© Colin Usher practicing as MicroTecture c 2025
How our Passive House works: page 2
Energy Generation
The south facing PV panels generate about 3,400kW hours/year. This electricity is fed back to the house to run appliances, the heating and hot water production. Excess electricity is sold back to a green energy supplier, reducing the carbon footprint of the house down to 11Kg/yr. The panels chosen are fitted as the roof covering instead of the roof tiles, resulting a more easily maintained and aesthetically pleasing outcome.Heating the Building (occassionally!)
An air to water heat pump used to supplement passive gains and provide hot water. The air to water heat pump (COP of 3) delivers warm water very efficiently to the buffer tank which supplies the underfloor heating serving most of the ground floor rooms. There is no heating to the upper floor (except for the bathroom and shower) as the house is kept at a constant temperature with the upper rooms being just 2C lower temperature than the lower rooms. The heat pump also supplies heat to the cylinder which provides hot water to all the wet rooms in the dwelling. Electricity is the only energy source for the house. Careful consideration has been given to the appliances in the house by the owner to ensure that these are all A* rated to keep the energy wastage to a minimum.Ventilation
A mechanical ventilation heat recovery system has been installed into the dwelling to ensure that the ventilation is fully controlled during winter months and when the house has been left unmonitored during holiday periods. As the house is sealed against wasteful air leakage a ventilation system is essential. This gently removes stale, warm, moist air out of the bathrooms, utility room and kitchen and introduces fresh air into all the living spaces. As the warm air is expelled it passes through a heat exchanger which is used to warm the incoming air. During this process a considerable amount of moisture condenses out of the air and has to be drained out into the waste drains.Performance
Average energy use of 3,250 kWhrs per year: a sixth of that allowable under Passivhaus Standard. Energy generation of 3,300 kWhrs per year. In addition, the house meets carbon zero by some measurement, although in reality it just has very low carbon emissions resulting in about 11 Kg of CO2 being produced per year when all the offsets are taken into account. No overheating occurred in summer due to the thermal mass, the deep reveals and overhanging eaves, the stack effect of the stair void and the efficient ventilation system. No cold bridging occurred, no draughts were discerned by the users and high levels of comfort were sustained throughout the year. Natural light floods the rooms during the day, with the centre of the house being lit from the roof windows above the stair. Throughout the house LED downlighters are used to provide high quality utility lighting and wall light, but these are only required the hours of darkness. A small number of low energy feature pendant lights augment the ultra low energy LEDs.Capital Cost
The project was constructed for the target cost of £240,000 which equates to £1,340 per m2, as tendered in 2012 [11 years on it is now double that cost]. This is not dissimilar to the more affordable bespoke private houses which the practice has been involved with in recent years. It shows that with careful cooperation between the client, architect and building contractor, extremely good value for money can be achieved. Construction costs have risen considerably, almost doubling since the house was designed over a decade ago, so it should be assumed that a construction cost of £2,500-3,000 per m2 should now be anticipated.Market Valuation
A valuation of the house soon after it was completed showed that it is worth what it cost to buy the land, demolish the previous property and build the new house. However if one takes into account the £2,500 per year saving on energy costs and the fact that there will be no significant repairs and maintenance required over the next 15-20 years, this can be seen as a very sound investment, along with being a comfortable and desirable place to live.
© Colin Usher practicing as MicroTecture c 2025
How our Passive House works: page 2
Energy Generation
The south facing PV panels generate about 3,400kW hours/year. This electricity is fed back to the house to run appliances, the heating and hot water production. Excess electricity is sold back to a green energy supplier, reducing the carbon footprint of the house down to 11Kg/yr. The panels chosen are fitted as the roof covering instead of the roof tiles, resulting a more easily maintained and aesthetically pleasing outcome.Heating the Building (occassionally!)
An air to water heat pump used to supplement passive gains and provide hot water. The air to water heat pump (COP of 3) delivers warm water very efficiently to the buffer tank which supplies the underfloor heating serving most of the ground floor rooms. There is no heating to the upper floor (except for the bathroom and shower) as the house is kept at a constant temperature with the upper rooms being just 2C lower temperature than the lower rooms. The heat pump also supplies heat to the cylinder which provides hot water to all the wet rooms in the dwelling. Electricity is the only energy source for the house. Careful consideration has been given to the appliances in the house by the owner to ensure that these are all A* rated to keep the energy wastage to a minimum.Ventilation
A mechanical ventilation heat recovery system has been installed into the dwelling to ensure that the ventilation is fully controlled during winter months and when the house has been left unmonitored during holiday periods. As the house is sealed against wasteful air leakage a ventilation system is essential. This gently removes stale, warm, moist air out of the bathrooms, utility room and kitchen and introduces fresh air into all the living spaces. As the warm air is expelled it passes through a heat exchanger which is used to warm the incoming air. During this process a considerable amount of moisture condenses out of the air and has to be drained out into the waste drains.Performance
Average energy use of 3,250 kWhrs per year: a sixth of that allowable under Passivhaus Standard. Energy generation of 3,300 kWhrs per year. In addition, the house meets carbon zero by some measurement, although in reality it just has very low carbon emissions resulting in about 11 Kg of CO2 being produced per year when all the offsets are taken into account. No overheating occurred in summer due to the thermal mass, the deep reveals and overhanging eaves, the stack effect of the stair void and the efficient ventilation system. No cold bridging occurred, no draughts were discerned by the users and high levels of comfort were sustained throughout the year. Natural light floods the rooms during the day, with the centre of the house being lit from the roof windows above the stair. Throughout the house LED downlighters are used to provide high quality utility lighting and wall light, but these are only required the hours of darkness. A small number of low energy feature pendant lights augment the ultra low energy LEDs.Capital Cost
The project was constructed for the target cost of £240,000 which equates to £1,340 per m2, as tendered in 2012 [11 years on it is now double that cost]. This is not dissimilar to the more affordable bespoke private houses which the practice has been involved with in recent years. It shows that with careful cooperation between the client, architect and building contractor, extremely good value for money can be achieved. Construction costs have risen considerably, almost doubling since the house was designed over a decade ago, so it should be assumed that a construction cost of £2,500-3,000 per m2 should now be anticipated.Market Valuation
A valuation of the house soon after it was completed showed that it is worth what it cost to buy the land, demolish the previous property and build the new house. However if one takes into account the £2,500 per year saving on energy costs and the fact that there will be no significant repairs and maintenance required over the next 15-20 years, this can be seen as a very sound investment, along with being a comfortable and desirable place to live.
