Tallinn University of Technology

Üllar Alev, a PhD student of the Nealy Zero Energy Buildings Research Group of the Department of Civil Engineering and Architecture at TTÜ School of Engineering, defended his doctoral thesis "Renovation and Energy Performance Improvement of Estonian Wooden Rural Houses".

In Estonia, there are more than 190,000 detached houses; 61% of these have wooden load-bearing structures. Approximately fifty per cent of the wooden houses are older than 100 years. "This already proves the durability of wooden houses and well-considered renovation would extend the service life of the houses for at least an additional 100 years. Only the inhabitants′ expectations for comfort have changed over time. There is, however, no insurmountable obstacle, which would prevent having conveniences and indoor climate in such houses equivalent to the the ones in modern dwellings after the houses have been thoroughly renovated," the author of the doctoral thesis Üllar Alev explains.

As a rule, the owners of rural houses renovate their houses step-by-step and often during a long period of time or almost continuously due to resource scarcity. The doctoral thesis concluded that such renovation works should be carried out simultaneously and must be carefully designed, which would reduce extra work, inconveniences accompanying construction works and, ultimately, the total cost of construction works.

The main damage to old log houses built before World War II has been caused by precipitation and soil moisture. "In most of the century-old log houses the first log rows and the rotten logs under the windows need to be replaced," Alev claims.

The weak spot in the structure of these log houses is lack of air tightness, which is why during renovation attention should be paid on sealing of log grooves and joints in the structure. In spite of sparse exterior envelope of the building, natural ventilation does not ensure adequate air exchange and a mechanical ventilation system with heat recovery needs to be installed to ensure good indoor climate.

Üllar Alev says, "Additional insulation of external walls significantly reduces the energy use of the houses. In the doctoral thesis I analysed also the possibilities for insulating external walls from interior side (where it is not possible to install exterior insulation), however, exterior insulation should definately be preferred."

By complete renovation (additional insulation, a ventilation system with heat recovery, an effective heating system and solar collectors or PV panels) depending on the state of the house, the heating costs of rural houses (incl. costs on ventilation and domestic hot water) can be reduced by two to four times while guaranteeing a significantly more convenient indoor climate.

"Improved indoor climate means warm floors, stable temperature (absence of hot evenings and cold mornings) and cleaner indoor air (less dust). These are the qualities the current owners of old log houses complained about in the research carried out in the framework of this doctoral thesis," Üllar Alev explains.

The supervisor of the doctoral thesis was Professor Targo Kalamees (TTÜ).
The opponents of the doctoral thesis were Professor Vasco Peixoto de Freitas (University of Porto) and Raimondas Bliudzius (Kaunas University of Technology).

Kersti Vähi, TTÜ Research Administration Office