BUILDING ENERGY RENOVATION THROUGH TIMBER PREFABRICATED MODULES

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modules setra 1Retrofitting to existing buildings for improved energy efficiency is technically possible but conditions vary in different regions in Europe. “Northern Europe” is spanning in north south direction equally long as the distance between Malmö and northern Tunisia. The challenge is to meet the varying climate for such a big area with one technical solution. The answer is modularity and moisture buffering materials.

 Challenges

The main challenges for building envelope systems in Nordic environment is a big variation of climate conditions, in which they should be applied, and the consequences related to that.

Nordenkarta

The big variation means also a big variation in conditions for building physics and installations close to the outermost climate shell. Due to a long cold period, condensation easily takes place inside the building envelope, unless completely closed for moisture diffusion from inside. The latter is difficult to achieve without intrusion to the residents of a building, and it cannot be assumed that the existing building has a reliable existing diffusion stop.

The cold climate means also that installations in the modules, for example hot water pipes, must be protected by more insulation than in other countries. This, in turn, might influence the architecture. The biggest hindrance to installations in façade elements is that the insurance companies require water pipes of any kind to be easily available for inspections. This is acting against the efficiency and insulation criteria where pipes should be long and well insulated (i.e. mounted on a continuous wall without difficult to inspect). A possible solution to this might be “pipes in pipe”, where a water leakage is collected in the external pipe and made visible for inspection.

The target with Setra’s Bertim modules was to enable the use of a diffusion open system, which should be more robust for different wall types of existing buildings. As long as the system allows for drying of condensation in a wall, less time need to be spent on defining the properties of a building in the feasibility- and design phases. The materials must also be able to buffer moisture for shorter periods of time without formation of free water occurring.

Another challenge is a relatively high labour cost in these countries - although a basic principle is similar in other European countries, it is more pronounced in northern Europe. This is reflected by the fact that Norway and Sweden are the most expensive European countries to build in.

For the renovation to be feasible the amount of time spent on the assembly must be reduced to a minimum. On-site work is also more expensive than off-site work in a factory due to lower efficiency and more complicated logistics. This calls for systems allowing very efficient processes. One example is that Setra has a requirement that connection to the existing building must be possible in one process step, i.e. that the element can be fixed to the wall without a prior preparation of the wall by connection battens or similar.

 

Bertim 2D modules, the solution

Setra made a layered solution to allow for different types of a priori building envelopes. The ideas are merged from different previous research projects, such as Klikk, Smart TES and TURIK.

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Figure 1. Horizontal section through a retrofitted outer wall, + - interior, - exterior. 1-existing building, 2-soft insulation with distance body between surfaces, 3-Xlam panel, 4-hard insulation, 5-ventilated air gap, 6-facade (any facade material).

All layers in the structure have their own function and properties. The cross-laminated timber panel (xlam, pos 3) is used for the accuracy in positioning of openings, which allows for a lean process between design and manufacturing. It can also carry the load and the additional materials in an efficient manner, it can facilitate assembly and is air-tight. The insulation layers (pos 2 and 4) have the main function to retain heat inside the building but also to stop fire spread within the building (pos 2) and between buildings (pos 4). Insulation thickness and material is adjusted in relation to the needs of the project. The ventilated facade support allows for any type of facade, although timber cladding has been used in the examples. The facade solution is efficiently stopping water transfer into the climate shell in areas where horizontal rain is common (coastal regions).

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Figure 2. Preliminary test production of Bertim elements in controlled factory environment

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Figure 3. Connectors must be adapted to different structures. Here is an example with a distance body (wood) and a connecting screw to a mineral based existing building.

 

The challenges are met by:

  • Diffusion open system (amount of design hours saving, less inferior with habitants)
  • Dean process between design and production (amount of design hours saving)
  • One-step assembly process (amount of on-site hours saving)
  • Freely selectable insulation thickness and type of insulation material (system adaptable to different conditions, north to south)
  • In-organic or tuned moisture buffering insulation materials (avoiding mould growth due condensation in the wall.)
  • Installations are positioned so that they can be inspected, in connection to gangways or balconies. “Pipe-in-pipe”, insulation and condensation protection is very important to avoid a free water formation due to condensation on cold ventilation and water pipes.
  • Warm air ventilation from a heat exchanger and warm-water pipes need a lot of insulation to prevent heat losses. The architecture must allow for thicker walls where such installations are positioned or more efficient insulation materials must be used in those positions.
  • Ventilated façade (efficiently stopping capillary suction of water from outside in all types of climate conditions)

Bertim elements is the solution if a robust technology solution is desired in combination with a quick assembly process with a minimum of disturbance of residents and neighbours.

 

Author: Mattias Brännström (Setra) and Magnus Fredriksson (LTU)

 

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