Wraparound Extensions: A Guide To L-Shaped Additions

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Written by Dan Marks

Written by Dan Marks

Wraparound extensions can provide additional living space, natural light, and improved aesthetics for a home. In this post, we will explore the benefits of a wraparound extension, the different types available, and the key considerations to keep in mind when planning and building one. Whether you are looking to add more space to your home or simply want to update its appearance, a wraparound extension can be a great option to consider.

A wraparound extension is designed to fit around the outside of an existing house to create more living space. Typically, this type of extension is the combination of two types of extension: 1) a side infill extension that encloses the outside space to the side of a projecting outrigger (between the outrigger and party wall/ boundary) and 2) a rear extension that encloses space to the rear of that same outrigger. The combination of those two areas forms an L-shape that wraps around the outrigger.

Before wraparound extension

Example: Semi-detached house with garage/ outhouse to the side and existing small rear extension.

Wraparound extension

Green illustrates the area of wraparound extension incorporating space previously occupied by the garage along the side and a smaller extension to the rear.

How much does a wraparound extension cost?

The cost of a wraparound extension will depend on a number of factors including:

1. Amount of new and refurbished space

You’ll want to carefully integrate the extended living space into the existing ground floor plan of your house. In order to achieve this, we tend to revisit the layout of the entire ground floor plan, or at the very least, the rear portion of that plan where old and new meet. So it makes sense to budget for this too. At the early stages of budgeting for a project, we advise our clients to allow for somewhere in the region of £2,500 +VAT per square metre for construction across the entire ground floor (or a portion of the ground floor that will be modified to integrate the extension) and the extended area itself. The cost per square metre of the extension will be higher, whilst modifications to existing space may well be lower. However, from our experience, blended across existing and new building elements, costs often average out at around £2,500 +VAT per square metre. This cost is for construction, finishes, fixtures and fittings but does not include consultant fees.


2. The amount of structural work

In extending your house with a wraparound extension you will be partially or wholly demolishing supporting walls on the side and rear of the house in order to integrate the new space with the existing one. In their place, you will need a structural solution to support the floor(s) above. This could be steel or engineered timber combined with new concrete footings for foundations. There’s a balance to be struck here; the greater the amount of demolition, the greater the openness and ability to integrate old with new, but also the greater the structural scheme – and associated cost. Personal preferences play a part too – you may like to retain some sense or memory of the building’s past and do this by retaining sections of previously external walls within the newly enclosed space. This will help limit the structural scheme and save some money.

Tip: The larger the spans of the supporting structure, the deeper and heavier that structure will need to be. Bear in mind that structural steel suppliers calculate the cost of their package based on weight. A strategically located structural post can be cleverly integrated into a room (even become a feature) and break a span in half, significantly reducing the depth and weight of the spanning structural support. Worth considering sometimes…


3. The overall level of specification

This one is self-explanatory but, even if you are on a tight budget, it’s worth thinking carefully about specifications and costs as not all savings are equal.

For example, you may be assessing two-floor finishes for your extension; one of them is a high-quality poured and polished concrete floor (at around £350 per sq.m installed) whilst the other is a large format porcelain lookalike concrete tile (at around 100 per sq.m installed). The poured concrete floor is 3.5 times the cost of a tiled floor and, assuming a floor area of 50sq.m (extension and existing rear of the house), the tiled floor represents a potential saving of 12.5k. Tempting! BUT, if you are spending anything north of 200k on your project that’s around 5% of the overall cost whilst being one of the most impactful items that will last a very long time and bring joy every time you set foot on it. We would argue that’s money worth spending. Find savings elsewhere.

It’s worth thinking consciously about priorities. A high-quality polished concrete floor may not be your thing but something else will that may, when viewed against cheaper alternatives, seem like an extravagance. However, if this is something impactful like lighting, an alternative floor finish, high-quality glazed doors etc it may be worth considering splashing out there and making savings elsewhere.


4. The ratio of glazing to solid building envelope

The amount of glazing and its specification will be a significant factor contributing to costs. At one end of the spectrum lies the glass box extension whilst at the other, solid construction with few and small windows. The amount and type of glazing should be driven by personal preferences as much as budgetary constraints. It’s important to appreciate that extending into the garden is an opportunity to create a better relationship between inside and out and an improved connection with nature. This could be extensive (with a glass box approach) or more subtle, for instance by placing windows strategically so that they frame key views or roof lights that allow sunlight to penetrate in a particular way at certain times of the day. All this should be considered against the potential cost for the supply and installation of glazing – a sort of cost-benefit analysis.

A few tips: as glazing frames slim down their cost generally goes up. With sliding or bifold doors to the garden, the cost increases disproportionately once these go above 2.5 metres in height.


Do you need planning permission for a wraparound extension?

You will need to obtain planning permission for a wraparound extension.

Whilst each component of the extension; the side infill and the rear extension, are covered under permitted development rights, once combined they become greater than the sum of those two parts and this is no longer permitted development.

Existing Ground Floor Plan

Existing semi-detached with garage

Proposed Ground Floor Plan after wraparound

With wraparound extension

How long does a wraparound extension take to build?

Once on site, the actual construction phase will vary depending on the size and complexity of your design (and your builder’s competence). 4-6 months is a reasonable range of time to allow for a high-quality product.

However, before you reach the site you will need to allow time for design development and the statutory planning process (8 weeks to determine a householder planning application.

You can find out more here about typical residential project timelines from architect appointment and start of design through the planning process and more about planning applications and associated timeframes.

Benefits of a wrap-around extension

  • This type of conversion maximises your floor space whilst minimising the reduction in the outdoor area.
  • A wrap-around conversion makes the most of alleyways and pathways running alongside your home that arent large enough to serve any other useful purpose.
  • Allows better connection to the garden
  • Brings more light into your home
  • Allows space for new rooms, such as playrooms, WCs, or a utility room
  • Opens up your kitchen area
  • These benefits mean that this extension is often used in denser urban areas where space is at a premium.

How to find a good architect

Before you look for an architect, consider creating a detailed brief to better communicate the project’s goals, constraints, and budget. We then suggest researching and creating a shortlist of potential architects, and carefully considering the level of involvement desired from the architect. Finally, we advise setting clear expectations and establishing a good working relationship with the chosen architect.

Read our detailed post on finding a good architect here.

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