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The following building regulations considerations apply when designing a one off / single unit house. A grant may be claimed for retro-fit applications.

Building Regulation Requirements

Part L of The Building Regulations relating to the conservation of fuel and energy was updated on the 1st July 2008. There is now a requirement for renewable energy to be incorporated into the dwelling.

Part L Conservation of Fuel and Energy
Part L Conservation of Fuel and Energy

A minimum of 10kWh/m2/yr of renewable energy needs to be installed on all new dwellings on which works commenced on or after 30th June 2008, certain arrangements are in place for works completed by 30th June 2009.

There are many technologies which can be used to comply with the regulations, wood pellets, wood gasification, heat pump and solar.

Solar is the most popular choice as it is relatively inexpensive to install on a new build and has very low maintenance associated with the installation. Please see the relevant pages on biomass and solar for further discussion regarding these technologies.

In order to demonstrate that the building complies with the regulations the official SEI DEAP software must be used, the current version of the software, DEAP III will clearly show if the heating system chosen will provide compliance for the development. As the renewable requirement is based on floor area, a larger system or a combination of technologies will be needed for larger houses.

Using solar panels with good performance data will mean that compliance with the regulations can be achieved using reduced collector area, thus reducing the over all cost of the system.

BER Chart
BER Chart

Not all Solar Collectors are Equal

Compliance with part 2L (b) of the Building Regulations 2007 may be achieved using renewable energy technologies.

A minimum energy input of 10 kWh/m2/annum contributing to energy use for domestic hot water heating, space heating or cooling is required.

The capacity of the Solar Thermal system will be calculated using the DEAP software.

The underlying calculation method in DEAP is based on the equation:

Qs = S x Zpanel x Aap x h0 x UF x f(a1/h0) x f(Veff/Vd)


  • Qs = solar input, kWh/year
  • S = total solar radiation on collector, kWh/m²/year.
  • Zpanel = overshading factor for the solar panel.
  • Aap = aperture area of collector, m²
  • h0 = zero-loss collector efficiency
  • UF = utilisation factor
  • a1 = linear heat loss coefficient of collector, W/m²K
  • f(a1/h0) = collector performance factor = 0.87 – 0.034 (a1/h0) + 0.0006 (a1/h0)²
  • Veff = effective solar volume, litresVd = daily hot water demand, litres
  • f(Veff/Vd) = solar storage volume factor = 1.0 + 0.2 ln(Veff/Vd) subject to f(Veff/Vd) <= 1.0

There are three groups of parameters used in the calculation:

  1. The hot water energy usage figures come from DEAP and are based on the house size and calculated distribution losses.
  2. The size of the twin coil solar tank and the volume of dedicated solar storage are entered into DEAP.
  3. The aperture area, optical efficiency and linear loss coefficient of the collector are also used.

Aperture Area: The area of the panel which collects energy

η0: Optical efficiency: This indicates the percentage of the solar rays penetrating the glass of the collector and being collected.

A1 and A2: The coefficients a1 and a2 describe the heat loss of the collector. They indicate the amount of heat that the collector loses to the atmosphere per m2 of aperture

Example: Building Regulation compliance for a house with a floor area of 180 square metres is required. A twin coil of solar tank of 300 L capacity will be used with a dedicated solar storage volume of 165 L. A minimum input of 1800 kWh per annum will be needed from the solar heating system.

Comparing two different collectors:

h0 a1 Aperture Area Required

Collector 1 0.734 1.529 4.5

Collector 2 0.752 3.55 5.9

Conclusion: There will be considerable differences in collector performance. Great care should be exercised when making comparisons.

A collector can have a high η0 which means it collects a lot of energy. But it can also have a high a1/a2 which means it doesn't retain the energy well. A collector can have a low η0 which means it does not collect much energy. But it can also have a low a1/a2 which means it retains most of the energy it collects.

A collector can sometimes compensate for poor efficiency figures by having a larger aperture area. Alternatively a collector with a small aperture area can sometimes have excellent efficiency figures and give a better output. This is important to note when designing a system, especially when roof space and/or finances are limited.

Should you require any assistance in determining the number of panels required for compliance with the above regulations, please contact RVR for advice.

Grants available

The Greener Homes Scheme

The Greener Homes Scheme was updated in July 2008 to Phase III. The homeowner can only apply for a grant under the Greener Homes Scheme if the house is over a year old, as the Building Regulations 2008 now govern new buildings.

You can read more at Homeowners:Solar_Grant_Information