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What is Passivhaus?

Q: What is a Passivhaus?

A: Passivhaus is a measured and certifiable low energy building standard which is up to 10 times better than UK Building Regulations. In ordinary houses, ¾ of the energy is wasted by space heating. A passivhaus uses about 1/20th to 1/30th the amount of a normal house. To achieve the Passivhaus standard the house has:

  • Very good levels of insulation with minimal thermal bridges
  • Is orientated to maximise heat energy from the winter sun, with large south facing triple-glazed windows
  • Draught free construction to minimise heat energy escaping from the building and preventing cold draughts
  • Excellent indoor air quality – even in winter when the draught-free windows are closed- provided by a heat recovery ventilation system with highly efficient heat recovery.

Where does the name Passivhaus come from?

A: The term ‘Passivhaus’ comes from the fact that the building is kept warm in winter by almost entirely passive means (heat from the sun and heat from the occupants body warmth and their appliances). It refers to a specific construction standard which was first developed in Germany in 1988. The Passivhaus Institute was founded in 1996 and there are now currently around 17,000 Passivhaus buildings worldwide - most of these are in Austria and Germany.  There are currently three certified Passivhaus buildings in Wales including this one.

Q: What is the payback time?

A: If energy prices remain constant then this house will become cheaper than an ordinary house built to Building Regulation standards after 19 years. However if energy prices rise by 5% each year the house will be cheaper than an ordinary Building Regulation house after 14 years. After 50 years, a standard house will have cost at least twice as much money as a Passivhaus.

Q: How does the heat recovery ventilation unit work?

A: Stale waste air is extracted from the kitchen and bathrooms, it passes through the unit (next to the front door) where 90% of the heat energy is transferred to the incoming fresh air to pre heat it (without mixing the air). This warmed fresh air is then supplied at a very low rate to all habitable rooms ensuring a very high level of indoor air quality. This works both ways so if the outside temperature is higher than the inside the system helps to maintain a comfortable internal environment. The fans are incredibly efficient and use only a tiny amount of electricity to run; 15 watts on extract and 15 watts on supply (winter only). The heat recovery ventilation unit actually saves 10 times more energy than it uses!


How much will a house like this save me on fuel bills?

A: Passivhaus dwellings typically achieve an energy saving of 90% compared to existing houses.  It is estimated that the total space heating costs will be £78.18, the electricity costs will be £217.62 and hot water heating cost will be £83. The total bills will therefore be £378.80. This does not take into consideration the money made from the Government feed-in tariff for the photovoltaic panels.  

Q: How is the house heated?

A: The heating requirement of the house is so low that it could be heated in winter by the heat from approximately 20 tea lights.  But normally the house is heated mostly by the sun. Even a bright overcast day will help heat the house because the triple glazed windows have a very special ultra-clear glass that soaks up heat from the sky and then holds it in the house. The house is so well insulated that the other things that usefully heat the house are people, pets, the fridges, the oven, the hot water tank and the television or computer. If there is ever a need for a little more heat, this is supplied through a small heating coil in the supply air of the heat recovery ventilation system. Also there are backup towel radiators in the WC and bathroom which can be switched on for a 30min or 1 hour boost of heat.

Q: Does all the insulation mean that the house overheats in the summer?

A: No, the insulation acts in the same way as a thermos flask - keeping the summer heat out and making the house cool in summer and warm in winter.


What maintenance does the house need?

A: Very little compared to a standard house. The filters in the heat recovery ventilation system need to be changed just once a year in the clean Welsh air. The solar panels will need to be serviced once every few years and the little back up boiler for the hot water will need a standard boiler service.  

Q: How thick are the walls?

A: The walls are just over half a meter thick. The wall build up is:

-        Welsh larch cladding

-        100mm Rigid wood fibre insulation

-        225mm thick timber frame with glass mineral wool insulation between battens

-        Draught proofing membrane

-        100mm of loose fill wood fibre insulation between battens

Q: How long did the house take to build?

A: The house started on site at the beginning of March - it took just under 5 months to complete.

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