Expert witnesses can have a key role to play in a construction dispute. These are people with a high level of knowledge and experience in their particular field. For example, in the event of a building collapse due to subsidence, you might need an expert witness with deep knowledge of soil stability and another who has considerable experience designing foundations to withstand shifting soils.
The main reason you need to call them is that someone has to decide what went wrong and who is to blame. The parties arguing over it will likely both think they are in the right and that the other side is to blame. So their version of events or their opinions about the matter cannot be entirely trusted, as they are not impartial.
The judge who presides over the dispute will have the final call. They will decide who has to compensate who or who has to remedy the problem. But they do not have the technical knowledge to make that decision themselves. Hence they rely on third-party experts – the expert witnesses – to interpret events for them so they can get a better grasp of the situation and arrive at a suitable resolution.
Expert witnesses are not entirely neutral
Each party can choose their own expert witnesses. They can use them to bolster their argument and counter the other party’s argument. While the witnesses should not be biased, each party can pick and discard expert witnesses, only using the ones that further their course in court.
So, for example, if someone accuses you of failing to check the subsoil properly you might hire three expert witnesses. Two of them might find that you were at fault and one say that you were not. You could heed the findings of the two, and accept that you might be better off trying to settle rather than go to court because there is a high chance you could lose. Or you could cast them aside and build your argument around the one who says you were blameless.
Those are not the kind of decisions you should make alone. Seeking guidance from someone who can interpret how a court might see the various arguments and help you develop the best strategy is wise.