Significance of Grandfather's house

Ruth and Lucille's grandfather builds the house over several years with his own hands and no knowledge of carpentry. It is built on high ground so it floods less than many houses in Fingerbone. It has many eccentric details, such as a trap door he creates to get into the upstairs bedroom because he fears the wall might collapse if he cut a door into it. The timid maiden aunts are afraid the house might collapse entirely, but their fears have some ground in reality.