Steel vs Timber Beams — UK Structural Guide
Comparing steel and timber structural beams for UK buildings — span capability, cost, fire rating, thermal bridging and installation considerations.
Side-by-Side Comparison
| Property | Steel (UB/RSJ) | Glulam Timber | LVL/Engineered Timber |
|---|---|---|---|
| Typical domestic span | Up to 10m+ | Up to 6-8m | Up to 5-7m |
| Depth for 4m span | 152-203mm | 250-350mm | 220-300mm |
| Weight (4m beam) | 80-160 kg | 40-70 kg | 30-55 kg |
| Beam cost (4m) | £200-400 | £150-350 | £120-280 |
| Fire resistance (unprotected) | 15-20 mins | 30-60 mins (charring) | 30-60 mins |
| Thermal conductivity | 50 W/mK (severe cold bridge) | 0.13 W/mK (negligible) | 0.13 W/mK |
| Ease of handling | Heavy — needs 2-3 people | Lighter — 1-2 people | Lightest option |
| On-site modification | Difficult (grinder/drill) | Easy (saw, chisel) | Easy |
| Lifespan | 100+ years | 50-100+ years | 50-100+ years |
Pros and Cons
Steel Beams
Pros
- + Spans longer distances
- + Shallower depth for same span
- + Higher load capacity
- + No shrinkage or movement
- + Standard sizes readily available
Cons
- - Heavy — difficult to manoeuvre
- - Severe thermal bridging
- - Needs fire protection (plasterboard)
- - Higher overall cost
- - Needs corrosion protection if exposed
Timber Beams
Pros
- + No thermal bridging
- + Better fire performance (charring)
- + Lighter — easier to install
- + Lower embodied carbon
- + Can be left exposed (aesthetic)
Cons
- - Deeper section needed for same span
- - More limited span capacity
- - Glulam can be expensive for large sizes
- - Susceptible to moisture damage
- - May need longer lead times
UK Cost Comparison (2026 Prices)
For a typical domestic wall removal (3.5m opening in a loadbearing wall):
| Cost Element | Steel (152x89 UB) | Glulam Timber |
|---|---|---|
| Structural engineer | £300-500 | £300-500 |
| Beam (supply) | £200-350 | £150-300 |
| Padstones | £40-80 | £40-80 |
| Installation labour | £800-1,400 | £600-1,100 |
| Fire protection / casing | £150-300 | £0-100 (if exposed) |
| Building Control | £250-400 | £250-400 |
| Total | £1,740-3,030 | £1,340-2,480 |
When to Choose Each
Choose Steel When
- Spans exceed 5m
- Heavy loads above (masonry, bathrooms)
- Minimum depth is critical (headroom)
- Internal beam (thermal bridging not an issue)
- Point loads or concentrated loading
Choose Timber When
- Beam is in an external wall
- Exposed beam aesthetic wanted
- Spans under 5m with moderate loads
- Low-carbon construction goals
- Difficult access (lighter to carry)
Related Calculators
- Lintel Sizing Calculator — calculate lintel size for window and door openings
- Steel Beam Calculator — size steel beams for domestic openings
How We Calculate This
Frequently Asked Questions
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Last updated: April 2026
All calculations are estimates. Verify with your supplier.