Eco house design built towards Passivhaus standards

This project is a nearly zero energy home built towards Passive House levels of super insulation, triple glazing, air-tightness, passive solar gain and thermal mass, with the benefit of solar thermal hot water panels on the roof, photovoltaic panel garden array & a wind turbine. Heating is via a ground source heat pump and a biomass wood stove. Mechanical heat recovery ventilation system guarantees pre warmed clean fresh air.

This project demonstrates best practice in home energy conservation (towards the German passivhaus standard), renewable energy use, water conservation & waste reduction.

The completed house is a low carbon, eco-dwelling within a traditional envelope but with a green oak framed living room with a biodiverse sedum roof.  Resources consumed in and during construction have been vigorously considered, and used as efficiently as possible, so that the resource can be reused or recycled without creating carbon emissions, pollution or rubbish. This awareness of the cyclical nature of the eco-systems offers a demonstration of a sustainable way forward in which we can live in balance with the natural world.

Passive House (Passivhaus Certified Design Standard)

The proposed house was built towards the Passivhaus standard. This is a successful European ultra-low energy standard for buildings. Passivhaus buildings use only a fraction of the energy for heating (90% less) compared with houses built to the standards required by current building regulations, and deliver low carbon solutions without needing excessive renewable energy. Where Passivhaus differs from UK building regulations and CSH is the requirement for an absolute level of energy consumption instead of improvement over a more basic specification.

eco architecture
eco architecture
passivhaus architects

The Passivhaus approach has three main strands:

  • Minimise heat loss – compact built form, super insulation and triple glazing.
  • Minimise ventilation heat loss – airtight construction and heat recovery ventilation.
  • Optimise solar gain for winter heat.

These factors combine to deliver a heating demand that can be met with a minimal heating system (it is recognised that to design a house that needs no heating at all is not economic). As well as very low heating bills, Passivhaus offers comfort and a healthy indoor environment. Attention to detail in design and construction ensures no draughts or cold spots wherever you are in the house. Heat recovery ventilation uses low power fans to provide ample fresh air day and night, warmed to room temperature by a heat exchanger transferring the heat from the exhaust air from kitchen and bathrooms to the incoming air.

Passivhaus is a rigorous energy standard; energy performance must be demonstrated through the use of the Passivhaus energy modelling software, which is specifically designed to model ultra-low energy buildings. This is backed up by air leakage tests and commissioning records of the heat recovery ventilation. The standard requires a predicted heating demand of 15kWh/m².a over the usable floor area, adapted for the local climate (average energy use for UK housing stock is around 200kWh/m².a and new-build ranges from 50-100 kWh/m².a). We have developed the design of the house as a compact plan. This form has minimised the heat loss from the house and enabled gains to be received from its share of winter and summer sunshine. Planning design shows that the house can achieve the certified Passivhaus standard. The insulation levels needed to do this can be met with traditional cavity wall construction or timber combined with triple glazed windows and airtightness provided by wet plaster and the roof vapour control layer.

The Passivhaus standard requires an airtightness of 0.6 ach (air changes per hour) @ 50Pa (current Building Regulations require 10.0 ach @ 50Pa). This high standard ensures draught-free comfort, protects the building fabric from condensation due to leakage of humid air, and ensures that the efficiency of the heat recovery ventilation is not bypassed by leakage ventilation.

Super Insulated, Thermal Mass Building Fabric

The super-insulated, low energy house was built using 500mm insulated walls and 600 mm insulated roof to give a consistent all over fabric U Value of less than 0.11 W/m2k. The house includes heavyweight thermal mass to smooth out temperature fluctuations. The windows are Low E argon filled triple glazed, to give a centre pane U value of 0.76 W/m2k. Cold bridging was avoided through careful detailing around all reveals. Incidental air infiltration will be kept to a minimum through airtight construction.


Zero CO2Passive and Active Solar Design

A large percentage of the high performance solar glazing is orientated south to the private back garden to obtain the benefit of passive solar gain to the living spaces. Shading prevents summertime overheating but permits low level winter sun to penetrate to the heart of the house. Windows to the more public north, east and west elevations that have less passive solar gain potential are in comparison deliberately kept more traditional in scale and modest in size to reduce heat loss.


Zero CO2 – Site Generated Solar Hot Water 

One the largest consumers of energy within any house is the heating of domestic hot water to service the kitchen and bathrooms. As part of the sustainable development, solar hot panels where mounted on the south-facing roof of the house to convert sunlight to domestic hot water. The south-facing roof structure provides optimum solar orientation without compromising the building appearance. A 6kW wind turbine in the garden produces all the other required domestic electric, much of which is exported back to the grid to create a small income stream from the renewable installation.

Zero CO2 Site Generated Renewable Electricity

A 4kW photovoltaic array mounted in the wildflower meadow in the garden produces most of the required domestic electric.

Ground Source Heat Pump Under Floor Heating System

The passive solar design layout to the super insulated building fabric with thermal mass reduces the heat losses to a minimum creating considerable thermal inertia eliminating the need for a full conventional central heating system. No central heating boiler run of fossil fuels has been required. A ground source to water heat pump extracts the latent heat below the ground and invests it in to a thermal mass water store cylinder via a heat exchanger to provide hot water to run an under floor heating system.

Zero CO2 – Bio-Mass Secondary Heating System

A very efficient 2 to 4 kW efficient space heater using biomass fuel from the land  provides a social focus to the kitchen / dining / living room and compliments the heat gains from the sun, the occupants, the household appliances and the re-circulated heat from the heat recovery ventilation system.

Low Energy Appliances

All appliances have been carefully considered to eliminate unnecessary electrical demand and to optimize the efficiency of the essential items (cooker, fridge, low energy lighting etc). All selected components are category A* rated for maximum efficiency and minimal electrical draw when in use.

Mechanical Ventilation With Heat Recovery

For winter months when the outside air is cold relative to the required inside temperature, a whole house clean air comfort ventilation system is fitted with heat recovery (to preheat incoming cool fresh air with outgoing warm stale air) is used to reduce space heating requirement to a minimum.


Water Use

Household and garden non-potable water requirements are met by collecting rainwater from the main roof via galvanized steel gutters and downpipes and storing it in water butts and a ‘Rainharvester’ underground storage tank. Water from underground storage is filtered and used for flushing toilets and the washing machine. The water butts are used for garden irrigation. Water efficient flush toilets have been used along with air rated flow restricted taps a maximum flush of 4 litres. Water use is being monitored to ensure a non-wasteful system of use is maintained.

Healthy Internal Environment

Scatter rugs over stone tiled and waxed timber boarded floors, organic non-volatile solvent paints, avoidance of formaldehyde and other toxic equivalents combined with natural materials and summer natural ventilation and a winter heat recovery mechanical ventilation system provides a healthy internal air quality.

Household Waste

Kitchen waste and garden debris material is composted until dry and inert and then returned as a valuable non-toxic fertilizer to the food growing areas of the garden and greenhouse.


Text by Andrew Yeats Eco Arc Architects Photos by 3B.