IF you are building or renovating a house you will inevitably hear the term ‘passive house’ or ‘passivhaus’, the word ‘passiv’ with a Teutonic clip of its ‘e’. For the uninitiated, this term, and the cheery declaration of ‘passivhaus standard’ slapped on a range of energy-efficient products, can be confusing. Passivhaus standards, or an approximation, will increasingly become the industry norm for house building, as all new homes are constructed to be carbon neutral, emitting no harmful gases as we heat our rooms and water.
Turn up the body heat
or a house to be deemed passive, it must draw a minimal amount of active external energy, if any at all (excluding solar), to run its space and water heating and keep it cool, where needed. Passive houses are sometimes termed ‘body heat houses’, as the warmth emanating from the people who live there, and the passive heating coming through the windows, is enough to keep them cosy.
In their most developed forms, these sustainable houses can become very active, selling energy back to the national energy grid. If you want to find out more about energy-positive housing, Google ‘Villa Åkarp’, the first of a new league of super homes constructed in Malmø Sweden.
Setting the standard
The energy standard for the true Passivhaus, is set by the PassivHaus Institute in Germany, and despite its rigorous demands, it remains a building concept not a brand. The concept was developed by Professors Bo Adamson of Sweden, and Wolfgang Feist of Germany and the first Passivhaus dwellings were constructed in Darmstadt in 1991. The criteria for a passive House per m² living area include a maximum of 15 kWh/m²yr annual space-heat requirement and no more than 42 kWh/ m²yr annual total amount of energy input.
A semi-detached, two storey Irish house built in the mid 1970s before the introduction of thermal insulation standards would have a space heating requirement of over 200kWh/m²yr and have a total primary energy demand of over 400 kWh/ m²yr. In short the energy efficiency of the Passivhaus is 90% better.
A passive house is highly insulated throughout every centimetre of the envelope, including walls, roof, floor slab, windows and doors, and has no ‘cold-bridging’ where heat jumps across one material to another. It’s air-tight to prevent thermal loss and uncontrolled air ingress. The ventilations is carefully managed through a mechanical and heat ventilations system, abbreviated as a MHRV (75% of the heat from exhaust air is transferred to the fresh air by means of a heat exchanger). In warm weather the Passivhaus will use passive cooling techniques, including strategic shading. A successful build means a comfortable temperature year round, healthy humidity, fresh, clean air, no draughts whatsoever and laughable fuel bills.
Setting the standard
Certified passive houses have been built here in Ireland since 2005 to the correct layout and orientation and with the key materials and techniques, achieving Passivhaus energy performance through a highly exacting, rigorous build. Retrofit projects (which have different Passivhaus standards) are also becoming very popular. When developing new housing, or renovating existing house stock, builders have been enthused to reach beyond the building regulations towards near passive standards with low-energy designs and materials. There are actually only 20,000 certified Passivhaus builds in the entire world. If something is certified fit to go into a Passivhaus (when perfectly installed), you can be fairly sure it’s top notch in terms of its insulation properties for example.
Passivhaus Beats BER
An energy efficient BER ‘A’ rated house shares a lot of common ground with a Passivhaus. However, an ‘A1’ rated house in BER terms is not necessarily worthy of Passivhaus certification, and a Passivhaus may not reach a BER ‘A1’ rating, as the two are surveyed using different methods. The only downside voiced by the industry for passive builds is in terms of the increased cost to build and one or two lifestyle challenges. The whole house is at one temperature for example, annoying if you prefer a cool bedroom and warm living room.
Worth the expense
If you’re keen on building a Passivhaus or renovating your home to as close to passive standards as possible, the capital investment will be greater. For renovations the layout of the house may have to change and improving the insulation performance of the entire house will be vital. However, the long range rewards in terms of running costs and the potentially increased value of a superbly well built house make it well worth consideration. Part ‘L’ of the Building Regulations has done a lot to pull new housing and improvements towards high energy efficient buildings. Exceeding the standard and aiming for passive or near passive performance is a sound guiding principle.
By Kya deLongchamps