We are residing our house with fiber cement panels and have added some wood trim. The panels have been painted with a flat finish and look great. Question is, does it matter if the wood trim is flat as well, or does it need to be satin or semi-gloss in order to seal better? What is "standard"? I would prefer flat. Any reason why we shouldn't do it that way?
Flat is fine.......to me it's just more of a dirt catcher than say a satin. Personally, I like Satin on the body of the house and Semi-gloss for trim. It's more tradition than anything else............having some gloss to the paint makes it much easier to clean, when, and if you happen to clean your siding down every couple years.
I agree with Gymschu that flat would be okay. It will be a definite dirt catcher, and that you may regret, because it will not wash very well. From a decorative standpoint I don't think it's the best choice. My personal preference is for flat or a very low luster for the field work and minimum of a satin trim. Color differences of low contrast will help accentuate but the sheen difference will add a little more punch. If you have a high color contast, you could easily get away with the same sheen levels. The house pictured below was done entirely with Cabot's ProVT solid latex stain, the only difference was the color. It looks great.