Acta Univ. Agric. Silvic. Mendelianae Brun. 2011, 59, 91-100
Published online 2014-06-14

Wood moisture monitoring during log house thermal insulation mounting

Pavla Kotásková1, Zdeňka Havířová2

1Ústav tvorby a ochrany krajiny, Mendelova univerzita v Brně, Zemědělská 1, 613 00 Brno, Česká republika
2Ústav základního zpracování dřeva, Mendelova univerzita v Brně, Zemědělská 1, 613 00 Brno, Česká republika

The current designs of thermal insulation for buildings concentrate on the achievement of the required heat transmission coefficient. However, another factor that cannot be neglected is the assessment of the possible water vapour condensation inside the construction.
The aim of the study was to find out whether the designed modification of the cladding structure of an existing log house will or will not lead to a risk of possible water vapour condensation in the walls after an additional thermal insulation mounting. The condensation could result in the increase in moisture of the walls and consequently the constructional timber, which would lead to the reduction of the timber construction strength, wood degradation by biotic factors – wood-destroying insects, mildew or wood-destroying fungi. The main task was to compare the theoretically established values of moisture of the constructional timber with the values measured inside the construction using a specific example of a thermal insulated log house. Three versions of thermal insulation were explored to find the solution of a log house reconstruction which would be the optimum for living purposes. Two versions deal with the cladding structure with the insulation from the interior, the third version deals with an external insulation.
In a calculation model the results can be affected to a great degree by input values (boundary conditions). This especially concerns the factor of vapour barrier diffusion resistance, which is entered in accordance with the producer’s specifications; however, its real value can be lower as it depends on the perfectness and correctness of the technological procedure. That is why the study also includes thermal technical calculations of all designed insulation versions in the most unfavourable situation, which includes the degradation of the vapour barrier down to 10% efficiency, i.e. the reduction of the diffusion resistance factor to 10% of the original value.
Moreover, the dependence of the weight moisture of timber inside the insulated cladding on temperature-moisture changes in the internal and external ambient environment was examined.


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