Basic solutions for the renovation of lightweight brick walls of Estonian detached houses

The aim of this work was to analyze the pre-renovation condition, renovation needs, heat loss before renovation and solutions to minimize heat loss of typical lightweight brick walls of Estonian private houses. Additional insulation of brick walls is necessary to reduce the heat loss of the building. On average, heat loss from the external walls of unrenovated detached houses accounts for 30% of total heat loss of the building. With additional 250 mm thermal insulation, the heat loss of the external wall decreases by 67 - 76 %. Only injection of foam inside the cavity wall cannot significantly decrease the thermal transmittance of external walls in Estonian cold climate. Due to the binding stones in the wall, thermal bridges remain and the insulation is not efficient. Additional insulation from the outside is more effective solution. Peer-review under the responsibility of the organizing committee of the ICMB23.


Introduction/Background
Considering the number of existing buildings, the percentage of already renovated buildings and the projected numbers of buildings falling out of use, more than 40 % of detached houses needing deep renovation (~100 000, their total floor area being 14 million m²).Although wood (log and timber frame) is the most typical external wall material in Estonia, the proportion of brick walls is 1/3.Due to the small size of detached houses and the high need for not energy-related renovation, the renovation of private houses is relatively more expensive than renovation of apartment building.The most cost-effective solutions are primarily in terms of technical service systems (installation of heat recovery ventilation, replacement of an inefficient heat source) [1].Additional insulation of the external wall is the single insulation measure with the greatest impact on improving energy performance.In order to achieve the lowest unit cost of energy savings, each measure should be used to the maximum (maximum thickness of the insulation layer), even if it increases the present value and package cost (€/m²).Based only on the cost-optimality of improving energy performance, the energy savings set as a goal in the Energy Performance of Buildings Directive (EPBD) will not be achieved, as a lower energy efficiency solution is preferred.The need to renovate buildings lies in other areas than just achieving energy savings -the indoor climate improves, the service life of the building is extended, occupant's well-being improves, we use buildings longer and thereby reduce the need to build new buildings, etc.The aim of this work was to analyse the pre-renovation condition, renovation needs, heat loss before renovation and solutions to minimize heat loss of typical lightweight brick walls of Estonian private houses.

Methods
Figure 1 presents the studied wall types.9 buildings (both renovated and unrenovated) from the period (1941-1990) were investigated.Building survey, measurement of thermal transmittance, temperature and relative humidity inside the wall, air leakage, thermography and whole building energy performance calculations were the methods used in this study.Along with hygrothermal performance design, additional thermal insulation solutions for building envelope were developed.Required additional insulation is presented as limit of specific heat loss divided by net area of rooms with indoor climate H, W/(m²•K) U thermal transmittance, W/(m²•K) A area of building envelope, m²  linear thermal transmittance, W/(m•K) l length of linear thermal bridge, m  infiltration airflow, m³/s c specific heat, J/(kg•K)  air density, kg/m³

Results and discussion
The thermal transmittance of light brick walls varies in the range U= 0.51 -0.32 W/(m²•K) and air leakage rate of old detached houses with brick wall [2] qE50  11 m³ /(h•m²).To minimise heat loss and air leakages renovation of these buildings is needed.If energy were extremely cheap and without emissions, these buildings could be used even without insulation.
Additional thermal insulation for brick detached houses in Estonian cold climate depends on energy performance ambition, types of ventilation (natural ventilation and mechanical ventilation with heat recovery) and heat source.The more efficient the building service systems and energy source (for room heating and domestic hot water (DHW)) are, the less additional thermal insulation of the building's external walls is needed to reach desired energy performance level, see Table 1 (real value depends on architecture of the building).Heat source impacts the limit H value with its efficiency (coefficient of performance, COP) and primary energy factor.Considering new windows (U= 0.9…1.1 W/(m²•K)), mechanical ventilation with heat recovery, insulation of roof and floor, required additional thermal insulation for external walls varies between 300 mm and 100 mm.Only injection of foam inside the cavity wall cannot significantly decrease the thermal transmittance of external walls in Estonian cold climate because the injected layer is too thin.Due to the binding stones in the wall and around windows, thermal bridges remain and the insulation is not efficient.Additional insulation from the outside is more effective solution.

Figure 2 .
Figure 2. A thermal image from the brick cavity external wall with injected foam insulation shows heat leaks around the false wall and windows, where cold bridges have been preserved.