@Tigga @Estecka Indeed! I assumed it would be the same for construction-sites as roads themselves are neutral. My bad!
So this issue is no issue if you can restrict them with your own construction-sites. Certainly not if you know that once the room is owned by you, you can remove the hostile construction-sites no sweat.
Thanks for the info and time guys! This issue is solved!
@estecka Thanks for the explanation again!
FIND_MY_CONSTRUCTION_SITES won't work on roads though 
but in general that is indeed what i use!
The whitelist/blacklist system is something i didn't think about, thanks 
it gave me some great ideas.
Otherwise yeah, I agree there should be a neat way to get rid of hostile constructions sites. Stepping on them seems almost too easy for me, and neither instinctive or fair, (and as we can see here, not reliable).
I'd rather see it that you could attack/dismantle sites to reduce their progress, and have them removed when the progress becomes negative. Or even have their progress decay out in unowned room.
That is what i was thinking as well, would be nice to have something in place like that.
@estecka thanks for trying and letting me know!
But that is kinda the problem 
my code is setup that i come into an external room i want to harvest energy in. I calculate the best path to each source, and let my builders build everything. If a previous player in that room has some construction-sites already i get rid of them by walking over them but i can't do that for the tunnels. So my builders will build the tunnels as well, which takes a lot of time and resources.
There is an easy work around, so no biggy, but i was just wondering if there would be something in the future to get rid of them.
Hello there,
First of all, i'm rather new to Screeps so i hope i'm posting this the right way.
Technical issue (for sure no bug)
Problem: When mining in an external room which i reserve i stumbled upon some tunnel construction-sites, i read in a few topics that you can walk over construction sites to remove them, but for tunnels this is not possible i guess.
Question: Do we have another way of removing them or are you guys thinking about this? Cause as far as i read the documentation roads are general non-owned construction-sites.
Work around: Checking how much energy the construction-site needs of is a valid option to ignore them, but just interesting is this is something that needs to be addressed in the future.
Thanks for checking this one out!
ps. i love the idea/implementation/game ! thx!