Causes of Sagging Wood

• The main cause of wood sagging in the middle is atmospheric moisture. Though the entire door absorbs moisture, the sides of the door are inserted into the wooden frame or panel. This puts all the weight and pressure on the center of the door. As the door continues to absorb moisture, it becomes heavier and heavier in the middle, ultimately losing its shape and sagging.
  
  

How to Prevent Sagging

• The sagging of garage doors from the middle, also commonly known as a garage door smile, can be easily prevented by using caulking, preferably acrylic latex, on both the inside and the outside of the door. Caulking should be installed where the door panel inserts into the door frame. This gives additional support to the door.
  
  

Finishing of Garage Doors

• The finishing of garage doors can also help prevent the sagging in the middle. Garage doors should have some kind of enforcement on the edges. Such reinforcements should be installed before the garage door is painted. There are also sag-eliminating devices that can be installed on the door, but these tend to be a expensive.
  
  

Need for Ventilation

• Because they house cars and other equipment, garages need proper ventilation. By installing vents on opposite sides of the garage, a regular draft can be maintained that lowers the relative humidity and therefore reduces the moisture content. When the moisture content in the air is low, it does not condense on the door, thus preventing sagging.
  
  

Garage Door Maintenance

• Because wooden garage doors are susceptible to absorbing moisture and becoming heavy, regular maintenance of the door is required. Due to the increased weight in the middle of the wooden door, the nuts and bolts may begin to come loose. This makes the door noisy and contorted. The metal rollers of the garage doors may also require regular oiling because they can get rusted due to the moisture in the air.