Search “RSJ span table” and you will find everything from tidy charts to wild forum guesses. This page is a planning table for common domestic openings in UK houses. It assumes simply supported Universal Beams, typical residential floor loads and sensible load widths. Change the roof load, wall above or room depth and the answer moves.
Not a design standard. Not Building Control evidence. For interactive sizing use the beam size calculator and the span table tool. Pair the numbers with the complete size chart when you need weights and section properties.
How to read this table
- Span = clear opening between supports
- Suggested planning section = common conversation starter, not a certified size
- Add about 150 mm bearing each end when ordering length
- Prefer a stiffer section if finishes are brittle or load width is wide
- Grade and restraint conditions are assumed “ordinary domestic”. Unusual details need engineering
If you only remember one thing: clear span is not cut length. Translate openings with the bearing length calculator.
Domestic floor beam — planning span table
| Clear span | Light / narrow load width | Typical domestic floor | Heavier / wider load |
|---|---|---|---|
| 2.5 m | 152×89×16 | 178×102×19 | 203×133×25 |
| 3.0 m | 178×102×19 | 178×102×19 / 203×133×25 | 203×133×25 |
| 3.5 m | 178×102×19 | 203×133×25 | 203×133×30 |
| 4.0 m | 203×133×25 | 203×133×25 / 254×146×31 | 254×146×31 |
| 4.5 m | 203×133×30 | 254×146×31 | 254×146×37 |
| 5.0 m | 254×146×31 | 254×146×37 / 305×165×40 | 305×165×40 |
| 5.5 m | 254×146×37 | 305×165×40 | 305×165×46 |
| 6.0 m | 305×165×40 | 305×165×46 / 356×171×45 | 356×171×51 |
Deep-dive guides: 3 m · 4 m · 5 m · 6 m.
What “light”, “typical” and “heavier” mean here
These columns are shorthand, not load cases from a code book.
Light / narrow load width usually means a modest floor area landing on the beam, often a corridor-like arrangement or a short room on one side only, with ordinary timber floor finishes.
Typical domestic floor is the busy middle: ordinary dead and imposed residential floor loads, rooms of normal depth, plasterboard ceilings, no wall continuing above.
Heavier / wider load covers deep rooms both sides, denser finishes (screeds, large tile areas), or anything that makes deflection sensitive. It is still not a roof or multi-storey wall load. Those sit outside this table.
If you are unsure which column fits, pick the heavier one for budgeting and let the engineer decide the real mark.
What this table deliberately ignores
Point loads from trimmer beams, cantilevers, partial fixity, wind on tall openings, snow on roofs, fire design, vibration from gym equipment, and historic fabric quirks. Those belong in engineer calculations.
Also ignored:
- timber frame vs masonry bearing differences beyond a generic warning
- unusual steel grades or stainless specials
- camber requirements
- moment connections and portal frames
- flitch beams and hybrid timber-steel options
If your opening carries a roof or a multi-storey wall, do not use the “typical floor” column. Start with a proper brief instead.
Deflection vs strength
Longer rows in the table jump sections because of stiffness, not just bending. A beam can have spare bending capacity and still fail a serviceability check.
Many domestic floors target about L/360 under the relevant load combination. Your engineer confirms the exact limit for the finishes and use class. At 4 m that is roughly 11 mm. At 5 m about 14 mm. At 6 m about 17 mm. Those millimetres are where cracked ceilings come from.
Check serviceability with the deflection calculator. Use it to understand why the table jumps size, not to certify a beam.
Related reading: RSJ beam deflection calculator guide and how much weight an RSJ can hold.
Padstones and bearings
Every row assumes proper bearings and padstones. Soft blockwork without a padstone is a classic failure pattern. See the padstone guide and padstone calculator tool.
Bearing length is commonly about 150 mm each end on domestic jobs, but drawings win. Do not shorten bearings to make a stock length fit.
How to use the table in a real briefing
- Measure clear span accurately
- Estimate load width each side (room depths contributing load)
- Note walls, roofs or point loads above
- Pick a planning column and section
- Convert to order length including bearings
- Sense-check weight for access (weight calculator)
- Sense-check cost band (cost calculator, sizes and prices)
- Hand the brief to a chartered structural engineer
- Order only the mark on the stamped drawing
That workflow stops the classic mistake of emailing a stockholder “4 m RSJ please” with no section, grade or end details.
Worked examples using the table
Example A — 3.0 m hallway opening
Clear span 3.0 m, joists from one side only over about 2.5 m, timber floor, no wall above. Planning column: light to typical. Sections often discussed: 178×102×19 or 203×133×25. Order length ~3.3 m. Details: 3 m span guide.
Example B — 4.0 m kitchen knock-through
Clear span 4.0 m, rooms both sides, ordinary domestic finishes. Planning column: typical, maybe heavier if tiles upstairs. Sections often discussed: 203×133×25 or 254×146×31. See 4 m guide and the kitchen case study.
Example C — 5.5 m open-plan rear
Clear span 5.5 m, deep rooms, large plaster ceilings. Planning column: heavier. Sections often discussed: 305×165×40–46. Expect cranage conversations. See 5 m and 6 m guides for logistics.
Interactive tools vs static tables
Static tables are good for scanning. Interactive tools are better when you want to nudge span, load or section and watch the estimate move. Use:
None of them replace calculations signed by an engineer for your address.
Related references
- Complete size chart
- Safe load tables
- Load span tables UK/EU
- RSJ beam sizes explained
- Install cost guide
FAQ
Can I show this table to Building Control?
You can show it as background reading. They will still want site-specific calculations and drawings.
Why do other websites list different sizes for the same span?
Different assumed loads, grades, deflection limits and optimism levels. Some charts are copied without context. Prefer engineer output for the building in front of you.
Does the table work for loft ridge beams?
Not reliably. Roof loads, snow combinations and restraint differ. Use loft-specific guidance such as RSJ for loft conversion and get proper design.
What if my span sits between rows?
Budget with the longer row. Millimetres matter less than load width and finishes when you are still planning.
Using the table with other tools
- Pick a planning band here or in the span table tool.
- Sense-check with beam size calculator.
- Check stiffness � deflection calculator.
- Convert to order length � bearing length calculator.
- Budget � cost calculator and install guide.
Deep dives by span: 3 m � 4 m � 5 m � 6 m.
Bottom line
Use the table to budget and brief. Use an engineer to design. Building Control wants calculations, not a screenshot of this page.
About Owen Briggs
Maintains RSJ.info calculators, size charts and reference tables. Focuses on usable planning tools with clear safety disclaimers.
