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MYTHS ABOUT PASSIVE HOUSE

This blog will be slightly different from any that we’ve wrote in the past. There are multiple misconceptions that PassiveHouse builders and designers will hear almost everyday, and today we decided to discuss what these are:

 

1. A Passive House Heats Itself – MYTH

 

This is not factually correct, because nothing heats itself. A Passive House needs to get the heat from somewhere, but a Passive House building retains the heat .

 

2. You Can’t Open the Windows in a Passive House – MYTH

 

This may be easy to buy into but in a Passive House there is nothing to stop you from opening the windows. It really depends on the time of the year and what you want as to whether you open the windows. In summer  it is likely that the mechanical ventilation would not be running anyway, so natural ventilation would be important and that means opening the windows. In winter there’s probably no need to open the windows because there’s enough fresh air and it doesn’t feel stale or stuffy. In a traditional buildings that’s why people tend to open the windows in winter because its stuffy, which is essentially the CO2 levels getting a bit high, whereas in a Passive House there’s constant ventilation in the background and there just would not be the need.

 

3. The Aesthetics of a Passive House are Not Good – MYTH

 

Many of the first buildings to meet the Passive House standard were located in Germany and Austria, and so had a continental aesthetic. As these buildings attracted a lot of publicity it is no great surprise that there is the perception that a Passive House will look a particular way. Also, many of the initial attempts at doing Passive House may have mimicked these buildings as designers were grappling with a new challenge.

 

4. A Passive House Must be Built with Sustainable Materials – MYTH

 

This one is interesting because he hears the other argument, that Passive House doesn’t put enough emphasis on encouraging use of natural materials. At Architype they have always had an interest in using healthy materials that don’t emit noxious fumes, so that there is no knock-on impact with occupants suffering from conditions such as asthma.

The choice of which materials to use in a Passive House will normally be determined by the designer or client’s preference. When it comes to insulation there are also complexities in balancing how much carbon might be involved in the materials, for example using polystyrene, and how much carbon is being saved due to the energy saving attributed to a good insulating material.

 

5. Building a Passive House is Too Expensive – IT DEPENDS

 

There’s quite a lot of published data which shows that Passive House buildings can cost more than non Passive House buildings. However, when designing a Passive House building it’s a quality assurance standard, so what gets built has to match what gets designed and it has to meet the appropriate standard of workmanship on site with the finishes, etc. Thus, comparing that with a building that only reaches standard building regulations, there’s very little quality assurance that a finished building matches what was designed at the outset. This means there is an issue of comparing like for like, because if that building was constructed exactly as it was designed it would probably cost slightly more than it did.

Another factor that increases cost is when existing plans are adapted to go down the Passive House route, which of course will add extra cost. The best way to approach Passive House is to have it as an objective from the very beginning. Take the budget and prioritise how the money will be spent. For example, in order to meet the standard there will need to be triple glazed windows, etc. This way, once the essentials have been priced up, there will be an amount of money with which to work. The building may need to take on a simple but elegant form but it will allow the overall budget to be balanced.

 

6. The Air is Too Dry in a Passive House – IT DEPENDS

 

This issue is more complex than it might seem on the surface. For an in-depth answer he suggests reading a paper on Passivhaus ventilation that Mark Siddall wrote for the AECB. However, most occupants are used to living in buildings that don’t perform very well and perhaps have more moisture than would be ideal (which may lead to environments that encourage mould growth and in turn can cause occupant respiratory difficulties such as asthma). In buildings which are built right – high levels of insulation, airtight, well ventilated, etc. – the humidity will definitely be lower in certain circumstances than traditionally constructed buildings. That’s not necessarily a bad thing because a drier building will tend to be a healthier building. If things are not balanced properly or something is not quite right, then it may feel slightly drier than is comfortable.

 

7. MVHR is Too Noisy – IT DEPENDS

 

Careful design and installation should mean that noise from MVHR is not an issue. In a Passive House building the MVHR should be in a separate area (like plant room or cupboard) but it can even be outside the building (providing good acoustic separation).

The Passive House standard also requires that background noise from MVHR should not be greater than the World Health Organization recommended noise levels for people to sleep comfortably. It’s also worth noting that the fans are running at an incredibly low speed so there should be very little noise coming from them.

Where there might be the possibility of sound travelling through the ducts from one room to another, there needs to be acoustic attenuation built in, which will eliminate the problem.

 

8. MVHR Costs More to Run Than the Energy it Saves – MYTH

 

Clearly when you move from a house without MVHR to one that does have MVHR, there is a new cost to pay. However, as discussed earlier, it is often difficult to compare like for like between a.Passive House and a non Passive House.

But, so long as the airtightness of the building reaches a certain level (approximately 1.5 air changes per hour), it’s been proven that the amount of energy saved and the cost of that energy saving is much greater than the cost of running the MVHR.

 

9. Mechanical Ventilation Has to be Running All the Time in a Passive House – MYTH

 

This one down by saying that at Architype they design their buildings to use natural ventilation in the summer and MVHR just for the winter months.

It should be easy to tell when to switch off the MVHR. When opening the window, if it feels dramatically colder outside than indoors then a lot of heat energy is being lost and there’s also a cold draught coming in. This would be when you would want the MVHR to be on. Alternatively, when opening the window if the fresh air coming in feels comfortable and there’s no cold draught, then probably you don’t need to have the MVHR running.

 

10. Mechanical Ventilation is Too Complicated to Use – MYTH

 

This is a myth because the controls are simple to understand with a small amount of training. Most people can operate a boiler, switching off the heating for the summer, for example. Mechanical ventilation is no more taxing.

 

11. You Can’t Have a Wood-burner in a Passive House – MYTH

 

This is more a case of there’s no need to have a wood-burner in a Passive House. People often desire them for emotive reasons because it’s nice to sit around a fire or to feel heat emanating from something.

Having a wood-burner in a Passive House is generally discouraged for a couple of reasons:

  • It would only be used for a very short time of the year
  • A lot of heat will be generated and that heat will be retained

 

12. Passive House Will Only Work on a Sunny Site – IT DEPENDS

 

Passive House does optimize the solar gain so as to make the most useful benefit of the heat from the sun. With a small building on a site that gets little sunlight it would be more of a challenge and would really have to be addressed on a specific case by case basis as to whether it was viable or not. As a building gets bigger the parameters change slightly. Architype’s schools as an example. Having more people in a building means there’s more heat energy being generated and so there’s less of a need for using heat from the sun.

 

interview with Elrond Burrell

done by  House Planning Help