Passive houses for active people

Highly economical passive houses are buildings of the future, which will, most probably, even in a decade still be a novelty to the housing market and the demand for them will only grow.

 

A passive house instead of a three-room apartment

Kārlis is a future passive house owner in the Imanta district in Rīga. Kārlis has walked a long road towards building a house, and what is more – a passive one. The idea for building such a house was born even before the major economic crisis of 2008. An addition to the family being on the way, they had the need for a bigger living space. Back then, in the summer of 2008, however, the undecorated 80 m². 3-room flat cost Kārlis’ family more than 115 000 €.

"It seemed to me that such a price for an apartment is simply unreasonable. Back then, it was possible to build a house of twice the dwelling space for a similar amount of money, excluding buying the plot itself. However, at that time, I saw one major flaw in owning a house – the very expensive heating. Some of my friends and acquaintances who owned a house were spending almost 300 € a month or more on heating. Therefore, I started looking for ways to construct a much warmer building. So, in early 2009 I discovered the passive houses”, the owner tells about his choice.

Like many other Latvians who reject everything that is new, at first Kārlis felt suspicious about the idea behind the passive houses. It seemed to him that the thicker than usual thermal insulation layers, impermeable quality of the building, ventilation ductwork system and it having no fire-place seemed to him quite an absurd project that would be difficult and expensive to implement. However, after months of researching the forums in the depths of the internet, his views changed.

“I decided that if I opt for designing and building a house after all, then the passive house will be my only choice. However, back in the day, there were close to no certified experts of the passive houses in Latvia and the ones that could be found charged nearly 10,000 € per project. Luckily, I met the right people on the internet who helped me make my dream come true.”

 

The more you eat, the hungrier you get

An architect was recruited for designing the project of the small house, and a designer did the calculations with the PHPP (Passive House Planning Package) software. So, in autumn of 2012 the first ideas were conceived.

Based on the experience of the first passive houses built in Latvia, the owner felt that it will be enough to lay the floor in 30-35 cm of foam, put a 30 cm thick layer of Neopor on the walls and stuff the roof with a wadding layer up to 40-45 cm in his quite warm and economical future house.

 

 

“It turns out that I was quite wrong. After entering the data into the PHPP software the results showed that the amount of energy needed for heating the building would be 30 kWh/m². In addition, the situation was made worse by the fact that the house was being built on a plot of modest 6 acres, due to the placement of which the sun heat was partially “eaten up” by the neighboring houses to its east and south.

The neighbouring building on the top of the adjoining hill obscured about 23% of the solar heat that the house should get per year. Even though there is no neighbor to the south of the house, when modelling a simple worst case scenario simulation, the PHPP software indicated that if such a neighbor were to appear, it might consume up to 29% of the solar heat. It is quite disappointing but you can’t really escape the circumstances”, Kārlis recalls the results drawn by the designers, as well as his short-lived disappointment.

The same way, while doing the initial calculations it was not taken into account that the small plot is not perfectly facing south. But after doing the needed corrections, it turned out that the amount of energy needed for the house had gone down to 21 kWh/m². To continue reducing the energy consumption of the house and striving for the passive house standard was quite difficult, but the goal was achieved in the end.

 

Foundation – the weak point of the house

Kārlis’ home was supposed to be built on the flat foundation that is so commonly used in building the passive houses, but he had to change his plans and opt for the bored piles instead. This decision was made due to the unfavorable geological placement conditions of the building.

"The geological tests done by removing 40 cm of soil from the area where the foundation of the house was marked, showed that in one corner of the plot soil of the required strength could be reached, while on the other side of the plot it would be necessary to dig more than 2.5 m deep. Moreover, sand had been compacted onto the whole plot without removing the soil beforehand meaning that sooner or later this layer of soil might start rotting. For that reason, in order to lay a flat foundation we would have had to dig approximately 3 m deep pit, pour and compact many layers of sand. It would have been very expensive. In short, due to the additional excavation, the flat foundation would have cost me much more, yet I was worried to take the risk and build the house on unsteady ground.

 

Inexpert constructors – a stab in the back when building the passive house

According to Kārlis, designing the passive house is not only easy but pleasant as well. However, the fun ends when the building process begins. Possibly one of the biggest troubles are building defects. You see, oftentimes constructors are used to building just the way they are used to and  the fact that the passive house requires a very careful and precise work, can be a big surprise to them.

The owner of the house learned his lesson the hard way when going away on a week-long holiday, he left the construction team of the hired company to insulate the foundation of the house unsupervised. Once returned, he realized that the construction team had done their work so poorly that it all ended in a swift and even rather unfriendly break-up. Luckily, the damage was averted, moreover, very accurately.

“I’m glad I decided to have an additional layer of insulation on the poles. Having unearthed the foundation, I saw that it was done by an ignoramus. The foam was placed unevenly. Not only we had it all corrected, also we additionally insulated the poles up to 1 m deep from the surface. Of course, we did not manage to completely avoid heat loss through the poles, but we reduced the loss there to a minimum. Still, the biggest overall drawback that my house has is its foundation," the owner admits.

 

A proper roof – extremely sturdy and warm

If there are no special plans for the walls of the house, they can be built from any construction supplies, the most important thing is to properly insulate them. The roof, on the other hand, is not quite as easy. To properly insulate the roof, as in this case, a layer of as much as 50 cm of thermal insulation material is necessary, besides, simple rafters are not the best solution. You see, no company produces rafters of such dimensions as we imagine them. An additional massive frame is necessary for this purpose. However, in the case of this passive house, the frame does not seem clumsy, as IPE beams – an innovation in this market – have been used for the roof construction. They are 40 cm in height, so additionally only 10 cm will need to be hammered out. The main body of this type of beam consists of an OSB sheet pasted between two squared timbers. They stand out due to their remarkably better heat conduction properties compared to wood, as the thermal material surrounds almost the entire beam. Only a very narrow part of the wood remains uninsulated, which is an extremely important detail for the passive house, because wood alone creates a certain thermal bridge.

 

 

"Wood is not as warm as foam or wadding. Furthermore, such beams are lighter than regular rafters, yet are just as strong. Also, their pricing was similar. It impressed me that going with this option would mean a nearly monolithic factory construction used in the house as opposed to a frame assembled on the spot, " explained the owner feeling highly confident about his choice.

 

Other features of the house

Currently, Kārlis together with his family is picking the windows for their house. The market provides a wide choice, however, the owners would best like windows that have been certified by the Passive House Institute in Darmstadt, Germany. The family is considering the options for the facade of the house, as well, still not puzzling over it as much at the moment. The right roof covering has already been found – already tiles adorn the building like a crown and no more embellishments need to be sought after. Here! The exterior of this house will be dominated by plaster and several dozen square meters of clinker tiles.

It also has to be noted that the total dwelling space of the house is rather moderate – only 140 m².  Besides, that is by no means a coincidence, as according to the calculations of the Passive House Institute an optimal dwelling space per family member is 35 m².

 

 

"That is exactly how big a space we are building. We opted out of having a garage, instead we will have only an unheated shed for cars and also an outdoor pantry. In short, compared to our initial ambitious plan we have now managed to save about 100 m² of space which would have required heating. Consequently, it also saved us a significant amount of money, which we instead invested into thicker insulation materials for the house. So, in the result we have spent the same amount of money that we planned to”, says the homeowner who is very satisfied with the results.

The heating system is the biggest current headache for the household members. They estimate that heating will require approximately 2100 kWh of energy per year. If  the house were to be heated with electricity alone, they would not by any means manage to clear the passive house standard, thus a different solution has to be found.

The homeowners will most likely opt out of using gas heating which would mean connecting the plot to a gas main separately, as this option would cause another thermal bridge. They are considering using heat pumps for heating and hot water as they get energy from the air – it is the so-called “air-to-water" system. Another option would be going for a borehole or the so-called “water-water” system, commonly referred to as geothermal heating. The first mentioned system is more acceptable due to the lower installation costs – it would cost approximately 4–7 thousand €. However, the SPF (seasonal performance factor) ratio for heat pumps reaches only 2,5 points.

Such a ratio indicates that the heating system is ineffective when the outside air temperature drops below -15°C. On the other hand, going for a borehole would cost more –  around 7–10 thousand €, but the SPF ratio for the geothermal heating method is higher – about 3,5 points.

“All these calculations must be done very precisely. If any of the structures suffer heat loss, then it must be compensated in others. If a power source does not meet the needs, a different one must be found. What matters is that we have almost reached the goal in any case. The house will be really warm, stable and economical and, what is most important, it will serve us, not the other way around. After all, these days when everyone is so busy, after a full day at work not many of us will be keen on fiddling in the boiler room, doing repairs as minor as they might be and so on. We have other ways to spend the money we earn. It is not for me to continuously invest into the house,” says the owner, sharing his views on the benefits of building the passive house and the future advantages of living in one.

The technical solutions applied by the specialists that Kārlis hired are not the only ones that the passive house builders in Latvia currently apply: already heated air is supplied to the buildings via underground tunnels – pipes laid underground or the so-called ground heat exchanger. Other methods include solar collectors, multi-purpose blinds, sheds, and canopies that divert the solar rays, as well as other solutions. There are plenty of clever ways to achieve high energy efficiency. However, it is essential to consult people who have complete and thorough knowledge of construction and building of the passive houses from the very beginning, starting with selection of the plot.

Better health, favorable microclimate to live in, low utility bills and many more similar details that will no longer bother you – those are the gains of choosing to live in the passive house. Plus, noisy neighbors or lengthy power outages during winter will no longer be a problem – such problems will be solved by the constructional features of the passive house.

These are the requirements for Kārlis’ house, so that it can meet the Passive house standard, meaning get by with 15 kWh/m² worth of energy for its heating needs:

• the floors must be insulated with a foam layer of 40 cm (U – 0,091 W/m²K or R-10,99 m²K/W),

• 35 cm layer of Neopor is needed on the walls (U – 0,082 W/m²K or R-12,19 m²K/W), 

• the roof must contain a 50 cm layer of mineral wool (U – 0,074 W/m²K or R-13,51 m²K/W), 

• the air circulation of the house must not exceed 0.4 times per hour at 50 Pa pressure difference between the inside and outside,

• recuperation efficiency factor – no less than 93%,

• the thermal conductivity of the windows must not exceed 0.8 W/m²K,

• similarly, an extremely high level of imperviousness of the house surfaces is also to be achieved, with high-efficiency recuperation, the best windows and minimum amount of thermal bridges. 

NOTE. The PHPP software indicates that heating 1m² of the house will require 15kWh of energy per year. This is only a forecast, as in the standard calculations the temperature of 20°C is normally planned to be maintained in the house during the heating season. So, when going for a higher temperature, the amount of the needed energy will also increase. Additionally, heating costs may also be increased by such things as frequent opening and closing of the front doors, thus letting in cold air that also needs to be warmed up.

 

An architect’s commentary

The placement of the house that is being built for Kārlis is nearly perfect according to the cardinal directions. The decision-making when striving for the Passive house standards was strongly influenced by the location of the plot. It would have been remarkably more difficult and costly to do something similar in a house with its windows facing north. However, nothing is impossible.

 

What is the most difficult aspect of designing a passive house? What would you recommend for people who also want a house of such type? What should be considered?

A lot of valuable information can be found on the internet, in the media or obtained directly from builders but it is often undigested and for someone who is not a specialist of the field, in other words - a builder, these are only fragments which are difficult to put into a clear picture. A project manager should still be put at the steering wheel together with a team of respective specialists. The architect plays an especially important role, as well as such other key persons as the person responsible for doing the energy consumption calculations, the constructor and the heating and ventilation specialists. It is, of course, possible to surmise which is the technically best solution, however, it is the calculations that show the precise picture.

Speaking of the main principles of designing energy efficient and economical houses, the easiest way to implement such projects is on plots facing south where there are no objects casting shadow. It is also important not to forget shading the windows during the summer, as due to wide uncovered windows significantly increase the possibility of overheated rooms. In addition, it is better not to include the garage into the heated area of the house. It is recommended to build a two-storey building with as few corners as possible, as such a shape is easier to be heated. Plus, any possible thermal bridges should be avoided.

From the technical point of view, it is better to avoid ventilated facade finishing systems or mount them on fiberglass parts. A flat roof would be particularly suitable, but if opting for a pitched roof, the IPE beams will be the best option. They provide much better thermal performance results than using the ordinary wooden rafters. You need to be ready for buying considerably more expensive windows, as it is advisable to choose the most thermal-resistant option available. Similarly, a recuperative ventilation system is necessary. In addition, excessively thickened heat insulation layers are unnecessary. For example, a layer of walls thermal insulation materials can be only 30-35 cm. A thicker layer will not deliver a better effect.

However, all this is only a series of well-known technical details, which cannot be followed blindly. It is important to remember that the goal is not to create an effect of a very cost-effective thermos but rather a high quality of life in an efficient house. It is important to keep in mind the aesthetics, proportions, and landscape. If the plot is located near a river or a forest or it has a great view to the north, it must not be ignored. It is equally as important not to ignore the natural lighting indoors, the feeling of the space, no matter how tempting it may seem to decrease the size of the windows for the sake of additional savings in kilowatt-hours. The individuals are the highest priority because the house is being built for them.

It would be great if investors and block-planners paid more attention to arranging their projects in such a way as to minimize the areas covered by shadows on the south side of the plots. Demand for such plots is growing rapidly, too.

 

Is the designing price for passive houses significantly different from the currently more popular energy class B houses?

In order to achieve a high energy performance class, already during the design stage, it is necessary to calculate the energy consumption and adjust the solutions taking into account the results obtained. Of course, the price will increase by 10–40%, depending on the complexity of the project. It is also important to note that it is preferable to prepare the heating and ventilation project parts simultaneously.

 

How long does it take to design such a house?

If the energy costs of the particular dwelling house are calculated during the design stage, the process can be prolonged by 1–2 months. This way an additional part of the design project is created and the architectural solutions must be coordinated, as well as adjusted according to the calculations done.

 

You have designed numerous energy-efficient houses. Have you managed to achieve similar results as with Kārlis’ house? If not, what were the obstacles?

Typically, the energy consumption needed for heating in the energy-efficient houses that we design falls into the range from 20 kWh/m² per year (consumption for an extremely compact two-storey or single-storey building that is nearly perfectly cube-shaped and has an attic) to 35 kWh/m² per year (consumption for a dwelling that has a less compact form – a larger one-storey house).This forecasted rate results from the calculation of costs performed during the design stage. In order to actually achieve such numbers in reality, it is required to ensure strict control of construction, testing and maintenance of the building. We are currently halfway through with preparing another project of a house the heating energy consumption goal of which is around 15 kWh/m² per year.

 

What kind of house according to the energy consumption needed for heating do prospective builders want currently?

When it comes to an energy-efficient house (not the passive one which has the specifically defined rate of not more than 15 kWh/m² of energy consumption for heating per year), people want for it to use from 20 kWh/m² to 35 kWh/m² of energy per year for heating. Such indicators help to meet the requirements for buildings of the A or even A+ energy efficiency class. This is exactly what I recommend to people currently planning to build. However, it is necessary to bear in mind that energy-efficient homes are different, due to architectural solutions that are affected by the sun they look slightly different. To the future residents, I recommend not to be afraid of a more modern-looking building with large windows and systems that form shadows on the south side, as well as modest-looking walls on the north side. And, considering that in each individual case conditions of the plot are different, you should trust a specialist from the very beginning.

 

A designer’s commentary


What is the most efficient heat source for a passive house according to the benefits of their price?

A single correct answer, possibly, does not even exist, it all depends on the specific situation. Technical regulations controlling the building energy performance certification and energy efficiency planning limit certain choices. Geothermal heat pumps and biofuel boilers have more advantages than others.

 

Is it difficult to build a passive house? What are their requirements for the climate conditions in Latvia, i.e., what thermal insulation material layers would you recommend for floors, walls, the roof?

The passive house, according to the regulations stipulated by the Passive House Institute in Darmstadt, Germany, is a house the energy consumption for the heating needs does not exceed 15kWh/m² per year. Otherwise, it is not the passive house. These requirements do not depend on the climate conditions. The thickness of the required thermal insulation layers is determined by the form of the building, its placement, the influence of “neighbors" casting shadow, static tightness levels and the ventilation system solutions. It is also necessary to point out that the energy consumption needed for heating the space is influenced not solely by the thickness of the thermal insulation. Using large quantities of insulation material, benefits of the excess layers are not proportional to the added amount of material. In such cases, the previously listed elements and thermal bridges which are evaluated in each individual situation, play an important role.

 

A ++ class houses have gained popularity. Are their requirements possible to comply with?

A brief overview of these requirements is hardly possible. The mandatory parameters for class A or A+ houses are actually possible to be implemented in residential buildings of one to two apartments. In order to achieve the passive house standard (15 kWh/m² – amount of energy needed per year for heating the building), most of the criteria are met. However, the buildings of the class A++ standard have additional requirements – such devices that use renewable resources for producing energy to be consumed in the building need to be installed.