How to add space to your home – traditional extension, modular building or an annexe?

Moving to a bigger property can be an expensive, arduous process – and upsetting if you love your current home. If you need more living space, you could instead try adding to your existing property with a traditional extension, modular build or garden annexe.

Innovative new construction techniques offer cost and time savings, with a range of styles and designs to suit different needs. Read on to discover which option may best suit your requirements. 

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Traditional extension

Built using materials such as concrete, bricks and wood, by a builder using an architect’s design, a traditional extension can take a variety of shapes, making it a versatile choice. It could be single or double storey, an extended porch, basement or even a garage.

Prices start from around £30,000 for a small, single-storey extension, to £120,000 or more for a large two-storey extension. 

For a typical residential extension that requires planning and building regulations approvals and a party wall agreement, allow a minimum of five to six months between appointing your architect and the building works starting. 

Once work begins, expect it to take around 14 weeks to complete. 

Ideally, plan for construction to take longer and be more expensive than you expect, so you’re prepared for any trouble along the way.

For full details on the process and how much you can expect to spend, read our guides to extension planning and extension costs

Modular building

Modular building is a modern method of construction where the components are created in a factory to a specification, then delivered and assembled on site. It’s typically a faster process than a traditional extension, and it tends to be less disruptive to your property.

An example of this type of construction is the Hup! system, created by roofing and extension specialists Ultraframe. The construction system is quick as the walls and roof ‘clip’ together, and their builds are certified to last for at least 60 years. 

Single-storey, bungalow and garden rooms are available, as are conservatory conversions, which use the existing base and foundations. The company is developing the possibility of double storey, loft conversions and whole-house concepts. 

Modular construction enables design flexibility. There are five different roofs to choose from to create vaulted, sloped, or flat ceilings, as well as a variety of external finishes including brick mesh, render or cedar. Windows and doors of any style and size can be placed anywhere in the design.

Hup! claims its system is five times faster to build than a traditional extension as it is not susceptible to weather delays and doesn’t require cement. 

Additionally, the entire project can be completed by one team, from the design through to the build and all the finishing touches including plastering and electrics, so you won’t need to schedule multiple teams of tradespeople. 

Hup! is compliant with building regulations and the planning permission requirements are the same as any other extension or conservatory.

The price will vary depending on the size, customisation, and whether there is an existing base and foundations to build on. As with any large home project, collect several quotes from different companies and explore all available options to see which best suits your needs.

It’s important for your building to be well insulated. Read our guide on how to insulate your home for tips to keep your property warm and energy efficient

Granny annexe

A standalone structure with a bathroom, kitchen and bedroom area, a granny annexe is usually built in the garden, near to the main home. Traditionally used to provide living space for an elderly relative, hence the name, this type of building could also be ideal for teenagers or young adults seeking more independence.

We looked at iHus, a UK-based specialist in building bespoke annexes, to use an example of this type of building. The company has a variety of standardised designs to use as a starting point, which can then be adapted and personalised as desired with their planning and design teams.

Prices range from £106,000 for the cheapest one-bedroom annexe, to £139,000 for the most expensive two-bedroom annexe, before customisation and extras are calculated. Including planning permission, consultation and building, an average project time is around five to six months. This is from sales consultation to having the keys in your hand. 

A compact annexe takes around seven to eight weeks to be built, on average, and a small two-bedroom annexe will take eight to 11 weeks. 

Things to consider when planning an annexe:

• Purpose Usually for a family member to move into, finding the perfect spot in the garden to build is important to give you both enough space and ensure privacy. 
• Garden size Space can be an issue, so work with the planning team to ensure you’re happy with how much outdoor room you’ll have left once the build is complete.
• Garden layout Existing setup and topography of your garden can determine where an annexe will best fit.
• Garden privacy Consider any issues around overlooking neighbours.
• Environmental factors Some gardens are particularly prone to flooding or may be located within an area with a high biodiversity contribution.
• Planning regulations iHus uses specialist planning consultancy NAPC to handle planning applications and they will flag any concerns during the design stage.

iHus offers a six-month aftercare service and a 10-year guarantee on all builds, but the quality and construction of modular building means they should last a long time. 

If you’re considering buying an annexe, try getting several quotes from different companies to compare costs and styles. We have used iHus as an example for what the process and prices of this building type might look like.

A new building project is the ideal time to consider other home improvements, such as underfloor heating. Our guide to underfloor heating costs and installation explains everything you need to know.