Say a house faces southeast and you have said very little. Southeast covers forty-five degrees, and within it sit three distinct mountains: SE1, SE2 and SE3. Two homes on the same street, both nominally southeast facing, can hold different charts.
That is why the practice insists on a compass reading rather than a description. Fifteen degrees is the resolution the method was built at, and rounding to the nearest of eight directions throws away exactly the information the chart depends on.
Take the reading at the main door, standing where the building faces, away from steel, wiring and your own phone case. Take it three times. If the three disagree by more than a degree or two, you are standing next to something magnetic.
None of this requires belief. It requires an accurate number, a known year of construction, and the discipline to redraw the chart when the era turns.