There’s no definite rules for this. But usually in the UK, the house number applies to the specific house/building, not the whole plot or garden etc.
So I think its best to tag the address on the house building area. So a closed way, tagged as building=house, addr:housenumber=1, addr:street=Streetname etc.
If the building is split into pieces, with different addresses (eg a semi-detached or terrace house), then draw them as separate areas, but sharing nodes on the dividing walls. This makes clear there are attached to each other. Then tag each part as building=house and the address etc.