How do I tell if a wall is load-bearing?

There is no completely reliable DIY test, and this is one of the few DIY questions where getting it wrong can collapse a building. The indicators below narrow it down; a structural engineer confirms it.

Indicators that a wall is likely load-bearing:

It runs perpendicular to the floor joists above. Joists span between supports, so a wall crossing them at right angles is probably carrying them. Determine joist direction from floorboard direction above (boards run perpendicular to joists), from the loft, or from below in a basement.

It is directly above another wall on the floor below, and ideally above a foundation. Loads must travel continuously down to the ground.

It is thicker than surrounding walls, or built of masonry rather than stud.

It is an external wall. These are almost always load-bearing.

It sits below a wall on the floor above.

It is at the centre of the building running along the main axis — a common position for a spine wall carrying joists from both sides.

Indicators it may not be: a thin timber stud partition that sounds hollow, running parallel to joists, not aligned with anything above or below, and not present on other floors.

Why the tests are unreliable. A stud wall can still be load-bearing. Walls can carry load from a roof rather than a floor. Previous alterations may have created unusual load paths. And non-load-bearing walls can still provide lateral restraint, preventing external walls from bowing — removing one of those causes problems even though it carries no vertical load.

What is required. In England and Wales, removing a load-bearing wall needs Building Regulations approval, structural calculations for a suitable beam, and appropriate support during work. A party wall requires notice to neighbours under the Party Wall Act.

Never remove anything before the beam and its supports are designed and ready.