The SBEM calculation engine requires confirmation that U-values for ground floors have been calculated with consideration for heat loss due to contact with the ground
From the SBEM Technical Manual
"The U-value for ground floors should be adjusted to account for insulation to counter the heat loss through contact with the ground (as a function of the ratio of exposed perimeter to floor area and the thermal resistance of the floor construction) following the guidance specified in section 3.5.2 of "CIBSE Guide Vol. A - 200 (and ISO 13370:2007 - Thermal Performance of Buildings - Heat Transfer via the Ground - Calculation Methods)"
By default, U-values for ground floors are considered as modified in accordance with BR 443:2003. In this case SBEM will use the user defined U-values. If the user defined ground floor U-values have not been modified to account for ground effect or edge insulation, the Ground floor U-values tick box should be unchecked and SBEM will make appropriate modifications of your U-values.