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.

Parallels: boat building and architecture

 

Several well-known architects (Norman Foster, Zaha Hadid, John Pawson, Frank Gehry, to name a few) have turned their hand to designing and building boats, and it is now common to find boat building technology and materials (such as custom composites) in modern building structures. Floating architecture is also becoming more and more popular. There seem to be natural parallels between the skills of the architect and the boatbuilder, particularly in the crafting of a wooden structure to create a functional and beautiful end result.

RISE-Boat-John Pawson

Making sense of lines

To the boatbuilder, ‘lofting’ is the creation of full-size topographical maps of a boat’s hull that allows the builder to make all the molds, patterns, parts and pieces accurately. The process of ‘laying down the lines’ is relatively similar to practices that go back to the 17th century, generating curved lines for the streamlined hull and keel of a vessel. Lines can be drawn on wood and the wood then cut for advanced woodworking. Today, boatbuilders, like architects, use computer-aided lofting to fine tune designs and produce a set of full-sized lines.

Following architectural conventions, a ‘lines plan’ slices through the boat in several directions and can be combined with a ‘table of offsets’. This contains reference points used in a similar way to latitude and longitude on maps to allow the use of coordinates to find specific points on the hull. This then allows the full scale model to be built.

Symmetry and alignment

Like architects, boat builders are focussed on what looks good. Subtle attention to detail, symmetry and proportion don’t necessarily make a boat float better but they do affect the appearance of the vessel. The ‘sheerline’ is the subtle and graceful curve that defines the uppermost edge of the hull. This is probably the most important feature on a boat and is often difficult to get ‘right’. Often, a 2D drawing of the sheerline will not look as attractive in three dimensions as the paper drawing cannot take into account real-life perspective.

Simple things like how screws line up are also important. Lined-up slots impart understated elegance, while randomly aligned slots might look unattractive.

Keeping with tradition

Wooden boat building has been described as “the quintissential industry“. Over time, boatbuilders will have found that certain woods are more suitable than others, and that locating sources for materials can be a challenge. This is a challenge also experienced by the architect who wishes to uses local materials to retain the sense of place and context of the structure.

Exploring Chailey Brick Factory

 

We recently attended a CPD tour organised by RIBA to the Ibstock brick factory in Chailey, near Lewes in Sussex. It was fascinating to see process of traditional stock brick manufacturing in one of the last remaining clamp-firing factories in Europe. We highly recommend a trip to the factory if you’re looking to source traditional stock bricks. This short post tells you a bit more about what we learned on our visit.

chailey-bricks

History

Clay products have been manufactured in Chailey for over 300 years, making it one of the oldest factories still in production in the UK. Its product range has changed over time and it now produces high quality, clamp-fired stock bricks and pavers with a range of colours and textures which give a unique charm. Bricks are known for being made in Chailey since the early 17th century. The current factory was built in 1946 in order to take advantage of modern production processes and the post-war building boom. The current owner, Ibstock Brick, acquired the site in 1996.

Making the bricks

At Chailey, weald clay is extracted from an onsite quarry behind the factory during the summer months. There are three different seams of clay in the quarry, all with different drying and firing characteristics. Clay is dug from a stockpile each day and fed into the factory, delivering a set amount of clay each hour. Clay is mixed with sand and pulverised fly ash, which help with the drying process, and with a blend of coke breezes, which is the fuel that fires the bricks. All the material is fed into a wet pan, where it is mixed and ground together and water is added. The material is forced through grids in the floor of the wet pan and onto a conveyor, after which it falls between two counter-rotating drums, with a gap of only 3mm between them. This is so that a small but consistent grade size is achieved.

The material is then mixed in a double-shafted mixer where two shafts churn the mix to ensure and smooth and workable consistency. The mix is then taken to a kettle where it is stored before being turned into bricks in a molding machine which is capable of making 12,000 bricks per hour. The excess clay is struck off before a palette is dropped onto the bottom of the bricks. Bricks are piled in stillages which are then put into the driers, where the bricks are dried over a 23 hour period. There are five dryers and each one holds 24,192 bricks. The temperature in the driers is slowly increased up to 110 degrees and approximately 17 tonnes of water is removed from the bricks.

The clamp

A clamp is ‘a carefully constructed stack of bricks’ in a large shed similar to a cowshed. Before going to the clamp, the dried bricks are inspected for defects and stacked into piles of 780 bricks (weighing 1.8 tonnes). These bricks are then laid on the floor of the clamp by hand by a setting team. Fire holes are built into the clamp before all the bricks are laid on top and the clamp is then covered in refractory insulation bricks and casing bricks which help to insulate the clamp during the firing process. Each clamp holds between 750,000 and 800,000 bricks and takes three weeks to build.

brick-clamp

Gas burners are used to ignite the fuel which was mixed into the body of the bricks during the clay preparation process. The bricks fire at over 1000 degrees centigrade and only start to cool down when all of the fuel has burnt out. The entire firing cycle takes three weeks. When the bricks have cooled sufficiently, the bricks are packed up by hand onto pallets by an eight man team. There is a strict sorting code and the bricks are sorted according to their quality and colour and then hand sorted into packs of 370 bricks. It takes approximately two weeks for the team to pack up a clamp.

clamp-full

The bricks

Chailey manufactures its range of distinctive bricks in both 65mm and 50 mm sizes and any of the bricks can be blended to create products to match up to existing brick work. Or, bespoke blends of bricks can be created. You can read more about the bricks made at Chailey on the Ibstock Brick website.

What is retrofit?

 

The 2008 Climate Change Act committed the UK to reducing its greenhouse gas (GHG) emissions by 80% by 2050 (against the 1990 baseline). The buildings sector accounts for 37% of total UK GHG emissions and, of these emissions, 65% are from the residential sector. With this in mind, there has been growth in the residential retrofit industry, whereby buildings are adapted to become more sustainable and energy-efficient, while in the non-domestic market, retrofit can often be part of a larger refurbishment project. The majority of our existing residential and commercial stock requires some level of retrofit to enable the government’s ambitious emissions targets to be reached. In this post, we look at some of the methods available for retrofit and consider the role of architects in the retrofit of existing buildings.

retrofit living spaces

Making homes more energy-efficient

A study in conducted in 2014 estimated that 40 million houses in the EU would have to be retrofitted by 2020 if the reduction of emissions is to stay on track. In general, retrofitting involves the use of new technologies and materials within the home, to increase energy efficiency. A popular and simple example is improving insulation. A new heating system might also be installed, or double glazing might be fitted. There is also the option to carry out a Passivhaus retrofit. Although it is more difficult to reach the exact requirements of the Passivhaus standard in a retrofit project, the Passivhaus Institut has developed the EnerPHit standard for projects that use the Passivhaus method to reduce fuel bills and heating demand.

High performance buildings

Conserving energy is not the only reason to retrofit a building. Improving indoor environmental quality, reducing dampness and mould will all lead to increased health and productivity levels of the building’s users (read more on our blog about sustainable architecture principles that improve health). A retrofit project also presents the opportunity to reassess the accessibility, safety and security of a building.

The role of the architect

Retrofitting the home to increase energy efficiency can have significant architectural implications for the interior/exterior of houses. Modern architects are well-placed to add creativity and innovation into the drive to retrofit existing housing stock, particularly those that may prove very expensive to retrofit. For example, historic buildings such as Edwardian terraces are protected, and increasing energy efficiency can pose a real challenge. There are exciting options to retain the facade and rebuild the living spaces within the building. Because architects have an overview of the whole build process, they tend to be well-placed to act as a lead co-ordinator in retrofit projects. If you are keen to implement the Passivhaus method, you are likely to need planning permission as the work may require external insulation or changes to the roof, for example. Again, an architect can help with this.

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.

Passivhaus explained

 

Increasing the energy efficiency of buildings is a key concern for a sustainable architect. In this blog post, we look at the basic principles of the Passivhaus (or Passive House) standard: a sustainable construction concept that is the fastest growing energy performance standard in the world. Developed in the early 1990s in Germany, the standard can be applied to any type of building – residential, commercial, public and industrial – in any part of the world. 30,000 buildings now have the standard worldwide, with more and more non-residential buildings such as administrative buildings and schools being built to Passivhaus standards. Passivhaus standard components are also being applied to retrofit projects.

Passive house

So, what exactly is a passive house?

Not to be confused with solar architecture, although it shares some common principles, the key concern for an architect designing a passive house is to reduce dramatically the need for space heating/cooling and primary energy consumption, while at the same time creating good, healthy indoor air quality.

A well-designed and constructed passive house can allow for energy savings of up to 90% when compared to typical building stock in Europe, and over 75% when compared with the average new build designed for low energy consumption. This means that passive house owners and tenants tend not to worry about rising energy prices – passive houses require less than 15 kWh/(m2/yr) for heating and cooling, compared to an average of 150 kWh/(m2/yr) for the space heating demands of a typical house built since 2000.

A passive house uses energy sources from within the building, such as body heat, heat from the sun or light bulbs, or heat from indoor appliances to create a comfortable, healthy living environment. A mechanical heat recovery ventilation system allows fresh air to enter the building without letting heat out, and allows heat contained in exhaust air to be reused. This highly efficient heat recovery system means that fresh air is supplied without draughts and guarantees low radon levels and improved health.

In order to ensure that the ventilation system is effective, a passive house must be properly insulated and airtight, allowing for minimal air leakages in and out of the building through thermal bridges such as the walls. This means that heat can be kept out during the summer and in during the winter. Windows are triple paned glazing and the whole building is oriented so that shade is received in the summer and low angle sunlight in the winter.

It is an exciting time to be working with the Passivhaus sustainable construction standard. Even though ventilation systems require an extra investment, passive house owners/users can save a considerable amount of money over the long-term in energy savings, with many projects showing how applying the standard can be surprisingly affordable as a new build. A Resolution of the European Parliament in 2008 called for implementation of the standard in all member states of the European Union by 2021. With 2020 as a deadline for all new buildings to be nearly ‘zero energy’, the Passivhaus standard provides architects across Europe with a robust, holistic set of guidelines for achieving this goal.

 

Sustainable architecture principles: environment, energy, efficiency

 

Buildings account for about half of the UK’s carbon dioxide (CO2) emissions. Globally, architecture was responsible for 40-50% of waste deposits in landfills at the turn of the new millennium, and 20-30% of greenhouse gas emissions.

The environmental integrity of a building (i.e. how it is designed and operated) is now a key consideration in the design of new buildings and the renovation of existing ones. More and more architects and designers are realising that good design improves quality of life and minimises harmful impacts on our health. Clients are also seeing the benefits of more environmentally responsible buildings through future-proofing, reduced operating costs, and comfort and health benefits. As a result, we are seeing more ‘sustainable architecture’ projects, which seek to minimise the negative environmental impact of buildings by efficiency and moderation in the use of materials, energy and development space.

Sustainable architects

So, what are the three main characteristics of a sustainable architecture project?

Environmentally-friendly building materials
A sustainable architect typically chooses to use environmentally-friendly building materials. The most desirable materials are those that are recycled or renewable, as well as those that require the least energy to manufacture. There is often a focus on using locally-obtained woods and stone, reducing the distance that materials travel before being used in the construction process and supporting local trades. There is a preference for wood that is harvested responsibly from certified forests and all other materials are non-synthetic and non-toxic. Recycling is at the heart of a sustainable architect’s design. Although recycled building materials were difficult to source in the early 1990s, there is now an active trade in recycled architectural salvage, particularly by specialist companies providing materials from demolition sites.

Energy and resource efficiency
Sustainable architecture is underpinned by a philosophy that advocates sustainable energy sources. Where feasible, steps are taken to design for energy efficiency, including the use of renewable energy sources such as wind, geothermal and solar. A sustainable architect recognises that the energy efficiency of buildings can be increased in a variety of ways. A building can be oriented to take full advantage of seasonal changes in the sun’s position, and energy-efficient lighting and appliances can be installed. Energy conservation is also key: buildings can be ‘weatherised’ for maximum protection against the loss of warm or cool air, and appropriate insulating materials and window glazing can be installed to reduce heat loss in ways that do not cause indoor humidity.

Efficient use of space
The sustainable architect recognises the importance of indoor environmental quality for affecting how an individual feels in a space and focuses on features such as a healthy indoor environment with adequate ventilation, temperature control, and the use of materials that do not emit toxic gases. The incorporation of earth shelters, roof gardens, and extensive planting throughout and around buildings is also encouraged. In the UK, a study by CABE (Commission for Architecture and the Built Environment, now Design Council Cabe) of five new academic buildings and campuses found that more than 70% of staff and students believed that the facilities and functions of the buildings they work in improved the way they felt and behaved.

Buildings built to the Passivhaus standard are a great example of these sustainable architecture and design principles in practice. We’ll be writing more about Passivhaus in our next post.