The energy efficiency rating is a measure of the overall efficiency of a home. The higher the rating the more energy efficient the home is and the lower the fuel bills will be. This score is found on an Energy Performance Certificates (EPCs), a mandatory document, in England and Wells, which states the energy efficiency of the building when rent or sold.

This is a result of European Union Directive 2002/91/EC relating to the energy performance of buildings. The principle of this directive is to make energy use in buildings transparent by the issuing of a certificate showing the energy rating of a property, along with recommendations on how to improve efficiency.

As Mr D. Tail demonstrates, a Passive house has a high rating because it has an excellent level of insulation and airtightness.

On the contrary an old Victorian house, non-insulated with uncontrolled draughts that let air come in and out, show a low rating.

However we should not lose hope if we own an old house. Today the construction market offer plenty of products that help us to improve the building performance of a house to an acceptable level, even a Victorian house.

#040 - LUX (lx)

Lux is an unit of measurement of the light intensity. It is also called illuminance which is the amount of luminous flux per unit area. Wikipedia may be of some help for you if you need further explanation.

However, just to give you an idea of what is like, 1 lux is equal to the illumination of a surface one metre away from a single candle. Some further examples is shown in Mr D Tail's post; the light levels are 200 lux in a bright living room, instead outdoor is about 100,000 lux in a direct sunlight. 

Pretty astonishing this comparison, inevitably it makes you reflect.

#032 - U-VALUE

The U-value is a measure of heat loss in a building element such as a wall, floor or roof. The higher the U-value the worse the thermal performance of the building envelope is. According to Passive House Design standards all elements of the external envelope of the building should combine to provide a U-value of not more than 0.15 W/(m2K).

In order to calculate the U-value we should know the build-up materials of the building element, their conductivity properties and thickness.

For instance, a 200mm brick wall have high conductivity and facilitate the passage of heat/cold, on the contrary a 100mm insulation panel, usually installed within the cavity of the external walls, has low conductivity and slowly release the heat/cold .

This is why a contemporary insulated house is more energy efficient of a Victorian house. Mr D. Tail is definitely feeling more comfortable in a well-insulated house with a low U-value building envelop.


Please help Mr D. Tail to spot the differences within a Passive House and Passive Solar House.

Passive House and Passive Solar House are design standards for energy use in all building type. The design process it helps to reduce the buildings ecological footprint which is sometime we should be worry about:

“In 2012, direct buildings emissions (mainly from the use of gas for heating) accounted for 37% of UK greenhouse gas emissions (91 MtCO2). Buildings also were responsible for 67% of electricity consumption and related (i.e. indirect) emissions.” From www.theccc.org.uk

The Passive House relay on energy conservation through super-insulation, the heat losses of the building are reduced so much that it hardly needs any heating at all. However it involves the use of mechanical and electrical devices.

The Passive Solar House instead relay to the sum. It distributes solar energy in the form of heat in the winter and reject solar heat in the summer, this system virtually does not involve the use of mechanical and electrical devices.

Both design standards are effective. The Passive Solar House design is performing better in sunnier climates white the Passive House design is performing better on colder climate.

The systems in reality are not perfect and without problem but they are a huge step forward the reduction of greenhouse gas emissions.

Useful links:

Passive Solar House Design

Passive House

Please note how beautiful is RayShelf