Cross-laminated timber vs steel: a practical comparison

Both materials have strong cases for mid-rise buildings, and the debate between them has moved well past the headline claims about carbon and speed. Which one wins depends on the site, the programme and the client’s priorities, and the honest answer is usually that both deserve a proper comparison rather than a default choice.

Weight and foundations

Timber frames are much lighter than an equivalent steel structure, roughly a fifth of the weight for a comparable mid-rise frame, which can reduce foundation costs meaningfully on poor ground and make crane selection easier since the loads being lifted and the loads being carried down to the ground are both smaller. On a site with existing foundations from a previous building, that weight difference can be the deciding factor in whether reuse of the substructure is possible at all.

Fire performance

Mass timber chars at a predictable rate when exposed to fire, which lets designers add a sacrificial layer of extra thickness calculated to burn away over the required fire rating while the structural core underneath keeps its strength. Steel, by contrast, loses strength quickly at high temperature and needs intumescent coatings, board encasement or other protection to reach the same rating, protection that adds cost, time and a maintenance obligation over the building’s life. Both approaches are well proven and both satisfy building codes when done correctly, but they require different specialist trades and different inspection regimes, which is worth factoring into programme and cost comparisons rather than treating fire protection as a rounding error.

Speed and tolerances

Steel arrives on site in longer members with connections that generations of engineers have refined, and steel erection crews are widely available with deep experience. Timber panels arrive cut to a precision that steel struggles to match, often accurate to a couple of millimetres, but that precision only pays off if moisture is controlled carefully throughout the build. A wet panel swells, a dry one shrinks, and either can throw off tolerances that were fine on the factory floor. Sites with covered storage and a clear plan for keeping panels dry from delivery to enclosure get the full benefit of timber’s precision; sites without one often find the benefit erodes.

Acoustics and servicing

Timber structures generally need more attention to acoustic separation between floors than an equivalent concrete or steel-and-concrete frame, since a lighter structure transmits impact and airborne sound more readily. This is solvable with the right floor build-up, but it is an extra design step that a steel-frame job with concrete floors may not need to the same degree. Running services through a mass timber frame also asks for more upfront coordination, since drilling and notching structural timber on site is far more restricted than doing the same to a steel beam, and most penetrations need to be planned into the panel design before it is manufactured.

Cost

Prices vary by region, by market conditions and by how mature the local supply chain is for each material, so a rule of thumb from one country rarely transfers cleanly to another. The comparison worth making is whole-programme cost, not just material price: faster erection, lighter foundations and less waste on one side against a more established trade base, simpler penetrations and often lower insurance premiums on the other. Run both numbers for the specific site and specific team before choosing, rather than relying on a general answer.