Who this guide is for
- Anyone laying out a plan where the upper floor structure has not yet been fixed
- Self-builders reading a structural layout for the first time
- Owners planning for future flexibility in a new house
- Anyone considering opening a wall in an existing building
- Buyers trying to understand which walls in a house are doing work
Span direction distributes the load path through the plan
Floor members deliver their load to the supports at their ends. Turn the direction and a different set of walls becomes the support, and the walls that were carrying become walls that are not. Nothing about the rooms changes; everything about which walls are working does.
That is why a span direction is a plan decision rather than a structural detail. It is settled while the layout is still moving, and it hands a particular set of walls a job they keep for the life of the building.
Loadbearing is not the only question
The library is careful here, and worth following exactly. A wall is judged loadbearing or not by what sits above it, ignoring the quite separate question of horizontal action. A wall can be carrying nothing vertically and still be part of the arrangement resisting horizontal force at that level.
Both questions land on the plan. Span direction decides the first. Where the resisting elements sit decides the second, and the entries note that if they are grouped towards one side, the parts of the building furthest from them travel furthest.
Which walls can later be opened
This is the part owners meet years later. A wall carrying a floor can still be opened, but doing so requires something to take over what it was carrying, and that something has to reach the ground. A wall carrying nothing may be simpler, unless it turns out to be part of the horizontal arrangement.
The entries frame the enquiry as a question rather than an inspection: if this wall is removed or opened up, what takes over its part in the arrangement. Partitions and stability walls can look identical once decorated, and the distinction is not thickness or material but whether the element is connected into the path.
- What is bearing on the wall, and where that load would go instead
- Whether the wall is part of the horizontal arrangement as well
- Whether the path can continue to the ground once it is diverted
- What temporary arrangement holds the building while the change is made
Walls have to arrive somewhere below
A support that stops at a level hands its work to whatever carries it across, and that transfer becomes the point everything above depends on. The entries use the same reasoning for stability: a wall that appears at every level except the ground storey is a different proposition from one that runs the full height.
At plan stage this is a stacking question. Walls chosen to carry an upper floor have to find something beneath them, and where they do not, a transfer element is introduced — which is a decision worth taking deliberately rather than discovering at the structural review.
The floor is also holding the walls
Span direction does not only decide what carries the floor. Where joists are built in or hung, the floor is also restraining the wall it bears on, so the connection serves the wall as much as the floor.
In a tied precast or concrete-topped floor the relationship goes further: the floor acts as a plate at that level, gathering horizontal force and delivering it into the walls, frame or cores. The direction the floor runs then interacts with where those receiving elements sit.
Changing the structure changes the answer
The same plan takes a different structure in different ways. A joisted floor spans in one direction between a pair of supports. A solid panel floor spans as a plate, and moving a wall to suit a layout removes bracing and enclosure along with the load path. A floor of precast units spans unit by unit to a set-out fixed before manufacture.
So a late change of floor structure is not neutral to the plan below. It can move which walls are carrying, which is why the two decisions are best taken in the same conversation.
What to ask while the plan is still moving
Ask which way each floor is intended to span, which walls that makes into supports, and whether those walls stack down to something. Then ask which walls the design is relying on for horizontal action, and whether the answer is recorded anywhere in writing. Both answers are cheap at plan stage and expensive afterwards.
Span direction at plan stage
- 1Ask which way each floor is intended to span.
- 2Identify which walls that makes into supports, and mark them on the plan.
- 3Check that each supporting wall has something beneath it at every level down to the ground.
- 4Ask where a transfer element would be needed if a wall does not stack.
- 5Ask which elements the design relies on for horizontal action, and whether that is written down.
- 6Ask whether those elements are balanced in plan or grouped to one side.
- 7Ask whether the floor is also restraining the walls it bears on.
- 8Consider which walls you might want to open later, and raise that while the layout is moving.
- 9Ask what would take over a wall's part in the arrangement if it were removed.
- 10Confirm that a change of floor structure is reviewed against the plan below rather than swapped in.
- 11Ask for the structural arrangement to be recorded so later work does not disturb it.
- 12Keep that record with the building, not only with the design team.
Common mistakes to avoid
- Treating span direction as a structural detail, when it distributes the load path through the plan below.
- Judging a wall only by what sits above it, ignoring the separate question of horizontal action.
- Assuming a partition and a stability wall can be told apart by thickness or material.
- Planning walls that do not stack, and leaving the transfer to be discovered at structural review.
- Grouping the resisting elements towards one side without anyone reviewing the plan arrangement.
- Changing the floor structure late without reviewing which walls that makes into supports.
- Leaving the arrangement unrecorded, so later alterations are made without knowing what belongs to it.
When to involve a professional
- Which elements carry load, and what happens if one is removed, is a determination for a qualified structural engineer for that building.
- Elements resisting horizontal action are frequently indistinguishable from ordinary walls and floors once finishes are in place.
- An alteration that appears local can change how a whole storey behaves, particularly where it touches a connection or a plate edge.
- Nothing here is a basis for deciding that a wall, a floor or an opening may be altered.
- No span, member size or capacity is stated here, and none can be inferred from it.
Frequently asked questions
Questions readers ask about this topic
How do I know which way my floor spans?
From the structural information rather than from the rooms. The entries are consistent that the arrangement cannot be read from a finished building, and that the drawings and the record of alterations are the only reliable statement of where it is.
If a wall carries nothing above it, can it be removed?
That is only half the question. A wall is judged loadbearing by what sits above it, ignoring the quite separate question of horizontal action, and a wall carrying no vertical load may still be part of the arrangement resisting force at that level.
Why does it matter whether walls stack?
Because a support that stops at a level hands its work to whatever carries it across, and that transfer becomes the point everything above depends on. Planning walls that stack keeps the load path continuous rather than requiring an element to carry it sideways.
Can I plan now for opening a wall later?
You can make the conversation possible. Asking at plan stage which walls become supports, and which the design relies on for horizontal action, gives a future designer the information to assess a change rather than having to investigate the building first.
Does the floor structure change which walls carry?
It can. A joisted floor spans between a pair of supports, a solid panel spans as a plate, and precast units span to a set-out fixed before manufacture. A late change of structure is therefore reviewed against the plan below rather than simply substituted.
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