After more than 25 years on TV, Grand Designs has witnessed hundreds of incredibly ambitious – and often far-fetched – builds. 

But the first episode of the new season, which airs tonight on Channel 4, host Kevin McCloud witnessed its most dramatic construction yet. 

Architect Howard and interior designer Sarah set out to build a radical floating home on a tidal estuary near Worthing – with the seemingly impossible requirement of needing to cope with high tides alternating with hours sitting in the mud. 

It made for a huge experiment, with £385,000 to spend over an 18 month schedule, and Howard and Sarah completing much of the work themselves – in what seemed a recipe for disaster. 

Designed to look like a boat, and nestled within an idiosyncratic houseboat community, underneath the steel structure was a very surprising material – an enormous and prefabricated polystyrene slab.

In February 2023, almost a full year into the project, Howard and Sarah began fabricating 16 polystyrene floats at a workshop in Sussex, using 200 square metres of the material. 

Sticking it together with 400 litres of polyurethane glue, activated by spraying it with water, the race was on to join the blocks of polystyrene together. 

However, they soon hit a hurdle as they raced against the clock. 

‘The key thing is, from the moment we start spraying it, we’ve got to be very quick getting it all assembled and strapped together so we can close the joints up nice and tightly,’ Howard explained. 

He soon realised that the block had been cut inaccurately – meaning that the project was off to a rocky start. 

Polystyrene is widely used for insulation in construction projects, making it popular and versatile.

The packaging material can be used in building homes in innovative technology, leaving space to pour concrete. 

However to build the base entirely from polystyrene, as in Howard and Sarah’s project, remains unusual. The lightweight material would mean their home could float – even while attached to a steel frame. 

The couple had already experienced a delay to the building process, as they firstly had to remove a derelict World War Two landing craft on their landing plot, which they’d purchased for £255,000. 

This alone took double the amount of time planned – while attempting to permanently moor the building site at the last minute added a further five months.

‘Our perfect project is unimaginably difficult and everyone else looks at it and thinks it’s impossible,’ Howard admitted. 

‘We need that combination of difficult and marvellous.’

Host Kevin meanwhile, admitted he thought the couple had ‘bitten off more than they can chew’.  

In June 2023, when Howard and Sarah had hoped to be living in their new home, they’d only just taken the first floats and steel beams onto the site. 

And it wasn’t until three years after the project began, in February 2025, that Kevin McCloud was able to visit Howard and Sarah to see if they’d managed to achieve their dream. 

The final result will be revealed in tonight’s episode. 

Elsewhere in the upcoming series, Kevin is set to give an update on the show’s ‘most heartbreaking house’. 

He reunited with Graeme and Melanie, who appeared in the 2023 season with the hopes of turning their garage plot in Hackney into the three-bedroom house.

Architect Graeme and graphic designer Melanie, from East London, met in tragic circumstances, having both lost their partners before finding love again together.   

The couple hoped to build a three-storey, three-bedroom home designed by Graeme which had enough space for Mel’s daughter Indie, 13, and Graeme’s daughter Isla, 15, to each have their own room – all on a budget of £450,000.

After both girls lost a parent (Isla’s mother passed away within weeks of Indie’s father’s death) Graeme stressed the need for the new family home to be a fresh start and a ‘statement’ for the family. 

The original episode ended on a cliffhanger, with the couple having run out of money and faced with the prospect of having to sell the unfinished property.

But returning for this year’s series of the architectural show, Kevin re-met with the couple who confirmed that building had finally been completed. 

Speaking in advance of the first episode premiering tonight, Kevin told OK: ‘They’ve finished it now.’  

The new season of Grand Designs airs on Wednesday at 9pm on Channel 4.