deeper than your neighbour’s.

Attention, please! The Party Wall Act is only relevant to England and Wales and has absolutely no bearing on party wall matters in Ireland. To make matters even more confusing the Irish courts may still refer to English Case Law when determining what judgement that the Irish court may make in both party wall and boundary wall disputes.

Boards.ie: Should I go with an agreed party wall straddling the boundary?

  • Dublin_Mom

My issue: neighbour building on a kitchen extension. Didn’t need pp as under area that is exempt. He is building right up to his boundary line, which I understand he is entitled to do.

However we want to extend next year, and this will mean we will be unable to access our wall to render it and make it damp proof.

So the question is, should we go with an agreed party wall straddling the boundary? But I am concerned when the time comes (we will have to apply for pp) he will not agree to our structure. He would not be a very agreeable character.

There was a stone party wall along the boundary between the 2 patios which we let the builders takedown. This wall extended out about 4 feet. Realise now we shouldn’t have done that…

We are sort of stuck between a rock and a hard place right now. Some info I have read says that building a party wall out on the boundary devalues your property?



Read Answers


18. Privacy

When extending your home, privacy may be the last thing on your mind. One problem that designers often have is that windows that allow natural light also expose the interior of your home to neighbours or passers-by.

There are a few ways to add a little privacy to your home. One-way window screens obstruct the view into your home, let natural light into your home, and don’t obstruct your view. Roof glazing can also brighten up your interior space if blinds cover your wall windows.

19. Tree Preservation Orders

Tree Preservation Orders (UK) apply to certain tree species and all conservation area trees that have a diameter of more than 75mm. Removing or pruning a tree that has the protection of a TPO is a criminal offence, and the local conservation authority may penalise an offender with a fine.

TPO’s can be a problem for homeowners that want to extend their existing buildings. If a tree with this protection stands in your way, you need the proper planning permission before you can start extending your structure. Contact your local council or conservation authority to arrange an inspection.

20. VAT Relief

Almost all extensions are subject to VAT on labour and materials. If you do the work yourself or employ the services of a tradesman who is not registered for VAT, you can save the VAT on the labour. You will, however, still have to pay VAT on materials at the standard rate of 20%.

If you extend a listed building, you are eligible for VAT relief. If you renovate a building that has been unoccupied for longer than two years, you are subject to VAT at a reduced rate of 5% instead of 20%.

All self-builds and extensions must follow the rules laid out in the Building Regulations and within Health & Safety legislation. Building Control is different in NI and ROI.

Please, learn The Self-Build VAT in Ireland Guide

21. Budgeting

An extension project is an affordable alternative to moving house. Creating extra living space and transforming your existing one can have the same benefits selling your home and buying a new one. The difference is that you won’t have to pay for moving fan hire and things like stamp duty.

House Extension

Budgeting is key to cost-efficiency and planning. Drawing up a budget beforehand will also ensure that you have the funds to complete the extension project.

Set a contingency of around 20% to cover unexpected costs. During the extension process, for example, problems with the existing building can become apparent. If you have a healthy contingency, this won’t be a problem for you.

22. Building Control

Before you can start the building process, you have to submit either a building notice or a full plan application to Building Control. Many homeowners prefer to file a building notice because it allows them to start the project immediately.

The problem with submitting a building notice instead of a full plan application is that Building Control doesn’t confirm that the design meets all the relevant build regulations. Providing a complete plan application eliminates the risk of non-compliance, and you will not be liable to correct any work at your expense.

23. Solar Gain

Solar gain refers to the increase in thermal energy of a space. Attempts to allow natural light in an interior space can often result in a solar gain. The rise in heat typically reduces the comfort levels in the extension, and the area may not be fit for use throughout the entire day.

The first step to prevent solar gain is to employ the services of an experienced designer. Changing the position of windows relative to reflective interior surfaces can go a long way to reduce glare. You can also add screen materials to lower the light intensity.

24. Size

People who are extending their homes tend to prioritise floor size above everything else. An extension doesn’t have to be as big as possible. Although excessive square meters are expensive, they are often wasted.

A structural add-on with a realistic floorspace can have a spacious feel. By using the correct design components and interior features, you can reflect natural light and link outdoor elements to your interior.

Overly large extensions can increase your property’s maintenance efforts and costs. A floor area that has a realistic size is functional and cost-effective.

25. Glass

According to Building Regulations, the total dimensions of glazed elements may not exceed 25% of an extension’s floor area. Glass doors and windows with standard dimensions can easily use up this 25%, especially if the extension is unusually small.

To prevent rejection by Building Control, you can try to show that the energy performance of the glazed extension is on par with a non-glazed extension. You can also commission an SAP assessment to prove that the carbon dioxide emission rate doesn’t exceed the emission of a fully compliant extension of the same size.

26. A Suitable Builder

Choose a builder that is reputable and willing to build a professional relationship with you. A good working relationship is the basis of clear communication and optimal efficiency.

To find a suitable builder, visit consumer sites and read reviews from previous clients. Contact the listed references and ask them if interaction with the builder is pleasant, and if they were satisfied with the quality of the builder’s materials and service.

If the builder has sufficient information about the extension project, they should be able to provide you with a fixed-price quotation. Try to avoid day rates if you can. Don’t work with a builder that doesn’t have contractors’ insurance for all risks.

27. Extending Electrics

For all extensions that don’t include a kitchen, it may be possible to extend the existing ring circuit. Regulations limit ring circuits to 100 square meters, but you can add any number of outlets to the system.

House Extension

The most significant benefit of adding a ring system is that it allows you the opportunity to increase the number of outlets you have in your home. Make use of the opportunity to replace your old single outlets with new double one.

If you are extending your kitchen, you have to add a circuit directly from the distribution board.

28. Extension Material Types

Before starting your house extension, you have to choose a material type. There are four different material types.

Rapid masonry construction materials from lightweight block manufacturers consist of thin joint masonry systems. Construction can take a little as a day, and the material is airtight and thermally efficient

Timber frame construction materials are just as effective as masonry and cost around the same. They also offer ample aesthetic appeal to an extension and last just as long as other material types.

Glass box extensions have a modern appearance and allow for sufficient natural light. Glass box extensions cost more than other material types.

Modular extensions are available in kit form and a wide range of sizes. This material type takes almost no time to build, it is affordable, and it has low planning permission requirements.

29. Roofing Materials

Each type of roofing material has its benefits and drawbacks. Before you start your housing extension, choose a roof covering that matches the roof of the existing structure.

Heavier roof coverings like concrete tiles require more support than, say, clay tiles. Certain types of roofing membrane can protect the extension’s roof against the elements and even damage by falling branches.

30. Estimated Time of Completion

Accept from the start that the extension project may take longer than expected. If you accept that there may be hold-ups, you will find it easier to manage your expectations. An extended project completion time can be particularly stressful if you live in your house, or if you have to arrange temporary accommodation for an extra week or two.

A clear channel of communication between you and the builder will ensure that you stay up to date on issues that can potentially halt the project. Contact the builder regularly to discuss their progress.

Our specialists based in Dublin and other cities in Ireland provides different house renovating services including house extensions. Please, do not hesitate to call us at +353 76 888 8869 if you have any questions.


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