Concrete vs steel frame: what to choose for a house in Batumi

The concrete vs steel frame question comes up when the sketch shows a living room without columns, a glass wall facing the sea or an extra storey on top of an old house. For an ordinary house in Batumi we usually choose concrete. If the concrete is dense and the cover is as specified in the design, salt moves towards the reinforcement slowly, and upkeep means a periodic check of the balconies and the plinth. We keep steel for jobs where a concrete frame would be too heavy or take too long.

Seismic load: mass versus joints

Both frames are designed to the Georgian seismic building code, and both pass the calculations if the structural engineer works them out for the specific ground conditions. The difference is where the safety margin comes from. Seismic load grows with the mass of the building, and a concrete house is heavier: thicker columns, more massive slabs, a bigger foundation.

A steel frame is lighter and more ductile: before it fails, it bends noticeably. But its reliability is concentrated in the joints, in the welds and bolts, which on site can easily end up different from the drawings. In a concrete frame the same goes for the reinforcement where columns meet slabs: the bars must extend into the joint by the length given in the design, and the stirrups must be spaced as specified.

Salt and humidity: where steel loses out by the sea

Salt gets into concrete as well, and by the sea it is the most common cause of damage to reinforced concrete. Chlorides reach the reinforcement, the steel rusts and splits the concrete from the inside. The protection is dense concrete and a cover of the thickness given in the design. That is why we check the spacers under the reinforcement and do not pour a slab if the mesh is lying directly on the formwork.

A mistake shows years later: a piece of concrete flakes off a balcony or the plinth, and underneath is a rusty bar. These spots get wet more often than the rest of the building, so they are checked from time to time and any crack is sealed before salty water reaches the reinforcement.

By the sea, a steel frame stands in salt air unless it is hidden inside the warm envelope of the house. Under ISO 12944, the coast falls into corrosivity categories C3 to C5 depending on how salty the air is, and right by the water the protection is chosen for C4–C5. That means hot-dip galvanising or a multi-coat paint system on a prepared surface. In the estimate it should be broken down coat by coat. A single line that just says "painting" is not enough.

Even good protection needs inspection. The weak spots are well known: the bearings of the terrace beams and the bottom of the columns next to the paving around the house, where splashes land. They are checked and touched up after every winter, and in a house that is rented out this job falls to whoever manages it.

Timing: getting the house weathertight before the autumn rains

In Batumi most of the rain falls from September to January, and April and May are the driest months. This gives the schedule a simple goal: by autumn the house should have a roof and closed openings, otherwise the interior work will drag on until spring.

A concrete frame rises floor by floor. Formwork, reinforcement and the pour come first, then the concrete gains strength, and only after that are the props under the slab removed. Every week of heavy rain delays a pour, and the shell of a two-storey house can easily stretch from spring to autumn.

A steel frame is fabricated in a workshop while the foundation is being built, and assembly on site takes noticeably less time. The time saving is real if the drawings for every beam are ready before the steel is ordered. With steel, a change during construction means a new part from the workshop and a pause, while with concrete it can often be sorted out on site before the pour.

Concrete vs steel frame in a house you rent out

The first thing guests notice is noise from the next room. Voices are stopped by the mass of a concrete slab, and footsteps by a floating screed on a soundproofing layer. A steel frame with light floors transmits impacts and vibration, so to get the same quiet, a slab is poured on profiled steel decking over the beams and a floating floor is added. In weight and cost, that is already close to a concrete frame.

Guests don't see wear on the frame itself, because the finishes cover it. The difference shows when you alter the house. In a concrete frame, a new opening in a load-bearing wall or slab is made only to a structural engineer's calculations, and cutting concrete is slow and noisy. In a steel frame, a beam can be strengthened or replaced on bolts, if the joint was designed that way from the start.

What to check if you are not on site

The two frames hide different things. In concrete, it is the cover and the joints between columns and slabs. In steel, it is the welds, the tightening of the bolts and the paint where a ceiling or lining will later cover the beam. We photograph these before they are closed up, and for steel it is worth adding coating thickness readings, taken with a gauge, to the report.

Repairs work differently too. A concrete frame needs little more than checks of the spots that get wet most often. But if rust does start, the repair is labour-intensive: open up the concrete, clean the bars and rebuild the cover with repair mortar. Steel is easier to inspect and touch up where needed, but this has to be done regularly, especially on the beachfront.