Removing a load bearing wall, and what it actually takes

Removing a load bearing wall, and what it actually takes

Almost every renovation I look at in Sydney has the same wish attached to it. Take out the wall between the kitchen and the living room, open the back of the house up to the garden, and get one big space instead of three small ones.

It is usually achievable. The part that surprises people is that the beam is the easy bit. What the beam sits on, and where that load ends up, is where the money and the risk live.

First question, is the wall carrying anything

Plenty of internal walls carry nothing but themselves. Plenty of walls that look like partitions are holding up a roof.

Three checks answer it most of the time. Look at which way the floor joists or ceiling joists run, because a wall running across the joists is usually supporting them. Look directly above in the roof space for struts, hanging beams or a wall bearing down. Look at the wall below in a two storey house, because a wall with nothing under it is a problem already.

The check people miss is bracing. A timber framed house resists wind through nominated bracing walls. A wall can carry almost no vertical load and still be a bracing element, and pulling it out quietly reduces the racking capacity of the whole house. That has to be replaced somewhere else in the plan.

What sets the beam size

Span and load, in that order. A four metre opening under a single storey roof is a different beam to a four metre opening under a second storey with a tiled roof over it.

The other control is deflection. Strength is not usually what governs a residential beam. Movement is. Plasterboard, tiled floors and frameless glass are brittle, and a beam that is strong enough but flexible enough to sag a few millimetres will crack the finishes above it within a year. So the beam is sized for how much it is allowed to move, which is why the steel that comes back is often deeper than an owner expects.

Steel or engineered timber both work. Steel gets you a shallower section for the same span, which matters when ceiling height is tight. Engineered timber is easier to get into a house that has no side access, and easier to fix to.

Where the load goes after the beam

This is the part that gets skipped, and it is the part that causes damage.

The wall used to spread its load evenly along a footing. The beam concentrates that same load into two points. Those two points now need something under them: a post or a pier, then a path down through the floor structure, then a footing that was never designed to take a concentrated load.

On a slab, that often means a pad footing cut in and poured under the bearing point. On a suspended timber floor it means a pier down to the ground. On a two storey house it means checking the wall below is capable of carrying the new point loads and not just the old spread ones.

If the bearing point lands near a boundary or near an existing footing edge, it may need widening. That is a geotechnical question as much as a structural one, because bearing pressure depends on what the soil under it can take.

Temporary works decide whether it goes smoothly

The roof and the floor above still need holding while the wall is out and before the beam is in. Props go in on both sides, they need to bear onto something solid rather than onto a floor that will punch, and they stay until the beam is in and the bearing points are complete.

Most of the cracking that shows up after this kind of job comes from propping that settled during the works, not from the finished design. It is worth having the temporary condition drawn rather than left to the day.

Approvals in New South Wales

Internal structural alterations generally sit inside complying development rather than a full development application, but the certifier still needs engineering documentation and a certificate that the design complies with the National Construction Code and the referenced Australian Standards.

That means drawings, not a verbal size. If the property is strata, the owners corporation has a separate approval process because the beam and its bearing points may touch common property.

What a sensible sequence looks like

Get the inspection first, before the kitchen is designed around an opening that may not be viable at that width.

Have the beam and the bearing designed together, with the footing checks included rather than deferred to site. Get the temporary propping specified. Then build.

We run this work constantly through our structural engineering service across Sydney. The jobs that go badly are almost never the ones where the beam was undersized. They are the ones where nobody looked at what the beam was standing on.