Modern houses are made, for the most part, of brick and concrete blocks. Topped with tiled roofs. At least in the UK. There is a lot of labour in making the bricks but a major reason that they were, historically, expensive was the cost of fuel. Where timber is used as the fuel there is substantial labour involved in gathering, storing and drying the wood and also in feeding the kilns. Using oil or gas as a fuel eliminates a major part of the labour. In a post-apocalyptic world fossil fuels would be in short supply, timber would once more be a significant energy source, to be husbanded.
If bricks become expensive then what are the alternatives? The obvious reversion is to wattle and daub construction. Strong wooden frames with the interstices filled with woven timber and covered with a clay, dung and sand mix that is then whitewashed to give some weather proofing. If the roof is thatched with reeds then the whole structure is organic and renewable with a much reduced embodied energy. The black and white appearance of many timber buildings in Britain is due to the Victorian habit of painting the timbers with tar. The original builders did not. I can only say that I lived in a house built in 1540 that had not had its outside timbers tarred and well… it was still there!
There is no reason why a house of this type shouldn’t be energy efficient, warm, elegant and comfortable. Walls can be made double thickness, packed with straw to trap air, or even, as the Romans did, built up from used and unrecyclable containers… in their case olive oil amphorae. Thatch can be a very efficient insulator, its major downside being the need to replace it every thirty years or so.
In some areas timber may be more limited. In those cases stone might be used. Or turf. The Vikings made many of their buildings from turf and the practice continued into the nineteenth century in some parts of Scandinavia. Again, thick earth walls, with thatch or even turf roofs, can be very warm and efficient houses. The materials are also available locally to the building, very important in a low energy density world, and are renewable. Taken to its logical conclusion you could build a city of terraced houses with their gardens on the roof, allowing compact building with comparatively large gardens. A city for hobbits!