the first Certified Passivhaus in England, by Seymour-Smith Architects

the AI PassivHaus

This is Concrete advertising campaign,  March 2011


Architects' Journal Specification, February 2011

Architects' Journal Buildings Library entry, February 2011


Build It Magazine, February 2011

Professional Builder, February 2011

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Specifier Select cover, February 2011


Professional Housebuilder & Property Developer, January 2011


QUBE Magazine, December 2010


[ark] Magazine, Q4 2010


Future Constructor & Architect, December 2010


e-architect website, November 2010

Underhill House

Development by Seymour-Smith Architects, Gloucestershire, England, UK, Europe

Located in the heart of the English Cotswolds, Hill Barn was a derelict 300-year old barn situated in a prominent and beautiful location on a hillside in an Area of Outstanding Natural Beauty (AONB).

Designed to safeguard an important local environment, the AONB designation made the prospect of obtaining planning permission for any development of the barn a daunting prospect.

To address this challenge, architect Helen Seymour-Smith developed a bold and ambitious proposal which involved a breakthrough building – called Underhill House - being constructed underneath and adjacent to the barn, which has now been carefully restored and will be used as an office for Helen’s architectural practice.

In contrast, the house - home for Helen, her husband and young son - is strikingly modern and designed to achieve Passivhaus standards. Dug into the hill and invisible from the surrounding countryside, the development has been designed to have minimal visual and environmental impact.

Despite a housing moratorium in the district of Stratford-upon-Avon, the local planning authority was impressed with the project’s eco-credentials and its sensitivity to the local surroundings and voted to approve the proposals. However, because the development would go against local planning policy, final approval could not be achieved until the plans had been submitted to the Government Office for the West Midlands for its review.

Final planning approval was eventually achieved on 14 November 2007 and granted under paragraph 11 of PPS7, a policy which gives special dispensation for new houses in open countryside which are considered to be ‘truly outstanding and ground-breaking’ and reflect ‘the highest standards in contemporary architecture’.

Underhill House was only the 10th in England to be granted planning under PPS7. Building work could get underway, with the first ground being turned in January 2009. Underhill House subsequently became the first certified, quality-approved Passivhaus in England in January 2010.

Designing for energy efficiency
Not only is the external form of Underhill House designed to minimise environmental impact, the interior form and construction materials were carefully chosen to make the building as environmentally sustainable as realistically possible.

Two sides of the L-shaped Underhill House face south and are glazed throughout with high-performance triple glazing, maximising solar gain and minimising heat loss. The rest of the structure is earth-sheltered and highly-insulated, creating the perfect passive solar design.

In addition, the structure of the underground house is constructed entirely from concrete, much of which has been left exposed internally to exploit the benefits of the thermal mass of the material. The basement walls, floors, and roof are all insulated with STYROFOAM-A materials from Dow Building Solutions and waterproofed externally for the same reason.

Chosen for its high moisture-resistance and compressive strength, STYROFOAM-A product FLOORMATE 300-A was installed below the vast concrete floor slab, helping to avoid thermal bridges at floor and wall junctions and achieving a U-value of 0.1 W/m2K.

Whilst more weight was given to reducing the carbon emissions from the building’s performance than to the embodied energy in the materials used, consideration has also been given to materials with recycled content. The concrete used contains PFA and GGBS as cement replacements. External paving uses the by product of the china clay industry, the screed is made of crushed glass bottles, and internal blockwork uses recycled sawdust.

Pholtovoltaics installed on the south facing wall generate most of the home’s electricity, whilst a mechanical ventilation system with heat recovery connects to the hot water store. One side of the barn roof is covered in a glass slate system with solar hot water collectors beneath, and there is a small back-up wood stove also connected to the hot water store. There is no boiler.

As a result of this carefully thought-through design, no manufactured energy is required to heat the building. Air tightness tests on the building - a key requirement for a structure to qualify for Passivhaus certification - gave impressive results, with Underhill House achieving an n50 result of 0.22 air changes an hour at 50 pascals. The already stringent Passivhaus requirement is 0.6 air changes an hour at 50 pascals.

Interior design and layout
The interior design is functional, stylish, industrial minimalism. The concrete structure is exposed and the galvanised steel ventilation ductwork and wiring conduits are celebrated rather than hidden.

There are dropped ceiling panels for acoustics and to define different areas within the large open plan main living space. Internal block walls have a thin spray applied plaster finish, and are mostly white to bounce light to the back of the plan, further aided by an innovative fibre optic lighting system.

The result according to the architect is like ‘loft living underground’ – and proof that Passivhaus construction standards and contemporary, striking design really can go hand in hand.


Architecture Today "EcoTech" Supplement, November 2010


Chris Evans is impressed... October 2010

The Architect's Journal, October 2010


The Independent website, October 2010

Is this the housing standard of the future?

By Emily Jenkinson

Energy secretary, Chris Huhne, noted in a speech to the Green Alliance recently that “a quarter of UK emissions come from the home.” Meanwhile, according to the Office for National Statistics, 60% of the UK’s local authorities experienced an increase in domestic emissions between 2007 and 2008, while only 40 percent experienced a decrease.

Search for the perfect furniture with The Independent house and home database, powered by mydeco.

The UK continues to lag behind Europe in terms of energy efficiency, but it’s an extravagance we can no longer afford – neither environmentally nor financially.

While we have all been aware for some time what the penalties are of failing to reduce carbon emissions, the news, post-recession, that energy bills in the UK are set to rise, yet again, by up to £150 a year is enough to make us all feel a little more green-minded. So how can we live more energy efficiently?

The government’s commitment to be the first country in the world to ensure that all new homes are ‘zero carbon’ by 2016 is a noble and ambitious one and in line with EU standards set to come in at this time.

Recently, the housebuilding industry has complained that this is an unrealistic target in a slumped housing market which would struggle to carry the cost. But, while builders gripe about the impossibility of making Britain’s homes green, a German standard for super-insulated housing is beginning to gather pace in the UK.

Passivhaus technology was developed in Germany in 1990 and is now widely used across Europe – particularly in Germany, Austria and Sweden. 90% more energy efficient than any normal home, a Passive House applies a number of strict building standards, which help to conserve heat by utilising heat sources and solar gains.

Passive Housing is “absolutely the best tool to achieve what we need to achieve in terms of reducing the carbon emissions in our houses,” says Helen Seymour-Smith, a self-employed architect, whose home, built beneath a 300-year-old derelict barn in the Cotswolds, recently featured on Grand Designs as the first accredited Passive House in England.

Triple-glazed along the south face, the house features solar panels and is earth-sheltered, encased in thick, high-tech concrete insulation and a soil jacket. Inside StoSilent Modular acoustic panels (made from 96% recycled glass) and StoColor Climasan, an odour-eating paint, help to complete a highly minimalist, eco-conscious interior.

“A Passive House is all about investing in the building’s fabric so that, as the building is in use, your carbon emissions will be so much less over time,” says Helen, who sees it as “much simpler” than the “over-complicated” Code for Sustainable Homes rating system, which, she points out, allows you to gain “extra points for putting in a bicycle rack or something and achieve a high level in the code, despite still using electric heating.”

The benefits of Passive Housing have “been proven in over 30,000 projects in Europe,” says Thomas Froelich, who set up The Passive House Centre in Scotland in 2009 as a way of supporting architects and builders in the execution of Passive Housing; educating the general public and housing associations; and certifying that houses conform to the Passive House criteria. “If it works in Germany and Austria, why shouldn’t it work in Britain? The hurdle at the moment is ignorance, but ignorance is slowly but surely coming to an end.”

One of the first myths to debunk about Passive Housing is that of cost. At the moment, says Froelich, you can expect to pay “about 10% more on your envelope to get your home to the passive house standard,” but, he points out, “the saving,” which is significant, "starts straight away.” Meanwhile, it is worth remembering that the Passive House technology, just like laptops and LED lighting, will get cheaper very quickly.

The second myth is that a Passive House has to look as terrifyingly modern and minimalist as Helen Seymour-Smith’s Cotswold home, which is, in fact, down to her and her husband’s own personal taste. This is the biggest misconception, says Froelich. “A Passive House doesn’t have to look like an energy efficient house. It’s just about applying the right materials, the right orientation, the right insulation, mechanical ventilation, heat recovery triple glazing and then you have 80% of the battle won. It’s very, very easy to apply.”

At the moment, there are 30 Passive Houses in the UK and The Passive House Centre in Scotland has many more projects underway. But Passive House standards are not just restricted to new builds. Retro-fit Passive House technology is also possible, and, though the application is often challenging, “it is terribly important that this market be taken seriously,” according to Helen, who points out that “dealing with our existing housing stock is obviously a much bigger deal than dealing with new builds, which are relatively easy to make energy efficient.”

Achieving zero-carbon homes by 2016 will require a leap of faith by housebuilders and developers, and most importantly, the house-buying general public. But, with better awareness and education about what exactly zero-carbon means, we will (and must) get there. As Froelich says, “Britain might be the furthest behind in Passive House technology, but it’s one of the fastest catching up. This is the standard of the future. There’s no other way around it if we want to get our co2 reduction down. We should not buy incentives, but build in the right way.”

Emily Jenkinson is interiors writer for furniture and interior design website

© The Independent 2010

Grand Designs Magazine, October 2010

First Past The Post

For the new TV series of Grand Designs, the super-eco Cotswold home of Helen and Chris Seymour-Smith is England's first-ever Passivhaus

Words: Luke Tebbutt
Photography: Chris Tubbs

Disappearing tricks usually involve coins, rabbits, or women in bikinis, but to kick off the latest series of Grand Designs, Helen and Chris Seymour-Smith have pulled off a much more ambitious feat: they have made a house disappear.

Dubbed the Cotswolds Stealth House, their four-bedroom new-build sits beneath a centuries-old barn on a hill, which they have restored. This was dictated by strict planning rules – in order to get permission the new house had to be all but invisible to the passing eye. ‘Loft living underground’ is what Helen calls it.

Others had tried and failed (including Duran Duran’s former drummer, who wanted to build a studio there), which the couple saw as an opportunity rather than a threat. ‘With every refusal there are a list of reasons, so we addressed every single one and they had nothing left to object to,’ says Helen, whose father sold them the land. Their saviour was a little-known paragraph in planning policy (paragraph 11 of Planning Policy Statement 7) that makes rare allowances for ‘truly outstanding and groundbreaking’ designs. Only around 10 houses have ever been built under this provision.

What makes Helen and Chris’s home so groundbreaking is its eco credentials. It’s England’s first certified PassivHaus – a German standard for super insulated and airtight homes that require no active heating or cooling systems, making bills a thing of the past. Helen and Chris’s will stay around 20C inside year round – even in the depths of winter – by virtue of its construction.

It’s wrapped top to toe in a layer of foam insulation, and all windows are triple glazed (with insulated frames) and face south to catch heat and light from the sun. The walls and roof are pre-cast eco-friendly concrete panels (made from a waste product from blast furnaces) which soak up and store heat like a giant radiator, and the floor is finished with a wonder screed that uses 100 per cent recycled glass for aggregate. Ventilation is also key in PassivHaus construction (it would be impossible to maintain an even temperature inside if you had to keep opening windows or vents to let fresh air in). Helen and Chris have a mechanical ventilation and heat recovery system, which extracts heat from stale air going out of the house (sucked from warmer rooms, such as the kitchen and bathroom) and mixes this with fresh air being drawn in to maintain that all-important even temperature inside.

The couple also have solar photovoltaic panels attached to the underground house to generate electricity and solar thermal tiles on one side of the barn to provide hot water. And just in case you think they are cheating by using a wood burning stove to heat the space, think again: it’s heat output to the room is minimal, with the vast majority used to heat water.

Helen and Chris reckon the house will earn them £1,000 a year thanks to the Government’s recently-introduced Feed-in Tariff which pays homeowners money over a set amount of time (25 years for photovoltaic panels) for electricity they generate and use from photovoltaics or wind turbines, and of course they will never have another utility bill, apart from for the phone, which is just as well. At £600,000, this is not a cheap build.

‘Essentially you’re front-loading all your utility bills on to the cost of the house,’ explains Helen, who financed the project from the sale of the much smaller London home she and Chris sold, plus a bit of money from the bank. ‘As far as we can see, it’s a no-brainer – especially if you’re doing a new-build.’

They say their biggest challenge was wading through what they call ‘eco babble’. ‘We just tried to research the materials and find out if it’s really green,’ says Chris. ‘Is it doing what it says it does? Because you get these materials that say it’s a green material because it’s recyclable.’

‘Oh I hate that word,’ adds Helen, though she’s glad to say things are changing. ‘It’s astonishing the difference now. I’m working on similar projects with clients and there is a plethora of lovely consultants who know what they’re talking about.’

The couple feel proud to have helped pave the way for this, and so they should. On a hill in one of England’s most idyllic spots, where you’re hard pushed to find anything that speaks of the past century, let alone this one, Helen and Chris have built something truly futuristic: a home with an environmental footprint as invisible as its appearance.

‘Part of the reason for doing this house was to put our money where our mouths are, and show people it can be done, it’s not insurmountable, and it doesn’t have to break the bank. I’d like to say to our son, “We did our bit. We tried to help”,’ says Chris, adding meekly. ‘Perhaps that’s too over the top?’

In an underground house, never.

© Grand Designs Magazine 2010

This Is Gloucestershire website, September 2010

Grand Design eco-builders don't get in a jam going underground

LIVING underground without heating may not be everyone's idea of a dream home. But for Helen and Chris Seymour-Smith it is the culmination of hard work and meticulous planning. Millions of viewers saw the green scheme come to life on Channel 4's Grand Designs – from a giant hole in the middle of the Cotswolds countryside to a state-of-the-art hidden home.

Built under the ruins of a 300-year-old barn, married architects Helen and Chris wanted it to be England's first accredited "passive" house – airtight and needing no heating – built to German Passivhaus eco standards. "It was a no-brainer when we came to building a new house," Helen said. "We believe strongly it's the best way of achieving a desperately-needed reduction in carbon emissions. We'll expect to be making more electricity than we use."

TV presenter Kevin McCloud worried the cavernous and minimalistic house could feel a bit cold and industrial. But the creative couple decided to dig deep because their design would not have got planning permission if it had been visible in the Cotswolds Area of Outstanding Natural Beauty, four miles from Moreton-in-Marsh. They used a planning law which allows a house of exemplary architectural merit to be built in open countryside.

"We wanted to build something crisp, modern and white and very un-Cotswolds," said Helen. "Building a subterranean house is a method that's allowed us to do that in the landscape we enjoy." The deeply-rooted home is blanketed with high-tech insulation and soil. It features solar panels and a row of south facing triple-glazing on to a courtyard. Helen said: "It's an absolute joy not having the view, so that every time we come out we just say 'wow'."

© This Is Gloucestershire 2010

Radio Times, Daily Mail, Telegraph 'Review', September 2010


Architects' Journal "Footprint" blog, February 2010

England’s first Passivhaus house

A house built beneath a 300-year old derelict barn in the Cotswolds has been certified this week as Passivhaus standard and is the first Passivhaus house in England.

Located in an Area of Outstanding Natural Beauty (AONB), Seymour Smith Architects’ Underhill House is designed for minimal visual and environmental impact. Constructed underneath and adjacent to a restored barn, the house is completely invisible from the surrounding countryside.

A concrete structure, largely pre-cast, is a critical element of the project’s environmental performance and was supplied by project partner Aggregate Industries. The precast concrete is exposed internally for thermal mass and also reduces waste through off-site construction. Dow Building Solutions‘ StyrofoamTM-A and FloormateTM 300-A beneath the floor slab enclose the entire structure. South-facing glazing maximises passive solar gain.

Air tightness tests on the building achieved 0.2198 air changes (ac/h) an hour at 50 pascals (pa), compared to the demanding Passivhaus requirement of 0.6 ac/h @ 50pa. The UK equivalent q50 result was 0.23 m3/h/m2.

Architect Helen Seymour-Smith said, ‘The Passivhaus design achieves a staggering 90% energy savings over that of an average house. With much of the concrete structure exposed internally, the interior has been carefully designed to show that concrete can play a positive part in environmentally friendly construction. Using the thermal mass from the concrete structure alongside highly-durable insulation has resulted in a highly energy efficient building.’

© The Architects' Journal 2010

Architecture Today, March 2009


Grand Designs Magazine, October 2008


Green Building Magazine, Summer 2008


Sunday Telegraph, 24th February 2008

The Green light for your eco-ambitions

Want to install solar power, recycle rainwater, even build your own lighthouse? It has never been easier, says Caroline McGhie

All homeowners these days probably suffer from carbon footprint anxiety, be it a vague worry about failing to compost the potato peelings to a fullblown drive to change those fossil fuelguzzling heaters to something more eco-friendly.

We know that 27 per cent of Britain's carbon emissions are produced at home. But whereas a few years ago it was hard to know how to clean up our lives, now there are real choices on offer.

Build it yourself

Imagine: A zero-carbon house buried in a hill in an Area of Outstanding Natural Beauty in the Cotswolds. It requires no manufactured energy to heat it and is tucked under the picturesque ruins of an old barn you have known since you were a child. You have designed it with your partner, and within two years you will sell your London cottage and move in with your family to start a new life.

This is what Helen Seymour-Smith, 32, is doing with her husband Chris, 41, and three-year-old son Ben on her father's farmland.

"Everyone thought we were mad," she says. "The planning officers were against it. The local authority has a moratorium on new houses. But under a little-known paragraph of planning policy which allows a new isolated house of 'exceptional quality and innovative nature' to be built once in a blue moon, it got planning permission."

She is still grinning from ear to ear. It's not as if people haven't tried to build there before – the former drummer of Duran Duran once tried to build a studio on the same spot. It is a distinctly unusual project.

The plan is to keep the ruins of the barn, which lie in the middle of a field, and build underneath them.

"We will make a kitchen garden in the ruins so that it is protected from the wind," says Helen. There will also be an underground garage and a wild meadow as a roof. One side of the house will peep out, facing uphill, and be entirely glazed.

"Being earth-sheltered and glazed to the south means it will qualify as a PassivHaus, which is a German super insulating concept the Building Research Establishment is promoting. They will hold our hands and help us with expertise.

"There are so many clever technologies available now. They are used anyway to create gyms and swimming pools under posh Kensington mansions. We have found a fabulous firm of structural engineers who will support the barn in mid-air while we go underneath it. We will use insulated formwork, which is like giant polystyrene Lego blocks filled with reinforced concrete, and we will be 90 per cent better than current building regulations require on insulation."

There will be solar panels for hot water, a back-up bio-fuel boiler, a sewage treatment system, triple glazing and a ventilation system which extracts stale hot air and uses it to heat fresh incoming air. Helen and Chris hope they will attract sponsorship for trying new methods.

Helen also hopes it can be a flagship to attract eco-projects in her work. She plans to move her architectural practice, which designs extensions and conversions (; 0207 871 4570), to a part of the barn which can be restored.

© The Telegraph 2008