The following FAQ comprises all the questions that we have been asked by people that are new to passive house. This FAQ is constantly expanding, with new questions added regularly. If you have a question that hasn't been answered, please send us a message via our contact page or call us on +353 (0) 404 25777. This FAQ is aimed at the general public and is therefore non-technical. Technical information on Passive House can be downloaded for free at the bottom of this page.

General Passive House Questions

If you do any internet searching on low energy housing you’ll come across multiple variations of terminology used which include the term ‘passive’ including ‘passive solar design’ and ‘passive stack ventilation’. When MosArt uses the term Passive House, we refer strictly to the standards and definitions set out by the Passivhaus Institut in Germany, including maximum space heating demand of 15kWh/m2/year, an airtightness level of 0.6 air changes per hour measured at 50 Pascal and a maximum primary energy use of 120 kWh/m2/year. Take care not to be confused by different terms – they clearly can have very different meanings.
Yes. Did you know that you can build apartment buildings, office blocks, schools, shops, factories, churches and even fire-stations (in other words, pretty much anything) to the Passive House standard?
Great, Fantastic. A Passive House will provide a long-life, low maintenance, light-filled and whole-house high comfort with extraordinary low heating bills and excellent indoor air quality. Plus, you can feel very proud of yourself for dramatically reducing your carbon footprint. ‘Inwardly satisfied’ probably best sums it up!
In short, it makes no sense not to. In the next 2 to 5 years, it is the ambition of the European Parliament that the Passive House would become the base standard of construction across the EU. Ireland is aiming to build to ‘Carbon-Neutral’ standards (yet to be defined precisely) by 2013, and that’s not too far away in terms of designing, planning and building a house. Our advice would be to think in the longer term about how energy efficient your project should be and, above all, don’t build a ‘dinosaur’ that will shortly be out of date regarding building standards.
Yes, of course. It is essential, however, that the house has been properly designed in PHPP and then well-executed on-site achieving the required levels of airtightness and low thermal bridging. There are over 15,000 Passive House’s throughout Europe, providing very high levels of comfort in climates that are much colder than that of Ireland.
Yes, of course you can. Even though a Passive House must be built to a high level of air-tightness, you can, if you wish, leave windows open whenever you want. People usually open windows in their homes to let fresh air in. You won’t feel the same need in a Passive House because the whole house is afforded with an abundance of fresh air 24/7 by the heat recovery ventilation system. Be aware that if you do leave windows or doors open in a Passive House during the heating season, then you will use more energy to keep the house warm, just as you would in a normal house. In the summer time, you can leave all the doors and windows open all day and all night if you wish – just as you might in a normal house.
Difficult to say, but achieving the required level of airtightness is probably the most challenging aspect. So often it can happen that there is insufficient thought given to sealing difficult junctions or around service pipes. Ensure that all members of the construction team are fully aware of the need to achieve an airtight construction. Otherwise, inevitably the plumbing or electrical installers will innocently tear through membranes to fit their services. It is typically much easier to achieve the required level of airtightness when using a system-builder (whether concrete or timber frame), where most of the construction (including fitting and sealing of windows) is carried out in a controlled factory environment. Building a passive house using direct-labour is a risky option, as it gives huge room for error given that there is no single person or contractor responsible for the overall performance of the project.
This is project dependent. However, what will surprise many people is that a Passive House would not necessarily achieve an A1 or even A2 rating. Achieving such a high rating would typically require the use of renewable energy technologies for generation of electrical energy, whether by wind turbine or photovoltaic panels. Such renewable technologies are not necessarily or even typically found on Passive Houses. Remember this, a Passive House is really superb at saving energy for heating, but otherwise is quite similar to normal houses in terms of energy use for lighting, pumps, household appliances and the likes. It is not, therefore, to be considered a ‘zero-carbon’ house.
Yes. SEI have recently launched (February 2009) ‘Guidelines for Upgrading Existing Dwellings in Ireland to the Passivhaus Standard’. A copy of these guidelines, which were co-drafted by MosArt, can be downloaded below.
Yes. It is indeed possible to build even better insulated houses than the Passive Houses standard, but it has been well proven that the cost of this is not economic in most instances (the law of diminishing returns applies). If renewable technologies such as a wind turbine and / or photovoltaic cells are used to generate electricity, then it is possible to have a ‘net-zero carbon’ home (where the amount of energy that you consume per year is equal to (or less than) the amount of energy that you produce on-site).
Yes. In order to achieve the Passive House standard, it is vital that the building design is tested and verified using the specialist PHPP software. At present there are relatively few consultants providing dedicated full passive house services in Ireland (MosArt being the first of these as far back as 2003).

Passive House Design & Construction

No. There might be an impression that Passive House’s have to be perfect cubes with no windows on the northern side, but this is not the case. It is best (most efficient and cheapest to construct) to create a compact shape (two storey is more efficient than a bungalow) with optimal solar gain, but the house designer should otherwise be free to create any bespoke design according to the Client’s needs. It is important that the Passive House concept can be adapted to local cultures, styles and building traditions.
Not necessarily. Sure enough, it is ideal to have south facing windows to harvest the free energy provided by that great big furnace in the sky. However, it is also possible to achieve the Passive House standard if your site does not lend itself to maximising solar gain (but you will probably have to compensate for this with additional insulation). All designs have to be tested and verified in the Passive House Planning Package (PHPP) software. If you have a wonderful view from the northern side of your house, you needn’t deny yourself of this. The Passive House is not so strict as many people think.
No, generally not. Of course, it is ideal to be able to design the building to face south, and to avoid over-shadowing by coniferous trees or buildings. However, if these conditions do not exist on your site, then don’t worry. Allowances can be made, and tested in the PHPP software, for any shortfall in terms of ideal orientation leading to reduced solar gain.
There are no strict rules in this regard. The critical issue is to achieve the U-values (thermal performance) required as identified by the PHPP. Thereafter, you can use whichever insulation type you prefer or can afford, whether polystyrene, cellulose, polyisocyuranate, strawbale, sheep wool and so forth. Some insulation types are better performing than others, requiring thinner walls, whereas other are less efficient and will require thicker walls.
Surprising to most people, but the answer is No – not necessarily. Many people incorrectly assume that having a lot of concrete (walls and floors) in a Passive House is essential to keep the house warm. They intuitively appreciate that these surfaces absorb heat from the sun during the day and then radiate this heat out at night. While this does indeed take place to some degree, it is not as beneficial (or indeed as necessary) as most people assume. Be aware that a concrete built house will generally have a slower response time (both in terms of heating up as well as cooling down) compared to a timber frame house.
Generally, yes. A passive house needs a lot more insulation than a typical house, and this is generally achieved by having significantly thicker walls. The thickness of walls depends on the U-values required which in turn is greatly dependant on the performance of the insulation, the type of construction (whether concrete or timber frame), overall design, orientation, compactness and so forth. You generally won’t notice the thick walls from the outside of the house, however, as the windows are placed in the insulation layer which is best placed towards the exterior of the building shell.
The safest answer to give here is Yes. All Passive House’s must be designed and tested using the specialist software PHPP and you might find, on occasion, that it is possible to use very high performance double glazing in some instances (though not necessarily throughout the entire house). If you do use double glazing, however, be aware that you will probably experience some thermal discomfort on cold winter nights whilst sitting close to such windows due to the temperature difference that will inevitably arise between the internal surface of the glass and the surrounding living space. Be aware that Passive House windows will take in more energy over the year than they let out (think about that for a moment ...), whereas the same cannot be said for even very high performing double-glazed windows. Lastly, did you know that double-glazed windows have been banned in Sweden since 1985?
Yes, you can, but take care that you don’t fall short of imminent building standards to be introduced to Ireland. Some people find themselves reluctant to go for the ‘full’ Passive House option expressing a preference for what might be referred to as ‘near passive’. This is to be expected for some people who might be reluctant to consider something as new to Ireland as the Passive House standard, requiring air-tightness, triple-glazing, super-insulation, heat recovery ventilation and so forth. In principle, if people have their minds made up against Passive House standard (or indeed feel they can’t afford this standard), then there is little that can be done to convince them otherwise. It is important to think of the following, however. The DoE have decided that all new residential construction must be built to a carbon neutral standard by 2013 – that’s just four years away. Building a Passive House is perhaps the most economical method of achieving this standard, coupled with renewable energy technologies (such as a wind turbine or photo-voltaic panels). It makes little sense to knowingly build to a standard which will soon be outdated, likely adversely affecting property value in the future. Furthermore, if you build a ‘low energy’ house or ‘near-passive’, you will still need to install a heating system that is capable of providing good comfort in the worst possible weather (even if this lasts only a short period in the winter). This means that you will need a much larger heating system than you would if you build a Passive House, most likely requiring additional investment for that system. Further, energy prices are set to increase in the future, perhaps offsetting any saving that you might make in not building to the Passive House standard. In the end, making any improvements to a building in terms of energy efficiency will prove worthwhile and we recommend pushing your budget as far as you can to reduce your energy costs in the future.

Passive House Back-up Heating

Yes. Sometimes you will find definitions of a Passive House as a building that doesn’t need any heating, but that is simply not true. You need what is referred to as a ‘back-up’ heating system, which is tiny in comparison to that required for a conventional house.
Typically any additional heating required is delivered using the mechanical ventilation system. The air passing around the house can be heated using a variety or combination of means whether electrical-based (such as with a heat pump) or using a pellet-boiler and / or solar panels. It is not usual to find (or indeed need) radiators or underfloor heating in a Passive House. If you really would like such systems, then of course they can be used. Be aware that in doing so, you are ‘doubling up’ the amount of services in your house, which will, in turn, increase the cost of construction.
Yes. A passive house is designed to deliver 20 degrees Celsius throughout the entire dwelling right throughout the heating season while using the minimum amount of energy. If you are a ‘hot house flower’ and prefer on occasion to have warmer temperatures, then your system should be designed so that you can ‘turn up the heat’, typically controlled using a conventional room thermostat. It’s your house, and you choose what temperature you like. It will often happen in a passive house that the temperatures upstairs will be slightly cooler (perhaps one degree C, for example) than downstairs. This can be as a result of the greater activity downstairs during the day (cooking, watching TV, lounging) compared to upstairs. Most people find this slight difference quite welcome, finding it more comfortable to sleep. You can if you wish design your Passive House to deliver specific pre-determined temperatures in different rooms, but this will probably require a more complex system and increase your costs. In the MosArt Out of the Blue house it has often been necessary to cool the house in winter for example at Christmas when there might be several guests visiting. There’s a really high tech solution to this problem, open the window!
Sorry, but the answer in this case is No. Having an open fireplace would dramatically reduce the efficiency of the mechanical heat recovery ventilation system (due to lack of airtightness). Furthermore, the open fireplace would introduce major drafts to the house as well lead to huge heat losses. However, there are other really clever means of having a real flame effect in your Passive House, including bio-ethanol fires as well as wood burning boilers or stoves with glass fronts. By the way, if you have young children in the house, please reassure them that Santa Claus knows the Passive House standard very well and he uses the ventilation system and some magic dust to bring the gifts into the house.
Yes, but only marginally and nothing as dramatic as with a normal house. Due to the high levels of insulation and draft-proofing in a Passive House, the heat loss in such a situation will be minimal (perhaps 2 to 3 degrees Celsius depending on duration and weather).

Passive House Ventilation System

Yes, but it makes no sense to do this. Let us explain. If you ventilate the house ‘naturally’, then you can only recover at best a relatively low proportion of the heat being lost from expelled air (40% heat recovery when ventilating naturally, compared with 85%+ with mechanical ventilation with heat recovery). Using what is referred to as a passive stack ventilation system will operate best when there is a substantial difference between indoor and outdoor temperature – this condition might not occur at certain times of the year, especially in the summer and thus you cannot be certain of achieving sufficient air exchange rates at all times in all rooms. Remember too that the ducting system used in the ventilation is used not only to transport fresh air around the house, but also to convey the back-up heating required. If you do not put in a mechanical ventilation system, you will probably have to install a conventional heating system (such as under-floor heating or radiators) incurring cost which might have paid for the ducting in the first place. Lastly, it has been well proven that ventilation systems are extremely efficient, provide a controlled ventilation rate throughout the house and ensure clean air through the use of filters.
No, because the house is provided with lots of fresh air using a ventilation system. One of the main benefits of building a Passive House is the high air quality. In normal houses, fresh air enters the building though a series of ‘hole-in-the-wall’ vents and / or through drafts. However, such means of ventilating are uncontrolled and you cannot be sure that all rooms at all times are being properly or sufficiently ventilated. The entire volume of air in a Passive House is changed on average between 8 to 12 times per day (depending on the setting of the system) ensuring very high air quality throughout.
Surprisingly, No. The air is delivered and extracted using two fans which use very little electrical power. As a rule of thumb, for an average house, the system would use a similar amount of energy as a 50 Watt bulb costing approximately €75 per year. Please note, that a highly efficient Passive House ventilation system should recover approximately five units of heating energy for every unit of electrical energy invested. Thus, the system might cost you €75 to operate per year, but could save you €375 per year in heating bills. If you are not happy using electrical energy to operate such a system, then you can use some means of generating your own power on-site such as with a wind turbine or using photo-voltaic panels. This will, however, significantly increase the cost of your project.
No. The ventilation system itself is housed in a very well insulated and airtight cabinet which is normally positioned in a utility room. The noise from the fans is no greater than that from a modern fridge. The ducting is fitted with what are referred to as ‘attenuators’ which reduce the sound of air passing through the system. In bedrooms the system, if properly fitted, will barely be audible at normal flow rates.
Similar to normal houses, all mechanical systems will cease to work. However, because Passive House’s are so well insulated, they will maintain a higher level of comfort for much longer than would a normal house in the event of a power failure. If the power cut lasts for a prolonged period (say, more than 12 hours), then the windows can be opened to provide fresh air if required. Power has been cut off to MosArt’s demonstration Passive House several times over the past few years (due to grid works in the neighbourhood) and this has never caused any inconvenience or discomfort. Carbon monoxide alarms can be fitted in the house to detect reduced air quality.
Yes, but it is more prudent not to do so. The benefit of connecting the extractor in the kitchen to the ventilation system is that you can use the heat generated in the process of cooking to warm the incoming fresh air. However, if you choose to do this, then there must be special filters on the end of the ducting eliminating any fat or grease getting into the ducts which would create both a health hazard and a fire risk. Furthermore, it must be possible to access the ducting located immediately above the extractor hood for occasional cleaning and / or replacement. It is safer to use a re-circulating extractor (not connected to the outside) with a charcoal filter, with the ventilation system extract located in the kitchen space but not close to the hob. Note: kitchen extractor hoods in a centralised ventilation system (as might arise in an apartment complex, for example) should never be connected to the mechanical heat recovery ventilation ducting due to risk of fire spread.

Passive House Costs & Savings

The cost of building a passive house would typically be greater than that of a conventional house – you wouldn’t expect it to be otherwise. The extra-over cost compared to conventional build is impossible to generalise and will depend greatly upon design, size of project, quality of finishes and so forth. The extra cost is, however, likely to be in the region of 10% to 15% (MosArt’s Out of the Blue demonstration home was 8% higher than conventional). With increasing energy prices, the question to ask yourself is ‘Can I afford not to build a Passive House’! Furthermore, with carbon-neutral housing due to be introduced to Ireland as soon as 2013, you need to consider adverse effects on the value of your property if you do not build to the highest possible standard. If you can’t afford to pay an extra 10% for construction costs, you could always reduce the size of your house by 10% to still come in on budget.
This will greatly depend on house size and fuel used. However, we can give you some rule of thumb here. Heating and hot-water costs should be in the region of €0.15 (15 Euro cent) per square metre per year. So, for a 200m2 house (2,200 square feet) heating and hot water costs (using bulk-delivered pellets) should be in the region of €300 per year. Please note that this example is provided for illustration purposes only. Cost of heating will depend on energy efficiency of heating system, heating method used and space heating requirement of your project.
No. There are, however, a series of grants currently available from SEI for various energy saving initiatives and details of these can be found at . While none of these pertain specifically to Passive Houses, the Low Carbon Homes scheme might provide some opportunity for grant-aid.


Passive House Intro

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Passive House FAQ

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Guidelines & Specs

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