Long-term high moisture is the cause of most sagging garage ceilings we have seen over the years. Yes, sometimes the sag is because the homeowner stacked boxes directly on the drywall in the attic or accidentally stepped off the bottom truss chord when moving around up there, but usually it is just high moisture. Most garages are not air conditioned and many folks in our area leave the garage door open on hot days. The humidity weakens the gypsum board and corrodes the fasteners, letting gravity start to slowly pull it downward. 

    Ceiling sag can be difficult to see when standing on the garage floor looking up, but easier to observe if you stand on a ladder with your head just below the ceiling and scan across it. And when you are actually in the attic above the garage it’s hard to miss.

   Sometimes the sag is at a center seam between two boards, like in the photo above (viewed from the attic), where the board has pulled completely away from the fasteners; but sagging at the edge of the ceiling is also common in older garages, like in the photo below. A small roof leak at the overhang nearby will speed things up. Plus, a washing machine and dryer in the garage generates additional moist air.

    Anything you can do to reduce the humidity in the garage—such as keeping the garage door closed and minimizing other activities that put moisture in the space—will reduce the likelihood of a ceiling problem.

    Here’s a photo from the attic above a garage ceiling that is very close to collapsing. The gray lines below the bottom chords of the front two trusses are where the ceiling was attached before it pulled away from the fasteners.

Also, see our blog posts How can I make my garage cooler in the Florida heat? and What are the code requirements for fire separation between an attached garage and the house?

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Here’s links to a collection of our other blog posts about STRUCTURE AND ROOMS:

• What are the building code requirements for notching and boring holes in a wall stud? 

• What causes dark or light "ghost" lines on ceilings and walls?

• Can you access or exit a bedroom through another bedroom?

• What is the difference between a carport and a garage? 

• What are simple ways to find the cause of a ceiling stain?

• What is the minimum size of habitable rooms in a house according to the building code? 

• Why is my garage ceiling sagging? 

• How can I identify what kind of wood flooring I am looking at?

• Why does my concrete floor slab sweat and get slippery?

• What is the minimum ceiling height for rooms in a house? 

• Why are there score line grooves in the concrete floor of the garage?

• How much can I cut out of a floor joist? 

• How can I tell if my floors are sloping?

• Why do the floors slope in this old house? 

• What are the common problems when a homeowner converts a garage to conditioned living space, such as a family room?

• How can I tell if a wall is load-bearing? Which walls can I take out? 

   Visit our STRUCTURE AND ROOMS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.