I would probably do this by having Pictures of the buildings' exteriors, which disappear as soon as you walk over the entrance to the house (and re-appear as soon as you walk back over the entrance to the outside).
The one catch is, as long as your maps are large enough to scroll (bigger than 17x13), you will need some kind of plugin which affixes Pictures to locations on the map (tiles), rather than to location onscreen. I think that there are plugins that do this; I just don't remember what they are called. Maybe someone who sees this will know, or you can ask on the Plugin Requests board.
- Alternatively, you could have large Event sprites with two pages (one visible and one not visible), with no event code within them, and have the not visible page be Page 2 and have a Condition Switch that is turned On/Off when you enter/leave the house by walking over certain tiles. This will allow you to get it working just fine without a plugin. The downside is that it can be a little finicky with where you place the event and the interior tiles below it, and if you already have lag the extra events on the map could exacerbate that lag.