What does it cost to extend your home?

 

We’re often asked how much a house extension costs in London. Extending the home is a popular option among clients who perhaps need another bedroom, an office space, or a living area, without the hassle (and stress) involved with moving house. Although home extensions in London generally cost more than elsewhere in the UK, they remain a viable and cost-effective option to create your ideal additional living space and increase the value of your home. In this post, we set out the main costs associated with a house extension project.

How much does it cost to extend your home

Harvist Road Glazed Envelope

Extending into the garden and optimising natural light

You generally have three options for extending your home: single storey, two storey or basement. The construction cost of extending the ground floor of your home (in a single storey) is, as a general rule, between £2,200 and £3,900 + VAT per square metre, depending on the level of the specification you decide on. This is a popular option for extending into the back garden to add a dining area, studio or additional living space. It is also an excellent way to bring more natural light into the property, with the ‘glazed envelope’ (like the one in the above image) making the new space feel very spacious and ‘open’. If you plan to use the new space for a kitchen or bathroom then the cost of the fitting will need to be included (typically expect an additional £10,000 + VAT for a kitchen [low-mid level of specification] or £5,000 + VAT for a bathroom [mid range]).

The value of two floors

A two-storey extension generally costs an additional 50% of the construction cost of a single storey extension. It gives you the option of adding an upstairs bedroom or other room and the investment will seem like good value as once the foundations and other structural supports are in place, you do not need to bear these costs again for the second storey. It is important to note that a two storey extension may impact on the amount of light reaching your garden and may also present additional complexity in the planning process (achieving consent for a two storey is often more difficult that for a single storey and sometimes not permitted at all for example in a Conservation Area).

Going underground

A basement addition tends to be the most expensive option per square metre because of the structural and construction complexity and risk. The construction cost of a new space in your basement in London is likely to amount to between £4,000 and £5,000 + VAT per square metre. The costs may be less if you have an existing basement which may instead need converting or extending partially.

Other costs to consider

In addition to the estimated costs set out above, you will also need to factor in the cost of the professional services that you require, such as an architect and any other consultants that you need to involve – for the majority of projects you’ll need a Structural Engineer, Party Wall Surveyor, Building Control Approved Inspector and sometimes a Mechanical & Electrical Engineer as well as a Quantity Surveyor. This typically adds 15-28% to the construction cost. There are also planning fees (£200 to £300 for a house extension, although some extensions may fall under Permitted Development Rights), home insurance costs, and VAT. The costs of windows, doors and central heating will also be in addition to the costs already listed.

Site access and other constraints

There can also be costs associated with mitigating the constraints of a site. For example, the soil type may affect the type of foundation required or the types of building material that can be used, or there may be trees, drainage or other pipework that need to be (re)moved to allow access. If your property is listed and/or situated in a conservation area, you will need to allow for higher costs overall.

Despite the long list of costs, a home extension can greatly improve your living space and also increase the value of your home by 10% to 30%. We take pride in the home extensions that we have completed for our clients and it is always a pleasure to bring more light and space into the home. You can browse some of our recent residential projects here. If you would like to discuss a potential project with us, please get in touch.

Permitted Development Rights III: Other projects

 

Our last two posts have covered Permitted Development Rights (PDR) in general, and house extensions under PDR in particular. In the final post in this short series, we consider some other types of projects that fall under PDR and do not require planning permission, and provide you with some information about the rules that you should be aware of. Specifically, we cover additions/alterations to the roof of a house, porches and other outbuildings or structures that you may wish to add.

Permitted Development Rights III

Making changes to your roof

Unless you live in a protected area and/or your house is listed, you can add to or change the side and back of your roof without requiring planning permission. You may wish to convert the loft and add dormer windows, or carry out alterations such as re-roofing or installing roof lights and/or windows.

As far as practicable, additions to the roof need to be at least 20cm above the original eaves, and no higher than the highest part of your house. It is possible to add up to 50 cubic metres to the original roof space (although this figure falls to 40 cubic metres for terraced houses). It is not possible to add a veranda, balcony, or any other type of raised platform. Similar to house extensions under PDR, the materials you use should be ‘similar’ to the materials on your existing roof.

Adding a porch

You can add a porch to your property that is up to 3 metres high and with a maximum area of 3 square metres. If the porch faces the road (which is often the case), it should be at least 2 metres from the edge of your plot.

Other buildings/structures

Under PDR, you can build any independent structure on your plot to the side and back of your house, as long as it is not another house or has more than one storey. For example, you may wish to add an outdoor office shed, a swimming pool, an animal pen or a heating tank.

The additional structure(s) may take up to half of the plot that is not taken up by the ‘original’ house (note that ‘original’ means the house as it was first built, or as it stood on 1 July 1948, if it was built prior to that date). The structure can be up to 3 metres in height. However, if the structure is within 2 metres of the house, the maximum height is reduced to 2.5 metres. If the structure has a double-pitched roof, a maximum of 4 metres in height is permitted.

As with roof alterations, your structure may not have a veranda, balcony or raised platform, and you will need planning permission if your house is listed or, in some cases, if you live in a protected area. Antennae are also not allowed on the structure.

You can read more detailed guidance about PDR for these types of projects (as well as adding hard surfaces to your plot and/or altering the chimneys and flues on your property) in the Householder Technical Guidance issued by the Department for Communities and Local Government. Note that the guidance applies to England and Wales and separate PDR guidance can be referred to for projects in Scotland and Northern Ireland.

Permitted Development Rights II: House extensions

 

An extension or addition to your home is something that you can do under ‘Permitted Development Rights’ (PDR), meaning that you do not need to apply for planning permission to undertake the work (see the general introduction to PDR in our last post). There are, however, certain limits and conditions that you need to be aware of and we cover some of those in this post.

Permitted Development Rights II

For all types of extension, no more than 50% of the area of land around the ‘original house’ can be covered by the addition (bear in mind that ‘original house’ means the house as it was first built, or as it stood on 1 July 1948, if it was built before then). You will need to check whether a previous owner added an extension as this is included in the calculation, as are sheds and any other outbuildings.

Single-storey extensions

For single-storey extensions, if the project is completed by 30 May 2019, the rear wall of a detached home can be extended by up eight metres. If you live in a semi-detached or terraced house, this is reduced to six metres. These upper limits have been temporarily increased and if you extend more than four metres beyond the rear wall (detached) or three metres (semi-detached/terraced), you will need to go through the Neighbour Consultation Scheme to notify the local planning authority of your intention to use PDR in this case.

Under PDR, the extension must not be to the front or side of the building (if it is, it requires planning permission). The materials used in the extension should be similar in appearance to those on the exterior of the rest of the house, and the extension must not exceed four metres in height.

Double-storey extensions

For higher extensions of more than one storey, the addition can be no higher than the existing house and it may not extend more than three metres beyond the rear wall. You will also need seven metres between any boundary opposite the rear wall of the house. As with single-storey extensions under PDR, the materials you use must be similar to the existing house, and there are some additional rules about upper floor/roof windows.

Other points to bear in mind

The permitted development allowances that we have described in this post apply to houses in England only. If you are seeking to alter or extend a flat/maisonette, a converted house (or a house created through the PDR to change use), other buildings, or your house is in an area where there may be a planning condition (e.g. protected/designated area), you will need to check separate guidance and rules with your local authority. Some local authorities are able to confirm in writing (for a small fee) whether or not a planning application is necessary. Most extensions still require approval under Building Regulations.

You can read more detailed guidance on the Department for Communities and Local Government Planning Portal, or contact us for advice about a project you are considering.

L-shaped dormer explained

 

Converting your loft can be good value for money when improving your home and increasing your living space. An L-shaped dormer loft conversion can be a good option for creating more room at the top of your home. Popular on period, terraced properties, this type of loft conversion creates a lot of space, usually adding at least a couple of rooms to your property. In this post, we give you a bit more information about what is involved in this type of conversion.

RISE Design Studio L-shaped Dormer

What does ‘dormer’ mean?

A ‘dormer’ loft conversion is a structural extension that projects vertically from the plane of a sloping roof. An L-shaped dormer typically involves constructing two dormers – one sits on the main body of the house and the other then extends out over the rear addition of the property. The dormers meet to create the ‘L’ shape. This type of conversion is most suited to Victorian and Edwardian properties that tend to have the kitchen and bathroom at the rear. An advantage of the L-shaped conversion is that you are able to replicate your first floor in terms of space and design.

Planning

Under Permitted Development Rights (introduced in 2008 by the Department of Communities and Local Government), you typically do not need to have planning permission to build a loft extension on a house if the extension is adding less than 50 cubic metres of new space to the property (and less than 40 cubic metres if the house is a terrace). However, there are some cases when you will need planning permission and it is wise to double check the requirements with your local authority before starting your project. For example, you will need planning permission if the side of your house with the conversion faces the road or if your house is in a designated area (e.g. conservation area, Area of Outstanding Natural Beauty, etc.). The conversion will still need Building Regulations approval and it is worth having an approved design before you start work.

Design and construction

On first glance, L-shaped dormers appear to have a flat roof. Instead, they tend to be built with a 1:50 fall to the side to ensure that water does not pool on the roof of the loft. To make the extension look less ‘top-heavy’, it is common to step the sides of the dormer slightly and create a small border around the edge of the structure, blending in with the existing slope of the roof. There are several other technical considerations to take into account during design and construction. For example, you will need to consider fire precautions and escape windows, ventilation measures (especially if the extension includes a bathroom or shower room), thermal and sound insulation of the new structure, and how you are going to supply electrics and heat to the new space. Investing in a good design will ensure that your extension adds to the ‘look and feel’ of the original property, rather than detracting from it.

Adding value to your home: extensions

 

Extending your home is something you might do for a variety of reasons. Perhaps your family has grown and you need an extra bedroom, or maybe you want some additional living space, a home office, or a way to bring in more natural light. Whatever the reason, extending your home is likely to add value to the price of your property, as well as make your home a more enjoyable and comfortable place to live. In this post, we look at options for extending your home, what value it might add to your property, and some recent projects of our own that show you the types of things that can be done.

Extension North London

What type of extension?

Extensions tend to range from adding a few square metres to the living area, to multi-room or multi-storey additions. Extensions require planning permission so it can be a good idea to look at what other people have done in the area and consider whether your plans are reasonable and realistic in comparison. It is important to work with an architect and/or builder that is recommended, either by someone you know or through trusted registers such as that held by the Royal Institute of British Architects (RIBA). It is sensible to work with an architect who has experience of work that suits your property’s style, as well as a track record of successful planning permission applications.

Will it add value?

In London, property costs around £5,000 to £10,000 per square metre. Outside London, these figures drop to between £900 and £2,000 per square metre. You can take these figures into account when estimating how much value an extension is likely to add to the value of your property. Multiply the area gained by the local price per square metre and then offset the cost of the project against this.

Some examples

We have completed a number of residential extension projects in London. These range from single storey rear extensions, to a three-storey extension and complete internal re-configuration.

To accommodate a growing family in West Finchley (North London), 110 square metres were added to the Cissbury Ring South Garden Rooms were added to allow an open-plan area that created more fluidity between the kitchen/dining and living area, as well as a new den and study.

It can also be an option to renovate and/or extend the basement of a property, which was the case in the Stockwell Garden Room (Lambeth, North London). The house was stripped back at the lower ground level to create a more workable basement that maximised the use of natural light.

Increasing the natural light in a property was also central to the Burrows Road Glazed Envelope project (Kensal Green), in which the existing ground floor was modernised to create more open-plan living space and a bright garden room with a glass roof was added to the kitchen at the rear.