These hexes are discussed in B23.211, and are nearly identical to buildings--and in fact are a rules sub-case of the single-story house (23.21). So I made the following table for myself to see how exactly they differ.
Looking over this thing, I'm thinking that the lumberyard is a great place to put your mortar. You can fire the thing, get a good terrain benefit, and even though you're in a valley, who cares? Height Advantage is NA for mortar fire! (Please correct me if I'm wrong about that.)
|Single-Story Wooden House||Lumberyard|
|LOS Obstacle?||Level 1||Level 1|
|Rally Bonus?||-1 DRM||None|
|Mortar Fire out of?||NA||Yes|
|EC DRM?||NA|| does apply|