Come and experience a Passivhaus build

3 April 2018 Paul Newman, Self Build Director
Image_Show Home_Elsworth_5
It’s not that often that one is presented with the opportunity to build a new permanent show house. For most businesses engaged in the self build sector, the opportunity never arises.

Our new house will be our 6th, but even so the responsibility to ‘get it right’ was one that weighed heavily.

So, after a lot of head-scratching and widespread consultation we decided that our 6th show house would;

•    Be a stylish, contemporary design that confirmed, unarguably, to the sector for once and for all that Potton don’t just do ‘traditional’ 
•    Provide a permanent show case for homes designed to achieve the current ultimate in energy efficiency performance– the Passivhaus standard.

We have previously designed all of our show homes in house. This time we took the brave, and slightly scary, decision to work with an external practice; the natural choice was HTA Design. Apart from being great designers, HTA is a practice that we have worked with on previous low energy housing developments.

The most notable of these is Hanham Hall in South Gloucestershire which was constructed for Barratts and was a large development of 180 zero carbon houses. HTA have a deep and genuine interest in sustainability and energy efficiency and were keen to learn with us and test themselves with the design and construction of a Passivhaus.

The Passivhaus standard originated in Germany and its development was led by Prof. Dr. Wolfgang Feist. It’s based on the idea that a home can be heated using warmed fresh air.

The amount of heat turns out to be 15kwh/sqm/year. This is about three times more efficient than current UK building regulations, and still more than twice as good as planned for the regulations in 2016 before the government irresponsibly canned them immediately after the last election.

Because air can only hold a small amount of heat, the house must be designed to need only a small amount of heating and must be designed and constructed thoughtfully and carefully.

To achieve the necessary level of performance Passivhaus homes must be ventilated using a mechanical system that pre-heats ventilation air by recovering the heat from stale air as it leaves the building.

This type of system is still relatively uncommon in the UK, but becoming more normal for highly insulated buildings. Older dwellings frequently have poorly fitting doors and windows and open joints between construction elements and are consequently draughty.

Essentially, many of us are used to having fresh air, provided via draughts, without having to open windows or to have a mechanical ventilation system. The ventilation system runs all the time, even in the summer, at a low level, so the fans don't make any noise, and the air is kept fresh through constant changes.

The key features of a Passivhaus building are:

•    very high levels of insulation
•    extremely high performance windows with insulated frames
•    airtight building fabric
•    'thermal bridge free' construction
•    a mechanical ventilation system with highly efficient heat recovery
•    accurate design using the Passive House Planning Package (PHPP)

A big effort is needed by the construction team to make the homes very highly insulated and airtight and so far there are few contractors and manufacturers in the UK who are skilled at doing it.

However, as more of these projects are constructed, the skill levels in the industry will grow to meet the demand and the workforce will gradually become used to the level of care and workmanship required.

Building a Passivhaus Show Home

A complete step by step guide, we take you through the story of building our Passivhaus show home. From the design process, constructing the superstructure, achieving airtightness right through to the finishing touches.
 

Download the guide here.

Building a Passivhaus Download

Why Passivhaus?

Exterior of Potton's Elsworth Show Home
Because of the long payback duration, say around 10 years, most people need reasons beyond simple energy efficiency and reduced fuel bills before they can be convinced that building a Passivhaus is a good idea.


The key reasons to construct a Passivhaus are:

•    Low running costs to help prevent future fuel poverty
•    Easy to live in with simple control systems
•    Thermally comfortable, with no draughts and an even temperature distribution
•    Good indoor air quality provided by the mechanical ventilation system
•    Excellent acoustic performance provided by a  combination of very well insulated walls, airtightness and triple glazed windows

For me, the biggest benefits of Passivhaus buildings is perhaps the least obvious one of the comfortable internal environment with an even internal heat distribution.

The stereotypical Passivhaus is a simple box, aimed at containing the most space as efficiently as possible and positioning a reasonable proportion of the windows where they will get winter sunshine.

This can cause the designer some difficulties as the site that is available may have nice views to the North, or may have a lot of trees or hedges to the south that cut out the sunlight.

As designers become more familiar with the standard, they will develop the skills to be more expressive with the design and take advantage of the benefits of the site and ensure that the designs they create can be constructed for a reasonable cost uplift.
Potton Passivhaus SECTION ILLUSTRATION

What about overheating?

Exterior - Potton's Elsworth show home
With very highly energy efficient homes there is a danger of overheating in the summer if there are large areas of unprotected glazing to the South and West.

Good design can overcome this by ensuring that such windows have appropriate shading by using overhangs or using shutters.

The Passivhaus Planning Package (PHPP), an essential tool used when designing a Passivhaus, checks that the property being designed will not overheat in service.

The Architecture and Sustainable Futures team at HTA worked collaboratively with our technical team to design a house that is ambitious in form and avoids the stereotypical Passivhaus perception of a simple box.

Derived from a desire to flood the interior with natural daylight, a series of simple design moves creatively breaks down ‘the Passivhaus box’, employing large openings and a distinctive butterfly roof, whilst simultaneously challenging and satisfying the requirements of Passivhaus Design Package.

There are certainly easier ways to design a Passivhaus, but we were building a show home and attempting to challenge perceptions of our business.

A top lit enclosed ‘courtyard’ sits at the heart of the home filling the deep plan with natural daylight, and acts as a focal point for open plan living. Flexible in arrangement, this series of interconnected spaces is designed to be adaptable to almost any occasion or lifestyle.

The large south facing space at the rear of the house is lined with heavyweight flooring and eight meters of full height glazing that opens out onto the garden under the overhang of the roof, blurring the line between interior and exterior.

The courtyard space at the centre of the house is not only intended to be flexible in use but also the unofficial hub of the home.

Solar Gain

Dining room - Potton's Elsworth show home st neots
The south-facing opening has been maximised to benefit from solar gains, which combined with other Passivhaus principles, helps to reduce the energy consumption of the house to 15kWh/m2/yr for heating.  

The roof overhang protects this glazing from excessive solar gains and overheating of the interior during the summer, whilst maximising solar gain during the winter months.

The new show house has been constructed using the Kingspan TEK Building System (structural insulated panels) and, with additional external insulation has a virtually ‘thermal bridge free’ construction.

The windows, which come from, Kloeber, are triple glazed and tightly sealed into the envelope to achieve reduced heat losses and a comfortable surface temperature.

The house is conceived as a brick clad box, which reveals spaced timber cladding from Vincent Timber at the points at which it is 'carved' away.

At the entrance, bricks sit above the cladding as it wraps around the corner and seamlessly continues inside to the main living space, guiding visitors into the house. Most Passivhaus use lightweight claddings carried by the structure of the building; insulated render is common.

Using bricks has added a further level of complication, due to the need to provide a separate foundation for them and we challenged ourselves further by selecting a longer, narrow format brick from Wienerburger.

Interior Design

Lounge area in Potton's Elsworth Show Home
The interior design of the house is anchored by a few key feature elements and particularly the stairs and the central flexible ‘courtyard’ space.

Ten years ago we offered our customers only a very limited choice of staircase design. The staircase in the new house moves things on another step and will feature closed solid timber treads with glass balustrading and most excitingly will be constructed from American dark walnut.

The interior design is pulled together with feature walls of stunning wallpaper from Mockbee & Co and paint finishes provided by Brewers. These independently owned UK businesses have both been wonderfully helpful in guiding our selections and then matching specific paint colours within those selections.

Over the past few years we have developed an increasingly strong partnership with Callerton and Cambridge Kitchens and Bathrooms. For the Elsworth, we agreed a design brief which required that the new kitchen would be simple with materials selected to be stylish yet cost-effective.

The kitchen is regularly described as the heart of the home and whilst for many this is undoubtedly true not everyone has the desire or inclination to spend an arguably disproportionate amount of their budget on the kitchen.
Callerton wanted to make a clear statement that great kitchens don’t have to be monstrously expensive.

The Kitchen

Kitchen in the Potton Elsworth Show Home
We also wanted to highlight that kitchen design should not be an afterthought and should instead be considered from an early stage of the design process. This is to ensure that the finished article properly meets the requirements of the occupiers.

This is particularly the case when designing a kitchen for a Passivhaus as the interface between the ventilation system in the house (MVHR) and the kitchen extract system is critical and the performance of the fittings will an impact on the energy consumed by the house and therefore the PHPP analysis.

I stressed earlier that the interior design for the house is intended to be simple, stylish and sophisticated. We have clearly carried this through into the kitchen design and the next challenge was to make sure that the three bathrooms followed suit.

The Elsworth has two en-suite bathrooms and a downstairs family bathroom. Each has been designed by the team at our partners Sottini to showcase their latest products and complement the other elements of the interior design of the house.

Sottini believe that function dictates form and the best designs are those that are clean and simple. This was reflected in the brief that we gave to them and the designs that they have created for us.

The week before the opening was busy and stressful and contained the usual number of early starts and late finishes but we just about got there.

We had over 300 visitors during the first 3 days of the house being opened and served up nearly as many glasses of fizz.

Do please come and visit the Elsworth and the other 4 houses at our Show Centre in Little Paxton. We are confident that they will inspire you as you take the first steps on your journey. For directions and opening times click here.
Potton Elsworth Passivhaus Show House

The Elsworth is open to the public

Come and expereience the Elsworth show house for yourself. Built using the Kingspan TEK Building System, this is the UK's first show home built to Passivhaus standard.

Take me to the Elsworth Show House

Potton

Potton Head Office

Eltisley Road

Great Gransden

Sandy

SG19 3AR

441767 676400

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