THEORY, CONSTRUCTION AND PERFORMANCE DATA

The house at 19 Lang Lane, West Kirby, was designed and constructed using the Passivhaus concept, but dramatically exceeds the energy efficiency levels of all low energy housing standards currently being used to judge success. Below we list the main issues addressed and the performance of the house during the first 2 years of habitation.

This house has been designed to prove the case that it is possible to build a high performance home at a competitive cost; but it also shows that the owners do not have to significantly change their lifestyles in order to live in such a building. This house is flexible, comfortable, it has high quality design features and includes the spaces and volumes which many modern homes omit. Yet it is eminently affordable.

The building does not look out of place in its suburban setting, but is bold and responds carefully to its site location. Internally the spaces feel generous without being excessive and the varied volumes of the rooms makes living there an enjoyable experience.

It was also easy to build. There were no complex construction processes. Any small house builder could construct a house like this with very little extra skill being required. Attention to detail is needed, particularly in relation to the air tightness, but thin joint blockwork lends itself to this as a matter of course.

This house is ground breaking by being simple and economical to build, comfortable to inhabit and by having low running costs and a tiny carbon footprint of just 11Kg/year. Yet no part of the aesthetics have been sacrificed to the functional brief.

The house is exceptionally well insulated to achieve a minimum U value of 0.1W/m2K. There are no traditional foundations, with the ground floor raft floating on 200mm of insulation. Windows and doors are triple glazed with a U of between 0.7 and 1 W/m2K. The insulation on the walls wrap round in front of each of the window and door frames preventing cold bridging.

In modern well insulated hoes the primary heat loss mechanism is through ventilation and air leakage through the fabric of the building and round the various construction discontinuities, such as window and door junctions with the walls. In this dwelling there are no draughts! The house is almost hermetically sealed. In winter a ventilation system has to be used – see an adjacent tab for details. Air tightness tested to 0.98m3/(h.m2).

Thin joint blockwork construction is a very air tight form of construction and used in conjunction with external wall insulation provides extremely robust results.

No draught = comfort!

In houses with draughty rooms the air temperature has to be much higher to offset the heat lost from the bodies of the people occupying the house. In this house that is never the case as the surface temperatures are always the safe and there is no discernable air movement.

Draught Lobbies

The house was designed to have a draught lobby at the front door and to use the unheated utility room to act as one at the rear. However this has proved to be almost unnecessary as the house is so well sealed. On a windy day one external door can be left open for some time without significant heat loss occurring because there is nowhere for the warm air within the house to be blown to – there is no exit route for the air. So only very localised cooling actually occurs.

The house is largely built of concrete to retain heat in winter and maintain a stable temperature in summer. This high thermal mass maintains a very stable internal thermal environment. Even in winter the building temperature only degrades by about 1 degree per day when the heating is switched off.

Ground floor: 200mm cast concrete with 100mm sand cement screed.

First floor: 200mm cast concrete with power floated finish. Direct plaster finish to underside.

External walls: 150mm thin joint light weight concrete blocks. Direct plaster finish to inside.

Internal walls and partitions: 100mm dense concrete blocks. Direct plaster finish to both sides.

Natural cooling by volume and mass: South facing ground floor rooms have 3m ceiling heights to ensure stratification of air allowing the warm air to rise to the ceiling and transfer heat into the concrete first floor, resulting in those rooms never rising above 22oC in the summer of 2014.

The central stair void rises 8.6m from the ground floor and acts as a chimney to remove hot air in summer. The 2 roof windows at the apex can be opened remotely to allow the escape of warm air.

The additional height in these rooms also results in the window heads being higher than normal for a modern house. As the daylight factor is significantly increased with increased window head height this has the added benefit of improving the natural daylighting in the living room and studio.

The south facing PV panels generate 3,338kW 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 to 11Kg/year.

The panels chosen are fitted as the roof covering instead of the roof tiles, resulting a more easily maintained and aesthetically pleasing outcome.

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 2oC 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.

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 sucks warm moist air out of the bathrooms, utility room and kitchen and blows 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.

Energy use of 3,453 kWhrs per year: a sixth of that allowable under Passivhaus Standard. Energy generation of 3,338 kWhrs per year. Energy usage from April 2014 to April 2015 was just under 3000 kWhrs (see Ecotricity letter above).

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. 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 are currently rising slightly, so this may not be remain at this level for long.

Market Valuation

A recent valuation of the house shows 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.