Radu de la Gulia House - structure and energy configuration project of a passive house

The meeting I had with Cătălin Caraza from Creative Engineering had as a reason and starting point of our discussion the structure and energy compliance project of the house of Ioana and Ciprian Radu, built by Litarh at Gulia, near Bucharest, a project he was directly involved in. There will be many references to first article about this house (in which I spoke to the architect and presented the construction), so, I advise you to re-read it first. Building houses as energy efficient as possible, reducing energy consumption for heating and cooling are very topical subjects, so our discussion was broader, very technical and touched on many topics of interest regarding timberframe houses. We talked about the journey the future homeowner has to go through to start building the house, principles of efficiency, costs, how much the structure costs out of the total cost of the house and other such topics.

The stages up to the lifting phase of the house structure

I started the discussion with this topic because Pierre Bortnovski (Team Built) the architect and site manager of the Gulia house, was saying that many people who want to build a house first end up in Creative Engineering (thanks to information on the net), but that this should not be the first step. We asked Catalin to tell us Who should a prospective homeowner turn to first?

"The first step is to find an architect. People come straight to us not knowing what we do. We do structural and energy compliance, energy compliance meaning sizing the layering, designing the energy efficiency rating, if you want a passive house. Because you need to know how you get to a passive house. How do you know what the windows should be, whether they're too big or too small, how do you know what characteristics the joinery must have respectivă?

Whoever wants a house goes to the architect first to whom he says, for example, I want a big, bright living room, 3 bedrooms, 2 bathrooms, these are the requirements. The architect draws up the functional scheme, the volumetry, and then it's up to the specialist teams - structures, installations, landscapers.

Without the technical project, only with the one made by the architect, construction cannot start, according to the law. It requires technical project with execution details, with materials, with everything. The builder appears at the end, after the project is complete with execution details, quantities, possibly 3D model.

With Vlad Liteanu (Litarh) it's simple, we work in the same software and send him the 3D model directly. We send as clearly as possible the execution details, the gauging of beams, columns or whatever else is in the project from a structural point of view, elements that we dimension and for which we are responsible, and he, on the basis of this project, makes a price offer to the client. The offer to the client comes after the architect has done the design and the structural design has been done. Several teams work on the complete project - the builder who makes the structure, those who make and fit the windows, the installation team, etc.

There are many people involved in the project until the house is ready. Pierre had at one point made a chart of all the people who worked on the house in Gulia and he had over 100 people involved. For everything to go well, someone has to take over as project manager."

What did the Creative Engineering project for the Gulia house consist of?

"As far as the Gulia house is concerned, we (Creative Engineering) I did the structural and energy compliance calculations. Conformance is the layering, why certain thicknesses of insulation are used in the wall, roof or floor. The client chooses the level of annual consumption they want to achieve, max. 15 kWh/m²/year if it is a passive house. From here, we have done the calculations starting from the foundation. The structural part involved sizing the beams, the floor, the layout of the interior walls. In timberframe houses the interior walls, even if they are thinner, can be used as load-bearing walls to unload certain forces from the roof. And even if they do not discharge any forces, the walls brace the house and thus play a structural role. We also give the fasteners, the corners. After the calculations we tell the builder if the wall studs need to be more than 625 mm, which is the usual pitch. The fastening details - foundation fastening corners, wall fastening corners, wall floor, floor wall - the wind and seismic resistance calculations are also done by us."

From what Catalin said I understand that a house designed to withstand earthquakes or wind, it will hold up, whether it's made of wood, brick or concrete. Construction results from calculations, and they tell you how thick the walls need to be and what type of corners and fasteners to use.

"We also did the energy compliance study. In this study, the house is modelled taking into account the possible neighbours. Even if they don't exist, it can be simulated according to zoning regulations. Any construction may have an impact on the shading of the house. The house has no neighbours now, and if everyone who builds nearby takes into account the regulations on proximity and height, there should be no problems in the future. Taking into account the orientation to the cardinal points and the climate data, the windows were chosen, the envelope was sized, the thermal insulation at the base, in the walls and on the roof was calculated.

We also do zonal modelling. We make a local model and vary the thickness of the insulation. It depends on the area the house is in. The calculation is done strictly on site, strictly with the geometry and position calculated. This house, on the same site, but rotated by 20°, would not have the same coefficients. Very important is the orientation - to the south are the large openings, and to the north, only the strictly necessary. This helps a lot in winter, when almost no heating is needed, but in summer it can lead to overheating. This is why shading elements (reframing, blinds) are needed.

Once all these calculations and simulations are completed, the builder takes over the 3D model and makes a technological design. Materials are sized with the designer's agreement that the structure has strength. The builder may introduce certain tolerances to allow for assembly. The modifications are very small and do not alter the calculations, but very useful for assembly. If there are changes to the design, they are made before construction starts, very rarely afterwards. If it is necessary, however, the changes involve costs because the strength calculations have to be redone."

What is the energy compliance of a building

The energy performance of a building is an important feature, as the energy used in a home increases maintenance costs and creates a significant amount of greenhouse gas pollution - the main cause of climate change. So it's not surprising that now, more than ever, energy efficiency is an important part of building design and construction. To this end, all new buildings, regardless of size, will have to meet minimum energy performance requirements, adapted to the climate in which they are built. These are requirements aimed at reducing the energy needed to maintain buildings, which climate change is driving us to follow. Energy-saving measures will benefit the environment, improve air quality, improve people's lives inside buildings and lower energy bills.

The discussion with Catalin continued with energy efficiency requirements, especially as more and more beneficiaries are getting informed and want to build passive or energy efficient houses. So, What should the houses being built from 2021 be like and how efficient can or should they be?

"The answer would be quite simple. Now, as of 2021, homes must fall within the nZEB standards, i.e. they cannot be anything other than energy efficient. In addition, they would have to use some renewable energy to meet the standard. In terms of efficiency, there are several levels. If we look at the graph below, we see that a passive house has a consumption of max. 15 kWh/m² per year, but a very efficient house is also one that has 30 kWh/m², it can even be certified. If people don't necessarily want a passive house, but they want an energy efficient one, we recommend this level, 30 kWh/m² per year. It's ok as consumption and although it seems like a small difference, the financial effort to get to the level of a passive house is much higher. The differences come from certified materials that are much more expensive."

When energy conforming a house, the principles to be followed are the same as for the passive house, but when the house is only energy efficient, the values are more permissive, less strict. The principles we are interested in are:

• very good thermal insulation
• as few thermal bridges as possible
• performance window
• airtight envelope tested with blower door
• air quality through ventilation and heat recovery."

Thermal insulation is a key point for reducing heat loss. Thermal insulation allows the inside of a house to be independent of the outside temperature, so it is much easier to maintain constant thermal comfort. Once the right temperature is reached inside the house, it should be maintained as much as possible by avoiding heat loss through good insulation of the foundation, walls and roof. In an energy efficient or passive house, the thickness of insulation is considerably greater than in a conventional house. The lower the insulation, the greater the heat exchange.

"Thermal bridges (areas where there is uncontrolled air exchange) should be totally broken, but that's the ideal. If they can't be broken, they should be diminished. For example, there is a thermal bridge in the laminated beams of the Gulia house that can't be completely removed, because the wood is penetrating the wall and coming out, and energy is lost through the wood. But it could be reduced. Two slabs of PURENIT, a material with a lower heat transfer coefficient (0.08), were placed between the wall and the beam. The metal piece holding the beam was clamped to the PURENIT and the PURENIT to the wall. The deck was not removed, but it was lowered. Without this intervention the loss through this area would have been much higher.

The window, there is a price difference between certified and non-certified joinery, and this difference is not small. The joinery has 3 important components that influence efficiency - the frame, the glass and the way they are joined together. The frame can be PVC, wood, wood with aluminium on the outside or aluminium. It has added low transmittance materials, visible in section, that make the thermal bridge between inside and outside broken. The most expensive windows are those made of aluminium and certified. To be very good they must have a heat transfer coefficient of less than 0.8 W/m²K. The connection between the window and the wall is also very important, as this is where important thermal bridges can occur, which can be detected by thermoscanning.

Envelope is everything that comes into contact with the outside environment - walls, foundation, roof. 20% of energy can be lost through the foundation, 25% through walls, 10-20% through windows and 25-35% through the roof. This is why the roof thermosystem layer is thicker. There must be no uncontrolled air exchange because it can lead to condensation, which is very dangerous for wooden houses. That's why all foils and layers used for insulation are closed inwards and open outwards so that water from wet processes can be removed. This is why OSB is not used on the outside because it is a barrier. In the Gulia house, DWD was used on the outside, a material with a fairly good coefficient of permeability that lets vapour escape. Basaltic wool was glued over the DWD. The adhesive was chosen to allow the vapours to escape. Then comes the plaster, with vapour permeability. The whole system has to be permeable, to let the vapors out."

Is house certification useful?

"For now, having a certified home doesn't bring any advantage in terms of taxes or any incentives given by the state. However, certification is a guarantee of the quality of the products used and the workmanship, it is a guarantee of a well-designed and executed house. As far as the certification of passive houses is concerned, a big problem for us and for architects is the lack of certification for the materials used, even by some major manufacturers. For the certification of passive or very energy efficient houses, you need a file with the documents of the materials used, technical documentation, photos of the execution, test results."

How much does the actual construction (structure) represent of the final price of the house?

"The structure has a big visual impact, but only accounts for 20-40% of the construction. So is its price. The price offer given by the builder only refers to the elevated construction. To this are added many other costs. In the end, with semi-finished interiors, i.e. without finishes that can greatly influence the cost (parquet, tiles, special wall finishes, etc.), the final price can be as high as 1800 euro/m² for a passive house on a CLT and around 1500 euro/m² for an energy efficient timberframe house (up to 90 kWh/m² per year). A brick house comes to around 1400 euro/m². We also have a video made by Marius (șoflete.ro) about how much the same house costs on different structures."

Talking to a specialist about home efficiency is very informative and convincing so that, in the end, you want to build the most energy efficient or passive house because you really understand how important it is for your future comfort. But for that you need to get the right architect, designer and builder and plan the construction in advance.