Openings and lintels

The break in the load path

In a wall the studs carry the load evenly downwards. An opening interrupts that: where there is an opening there is no stud.

The solution has two steps:

1. The lintel above the opening gathers the load and carries it to either side.
2. The jamb — the reinforced stud beside the opening — takes that increased load on downwards.

The lintel

It can be a boxed section, a truss or a built-up beam. The choice depends on the span and the load.

What to watch:

• deflection: too flexible a lintel spoils the operation of the window or door,
• bearing: concentrated pressure arises at the ends,
• the connection: how it hands the load to the jamb.

The jamb

Not simply “one more stud”: it carries an increased load, often as a boxed or multiple section. The load taken downwards has to be continuous to the foundation — if there is no proper support beneath the jamb, the load path breaks. Load path continuity.

The effect on the bracing

This is the easy one to forget. An opening breaks not only the vertical load path but also the bracing:

• less room is left for the diagonal strap,
• the continuity of the sheathing bracing is interrupted.

Which is why bracing a façade broken up by many large openings costs more. Designing a shear wall.

What the order of design means

The architecture sets where the openings go and the structure carries the consequence. If the opening layout is known at concept design, the structure can adapt to it — by placing the bracing bays deliberately, for example.

If instead the opening changes during detailed design, it affects everything from the lintel to the anchorage.

The manufacturing side

The members around an opening — lintel, jamb, transfer member, sill — are all made to size. A later change to an opening therefore has manufacturing consequences as well as design ones.

The point

An opening does two things: it interrupts the load path and it weakens the bracing. The first is easy to handle; the second affects the whole façade.