I have set my statusBar color to transparent for Lollipop only with the following line in my theme :
To achieve a completely transparent status bar, you have to use statusBarColor, which is only available on API 21 and above. windowTranslucentStatus is available on API 19 and above, but it adds a tinted background for the status bar. However, setting windowTranslucentStatus does achieve one thing that changing statusBarColor to transparent does not: it sets the SYSTEM_UI_FLAG_LAYOUT_STABLE and SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN flags. The easiest way to get the same effect is to manually set these flags, which effectively disables the insets imposed by the Android layout system and leaves you to fend for yourself.
You call this line in your onCreate method:
getWindow().getDecorView().setSystemUiVisibility( View.SYSTEM_UI_FLAG_LAYOUT_STABLE | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN);
Be sure to also set the transparency in /res/values-v21/styles.xml:
Or set the transparency programmatically:
The good side to this approach is that the same layouts and designs can also be used on API 19 by trading out the transparent status bar for the tinted translucent status bar.
If you only need to paint a background image under your status bar, instead of positioning a view behind it, this can be done by simply setting the background of your activity's theme to the desired image and setting the status bar transparency as shown in method #1. This was the method I used to create the screenshots for the Android Police article from a few months ago.
If you've got to ignore the standard system insets for some layouts while keeping them working in others, the only viable way to do it is to work with the often linked ScrimInsetsFrameLayout class. Of course, some of the things done in that class aren't necessary for all scenarios. For example, if you don't plan to use the synthetic status bar overlay, simply comment out everything in the init() method and don't bother adding anything to the attrs.xml file. I've seen this approach work, but I think you'll find that it brings some other implications that may be a lot of work to get around.
I also saw that you're opposed to wrapping multiple layouts. In the case of wrapping one layout inside of another, where both have match_parent for height and width, the performance implications are too trivial to worry about. Regardless, you can avoid that situation entirely by changing the class it extends from FrameLayout to any other type of Layout class you like. It will work just fine.