The Limestone Wall

The centre wall of our house is a Limestone feature wall. Not only will it look good, but it also acts as a thermal mass, absorbing heat in the winter (from the combustion heater we will put right in the middle of that big bit up there) and releasing it at night, keeping the house warm.
It works the same way as the cement will, absorbing heat in winter and releasing it.

In summer, there will be no direct sun into the house as we face true north, therefore in summer the cement and the limestone wall will stay cool, in return cooling the house.