Passive House Design

Air tightness

The insulation that is put into a building is useless if the building is full of drafts and leaks. Therefore air-tightness is extremely important and should be measured by a door blower test during construction. This will establish where the air leaks are and give a chance to remedy them before the building is completed. Many people are concerned about an air-tight building being stuffy or even suffocating. Thankfully the Passivhaus Institute has huge experience and has inspired a generation of whole house ventilation systems that both reduce energy loss and improve air quality. Heat Recovery Ventilation (HRV) systems are now readily available in Ireland, but it is important that your architect / designer knows how to select the correct unit, as they all have different qualities. A bonus of installing a HRV system is that you can be sure that the air quality is optimised and not affected by erratic weather changes, like wall vents are. This in the majority of cases will give a superior air quality to that found in most newly built houses.

Insulation

Ireland has a relatively mild climate, thanks to its maritime location and the Gulf Stream. Rain and precipitation should not be confused with coldness. It is true that Ireland receives a lot of rain, but it does not have that many frozen days, relative to eastern / northern Europe. This makes Ireland perfect for building passive houses and they are therefore relatively cheap to build. A passive house in Ireland basically needs a U-Value of 0.15Wm²/k for walls, roofs and floors, which amounts to about 330mm of insulation in roofs, 280mm in walls and 150mm in the floors.

Thermal bridging

High levels of insulation can be used in the walls, roof and floors, but if at every junction there is a gap with insulation missing it will lead to substantial heat loss over the area of the building. The only way to ensure minimal thermal bridging is to have the building correctly designed and detailed, and for this it is imperative that a skilled architect / designer is employed. Many companies offer thermal imaging studies of buildings, but these will only see the problems after the building is built. Remedying problems is difficult and expensive; therefore it is much more sensible to avoid the problems in the first place by using correct detailing.

Orientation

As solar gains are an important addition to heating a house, it is important that the house and windows are designed to take full advantage of direct sunlight. Basically, the majority of glazing should be on the south and east with the absolute minimum on the north. It is also useful to put service rooms like the utility and bathrooms on the north, where they do not need such large windows. Another advantage of correct orientation is that the house will be full of natural sunlight and feel bright and spacious.

Simple Form

The main aim here is to minimise the external building envelope because the high levels of insulation in external walls make them much more expensive to build. Basically a sphere is the most efficient shape, but this would be impracticable to build, so the next best is a cube. Having said this, it is not always the best shape for other reasons, like maximising the southern elevation or getting natural light into the centre of the house.

A few words on other terms:

The buzz word at the moment is “A1 rated”, which is the highest rating that can be achieved as part of the Irish building energy rating (BER). Although this system is definitely a move in the right direction, we have a few concerns with it.

1. Firstly the software used (DEAP) is based on the UK’s building energy rating software (SAP), which is now known to be flawed and is due a substantial upgrade. Therefore the Irish software is flawed, and as things take time it will be a while before the DEAP software is upgraded.
2. Second is that its primary goal is to reduce carbon dioxide emissions and not reduce energy consumed by the building, so potentially a poorly insulated building can achieve a higher rating by installing a large source of renewable energy. This is fine; apart from the fact that it means your building will cost more to run and this energy would be far better utilized serving other purposes such as the domestic electrical need. Also small scale renewable energy installations are not as efficient as larger ones.
3. The building energy rating and associated software cannot be relied on to assess the finished comfort of the building. Whereas with the PHPP passive house software it aims to achieve a comfort level in the building, summer or winter, day or night. This makes it a very valuable design tool.

Whether it is chosen to use the Pasiv Haus software or the BER software, the above points are relevant. In both cases it is imperative that you have some form of quality control onsite, because making it work in a piece of software is good, but if it does not happen in reality you will either be cold or pay more for fuel. Quality control could be by an educated builder or architect. Because the builder also stands to make profit by cutting back on elements (no matter how good he is), it is highly recommended to have an impartial advisor involved i.e. an experienced architect.

Other terms that are often thrown about are “zero energy” building or “zero carbon” buildings, depending on what side of the Atlantic you reside. Again they focus on reducing carbon emissions with solutions that supplement energy need with renewable energies rather than simply reducing the need in the first place.

While all of these terms are generally a move in the right direction, it is important that you understand them fully before you apply them to your building.

Some links to help you further understand Passive House design:
www.passiv.de
www.passivhaus.uk