Passive House Frequently Asked Questions
The following list of FAQs are those most often posed about Passive Houses. This will be expanded as more issues are raised concerning Passive Houses. Please note that the discussion below is aimed mostly at the general public and is therefore non-technical. All Passive House’s must be designed and tested in the specialist Passive House Planning Package Software by experienced Passive House experts.
Q: What is it like to live in a Passive House?
A: 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 smug’ probably best sums it up!
Q: Why should I bother building a Passive House?
A: In short, it makes no sense not to. In the next 2 to 5 years, it is hoped by 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 you project should be and, above all, don’t build a ‘dinosaur’.
Q: Can I be sure that my Passive House will ‘work’?
A: Yes, of course. It is essential, however, that the house has been properly designed in Passive HousePP and then well-executed on-site achieving the required levels of airtightness and low thermal bridging. There are over 20,000 Passive House’s throughout Europe, providing very high levels of comfort in climates that are much colder than Ireland.
Q: Does a Passive House need a heating system?
A: 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.
Q: What kind of heating system is typically used in a Passive House?
A: 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’ in the amount of services in your house which will increase the cost of construction.
Q: Do I have to have lots of south facing windows for the Passive House to work?
A: 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 HousePP 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.
Q: Does a Passive House have to follow a strict design style?
A: 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.
Q: Do you need a special site type if considering building a Passive House?
A: 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 Passive HousePP software, for any lack of ideal orientation or lack of direct solar gain.
Q: What constitutes a Passive House?
A: 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’, ‘passive stack ventilation’ and more besides). When we speak of 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.
Q: Can you achieve the Passive House standard for buildings other than just houses?
A: 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?
Q: What is the best insulation to use for a Passive House?
A: There are no strict rules in this regard. The critical issue is to achieve the U-values (thermal performance) required as identified by the Passive HousePP. 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.
Q: Does a concrete house (with high thermal mass) make it easier to achieve a Passive House?
A: Surprising to most people, but the answer is No. 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 imagine 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.
Q: Does a passive house have to have thick walls?
A: 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.
Q: Is it necessary to have triple glazed windows in a Passive House in Ireland?
A: The safest answer to give here is Yes. All Passive Houses must be designed and tested using the specialist software Passive HousePP 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 may experience some thermal discomfort on cold winter nights whilst sitting close to such windows due to the temperature difference that will inevitably arise. Be aware that Passive House windows will take in more energy over the year than they let out, whereas the same cannot be said for even very high performing double-glazed windows.
Q: Can you open the windows in a Passive House?
A: 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 drenched with 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.
Q: What is the most challenging aspect of building a Passive House?
A: 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, it will inevitably happen that 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 made in a factory environment. Building a passive house using direct-labour is a risky option in our opinion, with huge room for error given that there is no single person or contractor responsible for the overall performance of the project.
Q: Can I control the temperature in my Passive House?
A: 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 Wicklow 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!
Q: Is it unhealthy to live in an ‘air-tight’ house?
A: 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.
Q: Doesn’t the ventilation system use a lot of energy?
A: 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 €50 per year. Please note, however, that a highly efficient Passive House ventilation system should recover more than five units of heating energy for every unit of electrical energy invested. Taking the above case, the system might cost you €50 to operate per year, but should save you at least €250 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.
Q: Is the ventilation system noisy?
A: 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 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.
Q: What happens if there is a power-cut?
A: 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, then the windows can be opened to provide fresh air if required. Power has been cut off to the Wicklow 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.
Q: Can I connect the kitchen extractor to the ventilation system?
A: No, you should not do that due to the risk of fat or grease getting into the ducts which could create both a health hazard as well as fire risk. It is better to use a re-circulating extractor (not connected to the outside) with a charcoal filter overhead the cooker.
Q: What kind of maintenance is required in a Passive House?
A: The most important issue is to regularly replace the filters on the fresh-air ventilation system. These will have to be replaced or cleaned (depending on the type of system used) typically every nine months to one year. The back-up heating system will also need servicing depending on the system used, no different to a normal house. Otherwise, the philosophy of a Passive House is that it is a simple construction system that requires little specialist skills in operation or maintenance.
Q: Can I avoid using a Mechanical Ventilation System?
A: 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.
Q: Can I have an open fireplace in a Passive House?
A: Sorry, but the answer in this case is No. Having an open fireplace would render the mechanical heat recovery ventilation system useless (due to lack of airtightness). Furthermore, the open fireplace would introduce major drafts to the house as well lead to huge heat losses. 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.
Q: Will the house cool down if it is unoccupied and ‘unheated’ for a period in the winter?
A: Yes, but only marginally and nothing as dramatic as 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 degrees Celsius depending on duration of absence and weather).
Q: How much does a Passive House cost to build?
A: The cost of building a passive house would typically be greater than that for a conventional house – you wouldn’t expect it to be otherwise. The extra-over cost compared to conventional build is impossible to generalize and will depend greatly upon design, size of project, quality of finishes and so forth. Extra cost is, however, likely to be in the region of 5% to 15% but should be re-couped within approximately 7 to 10 years arising from savings on heating bills. 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.
Q: How much should it cost to heat my passive house for a year?
A: This will greatly depend on house size and fuel used. However, we can give you some rule of thumb here. The maximum allowable space heating requirement is 15 kWh/m2/year. So, for a 150m2 house (1,600 square feet), this would amount to 1,650 kWh per year. Taking the current cost of delivered energy from wood pellets (bulk delivered), the heating costs for a house of this size would be in the region of €100 for a full year.
Q: Can I build a ‘Near-Passive’ house?
A: 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. 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.
Q: Are there any special grants available for building Passive House’s?
A: No. There are a series of grants currently available from SEI for various energy saving initiatives and details of these can be found at http://www.sei.ie/grants/ . None of these pertain specifically to Passive Houses.
Q: What Building Energy Rating would a Passive House typically achieve?
A: This is project dependent. However, what will surprise many people is that a Passive House would not automatically 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.
Q: Can an existing building be upgraded to the Passive House Standard?
A: Yes. SEI launched (February 2009) ‘Guidelines for Upgrading Existing Dwellings in Ireland to the Passivhaus Standard’. A copy of these guidelines which were drafted by MosArt can be downloaded here.
Q: Is it possible to surpass the Passive House Standard?
A: 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).
Q: Do I need professional assistance to achieve a Passive House:
A: Yes. In order to achieve the Passive House standard, it is vital that the building design is tested and verified using the specialist software Passive House Planning Package. There are now many Certified Passive House Consultants in Ireland that can help in this process (click on this link to get their details).