Emplacements: what they do, costs and counters

Short answer

One per road. The right one makes its attackers take ×2 damage on that road.

What it does

An emplacement is a permanent defense on one road: Spikes, Tar or a Ballista. Build one per road once you have a Watchtower (level 1). It stays until you replace it.

Each answers one kind of attacker. Spikes shred Runners, Tar burns and slows Brutes, and a Ballista shoots down anything with the Climbing trait. The right one makes them take ×2 damage from your guards and towers on that road; any other still adds ×1.15.

Emplacement

Emplacement	Effect	Cost
Spikes	Runners take ×2 damage on this road; everyone else ×1.15.	120 scrap, 80 timber
Tar	Brutes take ×2 damage on this road; everyone else ×1.15. Brutes also walk 40 % slower.	100 timber, 80 biomass
Ballista	Climbers take ×2 damage on this road; everyone else ×1.15.	150 scrap, 100 timber, 20 serum

What answers what

Attackers	Emplacement	Stance
Runners	Spikes	Sally out
Brutes	Tar	Hold
Climbers	Ballista	Fall back
Shamblers	Any (small bonus)	Hold

Tips

Put Spikes on the road Runner raids keep using; they arrive first and fold fast.
Tar is the best answer to Brutes, which otherwise batter the gate down.
A Ballista only pays off against Climbers, so build one where raiders climb your barricades.

Questions

Which emplacement should I build in Voxhorde?

Match it to who attacks that road: Spikes for Runners, Tar for Brutes, a Ballista for Climbers. The right one makes them take ×2 damage; any other still adds ×1.15. You need a Watchtower (level 1).

Numbers come straight from the game's rules and update with every release.