Construction Elements

bm elements

Fabric heat loss is the rate at which heat is lost by conduction through building element, this depends on the temperature difference across the element, its area and its propensity to conduct heat. the rate at which of Building element conducts heat is given by its Uvalue. The construction section calculates the fabric heat loss for the dwelling and also the transfer of heat between rooms where there is a temperature difference. If you have two adjacent bedrooms ie they have the same internal temperature you do not need to consider the heat flow between the adjoining bedroom wall.

  • Enter a new construction element use the +New button
  • To edit the details of an existing element double-click selected row in the list.


Typical uvalues are available in the program from three different sources. In most cases the default values should be used. If you are considering upgrading the fabric elements of the building then please use the Uvalue calculator to calculate the revised Uvalue.

  • Default values from EN12831 domestic heating design guide
  • Individual calculations using the Uvalue calculator and typical building materials

External floor roof and wall elements

For the external surface area for each room create a new construction element and choose the appropriate element type and element details. The software will automatically assign the Uvalue.

  • Floor - enter the area of the floor.
  • Roof - select the roof options for insulation type, enter the area. If you have roof windows in the project the area of the window will be automatically deducted from the area of the roof.
  • Wall - enter the area of the wall. In the window section the area of the window is automatically deducted from the wall to which it belongs.

In all cases you need to assign the element to a room space. This will enable the calculation of the heat loss for the room.

Internal Walls

If you have adjoining rooms of different types where there is a temperature difference you need to enter an internal wall. From the element type select "internal wall" and also the construction details for the wall. Enter the Wall area and then assign the internal wall to the two rooms to which it applies using the space one and space two lists. The software will then calculate the heat flow between the rooms. This is important for Heat Pump emitter sizing.