Depends on house structure...
The whole WiFi marketing campaign has been blown out of all proportion, and truth lies buried far beneath the rubble.
Obviously the practical effectiveness of WiFi inside a building depends mainly on the number of walls and other obstacles, and the materials of which they are built.
In a flimsy house with interior walls made of wood or other light materials, WiFi can propagate fairly well. Likewise inside an office building with thin partitions. But if the internal walls are made of thick brick, stone or breezeblock, it's a different matter. Steel beams and girders, or even an unfortunately placed mirror can cause problems.
For many years now manufacturers have ignored the facts and advertised their WiFi products as capable of working well everywhere. That simply isn't true (and can't be if the the current law is respected).
I spent a lot of time struggling to get WiFi to work properly. Eventually I gave up and adopted mains powerline networking instead; I find it works perfectly. Moreover it's a lot more secure (not that I have much anyone would want to steal).