Active House Erasmushove – the Blue House


As the commissioner is a building physicist, comfort and health formed the very basis of the design. The house is designed inside out: starting point was determining what ideal indoor climate was desired for which rooms. Amount of daylight, direction of light (morning light in bedrooms, evening light in the living room, northern light at workplace), preferred temperature, amount of ventilation, location of ventilation grills, risk of drafts, all was considered. The floor plans and shape of the building came as a result of the indoor climate requirements. Bedrooms and bathroom are oriented towards the east, kitchen and living room towards south/west. All windows on south and west have dynamic external shading. There is no active cooling, but plenty operable windows with extensive possibilities for summer night cooling. Even during a heat wave with external temperatures approaching 40 degrees, indoor temperatures topped at 25 degrees C. Ventilation is mechanical and demand driven in a 2 zone setting (living and sleeping). Location of the ventilation grills is so that no draft complaints will occur. Average daylight factor of the whole house is above 5% Each room has its own thermostat, heating is through radiant floor, ceiling and/or wall heating.

Example: It has been a basis design parameter to have a minimum daylight level of 5% and it has been reached by use of daylight from minimum two orientations in all main rooms. All glazing areas towards the south and west must be shaded during warm periods and is supplemented with natural ventilation and thereby the indoor thermal comfort level during hot periods. The air quality in all main rooms is controlled when occupied and the ventilation is optimized to keep the CO2 level and humidity low.


The building is kept compact to minimize heat loss through the building shell. All windows feature triple glazing with a U value of 0,7 W/m2K. The ground floor/walls/roof have R-values of 5/6/8 m2K/W. The walls are made of cellular concrete, the insulation is 9 cm PIR plates with 2 cm of mineral wool to prevent false cavities. Extra care has been taken during construction to create an air tight construction. An air/water heat pump reclaims heat from stale ventilation air. Additional air needed for hot water for the heat pump is extracted at the top of the cavity under the integrated PV roof (see also drawing). Cold waste air from the heat pump is pumped (at another location) in the cavity under the PV to actively cool the PV cells, thus increasing their efficiency. Windows are positioned to gain optimal passive solar energy in winter. Heating is through low temperature water based capillary floor/wall/ceiling heating, with a reaction time of less than 1 hour, so it can be switched off, even in winter, when there is sufficient passive solar heat available. The house is all electric and fully energy neutral or even positive, having generated a surplus of 1350 kWh over 2018. Total energy demand is 42 kWh/m2, energy supply is 95 kWh/m2, primary energy demand is -46 kWh/m2.

Example: The basic focus within energy has been to minimize the use of energy and to optimize the building design. The heat loos through the climate shell has been minimized using the best insulation solutions, reduce thermal bridges and creating an air tight construction. Thereby the need for energy has reached a level of 20 kWh/m2 and with the supplementary use of energy for hot water, ventilation light etc, the overall energy use is below 40 kWh/m2. Using a heat pump with a COP of 3.5, the final need of energy has reached a level of 20 kWh/m2. The supply of electricity is based on 50% renewable energy in the grid and the supplementary renewable energy are supplied with PV installed on the garage.


The materials on the facade were chosen to require little maintenance and age beautifully. The wooden cladding is FSC Douglas wood, treated with nontoxic biologic paint. The cladding well ventilated to prevent buildup of moisture. Window frames are modified softwood with 25 years warranty. The paints on the window frames and the triple glass panes are Cradle-tocradle certified. The brick cladding requires no maintenance and is from nationally sourced clay which is considered renewable in The Netherlands. The main structure is from cellular concrete, which has only 25% of the CO2 emissions of regular concrete and can be recycled at the end of life stage. Rain water is captured on the green roof and detached from the main sewer. It is allowed to infiltrate locally. Freshwater consumption is less than half the national average. The total cost of the house is comparable to regular new construction, but it has much better performances all around.

Example: The design on the load bearing structure has been based on an expectation that the concrete structure will be reused when the building is out of use after 100 years. The outer surface is based on a wooden structure that are ventilated and protected from direct rain, reducing the need for surface treatment. The wood used are certified and comes from forests that are FSC certified. In order to reduce the use of water a structure for use of rain water for toilets and gardening has been established.

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