A garden room that gets used in February

Single-storey rear rooms have a reputation for being too cold in winter and too hot in July, and it is deserved — but only for the ones built as an afterthought. Build the same room with a proper insulated floor and roof build-up, thermally broken glazing and a heat source that is actually on the system, and it becomes the room the house revolves around.

The junction where the new roof meets the old wall is where these rooms leak, so that detail gets the attention. So does the threshold, where the internal floor level, the external paving level and the damp-proof course all have to agree with each other.

It is also worth deciding early what the room is for. A dining room wants a different glazing orientation and a very different lighting plan from a snug.