The Elsworth Show House

3 April 2018 Paul Newman, Self Build Director
Image of Potton's Passivhaus show home
For many businesses in the self-build sector, the opportunity to build a new permanent show house rarely arises, but at Potton, we have been extremely fortunate to build the Elsworth Show Home —  the UK’s first permanent show home built to Passivhaus standard.

Although we already have multiple show homes, the responsibility to “get it right” was one that weighed heavily. So after a lot of head-scratching and widespread consultation, we decided that this timber frame house build would:

A.  Be a stylish, contemporary design that undisputedly confirmed to the sector that Potton doesn’t just do “traditional”.

B. Provide a permanent showcase for homes designed to achieve the ultimate in energy-efficiency performance — the Passivhaus standard.

At Potton, 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, and the natural choice was HTA Design — as well as being great designers, HTA has worked with us previously on low-energy housing developments.

The most notable of these previous developments is Hanham Hall in South Gloucestershire, which was constructed for Barratt Homes and was a large development of 180 zero-carbon houses. HTA has a deep and genuine interest in sustainability and energy efficiency, so the team was 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 Dr Wolfgang Feist. It’s based on the idea that a home can be heated (around 5kwh/sqm/year) using warmed fresh air, which is about three times more efficient than current UK building regulations.

Passivhaus Airtightness & Ventilation

As air can only hold a small amount of heat, the house must be thoughtfully designed and constructed to need only a small amount of heating. To achieve the necessary level of performance, Passivhaus homes must be ventilated using a mechanical system that preheats 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 it’s increasingly becoming the norm for highly insulated buildings. Older dwellings frequently have poorly fitting doors, windows and open joints between construction elements, which consequently, makes them draughty.

Essentially, many of us are used to having fresh air via draughts without having to open windows or having a mechanical ventilation system. To keep the air fresh through constant changes, the ventilation system runs at a low level at all times, even in the summer.

The key features of a Passivhaus Building

•    High levels of insulation
•    High-performance windows with insulated frame
•    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 huge effort is needed by the construction team to make a Passivhaus building highly insulated and airtight and so far, there are few contractors and manufacturers in the UK who are skilled at doing it. To learn more about the careful planning needed for this part of the build, read How to Build an Airtight Structure from our Passivhaus Build Knowledge Base.

However, as more Passivhaus projects are constructed, the skill levels in the industry will grow to meet demand and the workforce will gradually become accustomed 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 Build a Passivhaus?

As there is a long payback duration (around 10 years), most people need reasons beyond simple energy efficiency and reduced fuel bills before they are convinced that building a Passivhaus is a good idea.

The Key Reasons to Construct a Passivhaus

•    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

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 available site may have nice views to the north or there may be a lot of trees or hedges to the south that cut out sunlight.

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

What about Overheating?

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, though, by ensuring that such windows have appropriate shading by using overhangs or shutters.

The Passivhaus Planning Package (PHPP) is an essential tool to use when designing a Passivhaus. It checks that the designed property will not overheat in service. Furthermore, the HTA Architecture and Sustainable Futures team worked collaboratively with our technical team at Potton 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” to make use of large openings and a distinctive butterfly roof while simultaneously challenging and satisfying the requirements of the Passivhaus Design Package. There are certainly easier ways to design a Passivhaus, but we have built the Elsworth Show home to challenge the perceptions of our business.

A top-lit enclosed “courtyard” sits at the heart of the home, filling the plane with natural daylight and acting as a focal point for open-plan living. With some flexibility in the arrangement, these interconnected spaces are designed to be adaptable to almost any occasion or lifestyle.

Additionally, 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, which blurs 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 to be used as 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 while maximising solar gain during the winter months.

The new Elsworth show home has been constructed using the Kingspan TEK Building System (structural insulated panels) and with additional external insulation, it 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 (timber frame house build) from Vincent Timber.

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. Using bricks added a further level of complication, due to the need to provide a separate foundation for them, so 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, particularly the stairs and the central flexible “courtyard” space. Ten years ago, we offered our customers a very limited choice of staircase design. However, the staircase in the new house features closed solid timber treads with glass balustrading and, most excitingly, is 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 choosing specific paint colours to match.

For more information, read The All-Important Finishing Touches from our Passivhaus Build Knowledge Base.

The Kitchen

Kitchen in the Potton Elsworth Show Home
The kitchen is regularly described as the heart of the home and while 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.

Over the past few years, we have developed an increasingly strong partnership with Callerton and Cambridge Kitchens and Bathrooms. For the Elsworth, we agreed on a design brief for a simple kitchen, selecting stylish yet cost-effective materials. Callerton wanted to make a clear statement that great kitchens don’t have to be monstrously expensive.

Furthermore, we also wanted to highlight that kitchen design should not be an afterthought. Instead, it should be considered thoughtfully from an early stage of the design process to ensure that the finished article properly meets the requirements of the occupiers.

This is especially 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. Additionally, the performance of the fittings will have an impact on the energy consumed by the house and, therefore, the PHPP analysis.

The Bathroom

Sottini Bathroom in the Potton Elsworth Show Home
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 its latest products and complement the other interior design elements of the house. Sottini believes that function dictates form and the best designs are those that are clean and simple. This was reflected in the brief that we provided and the designs Sottini created for us.

Read our Passivhaus Build Knowledge Base for more information on how to build a Passivhaus property, with commentary from Self Build Director Paul Newman, Project Manager Brent Ackerman and Architect Rory Bergin from HTA Design LLP.

The Elsworth Show Home Opening

Potton Elsworth Show Home Bedroom
The week before the grand opening of the Elsworth Show Home was busy and stressful, and it contained the usual number of early starts and late finishes, but we just about got there. We had over 300 visitors during the first three days of the house being opened and served up nearly as many glasses of fizz!
Potton Elsworth Passivhaus Show House

The Elsworth is open to the public

The Elsworth Show Home is now open to view, along with the other four houses at our Show Centre in Little Paxton. We are confident that they will inspire you as you take the first steps on your Passivhaus journey. View directions and opening times here.

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