For exterior painting, you need a finish that is appropriate for the walls, trims, windows and everything else. It is best that these elements are painted with different finishes regardless of what colour they are. If you use the same finish everywhere, this can create a flat, one-dimensional effect. Generally, you will have three options, though the actual options may vary depending on the manufacturer.
Flat Finish: For Walls Only
A flat finish is the most porous and the least light reflective. The benefit of this is that is will hide any flaws and imperfections on the exterior walls. So if the surface is less than perfect, this finish will flatter it the most.
However, the more porous a paint is, the less durable it is as well. So flat paint is not suitable for high-use elements that are frequently touched, such as doors, window and railings. The matte surface will show dirt easily but will not be able to withstand constant cleaning. Lighter colours also will make grime more obvious. Flat finishes, then, are best reserved for wall areas which are rarely touched.
Satin Finishes: The Most Versatile
This is a popular finish for home exteriors. It has a slight subtle sheen that flatters walls perfectly; it is neither too matte nor too shiny. Satin surfaces are also easy to clean using pressure washing. For houses that are painted using a flat paint on the walls, this provides a good option for the trimming. Such a contrast will create depth and give an attractive multi-dimensional effect.
Satin finishes are less porous and more durable than flat paint, but they still don't wear well when used in high-traffic areas. If you like this level of sheen, however, you might be able to source an exterior satin paint that is specially designed to endure heavy use.
Gloss Finishes: Best For Details
Gloss finishes are the most robust and least porous of the three; they are also easiest to clean. But they are best used in small amounts. If you paint exterior walls entirely in gloss, it can produce a shiny, synthetic effect.
Gloss paint will tend to magnify every surface flaw and blemish in any case. So it is best reserved for areas that need a hardwearing finish. If you want to highlight a particular architectural feature of your house, though, painting it with gloss will help to make it a stand-out feature.