Base structure for timber construction

What does the new base for timber buildings look like?

The Eberl Thermosockel consists of two recycled insulation materials. The load-bearing ""framework" comprises Purenit, a highly compressed functional material based on PUR foam with a high insulation value. This wall element is then filled with thermally processed waste glass, whereby the form of the filling depends on the construction and intended use.

What is its special feature?

Since the load-bearing material is itself an insulating material, thermal bridges are prevented; whilst at the same time, it can also take on a structural function due to the dense compression. It is moisture resistant, durable and easy to work with. The thermal conductivity of the building material is between ʎ0,078 and ʎ0,086, the compressive strength about 1.8 MPa. Sealing is also possible with all common sealants and elastomer bitumen membranes.

What was the initial problem?

Austrian standard (ÖNORM) B 2320 stipulates that substandard wood must not be used. Because of this, solutions were proposed in ÖNORM B 2320 and B 3691 that are very costly and time-consuming, such as lowering the ground, grates with seepage behind etc. In addition to the requirements for durability, moisture resistance and stability, such a base should also be independent of any previous work, such as inaccuracies in concreting. Working with usual carpentry machines also played a role.

How was it developed?

The thermal base came about more or less as a by-product of my Master's thesis. Two years ago, test bases were built and then tested for suitability and applicability in terms of building physics at the Department of Building Physics at Graz University of Technology in November 2016. These bases were later subjected to a pressure test at the BVFS in Salzburg. The test results led to the idea of patenting the product. In the meantime, a sound insulation test has also been carried out by Holzforschung Austria, which certifies that our base element provides better sound insulation in the high-frequency range compared to a conventional wooden crossbar wall.

How does this patent differ from other products?

The patent application was filed in June 2019. In the course of this, it became apparent that there are practically no other products on the market. The traditional concrete base has poor insultation values, which would have to be insulated with disproportionately thick insulation compared to a standard timber framed wall. The lowering of the level with the addition of material that allows seepage and additional construction measures are costly and time-consuming. With this base element, connecting the levels inside and outside at the same height is straightforward from a building physics point of view and possible without further measures. Lowering the water-bearing level outside is also no longer necessary.

Where does this base problem occur?

Wherever substandard timber-wall joins are made. During building work and especially in the floor and door area, it is essential that no water or moisture penetration occurs - something which poses a great challenge for craftsmen and builders. The biggest problem occurs where the level should be the same on the outside and inside. This of course also affects patios and terraces. Accessibility issues can be fulfilled in this way.

How can accessibility issues be met in accordance with ÖNORM B1600?

In timber construction, the ground is usually lowered according to ÖNORM B 2320 or costly special solutions are necessary. Ramps in front of the building are also possible to ensure access for disabled persons. With this base solution, it is possible to align the outside level (according to ÖN B 1600) with the level of the doorstep.

How is the base made? How are the joins made?

The Purenit panels are supplied in standard sizes and made into 16 cm- and 20 cm-wide base elements of various heights by us. These are then screwed and glued, and the glass foam filling is also affixed. The base elements are mounted to the traditional timber frame wall. Separate assembly of the base and timber framed walls is also possible. As there is a joint at the transition from the base to the timber construction, this must either be stabilised with a bracket or screwed to the inside with a 25 mm thick OSB board. Screws in combination with gluing (depending on the horizontal load) can also fulfil the static requirements.

How does the base solution stand the test of long-term use?

After the structural-physical tests by TU Graz and BVFS Salzburg, the base was used for the first time at the "Kasermandl" Mountain Restaurant in the Penken ski area at almost 2,000 m above sea level. Therefore, there is no long-term experience yet. The mountain restaurant is the ideal object for this because there can be snow on the mountain for about six months. Also, due to its exposed location, the building is repeatedly subject to greater moisture from driving rain. Since it is almost impossible to put such a large building under a dry roof during the construction phase, it is all the more important that the base area is unproblematic with regard to moisture. This is de facto not possible with a normal timber framed wall, i.e. moisture inevitably enters a normal timber framed wall in the base area during the building phase, which can then no longer escape after sealing. Our project partner Murexin also has an appropriate sealing solution for all openings such as doors.

Who produces the base?

The Thermosockel is currently produced and distributed by Zimmerei Eberl e.U. The standard height is 50-57 cm: this corresponds to a 30 cm splash area plus floor structure and leeway. The cost is around € 150 - € 200 per linear metre, depending on the thickness of the wall. In fact, however, the cost of the timber frame/BSP wall etc. for the base area needs to be deducted from the wall costs, which gives an effective additional cost of approx. € 100.