In principle, but not on paper

Peter and Alison Stopp, with their son Tom, have built a PassivHaus on a hill in Carmarthenshire. It is a lovely house on an even more lovely plot. The trouble is, it is not a PassivHaus. It is close, but it is not quite there — as it has not been certified. The Stopps know that and don’t really care. What they wanted was a low-energy house that was as eco-friendly as possible. They came to PassivHaus as an affordable, practical alternative. What they have is a warm, comfortable and very low-energy house, with no central heating. It has a woodburning stove in the lounge, heat-recovery ventilation, and solar panels on the roof, but no boiler, no underfloor heating.

So what is the point?

Hanse Haus are perhaps the pre-eminent PassivHaus builder in Germany and the UK. Their CEO, Marco Hammer, says: “The motivation is money. It is about capital cost over running cost. Capital cost is in the owner’s hands but running costs are dictated by others.” True, but a shade cynical perhaps. Some people may be motivated by other things and see the money as a bonus. Bruno Klienheinz, the Hanse Haus sales director, has a slightly different view. “We need rules to control us. People chose PassivHaus because it provides rules they can trust.”

PassivHaus has become a convenient shorthand for a low-energy house and is perceived as being eco-friendly and sustainable. In energy terms that is true but it addresses none of the other issues relating to sustainability. In fact, a PassivHaus is likely to score no more than Level 4 on the Code for Sustainable Homes.

It is also true that self-builders are increasingly looking for a standard. Eco, Green, Sustainable — the words don’t really mean anything. The Code for Sustainable Homes is too big, too complex and too bureaucratic. However, PassivHaus is relatively simple and measurable. If the resulting house is not actually PassivHaus, then so be it — so long as it meets the preconceived idea of being low-energy and eco-friendly. According to the Stopps, living in a PassivHaus is a different experience. “It is an airtight house,” said Peter Stopp. “It tested at 1.93m3/hr which is pretty good. [Note: current Building Regulations calls for not more than 10m³/hr.] We were worried that we would not be able to open the windows but we do — you just have to turn the ventilation system off.”

The idea vs. the standard

In recent years, PassivHaus has moved to more closely self-regulate — through certification and a list of approved products. The reason for this is to ensure that homes that set out to be PassivHauses actually end up being so — the main failing in many so-called eco homes is that they are very efficient on plan, but by the time they have been built and corners cut, they perform considerably worse. This will add no less than £10,000 to the build cost — and according to Hanse Haus getting a certified PassivHaus could add 20% to the build cost.

What the Stopps wanted was a warm, welcoming, comfortable house with the lowest energy use possible, and built to a reasonable budget. That is what they got and they are very happy with it. “We would certainly go PassivHaus again”, said Peter Stopp, “but certifying is too expensive and pointless.” And you have to see his point. The house is great and does not need the certificate. It is said to add value to the house but that is still to be proved and the difference between the Stopps’ non-PassivHaus and the Stents’ certified PassivHaus, in terms of its efficiency, is difficult to see. The Stents will have better thermal performance and it will cost less to run, but it is likely to be in the region of £5 to £10 per month. Whether that is enough to justify the extra investment is the issue.

The outlook

The idea of PassivHaus is gaining momentum. Whilst to date the Government’s green building initiatives have concentrated on renewables, PassivHaus stands out because it concentrates solely on energy efficiency. It’s also unique in that it has become internationally recognised as the gold standard of low energy building, and PassivHauses are now springing up all around the world, in all manner of climates, using a wide variety of building methods.

Passivhaus Essentials

  The Ecopassiv timber low-energy window has a polyurethane thermal break and is a cost-effective solution. Its low U-value of just 0.75 makes it PassivHaus compatible. From £212/m². Other manufacturers include Optiwin, Internorm and ENERSign.
  Airtightness is critical to the success of a PassivHaus and so you’ll need plenty of good airtightness tape for the details. One of the best around is the Pro Clima Contega FC, £19 for a 15m roll.
  Make your walls and roof airtight with a good quality membrane, such as this Intello Plus, again from Pro Clima. £166 for a 50m roll (1.5m wide).
  The essential element in a Passivhaus is a mechanical heat recovery system. Expect to pay £3-5,000 for a typical set-up.

The Innovative Design

Helen Seymour-Smith’s passivhaus features external wall insulation

One of the UK’s pioneering PassivHaus homes – the AI?PassivHaus in the Cotswolds, which is part new build and part buried underneath an existing barn, designed by Seymour-Smith Architects and recently featured on Grand Designs – incorporates many of the typical PassivHaus products (such as triple-glazed Optiwin windows).?But it also features an interesting external wall insulation (EWI) system from Sto (sto.co.uk)?which wraps around solid block walls, rather than a cavity approach. The StoTherm Classic EWI?system is a multi-layered system incorporating expanded polystyrene insulation and allows the building to achieve the necessary U-value of at least 0.15. One of its key benefits is that the wraparound insulation reduces the potential for cold bridging. Additionally the solid rendered finish, combined with Sto’s Turbofix adhesive foam, improves airtightness.

For architect and owner Helen Seymour- Smith, the PassivHaus route was a no-brainer.?“Why wouldn’t you want your house to have such a thermally efficient envelope and design that it only requires very minimal heating?”?she says. “The only downside is that you have to invest more money and effort to achieve this, but if you are able to look at it as simply front-loading your utility bills, then it makes perfect sense.

“Is it worth the extra effort? Absolutely! We are enjoying life in an immensely comfortable house, which is primarily heated by the sun, with just one small wood stove for back-up. The internal air quality is fantastic, and the temperature stays around 21°C.”

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