Light gauge steel house in Batumi: a light steel frame by the sea

How a light gauge steel house is built

Light gauge steel (LGS) framing is a frame of cold-formed galvanised steel sections, which in our houses are usually 1 to 2 mm thick: the exact thickness of each member is set by the structural engineer. The wall studs, floor joists and roof trusses are produced on a roll-forming line from the engineer's files. The line also punches holes for screws and cables and marks every part, so on the plot the kit is put together by number, without welding. The sections for plasterboard sold in a DIY store look similar, but they are made for partitions only.

A wall gets its stiffness from boards screwed to the studs at the screw spacing set by the calculation, or from X-bracing made of steel strap. We usually space the studs at 600 mm, and closer under heavy loads, as the structural engineer decides. The floor is built from joists or light trusses, and if it has to carry a screed or large-format tiles, the engineer calculates it separately.

Zinc, cut edges and water: protecting the steel by the sea

A section one or two millimetres thick relies entirely on its factory zinc coating, and if water eats through the zinc, the steel underneath will not last long. How LGS differs from heavy rolled steel in this respect is explained in the comparison of structural steel and light gauge steel. On site this leads to some specific rules:

• we write the zinc coating class into the section specification: on our builds it is at least 275 g/m², and for a house closer to the shore a thicker zinc or a zinc-magnesium coating;
• on the plot the sections are cut with snips or a metal saw, never with an angle grinder: the abrasive disc burns the zinc off along the edge, and that is exactly where rust starts;
• a damp-proof strip goes under the bottom track, the steel never touches concrete or soil, and the plinth is raised above the paving around the house;
• the screws have a coating at least as good as the one on the sections, and on the facade and roof they are stainless steel;
• copper pipes and aluminium frames are separated from the steel by isolating pads, so that corrosion does not start inside a damp wall where two different metals meet.

More dangerous than salty air is water that gets into the wall unnoticed for years, at a window, a downpipe or a roof junction. We water-test these details before the inner lining goes on.

Thermal bridges: insulation goes on the outside of the frame too

Steel conducts heat hundreds of times better than timber, so mineral wool between the studs is not enough on its own: the cold passes straight through every stud, from the facade to the plasterboard. In winter condensation forms on the steel, and dark stripes show through on the plasterboard along the lines of the studs, because dust settles where the surface is colder. In summer, with the air conditioning on, humid outdoor air looks for a cold surface inside the wall, and once again it finds the steel.

So part of the insulation goes on as a continuous layer over the outer sheathing, under the facade, and the engineer calculates how much goes outside and how much between the studs: the steel must not get colder than the dew point, either in January or in August with the air conditioning running. How a steel frame differs from a timber one here is explained in the comparison of light gauge steel and timber frame. On site we watch the details: terrace and canopy beams are fixed through thermal break pads, and the steel around the windows is insulated as thoroughly as a solid wall.

Anchors, bracing and level foundations against tremors and wind

Its low weight means an LGS house takes a smaller seismic load, and its weak points lie in the connections. The thin wall of a section cannot hold a bolt the way thick rolled steel does, so the force from the wall to the foundations is transferred by anchor brackets (hold-downs), screwed to the stud as the calculation specifies. Shear walls work through their sheathing or X-bracing straps, and the straps are tensioned during assembly: a slack one only starts working once the frame has already moved. The design method is described on the page about earthquake-resistant construction.

An LGS frame is precise, and it does not forgive an uneven foundation. We bring the top of the slab under the walls to level within a few millimetres; otherwise the track ends up sitting on packers, and the anchor does not work the way the calculation assumes. Anchors are set with a template before the pour, or drilled to the setting-out afterwards, and before the boards go on, the site foreman photographs each one so that the washer, the nut and the bracket on the stud are all visible.

Foundations and facade for an LGS house

The foundation type for LGS is chosen according to the ground and the terrain. Most often it is a slab or piles with ground beams, and in both cases the top under the tracks is brought to level, as described above. A slab for an LGS house costs from 390 to 480 ₾ per m² of footprint.

The facade of such a house is either ventilated cladding or a thin render over insulation: ETICS (insulated render) costs from 205 ₾ per m², while a ventilated facade in fibre cement or rhombus boards costs more but lets moisture out of the wall better. Both options by the sea are compared in ventilated facades and ETICS. Brick or stone facing needs a foundation of its own.

Where LGS fits in Batumi and Adjara, and where it doesn't

LGS works best for a one- or two-storey house of simple shape, a guest cabin next to the main house, and an extension. It is a real help on a plot on a slope that a crane cannot reach: two workers can carry the heaviest part. It also suits an attic floor on top of an old house, if the old walls can take it: it goes up quickly with almost no wet work, and you can go on living downstairs.

LGS is a weaker choice where the floors are heavy: a pool or a garden on the roof, large cantilevers. On a slope, the lower floor cut into the ground is concrete in any case: the steel must not stand in the soil and hold back its pressure. On the beachfront we use LGS only if no stud is exposed to the outside, and open terraces are built from painted rolled steel. For a house of three storeys or more we usually price both LGS and cast-in-place concrete and show you both estimates.

Wiring and concealed work in a steel wall

In an LGS house the cables run through the factory holes in the studs, and every hole gets a plastic grommet: the edge of a thin section is sharp, and in time it cuts through the insulation. An electrician may drill a load-bearing stud for a new cable run only where the structural engineer has allowed it. For the kitchen, the water heater, the TV and the outdoor unit of the air conditioner, we fit a horizontal steel noggin or plywood between the studs before the boards go on, because plasterboard will not hold anything heavy.

Before boarding, the site foreman photographs each wall in full and the details close up: holes filled with screws, the strip under the track, the grommets and the backing for fixings. The photos go into the handover file: later they show where to find a stud for a shelf or where a cable runs, without opening up the wall.

How much a light gauge steel house costs in Batumi

The shell of an LGS house costs from 900 to 1,080 ₾ per m² of floor area. The price includes the foundations, the frame of the walls, floors and roof, insulation, sheathing and the roof covering. Windows, building services and finishing are not included, and the design is priced separately. A turnkey LGS house starts from 1,800 ₾ per m².

A light gauge steel frame wall with insulation and boarding costs from 220 ₾ per m² of wall, which is a useful guide for an extension. For comparison, a timber frame shell starts from 750 ₾ per m², and a shell on a hot-rolled steel frame from 990 ₾. Costs go up with thick zinc and stainless fixings near the water, external insulation, piles on a slope and a ventilated facade, and come down with a simple shape and a gable roof.

We send a preliminary estimate for the shell from a sketch and photos of the plot within 24 hours on business days. The final cost is set on the basis of the design, after a visit to the plot and once the estimate is agreed, and in the contract the price is broken down by stage.