After you have opened the pop up window you can choose from any location where your object should be connected with. Normally that could be an enclosure within a room. The room itself is children of the house. And… here it comes... the house has to be the 'root-location'. Try choosing that in your house object. Click on it in the pop up window and wait until it reads 'root-location' at the bottom of the window. After that click 'Save'. And then 'save' again in the category where you have opened the window.
