PassivHaus -Conservation Area Central Cheltenham

CONSTRUCTION – A beautifully designed modern 4 bedroom  detached house contructed to passivhaus standards with high density bricks and 300mm insulation

KEY FEATURES–

Super insulated walls, roof and floor – virtually no space heating required

Fully triple glazed & High performance insulated door – High heat retention & airtightness

Mechanical Ventilation with heat recovery – controlled air flow eliminating any condensation issues

2 Ecocent Air source heat pumps – one feeding the ventilation system, and one for the domestic hot water

Solar PV providing enough electricity to match consumption

3000 litre underground rainwater harvesting system

A SAP rating of 116!

The occupants were living in a cold, draughty and inefficient Victorian house and were interested in living in a more environmentally friendly way as well as keeping warm in winter. Moving away from the area was something that they did not want to do having put down roots for a number of years in Cheltenham, as well as having family commitments. A 1950s detached house came up for sale just around the corner from where they lived that had not been improved since it was built. They saw an opportunity, and bought the house in 2011. Demolishing the existing house and contracting an architect to design a new passivhaus for them on the existing plot.

 

The owners estimated that they used around 55,000 kWh of energy per year in their Victorian home and had an initial aim to reduce their energy use in the new home by half to no more than 27000 kWh. In fact they now only use around 9,000 kWh a year.

The design and planning process to complete the house took around 12 months. As the house is in a conservation area there were planning requirements to consider, such as ensuring that the house look was in ‘keeping’ with the built characteristics of the area.

The build time was a further 12 months and the couple moved into the house in April 2013. A competitive tender was undertaken to employ the builder and the build process proved to be challenging for the builder and the trades employed to complete the house, particularly for those not familiar with the air tightness requirements to reach passivhaus standard. Educating all involved to ensure there was no air leakage was key in making the house ‘passive’.

The house has half metre thick walls, 200mm of which comprises high density compressed ash bricks set in a thin lime mortar to reduce air leakage and 300mm of insulation. To help in ensuring the house remained ‘in keeping’ with the housing stock in the area, some of the homes façade comprises an acrylic & render brick slip finish.

As well as super insulated walls, loft ,floors and doors ,triple glazed windows and low energy bulbs the house is designed to maximise benefits from the sun. The majority of windows are on the south facing side of the house, and the solar PV canopy above the ground floor is designed to shade the living areas of the house in the summer months whilst also maximising solar electric generation.

Renewable energy & heating

Although a passivhaus does not specify renewable energy requirements, the owners wanted to include solar photovoltaics in an aim to be energy neutral. A 10 kWp PV array was installed on the south facing roof of the house which generates an income of around £1500 a year from the governments ‘feed in tariff’ scheme. The homes total electric cost per year typically amounts to around £850 a year.

The only space heating in the home is provided by the MVHR which is assisted by a small Earth Save Products Ecocent air to water heat pump with thermal store. Hot water is provided by a separate Ecocent heat pump, with both Ecocent’s benefitting from the energy generated from the solar PV system. This system can draw heat from a thermal store when the temperature of the air being drawn into the house is below the desired comfort level. The window design and layout takes full advantage of solar gain in the winter when the sun is low in the sky but allows virtually no solar gain during the summer when additional heat would be unwelcome.

Although a conventional heating system is not required in a passive house, the owners did look into fitting a wood burning stove to provide a focal point to the main living area. Unfortunately, the relatively high heat output of even the smallest stoves and smoke control requirements proved to not make this possible. Not having a focal point heater is one thing they do miss.

Living in a airtight Passivhaus doesn’t mean living in an airlock!

We have lived in our Passivhaus for over two years and we love it. We are often asked whether living in an airtight construction means not being able to open the doors and windows. The answer is we are free to open the doors and windows whenever we like, and we do. In deep winter we keep everything closed as you would in any house and on very hot days we close doors and windows to keep the house cool. For the rest of the year we use windows and doors the way we would in any other house.
 
The ambient temperature remains consistent throughout the house and throughout the year. The mechanical ventilation means that there is no condensation. The resultant environment is calm and very comfortable.
 
In terms of energy efficiency the house has performed very well. Our annual consumption is c.9,500 kWh and the solar PVs produce over 9,800 kWh per year. Clearly the PVs produce more than we need in the summer and less than we need in the winter but across the year we have achieved our aim of being energy neutral.    

I love the fact that is always warm enough and that the house makes very low demands on the environment.

  
A passivhaus refers to a voluntary building standard developed by the Passivhaus Institute in Germany. To reach passivhaus standard the house must be airtight and have minimal heating and cooling demands. This standard is often reached by using mechanical ventilation and employing a number of passive measures in the building design and process such as insulation, heat recovery, orientation to maximise solar gains and solar shading and elimination of thermal bridges (cold spots).

  

For further details of the build specifics of this home and others built to passivhaus standard, visit the passive house database (see Resources) at: http://www.passivhausprojekte.de/index.php?lang=en#d_3809

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