Steel or timber for a structural opening

Steel beams

Steel universal beams (UBs) carry more load relative to their depth than almost any timber alternative, which matters most where ceiling height is tight or where the opening spans a long distance. They're the standard choice for most load-bearing wall removals in South Devon's brick and blockwork housing stock, from Victorian terraces to 1930s semis.

Steel needs to be sized by calculation from a structural engineer, factoring in the load from floors and roof above, the span, and how the beam bears onto the wall either side, usually onto padstones that spread the load into the masonry. It also needs fire protection in most habitable spaces, typically boxed in with plasterboard, and can be prone to cold bridging and condensation if not detailed with a thermal break where it meets an external wall.

Engineered timber beams

Glulam and laminated veneer lumber (LVL) beams offer good strength for their weight and can be left exposed as a feature in a way steel rarely is without extra cladding, which appeals in period properties where an exposed timber beam suits the character of the room. They're lighter to handle on site, which can matter in properties with restricted access such as narrow terraced housing.

For an equivalent span and load, engineered timber generally needs to be deeper than steel, which can be a problem where ceiling height is already tight. It's also more sensitive to moisture over its lifespan than steel, so needs to be kept away from damp masonry or exposed positions unless specifically treated and detailed for that exposure.

What has to happen around the beam regardless of material

Whichever material is chosen, the wall either side of the opening needs adequate bearing, usually via padstones or a strengthened section of masonry, calculated to spread the beam's load without crushing or cracking the wall below. Temporary propping supports the structure above while the old wall is removed and the beam is installed, and this sequencing needs planning before any wall comes out.

Building control sign-off requires the structural calculations regardless of whether steel or timber is used, and inspection at first fix stage before the beam is boxed in or plastered over.

• Always get the beam sized by a structural engineer, not estimated on site
• Confirm bearing and padstone requirements at both ends of the opening
• Plan temporary propping before any load-bearing wall is removed
• Check fire protection requirements if the beam will be exposed to a habitable room

Cost and disruption differences

Steel beams typically need to be delivered pre-cut to length and manoeuvred into a tight opening, sometimes requiring temporary removal of a window or larger disruption if access is restricted, particularly in terraced housing. Timber beams, being lighter, are sometimes easier to install through standard doorways, which can reduce disruption on properties with awkward access.

Fire protection and finishing costs differ too. A steel beam boxed in with plasterboard adds a finishing step that an exposed timber beam doesn't need, while a timber beam intended to be exposed needs a higher quality finish specified from the outset since any surface defects will be visible.

How to get the specification right

Never accept a beam size or material choice without a structural engineer's calculation in writing, and make sure the calculation accounts for the actual loads on your specific property, not a generic assumption. Ask whether the quote includes padstones, propping, fire protection and making good, since these are often priced separately and can be missed from an initial figure.

If you want an exposed timber beam as a design feature, confirm this with the engineer early, since it affects both the sizing calculation and the finish specification needed.

Common questions