Most knock-throughs, kitchen extensions and chimney breast removals in London end with a steel beam carrying the house above. Building Control will normally ask for structural calculations that prove the beam, the supports at each end and the walls and foundations below can carry the load safely. These are the questions London homeowners ask us most often about steel beams and the calculations behind them.
Is it an RSJ or a universal beam?
"RSJ" (rolled steel joist) is the name most people use for any steel beam in a house. In practice, most beams used in homes today are universal beams (UB). Other common options are universal columns (UC) where headroom is tight, pairs of channels (PFC) bolted together, and flitch beams, which are timber joists with a steel plate bolted between them. The engineer picks the section that suits the load, the span, the headroom and how the beam will be installed.
Do I need a structural engineer to size a steel beam?
In almost every case, yes. Removing or opening up a load-bearing wall is building work under the Building Regulations, and your building control body will want to see calculations. A builder's rule of thumb or a supplier's span table only covers the beam. It does not check what sits above it (floors, walls, roof, a chimney stack) or what is below each end (the wall, the padstone and the foundation). That load path is what the engineer checks.
What do steel beam calculations include?
A typical calculation package for a domestic steel beam covers:
- The loads coming down onto the beam from the roof, floors and walls above
- The beam size and steel grade, checked for strength and for deflection (how much it bends), so ceilings and finishes do not crack
- The bearings at each end: padstones, posts or columns, and their bases
- Connections, where one beam meets another or sits on a post
- A check of the walls and foundations that will take the new concentrated loads
- Notes on temporary propping and on fire protection
The output is a set of calculations and a simple drawing or sketch that the builder and the Building Control inspector can follow.
What is a padstone and why do I need one?
A steel beam gathers load that used to be spread along a whole wall and delivers it onto two small areas at its ends. A padstone is a block of dense concrete or engineering brick under each end of the beam that spreads that concentrated load into the wall below, so the brickwork does not crush or crack. The Planning Portal's guidance says a new beam should normally have at least 150 mm of bearing onto the wall at each end. Your engineer will size the padstones and confirm the bearing for your beam.
Does a steel beam need fire protection?
Yes, normally. The Planning Portal's guidance is that a steel beam should normally be protected so that it has 30 minutes' resistance to fire. This is usually done by boxing the beam in with fire-rated plasterboard or by coating it with intumescent paint, which swells up in a fire and insulates the steel. Some buildings, such as flats or taller houses, can need a longer period, so check what your building control body expects.
How is the house held up while the wall comes out?
Before the wall is removed, the builder supports the structure above with temporary works, typically steel needles through the wall carried on adjustable props. The props stay in place until the new beam is installed, packed tight onto its padstones and the mortar has gained strength. The engineer's calculations can include notes on the propping and the order of work. On site, the builder is responsible for carrying it out safely.
Will I need a party wall notice?
If the beam will bear on, or be cut into, a wall you share with a neighbour, the Party Wall etc. Act 1996 will usually apply. Notice for work to a party wall normally has to be served at least two months before the work starts, so it is worth raising early. The engineer's drawing will show where the beam bears, which helps the party wall surveyor if one is appointed.
Can I remove a wall in a flat?
Often, but leaseholders usually need the freeholder's consent first, and the freeholder or managing agent will normally ask for a structural report and calculations. We explain what that report needs to show in what a right-to-alter structural report must show.
What does Building Control check?
The inspector reviews the calculations and normally inspects the work on site, often when the beam is in place on its padstones and before it is boxed in. When the job is signed off you receive a completion certificate. Keep it, with the calculations: buyers' solicitors and mortgage lenders often ask for both when you sell.
What will the engineer need from me?
- Which wall you want to remove or open up, and the size of opening you want
- Floor plans or simple sketches with measurements, if you have them
- Photos of the wall, the rooms above it and the loft
- What sits above: another floor, a bathroom, a chimney stack, a loft conversion
- Any cracks or past movement you know about
- Access for a site visit, so the engineer can see how the house is built
Steel beams for chimney breasts, extensions and lofts
The same principles apply when a beam supports a chimney stack, the back wall of a house that is being extended, or a new loft floor. For more detail see chimney breast removal calculations explained, load-bearing wall removal in London homes, our London extension FAQ and our loft conversion structural engineer FAQ.
Steel beam calculations in London
Laytoe Structures is a firm of structural engineers based in Chiswick, W4, working across London. Since 2016 we have carried out more than 2,700 projects, including structural surveys, and we provide structural calculations and steel beam design for load-bearing wall removal, chimney breast removal, extensions and loft conversions, ready for Building Control. See our extension and loft calculations service, request a quotation or call 020 3983 5057.