Joining two words to make a single word
We call the "single words" you're talking about compound words.
It sounds like you're torn between creating closed and open compound words. The way to choose is to look at what other people are doing. The English language is always being reshaped by how we use it, so while "living room" might be two words today, who knows what will happen in 10 years!
In technical writing, readability always comes first. Choose whatever you think will make your writing more clear and understandable.