Passivhaus: The Last Word in Green Building?

PassivHaus is a design standard – established in Darmstadt, Germany in 1996 – for energyefficient housing. A house built to current Building Regulations will consume around 55kWh/m²/year for space heating or about 80kWh/m²/yr for heating and hot water. By comparison, a house built to PassivHaus standards will consume less than 15kWh/m²/yr for heating or less than 42kWh/m²/yr including hot water.

On Sunday 17th May 2009, Hanse Haus, one of the three biggest German off-site manufacturing companies, built a 180m² PassivHaus at its factory site in Oberleichtersbach (ABOVE). What was most remarkable was that it was erected in a day — in total seven-and-a-half hours from a clear floor slab to a wind- and water-tight house. Which gave me about six hours to wander around the Hanse Haus plant asking technical questions. And the question that kept coming up was, Why build to PassivHaus standard?

Hanse Haus, like all off-site manufacturing companies, takes energy efficiency very seriously. It is its principal design parameter. Even its base standard house is twice as efficient as a house built to UK Building Regulations. PassivHaus would seem a natural progression, and the company has built many of them across Europe.

The picture below is a typical wall section for a PassivHaus build, which is based around using SIPs (structural insulated panels) .SIPs inherently provide reasonable levels of airtightness but every joint is taped to ensure air movement of just 0.6m³/hr — the current Building Regulations standard is 10m³/hr.

What you get is a house that needs little or no dedicated heating – which is what PassivHaus means: a house that is passively heated – although generally a heat pump is installed. The Hanse Haus show house has a 3.5kW heat pump and an underfloor heating system, as well as heat-recovery ventilation. This seems a bit belt-andbraces, but apparently customers like it. As a result the Hanse Haus PassivHaus will be 15% to 25% more expensive than its standard build.

The Passivhaus Wall A typical wall section in a PassivHaus will have a single-skin SIP 145mm thick with 300mm external insulation, with a further 150mm insulation under the wall slab and 300mm in the roof. It will have double-glazed windows to the north and triple glazing to the south.

The Living Experience

The PassivHaus is super insulated, relatively airtight and very efficient. That means running costs will be low. It can be argued that PassivHaus sacrifices all other things on the altar of energy efficiency. Airtightness means mechanical heat-recovery ventilation is essential and that leads to a clean, homogenous atmosphere. That in turn means that the temperature will tend to be the same throughout the house. Some building design scientists maintain, however, that bedrooms need to be cooler to allow good-quality sleep.

This airtightness also means that windows can’t be opened if the efficiency is to be maintained. And you can’t have features like woodburning stoves or open fires because they are just not airtight enough. So why have a PassivHaus? When the question was put to Bruno Kleinheinz, the Hanse Haus sales director, he paused a moment and said, “My house costs 25 euro per month to heat. If I upgraded to PassivHaus it might cost 20 euro.” His shrug was expressive, and the point taken.

The Alternatives

Activhaus is a standard that comes out of Denmark. The idea is simply a house that produces more energy than it consumes. This may not seem like a big move from PassivHaus but it is actually a very significant change. What it means is that you can have any house you like, live in it how you like, and use as much energy as you like, so long as you contribute more energy than you use. So it would be sensible to abandon tumble dryers, electric heaters and air conditioning, but you can open the windows and use the heating system.

Minergie is a Swiss standard that is very similar to PassivHaus in that it requires high levels of thermal efficiency, but it incorporates more eco features. Water use, air quality, noise, recycling and fossil fuel use all fall within the Minergie standard. It maintains that comfort is the key driver so a lot of attention is given to air quality and maintaining a comfortable living environment, with minimum energy use.

ABOVE: Minergie is the Swiss’ own version of PassivHaus, which incorporates more eco features, including heat pumps, solar collectors and wood-fired heating. At present, around 13% of new buildings in Switzerland are Minergie certified. These are mostly residential buildings.

Super E — the Canadian standard which is arguably the most commercially successful system for energy-efficient housing. There are more than 500 Super E houses in the UK — more than all the other standards combined. Principally because it is less prescriptive and more flexible than the other systems.

AECB – the UK’s Association of Environment Conscious Building – has three levels to its standard: Silver, PassivHaus and Gold. The standards focus on CO2 emissions and AECB suggests that the Silver standard will reduce emissions by 50% compared to a Part L Building Regulations standard, PassivHaus by 80% and its Gold standard by 95%.

And let’s not forget our Code for Sustainable Homes. Maybe what all these standards are saying is that the day of the conventional brick-and-block house is over. Energy efficiency is the way forward and there are plenty of ways to get there.

The Danish Activhaus

H&R recently visited this Activhaus (BELOW) in Lystrup, just north of Aarhus, Denmark. The house was built by window and rooflight manufacturers Velfac and Velux as an attestation that, although a house should indeed be well insulated and self-sufficient – producing more CO2 than it consumes – it should also be pleasant to live in, with ample daylight and fresh air — no restrictions on opening windows here. The windows are oriented so that light floods the house from every angle — when you stand in the centre of the house, you can see outside on all four sides. External shutters and a brise-soliel provide protection against overheating on the hottest days. Solar cells, solar heating and a heat pump provide electricity, hot water and room heating.

"We Built the UK's First Bespoke Super E House"

Doug Stewart’s interest in sustainable construction led him and his wife, Sarah, to build the first bespoke self-build Super E house in the UK (PICTURED BELOW) — on an elevated countryside site in Torpoint, Devon. The engineered timber structure with panelised walls has been clad with cedar on a local stone plinth. Heavy Fermacell boards and Excel Warmcel cellulose insulation keep the house as well insulated as possible, while a heat-recovery ventilation system minimises heat loss. A ground-source heat pump supplies heat to the underfloor heating and hot water from under ground heat-collecting panels. “People wrongly assume that with an airtight house you need to keep all of the windows shut, which just isn’t true,” says Sarah. “The house has exceeded our expectations and is really wonderful to live in.”
Read more about this house

PassivHaus reading

• PassivHaus: The Green Standard?
  

• The UK's First PassivHaus
  

• PassivHaus Analysis

• PassivHaus Pioneer: Interview with Wolfgang Feist 

Readers' Green Homes:

• An Eco Home Built to PassivHaus Standards
• A Kit House From Germany
• A Cottage Style Eco Home

Further reading:

• Airtight Homes: Your Questions Answered
• How to Achieve Level 3 of the Code for Sustainable Homes
• How to Save Energy in Your Self Build
• Are Off Site Kit Houses a Greener Way to Self Build?