Roof

• When a roof leaks over the course of several years, the wood base of the roof begins to rot. An ice dam that is allowed to form and remain for an entire winter can accelerate roof rot and begin to open up other holes in your roof where leaking can occur. The weakened roof also becomes unable to sustain the weight of heavy snow and, over time, it can collapse.
  
  

Ceiling

• As a roof leaks, the water drips down to your ceiling. If you have a drywall ceiling, then the constant leak of water will start to cause the ceiling to sag and crumble. If you have a ceiling made of compressed cardboard or some other composite material, then the leaking water from ice will cause the ceiling to start to warp. Ice dams become especially damaging because the leaking can go on for weeks, even months, and continue to damage your ceiling.
  
  

Walls

• Because an ice dam builds up in your gutters, the ice has a chance to collect around your downspout and near the walls of your home. Then as the roof leaks, it can leak down into the top of your walls and start to damage your drywall. Your paint will begin to bubble up and peel, and holes can develop in the wall where the drywall has been weakened by persistent ice melting.
  
  

Floors

• As water from an ice dam is allowed to leak down your walls, it will eventually start to cause damage to your flooring. Rugs will become soaked with the leaking ice water and may need to be replaced if mold begins to form. Laminate flooring will start to decay as water gets in to the sides and underneath the laminate. If the water gets to your plywood subfloor, then it can start to weaken the subfloor just as it does with the plywood on your roof.