All our log houses are manufactured in Finland where they have much greater extremes of temperature than the UK. They are designed to use as little energy as practicable in winter and remain cool in summer. You can specify as much depth of insulation as you want to achieve a target U value (we can guide you here, and it will depend on the insulation you choose to use). Wood is good at retaining heat and the log walls contribute to the overall efficiency of the house.