Passive House Retrofit

From Bere Architects

Passiv Haus is an excellent German energy standard for building new homes. It is a system that relies on making houses really airtight and insulating. Insolation then provides much of the heat energy for the house. Fresh air is supplied via a Mechanical Ventilation Heat Recovery (MVHR) system. This means that it extracts the stale moist air and uses this to preheat the incoming fresh air. This keeps heat loses to a minimum and hence means that heating bills are virtually non-existent.

Designing for this system to work in a new home requires the use of a spreadsheet called the Passiv Haus Planning Package (PHPP). Using this accurate system one can design a building with a primary heat demand of around 15 kWh / sq m per annum. This compares to a new building in the UK that complies to the latest building regulations, that will have a primary heat load of around 85 kWh / sq m per annum. So this means that Passiv Haus is around 9 times more efficient than a modern house.

But is it possible to make an old house into a Passiv Haus? Well, not even Passiv Haus Institute think that this is really possible, however the basic principles can still be applied. So they came up with the EnerPHit standard. The EnerPHit standard relaxes the requirement down 25 kWh / sq m per annum. So still about a quarter of the primary heating energy of a modern new build.

Sounds impossible? Well for many houses I think that it is impossible, especially where you are dealing with old solid and breathable walls. The risks involved in this type of construction are really too great to seriously contemplate, although there are people who have attempted it. The risks associated with ‘deep retrofit’ and the use of high performance materials when one is exposed to a fair amount of wind driven rain, increase to an extent where the whole project might be compromised and hence and savings would rapidly disappear.

There are houses, though where this ‘deep’ EnerPHit retrofit is possible. Most typically this is where you are starting with a modern cavity walled house. Here the materials used and the basic philosophy can overlap with the Passiv Haus concept. However it is still a mammoth task to upgrade a house from 120 – 150 kWh per sqm per annum down to around 25.

To undertake an EnerPHit project one has to have a real drive, vision and passion. A long term commitment to a house is also needed as it takes a while for any savings to start to pay back the capital outlays.

Personally I think that whilst the carbon savings are huge and hence it is absolutely the right thing to do for the planet, most owners will be doing it to get different types of satisfaction. Things like ‘better internal environment’, ‘feel good factor’ and ‘future-proofing ones energy bills’ will be more like the real driving force rather than purely an economic one.

The costs involved has meant that many of these EnerPHit projects have been either done as demonstrations, or by people with too much money on the SE of England. However, we do have a pioneer in Cardiff. To get a glimpse of the work that has been undertaken have a look at this amazing blog.

EnerPHit is not for all, but certainly there are huge advantages in doing retrofit properly and well and having the discipline of EnerPHit can be key in this. For more information have a look at the Passive House Trust website