Thermal conductivity of hermetic edge-sealing materials plays an important part in the thermal transmittance (U-value) of the triple vacuum glazing. Thermal conductivity of Cerasolzer CS186 alloy and J-B Weld epoxy-steel resin were measured and validated with the mild-steel and indium using transient plane source method with a sensor element of double spiral and resistance thermometer in a hot disk thermal constants analyser TPS2500s are reported. The thermal conductivity data of Cerasolzer CS186 alloy and J-B Weld epoxy steel resin were measured to be 46.49 W m⁻¹ K⁻¹ and 7.47 W m⁻¹ K⁻¹, with the deviations (using analytical method) of ±4% and ±7% respectively. These values were utilised to predict the thermal transmittance value of triple vacuum glazing using 3D finite element model. The simulated results show the centre-of-glass and total U-value of 300 mm × 300 mm triple vacuum glazing to be 0.33 W m⁻² K⁻¹ and 1.05 W m⁻² K⁻¹, respectively. The influence of such a wide edge seal on the temperature loss spreading from the edge to the central glazing area is analysed, in which the predictions show wider edge seal has affected the centre-of-glass U-value to 0.043 W m⁻² K⁻¹ due to the temperature gradient loss spread to 54 mm and 84 mm on the cold and warm side respectively.