In the UK from mid October darkness descends around 6.00pm and once daylight saving ends on the last Sunday in October darkness can generally be predicted for 5.00pm. If you are selling or renting a property, there has been a legal requirement since 2007 for the owner of the property to obtain an Energy Performance Certificate ‘ EPC. This requires a visual inspection of the property in question both internally and externally and it is for this reason that darkness may affect your EPC.

Qualified Energy Assessors use a highly specialised piece of software known as RdSAP to produce your EPC. But the key to this software producing accurate results is the data that is entered by the Energy Assessor.

Once of the most critical aspect of the data that is collected is the external fabric of the building. This must be recorded as one of the following; Stone (Granite or Sandstone), Solid Brick, Cavity, Timber Frame, System Built or Cob. Identifying which of these options has been employed in the construction of the building can be undertaken in various ways including physical measurement and enquiries with the local authority. However the most effective method will be the visual inspection. Typically the Energy Assessor will be looking at the material used to build the walls and how this material has been constructed to produce the finished wall. Another factor will be the age of the building and the construction methods likely to have been employed at this time.

75% of residential property in the UK is of brick construction and this is generally identified by the actual physical presence of bricks in the walls. However bricks alone would not be conclusive as a property apparently constructed with bricks can either be cavity wall or solid wall. In some cases it may be timber framed with a brick outer covering. This is where the skill of the Energy Assessor is brought into play, as it is the way in which the bricks were laid that will identify the true wall type.

If the bricks are laid in what may appear as a slightly random fashion with both long and short sides of the brick showing, then this will ‘english bond’ or one of a number of other brick bonds associated with solid wall construction.

If the bricks are all laid in a near identical fashion with the long side only visible then a construction technique known a ‘stretcher’ bond has been used and this will identify the wall as cavity or timber framed.

The distinction between cavity and timber framed walls is more complex but the energy assessor will looking at whether the window frames are set deeply into the reveals and whether there are small vertical ventilation slots present in the walls. A combination of these factors is a clear indication that the property has timber framed construction. An internal inspection of the loft will generally confirm this.

Similar techniques are employed when an energy assessor encounters the other types of wall construction however the overriding factor in the assessment process is the ability of the energy assessor to clearly see the wall in question. On this basis, the EPC must be undertaken in good light conditions to avoid an inaccurate EPC.

Chris Grant is a qualified energy assessor and director of EPC Choice‘ one the UK’s leading providers of the EPC.