Study of Thermal Transmittance of External Timber Frame Wall Compared to Masonry External Wall

Based on the analysis and comparison between conventional and prefabricated construction, conclusions can be drawn about the advantages and disadvantages of both conventional and timber frame construction. Knowledge of the advantages and disadvantages of each construction method is crucial and can influence the investor's final decision.

Results

Based on the analysis and comparison between conventional and prefabricated construction, conclusions can be drawn about the advantages and disadvantages of both conventional and timber frame construction. Knowledge of the advantages and disadvantages of each construction method is crucial and can influence the investor's final decision. Among the most important advantages of prefabricated construction are rapid execution and occupancy, construction can take place in any season, as the elements of the prefabricated house are assembled in production. In production, the elements are manufactured according to plans, enabling subsequent precise and rapid assembly.

Rapid construction also means shorter environmental impact. In conventional construction, building proceeds gradually, in phases. Conventional construction is also called wet construction, due to the water content in binders, which must evaporate to prevent moisture accumulation in interior spaces later.

Regarding installed materials, the prefabricated house contains largely ecologically acceptable, health-safe building materials. Here, timber can be highlighted as the main structural building material of prefabricated buildings, which, due to the method of acquisition, transport, processing and manufacturing, is the least environmentally burdensome building material, whilst this cannot be said for bricks. As a second building material in prefabricated buildings, gypsum-fibre board is used, which is equally ecologically sound, composed of gypsum, water and cellulose fibres.

Since we spend a great deal of time in enclosed spaces, it is important to create a healthy living climate, which prefabricated buildings also provide due to their structural composition. In prefabricated construction, due to thinner walls with the same external dimensions, a larger living area is gained compared to conventional construction, however, it can be said that the prefabricated building has low thermal mass, as it cools quickly when heating is interrupted and vice versa, whilst conventional construction has longer thermal mass.

Energy efficiency is one of the very important properties that means long-term energy savings. Timber as the main structural building material is also a much better thermal insulator than brick in conventional construction. Disadvantages of timber frame construction arise when timber as the main structural material is not sufficiently dry.

In such cases, cracks at joints may occur. It is also not suitable for placement in more flood-prone areas, as it is less resistant to water and moisture. In the practical part of the diploma thesis, by changing the floor plan drawing from a masonry single-family house to prefabricated, as shown in annexes no. 4 and 10, a change in living area was made, as in the prefabricated house compared to conventional construction, the area increases due to thinner walls. A comparison was made between the external prefabricated wall and the external conventional wall. The external timber frame wall, which consists of gypsum-fibre board, PE foil, timber, where studs are spaced at 625 mm, for example neopor and render with a total thickness of 335 mm, at external temperature – 5 °C and internal temperature 20 °C and external humidity 80 % and internal humidity 50 %, gives a thermal transmittance result of U = 0.120W/(m²K).

With this composition of external prefabricated wall, no condensation water forms. This means that under these conditions, mould is not expected. The weight of this external timber frame wall is 56 kg/m².

The external masonry wall with a total composition of 335 mm at external temperature – 5 °C and internal temperature 20 °C and external humidity 80 % and internal humidity 50 % gives a thermal transmittance result of U = 0.179W/(m²K). With this composition of external masonry wall, no condensation water is present. The weight of this external masonry wall is 166 kg/m².

The external masonry wall is heavier compared to the external timber frame wall despite the same thickness. Based on the assumption, it can be concluded that the external timber frame wall with a thickness of 335 mm with structural composition of gypsum-fibre board, timber, neopor and render has better thermal transmittance than the external masonry wall with a thickness of 335 mm with structural composition of gypsum board, brick, neopor and render. In the structure, moisture is not present in either the masonry or the prefabricated external wall.

The phase shift is 12.8 h for the masonry external wall with a thickness of 335 mm and is longer than for the prefabricated external wall with a thickness of 335 mm, where it is 11.5 h. In the event that a greater phase shift were desired in the prefabricated external wall, the structure of the prefabricated wall would have to contain timber insulation and timber façade board. Based on the analysis and comparison of the properties of prefabricated and conventional construction, it can be said that the set objective was achieved, as the conclusion was reached that prefabricated timber construction with pre-manufactured elements proceeds more rapidly, as the installation of prefabricated timber elements of a single-family house on the construction site is completed in seven days.

It is very important that external prefabricated walls, despite the same thickness, have better thermal transmittance than masonry houses, as details are resolved from the first phase of design, enabling the smallest possible heat loss. Attention is additionally directed to ensuring that penetrations are as small as possible and that the insulation layer is not interrupted anywhere. Based on the comparison carried out between the prefabricated timber and masonry house, prefabricated construction would be recommended to investors when building, due to natural installation materials, which are also more ecologically suitable, rapid installation of timber frame structure, lower energy consumption, lightweight structure and of course due to the proven better thermal transmittance, which was verified with the U-wert.net programme.

Condensation water does not form in either wall. Walls of timber frame houses are better thermally insulated than walls of conventionally built houses. Consequently, this means that with good airtightness of the prefabricated building (good wall joints, good seals on windows, doors), considerable thermal energy is saved.