Moisture Makes Paint Peel
The moisture damage to this patio ceiling could have been created from a
variety of other problems. However, the most common problem you're going to
have in a situation like this underneath an exterior patio cover will
usually have something to do with the roofing or roof covering.
The first thing I would check would be the roof shingles, make sure the roof is in good shape and isn't damaged or missing shingles.
The paint could also be peeling, because the surface wasn't cleaned properly before the next layer of paint was applied. Some exterior and interior walls and ceilings will get dirty and sometimes even develop some type of oily film and if this layer of grime isn't removed, then there's a good chance the paint won't stick and end up peeling off like this.
Paint can also peel and flake off, when it's overly thinned out. For example if you have one gallon of water based paint and mix it with 1 gallon of water, it might not stick as well to the next surface you're planning on applying to.
I've also seen paint do this when applied to wood with high levels of moisture. For example, one time I painted a wet 2 x 4 that was recently purchased from the lumberyard and within a few months, the paint started flaking off.
If you're planning on painting any wood, make sure it's dry and process used for this is usually referred to as kiln dried. This is when they dry large amounts of lumber inside of heated or well ventilated tents or buildings.
Again, there could be a variety of reasons why the paint is peeling off
of this green door, but most of them are going to be related to moisture. If
the door wasn't thoroughly painted, then it won't take long for moisture to
seep into any small gaps or cracks, eventually separating the paint from the
However, I've seen this before and would be willing to bet $100 that the bottom of this door was never painted. Eventually over time debris like leaves and twigs you see on the ground in the picture above got stuck under the door. This in itself wouldn't create a problem, however wet debris would.
The wet debris acts like a sponge and if enough debris starts to decompose around the base of the door, it can actually form a thick layer at the base of the door and absorb moisture out of the concrete, allowing moisture to absorb into the wood, regularly.
It's hard to imagine, but regular maintenance and cleaning probably would have prevented the paint from peeling off of this door.