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Passive Homes

The Passive House

The modern concept of the Passive House was developed by Dr. Wolfgang Feist, the founder of the Passive House Institute in Darmstadt, Germany. Yet many of his ideas are already evident in some of the most ancient dwellings right on our doorstep. In his book on rural Ireland, Arthur Young commented on how the use of heavy mud walls and thatch roofs produced a much "warmer abode" compared to the use of thin brick walls and slate roofs by his own countrymen.We have all seen relics of this house type which features a long front wall with larger windows facing the sun while on the north-facing side there are fewer and smaller windows. Although not perfect from many other design standpoints, we can all understand how the sunlight streaming through the windows warms the interior of the dwelling while the heavy walls and thatch roof insulate the occupants from the worst of the winter weather. In the heady days of summer, the opposite is the case where the interior of the house remains noticeably cooler than outside. The challenge for Dr. Feist, when he first started working on the notion of a "passive house" over thirty years ago, was to apply these simple ideas in a modern context so as to eliminate, as much as possible, our dependence on fuelled energy sources such as oil, coal, gas and wood.

Cost Analysis

Passive House is designed to have a minimal requirement for space and water heating, leading to exceptionally low running costs. But this also has the effect of eliminating the need for fans and air conditioning during warm weather. How much did your oil or gas bills run to last year, not to mention the "not-so-incidental" electricity costs? If passive technology can reduce these bills by as much as 90% then it is worth pondering how much could be saved over a ten-year period and what could have been done with all that "wasted" money. Perhaps an extra family holiday every year, paying off the mortgage early or topping up your retirement fund. But there are other financial benefits. In an era when Building Energy Rating (BER) is King, passive homes stand to produce the greatest gains in long term property values. The advent of a carbon tax on homes will also figure prominently in the cost-benefit analysis. It makes a lot of sense to look at these factors now before committing to a long-term investment that may lumber the unwary home buyer with a penal tax as well as a poorly performing home that is hard to sell on without making expensive and unwieldy alterations. Of course, there are many other "hidden" savings bound up with health, vitality, comfort and stress-free living which can only benefit from the sympathetic nature of passive home design. This translates into exceptional air quality, draught-free interiors and low ambient noise while also avoiding excesses of temperature and humidity. Not only do humans benefit from such a pleasant environment but there are undoubted savings in general maintenance overheads. This is particularly true of the Irish climate where dampness during low temperature cycles has a cumulative effect in even the best of traditional homes.

But what about the initial build cost? Does this not far outweigh the advantages? Early adopters of passive construction techniques in Ireland faced a cost penalty of about 10% on conventional builds. But that is coming down rapidly with the economies of scale that can be expected when any nascent market achieves critical mass. Special-purpose materials that were previously imported are now available from local suppliers while forward-thinking construction firms are already moving rapidly up the learning curve. Until recently, passive houses constructed locally have largely been "objects of curiosity" reflecting their Scandinavian, German and Austrian origins. These homes carried a considerable burden in transport costs and often required bringing in specialist construction personnel from abroad. But this all changed in 2008 with the construction of a passive house in Killann, Co. Wexford by two local firms, Shoalwater Timerframe and Michael Bennett & Sons. The invaluable experience gained from this flagship project led to Ireland's first passive residential development at Grange Lough in Rosslare. This eight-home project has been widely acclaimed for its cost-effectiveness, the uniquely Irish flavour of its design and the high percentage of locally sourced materials. As a testament to this successful partnership, Grange Lough went on to win the national Isover Energy Efficiency Award in 2011.

Building Regulations

A Passive House should not be confused with an A-rated home built to current building standards. A passive house certified by the Passive House Institute in Germany meets an altogether more rigid specification. The Department of the Environment is already increasing the standards set by building regulators and aims to further tighten these on a phased basis over the coming years. This will inevitably lead to all new dwellings being built to a passive standard. Over the last ten years, thousands of passive houses have been constructed on mainland Europe, mostly in Germany, Austria and Scandinavia where climatic conditions are far more extreme than our own. The Irish climate actually makes passive design a far simpler task given that the average difference between inside and outside temperatures is much less that what our European neighbours have to contend with. This can only contribute to a regulatory environment that incentivises this type of home construction while lowering the nation's carbon footprint and reducing our dependency on energy imports and the world's dwindling supply of fossil fuels. 

What Makes it Work?

In coming up with a design solution, one of the biggest challenges is retaining the heat within the fabric of the dwelling created by the various "passive" energy sources, such as the sun, the body heat of the occupants, electrical appliances and lighting. Cookers, fridges and deep freezes all give off valuable heat which is lost to the environment with a conventional build. Even more amazing is the fact that ten people sitting in a room emit as much energy as a one kilowatt heater, something to watch out for at your next house party. So how is the passive heat retained without everybody suffering from oxygen loss or worse?


The problem is solved by the use of a mechanical Heat Recovery Ventilation (HRV) system which is installed during the construction stage. This clever piece of technology manages to expel stale air and bring in fresh air from outside without any perceptible loss of heat energy within the home. An efficient heat exchanger collects the heat from the outgoing air which is used to warm up the incoming air.The HRV is controlled by a small electrical fan which delivers a minimum of one complete air change per hour. The rate can be increased to remove excess hot air, for example if your house party got out of hand. Of course, opening doors and windows can achieve the same end but would exceptional