We have a one story, one room addition on our home, it was here when we bought the house. We tore the old roofs (many) off and replaced new plywood sheathing and shingles 2 years ago. We have also replaced windows and installed exterior insulation and siding. We have since noticed the roof bowing in the center. We discovered after tearing the floor off that there is no fondation at all, the builders used railroad ties and boulders!! To make matters worse the sills are all rotted and the west facing wall studs are rotted also. The floor joists are not attached to anything either, they were toe nailed to a board under just infront of the sill. The floor joist are at least 2 feet shorter than the width of the room. The room measures 13x10. We thought about using Pier fondation. The question is, how do you support a wall that has rotted sills. Its a wonder this room hadnt collapsed! Can anyone help? I would hate to tear it down after putting on a new roof, insulation and siding.