Two families hope to save cash and supersize their homes. In Ascot, the Ioannidis family want to create a multigenerational home by doubling their 50s semi-detached house. Daughter Helena and her fiancé Andy are paying the mortgage and parents Paris and Zanette are funding the build from their life savings. Sparks fly from the start between daughter Helena and father Paris, who also project manages the build. In Maidstone, Ben and Eloise Barratt want to double the living space in their cramped 1960s detached home. As well as having a new baby on the way, web-business owner and salesman Ben is piling on the pressure by project managing the build himself.

Builder Greg Pritchard and his wife Jo bought their barely habitable Bracknell property four years ago. But with the arrival of baby Sam progress trickled to a halt. Greg and Jo have an amazing view, but the challenge is to design a property to do it justice. In Cheshire, recruitment director Becky and mechanical engineer Mark Ridley live in a 200-year-old cottage with their two children. They want to add a massive extension and give it a modern revamp while making the most of its original charm.

Young couple Richard and Sarah bought a picture perfect cottage in Ardens Grafton in the lovely Warwickshire countryside, which, like many rural properties, has been extended, bit-by-bit over time. The result is a hotchpotch of buildings extending out from the original Victorian house and ending with a side extension bolted on in the 1950s. Richard and Sarah have a limited budget, so to save cash they're doing the demolition themselves, which unearths a few problems. And in the gorgeous seaside town of Whitstable, Kent, Paul and Laura plan to dramatically transform their 1930s terrace. Using a long-saved but limited budget, they want to build an extension that will give them twice the space - but remain as ecologically friendly as possible. Can they balance a limited budget with their strict eco principles?

Jackie and Russell want to extend their rundown 1930s semi in Cheshire, while in Bristol Neil and Anita plan a granny flat for Anita's mum and dad. Jackie and Russell are desperate to get to work on the property they bought three years ago with a view to extending. But soon after their purchase, Russell lost his job, work never started, and they've been camping ever since in a house which is totally unsuitable. But now the plans for a gigantic extension are back on, only for disaster to strike yet again halfway through the build when Russell loses his job for a second time.

Sarah Beeny meets newlyweds Andrew and Angharad in Northamptonshire and Vicki in Sussex, who needs more space for her two small kids. In Church Brampton, Northamptonshire, newlywed couple Andrew and Angharad Garner bought a country home with a problem - it had a neighbour's access alley running along the side wall of the house. To put it simply, if they build an extension, they will have to leave an alleyway running slap bang through the middle of their house. In East Preston, Sussex, single mum Vicki Thorne is in need of a workable home for her typically energetic four-year-old and for his big sister six-year-old Iona-May, who has (quadriplegic) cerebral palsy. Vicki and her mum have spent the last two years raising the funds from donations to pay for the £60,000 needed for the building work.

Sarah meets scientist Jo and computer engineer Keith Mortimer In Swindon, Wiltshire. The couple have grand plans to more than double the size of their four bed 1930s house with a two storey wraparound extension. In St Albans, Hertfordshire, Sarah meets Mei and Yui Tse, who are planning their home's second expansion in four years.

Sarah visits a tiny two-bed house in Horsham, West Sussex, where the owners have run out of space, and a massive build in the affluent London borough of Wandsworth. In Horsham, West Sussex, Jason, Sarah and their two-year-old son Harley need more room. Plasterer Jason pulls in favours from mates in the trade to help with their extension project, but on Day1 they hit upon a real stink - a sewage pipe. In the affluent London borough of Wandsworth, south London, Charlie, Claire and baby Tommy live in a pokey two-bed Victorian terrace. With Charlie busy at work, Claire takes charge of their massive build, which they plan to decorate in a country-house style.

In Horndean, Hampshire, Sarah meets Pete and Teressa Mitchie and their two kids. They urgently need more space, but six weeks into the build their builder pulls out and Tress is forced to take on project managing. Is a prefabricated loft built off-site the answer to the Mitchie's needs? In Porchester near Portsmouth, free spirits Ben and Kathryn want to create a floating home at sea, gambling £35,000 to buy an ex-military barge to transform into their dream home. But there are major set-backs in store...

In St Ippolyts in Hertfordshire, Sarah meets Ben and his French housewife Alex and the couple's six children. The family want to turn their tiny three bedroom home into a stylish six bedder, but on a very tight budget. In Clapham, south London, Stephen and Tara are feeling the squeeze and want to dig out their basement. But once digging commences the costs start to spiral.

In Elstree, Hertfordshire, Sarah Beeny meets Oliver and Lucie Herman, whose £900,000 property once doubled as a dentist's surgery. The couple have taken on the challenge of transforming the building into a stunning new home with a whopping £200,000 to spend. However, the budget still skyrockets out of control. In Liss, Hampshire, Graham and Alana Tourell want to restore a former post office - a stunning arts and crafts period property - into a home. But sourcing original and reclaimed items for the renovation doesn't come cheap and takes months.