passive heat storage, tile
My house was somewhat designed by the previous owner to get passive solar heat, it is orientated to the south, it has skylights on south that let the low winter sun penetrate deeper, it was built with a lowered floor area all along the length of the first floor for a thick tile job to store some heat.
None of these measures were implemented as well as they could have been, the skylights for example let in an awful lot of summer heat that I don't want, they would have been better if they were dormer windows so that the glass was more upright and so would select winter vs summer sun. The back wall should have had 2 layers of drywall vs one layer to store more heat. And, the owner installer when they tilled in the mid seventies filled part of the lowered floor area with 3/4 inch particle board to save work, which meant that the mortar bed was not as thick as it was designed to be. They did use 3/4 inch thick tile.
Some tiles have broken over time, and I can't match it, so I had to replace it. So I ripped out the particle board and now have a thick mortar bed, today just finished the deck mud and it is over 2 inches thick, total thickness is 2 5/8" of mortared and tile over about 120 sq foot area down the length of the house.
Photo is mortar bed in progress, the stuff applied is deck mud, it is like building a sand castle, it is mostly sand