A useful guide when considering a house extension for your new property

House Extension Guide

We are often approached by people who have just bought or who are looking to buy a new home and hope to add a house extension.

This is clearly an exciting time for the family and we are delighted to help make the dream happen. However, prior research into the feasibility of building a house extension is really important. There are a number of points to take into account – ideally, before the decision to purchase a property is made.

Knowing the key aspects to look for while viewing a property will determine whether there is enough potential to extend the house and will avoid the disappointment of discovering, too late, that there are key reasons why the proposed extension will not be possible.

In this post we would like to share some useful tips to bear in mind when choosing a property with a view to extending.

Permitted development or needing planning permission

There are generally two types of house extension – those needing planning permission, and those that are allowed without planning permission, described as permitted development. The legislation and guidelines surrounding this issue are complex and we would recommend that professionals are consulted in order that a potential buyer can proceed with the purchasing process with the correct knowledge. You can read further information surrounding this by clicking this text to see our Planing Permission Page.

Type of building and property age

To begin with, we would suggest considering the age of the property. Older houses may well be part of a conservation area which – under planning legislation – limits the range of potential extension options due to the need to preserve the character of historic streets and townscapes.

On the other hand, houses built in recent years (especially on new housing developments) will often have permitted development rights withdrawn by the local planning authority as the developer has already maximised the allowable size of the properties during negotiations in order to achieve planning consent for the development. This means these houses do not benefit from an ability to construct otherwise permitted development extensions without requiring planning permission.

The best houses to look at for extending tend to be houses that were built somewhere in the middle age range, that are not part of a large development and are not in conservation areas. We should say that not all new houses have had permitted development rights removed, just that it is wise to consider this. Certain extensions, especially to the rear, would also be allowable even in conservation areas.

Main types of houses when considering an extension

Main types of houses to show different settings of the building within the plot

Another factor to consider is the type of building. Mid-terrace houses are the densest housing type as there is a neighbour attached to both sides of the property. This limits the extension possibilities to either a single-storey rear house extension to increase the kitchen size or a loft conversion for additional bedroom/ensuite, although not all terraced properties have sufficient headroom in the roof to carry out a conversion.

Semi-detached houses have a neighbour on only one side and, usually but not always, a drive on the other side. If there is sufficient space to the side it provides an opportunity to extend sideways over the drive with either a single-storey or double-storey extension. A single-storey rear extension is usually not a problem. A semi-detached property will often – subject to planning restraints and the house’s position in relation to its neighbours – be able to increase the number of bedrooms via a two-storey extension, perhaps add an ensuite shower room and also enjoy a larger kitchen/dining/living area with maybe a separate utility room and wc downstairs.

Detached properties are the most flexible to design a house extension for as they will have free space around the perimeter of the house and they therefore offer the widest range of potential extension opportunities.

The geographical area

Certainly within a few miles, the expense of construction – the labour, materials and professional services cost – is the same whether the property is in one of the more desirable and prestigious areas of a town or city or in a less-well off location. However, whilst an extension can greatly enhance the value of a property in an affluent area and make it a more attractive proposition when the time comes to sell, a similar extension on the same size house in a less wealthy area may take many years to recoup the investment spent on the extension.

Before embarking on a project to design and build a house extension, if in doubt, we would always recommend researching the market and perhaps also speaking with a couple of local estate agents to get their views. This could save an expensive mistake – the best laid plans can sometimes alter unexpectedly and the ability to recover the extension costs following a change of circumstances should be at least considered at the outset.

What to look for when having a specific extension type in mind

Homeowners have differing needs when deciding to embark on an extension project. These can vary from a couple just starting a family and needing an extra bedroom, to empty-nesters downsizing but wanting to increase the area available for entertaining when the extended family comes visiting, to separate families merging to become a new single unit who might need additional bedrooms to accommodate two sets of children, some of whom may visit for a night or two each week but who still need their own space and privacy. Others are just wishing to spread their wings and take advantage of their more advanced positions at work to spend some of that new cash on enhancing their living space and enjoying the benefits of their hard-earned success.

Rear extensions

Planning a rear house extension for your property

Example of a rear house extension for a semi-detached property with a 3m space required at the back of the house

Single-storey rear house extensions are probably the most common type of extension since the majority of properties have enough garden length to accommodate them and there are generally no issues with the neighbouring properties. They are usually used to extend the kitchen/dining/living area of the house and create a feeling of connection between the indoors and the garden.

Double-storey rear house extensions are rarer because of potential Right to Light issues arising from the proximity of neighbours’ windows. This is why double-storey rear extensions are unlikely to be achieved these days for semi-detached properties or terraced houses, although historic two-storey ‘off-shot’ extensions can be found on older terraced properties. However, due to the distance from their closest neighbours, detached houses are often suitable for a double storey rear house extension.

Due to these factors, single-storey rear extensions are by far the most popular type of house extension. One point to bear in mind here is the length of a proposed extension stretching towards the garden – the standard is 3 to 4 metres – but this can be affected by the specific setting in relation to the neighbour’s property. If, for example, a neighbour’s property is significantly lower ie downhill it could result in an overbearing extension and therefore not be allowed.

So, when choosing a new property that you’d like to extend to the rearyou should look for space at the rear of the property that would allow for an extension of at least three metres in length, with around 8-10m of garden remaining. The distance to the rear garden boundary can be an issue so a long garden is always helpful when determining the length of an allowable extension.

Side extensions

Planning a side house extension for your property

Example of a side house extension with at least 2.8m width required at the side of the property for optimal layout options

Side extensions can be single-storey but double-storey side house extensions are more popular and provide home owners a greater return on their investment when the project is complete.

On the ground floor, side house extensions provide additional areas such as bike storage, garage, utility room, downstairs WC/shower room and perhaps an extended kitchen. Upstairs, side extensions provide additional bedrooms and/or shower rooms and bathrooms.

As a general rule, the type or number of ground floor rooms that are positioned within a side extension are not affected by the specific width of the extension, except that the rooms will be larger or smaller depending on the available space.

Upstairs, however, the number or type of rooms depends on the ‘spare land’ width to the side of the house. The increased number of bedrooms achieved within a side extension can be fundamental to the enlarged house’s value, which means the available width is crucial if the homeowner is to enjoy a satisfactory return on their investment.

When we and our clients consider the feasibility of a double story side extension, the most important consideration is how it would be accessed from the upstairs floor as this is the storey where additional bedrooms are created. A key factor is whether the newly-formed bedrooms will be single or double as this will impact not only on the family’s enjoyment of the new space but, importantly, on the resale value of the property.

This is where the importance of the space to the side of the house (or the separation distance between the two properties, often the drive width) where the extension will be built comes into play. The minimum width required for a double bedroom is between 2.4 to 2.6 metres and another 0.3 – 0.35 metres will be required for the external wall. This means that, if a double bedroom is to fit in the extension, the drive on which the house extension is going to be built has to be at least 2.8 metres wide. If the drive is narrower than that, then the rooms upstairs are likely to remain single bedrooms.

To summarise, the criteria to look for is around 2.8 metres in the width of a drive or additional space at the side of the property in order to allow for a double storey side extension.

Terracing effect needs to be avoided with side extensions

Terracing effect of some side house extension

Example of a terracing effect on the right image due to both properties building double storey extensions over their drives

It is worth mentioning that side extensions are not always straight forward with semi-detached properties – when, or if, each homeowner extends their semi-detached property across the driveway, it can create a ‘terracing’ effect which significantly changes the street scene and the character of the area. There ceases to be a clear gap to differentiate between properties, resulting in a muddled and often unattractive line of virtually joined-together houses.

These unwanted consequences are something that planning authorities are mindful of and often limits are imposed in order to prevent this terracing result. As a result of that, the first neighbour to extend over their drive is likely to be granted planning permission as this does not impact on the presence of the adjoining driveway. Unfortunately, the second neighbour to decide to extend over the drive (therefore creating a terracing affect as there is no longer a drive-width to separate the properties) may not always get permission to do this.

So, whoever extends over their drive first in a semi-detached property situation tends to be granted permission. If you are looking for a property to extend with a double storey on the side it is better to choose one where the neighbour on the drive side has not already extended across their own driveway.

‘Wraparound’ extensions

Wrap around consideration for house extensions

Example of a wraparound house extension with the red colour marking the ‘wraparound’ element requiring planning permission

This is the term used for a house extension – whether single or double-storey – that extends beyond the side towards the rear, the ‘square’ that is neither strictly speaking a side nor a rear extension but that fills in the gap where they meet. This always requires planning permission.

Front extensions

Planning a front house extension for your property

Example of a front house extension breaching the building line marked in red and impacting the street scene

If considering purchasing a house to which a front extension will be required, caution should be exercised as there is limited scope regarding what can be constructed. The majority of the houses in the UK are set in a well-defined townscape character and street scene and, as a matter of policy, planning authorities aim to preserve the look of the existing street, with the exception of small porches which can usually be constructed as permitted development.

More variety in front extensions can sometimes be achieved with detached houses, or houses that are set in a street where there is no dominant character of properties and each building is relatively different. In essence, the stronger the character of the street, the more restricted and complicated it is to develop an extension at the front of a property.

Loft conversions

Planning a loft conversion for your property

Principle of a loft conversion with a dormer window to show the minimum ceiling height required to create a usable space

Loft conversions can be a great way to add a master bedroom with an ensuite bathroom or a couple of smaller bedrooms. The first thing to consider if hoping for a loft conversion is the height available for the new room. It needs to be high enough to accommodate not only upgraded joist thickness (a standard roof space will have ceiling joists rather than thicker floor joists that are capable of taking the weight of furniture and living accommodation) but also insulation and plastering to the new ceiling.

Even though someone may claim that a somewhat restricted ceiling height is fine for their particular family or use, the distance on the stairs to the ceiling above is prescribed by building regulations – this generally has to be 2m, and a lobby has to be created for fire regulations at either the top or bottom of the stairs to the new attic. Practically speaking, this tends to mean that the headroom in a loft conversion has to be a minimum of 2m, and a headroom of 2.2m plus would be considered more comfortable.

A second thing to consider is the staircase to access the attic accommodation. Often this requires a new staircase to be designed, and this usually – but not always – means losing a room in the floor below. In an average three bedroom semi-detached house it is often the small box bedroom that has to be lost in order to accommodate the new staircase going into the attic.

When considering a new purchase, a spacious landing area on the first floor, especially if there is a generous floor-to-ceiling height, indicates a good chance of extending into the loft without losing room space on the first floor.

A great indication of the feasibility of extending a house into the roof space is if similar-style houses in the neighbourhood have dormer windows as this makes it very likely there will be sufficient head height.

Basement conversions

Planning a basement conversion for your property

Principle of a basement conversion to show the required minimum ceiling height and sources of natural light

A basement conversion, especially in a hilly location such as Sheffield where often land drops away to the rear or where houses already have a cellar, can seem like an ideal way to extend a property. However, it is not always a simple option.

A newly created living space in the basement will require a source of natural light and often requires a separate fire escape if the main route out of the new room/s would be hindered in the event of a fire suddenly breaking out in the kitchen.

A ‘light well’ that combines the requirement for natural light with the facility to escape in the event of an emergency is often a solution. However, if a light well is in front of the house this can be difficult to achieve for properties in a conservation area or where a light well will impact on the street scene. It can be surprising to discover precisely how much space is needed so research before purchasing a property is helpful.

Another point to consider is that converting a basement often requires digging under the existing structure. There are a number of factors involved here such as: the condition of the ground (including type of soil, water table, possible underground spring or stream) and the existing building’s footings that may need to be underpinned during the construction process in order to facilitate the newly created room.

These unknowns can vary significantly, impacting the cost of construction and sometimes making the project unfeasible. Due to this level of uncertainty, and the relatively low quality of space (not to mention the lack of natural light and views), basement conversions are often the last resort to extend the property if other ways of extending are not feasible.

We are ready to make the best use of your new property

These are only a few of the different aspects to consider before choosing the right property with the intention to extend it in future but we hope that this blog post will help you to understand different considerations and make the right decisions when choosing your future home. You can click the text here to see further reading on our House Extensions Page, as well as our 2D and 3D Drawings For House Extensions Page.

If you intend to extend your property we would welcome you to contact us to discuss our architectural design services. We will help you to make the best use of the potential that your new home may have.

We provide friendly and impartial advice at every stage of your house purchase as well as once you have moved in and are always available to talk through with you the options available to you. You can click the text here to see our contact information, or send your enquiry to studio@ecclesall.design by email.

We look forward to hearing from you.


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