Single-family house, Graz | Austria

The requirements

Project Single-family house
Place Graz, Austria
Year of construction 2008

Wood construction
carried out by
GriffnerHaus AG
Architect Harald Kurath
Statics Binderholz
Bausysteme GmbH

Most family houses are designed for three to four occupants. Such standard plans were not an option for this house near Graz because it was destined to become the new home for a family of five. Another challenge was presented by the desire to have the ground floor dedicated exclusively to shared living. All bedrooms and areas of retreat for the members of the family were to be located upstairs.

In addition, the client family produced a comprehensive set of requirements for the architect. The following points needed to be considered in the plans:

Costs: Tight and clearly defined budget.
Spatial planning:
All rooms were to be capable of being used to their full height and have a compact size.
Open-space principle:
As few load-bearing internal walls as possible in order to be able to adapt the interior of the house flexibly to different life circumstances.
As the house is near to an area prone to flooding, the house may not have a basement.
Space on offer:
A sufficient amount of space must also be allocated for guests.
Construction method:
With solid timber elements (CLT BBS) in visual quality. This is because the clients both have a close affinity with wood that was forged during their childhood, and they want to live in a house constructed mainly from this natural building material.
Straight lines, clear and not fancy.
The house must blend harmoniously into the very rural landscape and have a timeless modern appearance.

The planning

The architect designed an L-shaped outline plan for this dwelling. He designed part of the house over two floors in order to meet the requirement for "live downstairs, sleep upstairs". The other part of the building was to be constructed on one level, serve as a substitute for the basement and provide space for an office and TV area which can also be utilised as a guest area. In addition, on the ground floor a large living, dining and kitchen area covering around 55 m2 with plenty of space for living was to be produced. A separate bedroom for guests was also planned: with access to the wellness section including a shower and WC. This means that guests will essentially have their own bathroom. The clients were also won over by the plans for upstairs: Over around 78 m2 of useful floor space, the architect managed to accommodate three children's bedrooms, a master bedroom with a dressing room, a spacious bathroom and a balcony. Everything appeared compact and yet spacious.

Based on these plans, all the other requirements were met as follows:

Utilisation of space: Thanks to the flat roof, all rooms can be used to their full height, with a clear ceiling height of 2.65 m throughout the house.
Open-space principle: The building does not require any load-bearing internal walls. This task is performed in the main by the external walls. Made from 5-layer binderholz BBS wall elements, they are designed to be load-bearing and stiffening. Pillars and glulam (glued laminated timber) beams provide the load-bearing support inside the house.
Construction method:
Like the external walls, all ceilings and roofs are also made from solid wood in visual quality.
Architecture: The timelessly modern box character of the building has a linear and clear appearance.
Environment: With its larch facade, the house fits in very well with the environment and blends in with the surrounding forests and agricultural buildings.

Space on offer: The 2-storey part of the house offers around 156 m2 of net living space.
Then there is also the single-storey section with plenty of room for guests.
Costs: The budget was met exactly.

The implementation

Following careful consideration, the client decided to have the new building constructed as a prefabricated house with a solid wood design.

There were three arguments in favour of a prefabricated house:
1. The prefabricated housing company guaranteed a maximum build time of three months for the turnkey construction of the house starting from the foundation slab.

2. The high degree of prefabrication of the walls guarantees a high level of quality.
3. The quoted construction costs are guaranteed final costs.

As soon as the order was placed, the implementation work began. The builder prepared the plot and had an access road, all of the connections and the foundation slab put in place. Alongside this all of the solid wooden walls required were produced in the space of just two weeks; they were prefabricated at the factory of the prefabricated house manufacturer so they were ready for installation.

The key to this intense level of prefabrication was a digital 3D model, created by the production planning experts from binderholz Bausysteme. The 3D model shows the precise arrangement of the BBS 125 wall elements. This meant that the element size of 125 cm could be optimally utilised and the cross-laminated timber waste was reduced enormously.

The external wall of the house is made up of vertical BBS 125 wall elements and a frame made of glulam (glued laminated timber) running around it. With this combination, a large proportion of the openings in the building are surrounded with solid wood, which once again considerably reduces the amount of BBS waste. In addition, all of the design superstructures were planned in precise detail through to installation and prefabricated precisely at the factory.

When it came to the design of the flat roof, the prefabricated house manufacturer followed the DA06 a structure, as is described in the binderholz solid timber manual. This structure has the following advantages: Thanks to its effective storage mass of around 40 kg/m2 it achieves a high thermal insulation value in winter, very good thermal protection in summer and more than adequate noise insulation of 57 dB.

More about flat roof construction DA06a

The staff from the timber construction company installed the first wall of the house on Monday, 30 June 2008. The shell construction was completed on Wednesday, 2 July 2008.

Assembly Video

The installation work for the entire house was completed after just two days. Whether it was electrical work, water connections or underfloor heating, all of the fitters unanimously confirmed: "The solid timber components are outstandingly well suited to rapid and easy assembly of the installations."

Although things got fairly tight towards the end of the scheduled construction period, the site was never hectic. The builder finished off working outside, the prefabricated house company worked on the inside and outside of the house, floorers and staircase fitters were still employed along with the fitter in the bathroom and the furniture store in the kitchen and bathroom.

The build culminated on 13 September 2008: The client family took over the turnkey house and was able to move in on schedule.

... and today

Since 2013 the house has also included a garage with storage space. It was easy to add this extension. It is made completely of BBS solid timber - with visible surfaces inside - and meets fire class REI 60. The official certificate was quickly obtained. This was done using the classification reports from binderholz Bausysteme and its fire-safety calculation for the BBS components. The children of the client family, who are now teenagers, "take over" the garage as a party room on an increasingly frequent basis. The client says: "The solid timber components were hardly insulated, yet now it is not just our children who know that rooms made from solid timber are pleasantly cool in summer and are easy to heat and nice and warm in winter."

Report on the experience of the clients

August 2014

"We have now been living in our solid timber house for almost six years. After this length of time, you often hear homeowners saying: ‘If we were to build again, we would do lots of things differently...’ This is not true in our case. Everything is right, we would do exactly the same things if we built the house again.

The arrangement of the rooms is exactly what we wanted. Even upstairs the rooms are perfectly proportioned, we do not have an inch of space too much or too little. The large windows flood our house with light. We therefore often have the impression of sitting outside on the lawn - for example if we are enjoying spending time with our children at the dining table.
 The level of thermal insulation in our house is ideal. We heat it using an air/water heat pump that also provides the hot water all year round. The annual heating and hot water costs are between 750 and 800 euros. According to the energy performance certificate, our demand ought to be much higher.

The fact that it is not is definitely down to the warm surfaces of the solid wood components and the high thermal storage capacity of solid wood. The wood has a pleasingly positive impact on us and also affects the room temperature required to feel comfortable in winter. We then heat the living rooms up to around 21°C using our low-temperature underfloor heating. On cold, clear winter days the sun helps and also contributes in a big way to heating the house through the large windows, for free!

What was very important and the right option for thermal insulation in summer was our decision to opt for functional shading on the windows. On the ground floor we chose vertical sun blinds and upstairs we chose external blinds. If only the summers were still so hot: We have never had any days on which the difference between the outside and inside temperature was not at least 5°C. On hot summer days, we therefore like to cool ourselves down inside the house.

Besides the temperature, we also regularly measure the level of humidity in the air in the outside and inside area of the house. It always ranges between 40 and 65 %, now even without air humidifiers. In the first two years after we moved in, we had some installed. This was done on the recommendation of binderholz Bausysteme to prevent the BBS components from drying out too quickly in the first two heating periods. We had most of the solid BBS components glazed white, including in the kitchen and the hallway. They do of course from time to time pick up dirt, but this can be wiped off with surprising ease. With stubborn areas of dirt, we simply reapply the glaze in some areas, and everything looks as good as new.

The house is the focal point of our life. For us it represents home, a meeting place, an oasis, comfort, sanctuary and security.
It is generally accepted that it is only after you have used an item you have purchased that you know whether or not you have bought quality.

We bought a solid wooden house and got a quality place to live!"

Photos: ©binderholz

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