The AECB Gold Standard approximates the Passivhaus standard in a UK context. The details can be downloaded for free for AECB Members (it would be worth joining just to get them)

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Passivhaus 101

The german Passivhaus standard was devised and refined by Professors Bo Adamson and Wolfgang Feist who went on to form the Passivhaus Institute. It was developed as an absolute standard with the overall efficiency of the building very tightly proscribed.

It works on the simple idea that by having a correctly orientated building that is very well insulated with high performance doors and windows and the whole building being very airtight.

Although I say this is simple the devil is in the details to achieve this level of efficiency requires that at every stage of the building process the details are checked against the Passivhaus standard.

The headline figures are the building must not use more than 15 kWh/m² per year for heating and cooling (current new builds would be about 55in theory often higher in practice) this should be achievable from the heat produced by the daily use of the building, people, appliances, sunlight etc. It is foreseen that for short times in the winter a small amount of background heating may be needed. As the small amount of heat needed is valuable Passivhaus buildings will need to include a ventilation system that not only ventilates but uses the heat from the air being removed to heat the incoming air. This is achieved by using a MHVR (mechanical ventilation with heat recovery) system. These can return around 90% of the heat to the building if they are well specified. A good MHVR system only uses a high efficiency fan of around 25 watts. So this would cost about 50p per week to run.

Total energy consumption (energy for heating, hot water and electricity) must not be more than 42 kWh/m² per year.

Total primary energy (source energy for electricity and etc.) consumption (primary energy for heating, hot water and electricity) must not be more than 120 kWh/m² per year.

The effectiveness of the thermal performance of the building fabric is measured using U values the lower the U value the better the insulation so for instance the 2002 Building regulation insulation levels for a wall was a U Value of 0.35 the Passivhaus standard would be around 0.12. This may mean that you may well be looking at a wall with insulation 350mm thick.

As well has very high levels of insulation The building needs to be very well detailed in terms of airtightness. The mantra is Build Tight Ventilate Right. The building must be very well ventilated for it to be healthy to live in and prevent condensation problems. Any unplanned holes in the building fabric will cause drafts these will hugely affect the overall thermal performance of the building as well as making it uncomfortable to live in they could also cause problems with condensation in the building fabric. This level of airtightness is best tested during the build and on completion. To achieve the required levels of airtightness to comply with Passivhaus Standard their should be no more than 0.6 Air Changes per hour (the current building regulations are 10)

The only way to achieve this standard the plans should be run through a computer programme called the PHPP (Passivhaus Planning Package). This should be seen as a design tool and used from the early stages of the design taking in to account the building type, construction method, location, direction and size. This is essential it is not enough to buy a building that claims to be Passivhaus. You will need to find a specialist who has the package and been trained in it’s use. Currently their are only a few of these but their number is increasing as this is the best low energy package available.

To show how far behind we are in the UK we currently have a couple of certified Passivehaus standard houses, where as Austria is insisting that all new home achieve this standard.

The AECB Gold Standard approximates the Passivhaus standard in a UK context. The details can be downloaded for free for AECB Members (it would be worth joining just to get them as they are very well detailed)

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