Grand Designs presenter Kevin McCloud says these houses aren't big, but are clever in the way they convey a sense of space on the most restricted of sites. And the architects who designed them are "conjurors of space" and "almost defy the laws of physics."
1. GREAT PYRAMID OF EAST LONDON
Garden House, Hackney
A cramped artists' studio was demolished on a tiny plot in east London to make way for one of the most exquisite entries in this year's Riba competition.
The 1,100sq ft space features a bedroom, bathroom, living area and kitchen downstairs and a light-filled workspace upstairs, but the crowning glory is its roof garden.
Costume artists Paddy and Keir gained a third more space from the studio-cum-flat, and architect Nick Hayhurst admits the roof garden design was initially designed to placate the neighbours.
The bespoke stainless steel troughs have been filled by Keir with 800 varieties of plants, and the neighbours get the best view of it.
Inside, the house was finished simply but luxuriously, with stone floors, ingenious oak cabinetry hiding plenty of storage space and a steel staircase that appears to float before transforming itself into a shelf space at the top of the steps.
Kevin concludes that the house is like "a sewing box, a glorious, traditional little wooden box crowned with this fabulous collection of jewels from the natural world, a fantastic pin cushion".
2. DIZZYING GLASS FLOORS
Modern Mews, W1, London
Visitors to Dan and Ruth's mews house in central London are advised not to wear short skirts because the house has central glass floors from top to bottom.
The couple planned to start a family but wanted to stay put, so employed architect Phil Coffey to install a central, sculptural staircase that brought heaps of light even into the basement living room.
A huge skylight was part of the original plan, but the couple decided that instead of translucent glass, they wanted it to be totally transparent.
Dan says: "We were so enamoured of the idea that you can see and speak and wave through the glass. However, we're not going to be having a Marilyn Monroe-themed party any time soon."
The decor was inspired by the couple's honeymoon in Japan and includes sliding wooden framed doors with translucent paper panels and plenty of hidden storage.
Kevin says of the house that Riba judges admired the way it "reinvents space" and is "a clear single idea executed with precision and romance".
3. THE ULTIMATE SHED
North Vat, Dungeness, Kent
North Vat is named after the huge cast-iron cauldron that sits in the front garden of this house and which was used by fishermen to boil their nets in tannin to preserve them.
When Pauline and David decided to leave London for Dungeness and wanted to build their dream home, they were told by planners that it couldn't take up more space than the original wooden house and should resemble the style of the fishermen's huts that dot the coastline.
Pauline says: "We asked ourselves, 'What do we need? We need a room with a shelf above for the bed.' "
The simple concept led architect Sinisa Rodic to create a 1,200 sq ft house made up of one big shed linked by a glass corridor to two baby sheds each housing a guest bedroom.
Being on the beach, the couple wanted the best view of the sea and plenty of cleverly placed windows to bring in the light all day.
David says of the way the sun streams in from dawn to dusk all year round: "It's like one big clock of the seasons."
The Riba judges praised the house's elegant mix of high architecture and beach living.
4. STEALTHY EXTENSION
Contemporary Lean-to, Harrogate, Yorkshire
A dingy basement in a beautiful Victorian house was transformed by an ingenious extension of just 700 sq ft.
Architect Ruth Donnelly created the addition for a family who wanted to watch and hear their children play downstairs or in the garden, while entertaining upstairs.
The so-called lean-to extension looks unlike any other lean-to because it was made from fibre cement board and glazed from top to bottom.
Kevin says the material is not only sleek, but cost-effective and visiting Riba judge Damion Burrows praises the extension's "stealth-like shape".
Kevin concludes that the dark, flat finish of the fibre cement board respects the home's Victorian character while giving a new lease of life to the basement.
5. LIVE-IN ART GALLERY
The Narrow House, Hove, East Sussex
The home of art collector Rose and her husband Brian was full to the brim with the paintings she had amassed since 1963.
But that house was four times the size of the plot they moved on to - the site of their old garage next door.
Rose says that when she was looking for someone to meet the challenge,"it had to be someone who could make a wonderful in a tiny space. If you have as much space as you want, you don't build a good house."
Architects Amir Sanei and Abigail Hopkins rose to the challenge fantastically well, creating 1,700sq ft of space in a spot designed to park a car.
Taking inspiration from architect Sir John Soane who stored his vast art collection behind a series of folding walls, they used steel mesh doors throughout the house that hide in walls, sit behind doors and even cover the windows when all the couple want to do is look at art instead of the sea.
Kevin says: "It wonderfully demonstrates just how much house you can get out of a very restricted site, it is both a home and a storage box full of wit and surprise."
Grand Designs: House of the Year is on Channel 4 on Thursdays at 9pm
Of the five houses detailed here, two will be placed on the Riba House of the Year shortlist and their names will be announced at the end of the show