Galvanised steel or timber:
what makes a house last

A timber frame and galvanised steel panels age in different ways. Timber is damaged by moisture and insects, steel by corrosion and high heat. This article looks at what breaks down each material, which standards describe the process, and what to ask a manufacturer before you sign a contract.

How zinc protects steel and what decides how long it lasts

A zinc coating protects steel in two ways. First, it keeps air and water off the steel. Where the coating is scratched, a galvanic couple forms next to the damage and the zinc corrodes instead of the steel, sacrificing itself. That is how the UK’s Galvanizers Association explains it. The American Galvanizers Association (AGA) adds that the same mechanism also protects edges cut after galvanising.

For the sheet steel used in thin-walled profiles and panels, the coating is designated under EN 10346: Z100, Z140, Z200, Z275 and so on. The number is the zinc mass in g/m², both sides combined. The steelworks U.S. Steel Košice gives a rule of thumb: 7 g/m² equals roughly 1 µm of zinc. So Z275 carries about 20 µm per side, and Z100 about 7 µm.

How long that layer lasts depends on the atmosphere. ISO 9223:2012 sorts atmospheres into corrosivity categories, and AGA lists zinc corrosion rates for each of them:

• C2 (low; rural areas with minimal pollution): 0.1–0.7 µm per year;
• C3 (medium; towns and cities): 0.7–2.1 µm per year;
• C4 (high; industrial zones and coastline within a kilometre of the sea): 2.1–4.2 µm per year;
• C5 and CX: 4.2 to 25 µm per year.

The Hot Dip Galvanizers Association of Southern Africa (HDGASA) gives example environments for each category. Coating life depends mostly on thickness, as the Galvanizers Association points out: a thicker layer lasts longer. Using the rates above, an unprotected Z275 sheet exposed outdoors in a C3 urban atmosphere would lose its 20 µm of zinc in 10–28 years. Inside a wall, behind cladding and insulation, conditions are milder, though how much milder depends on the junction details. So ask the manufacturer for the coating class and the standard, and find out how cut edges and fixing holes are protected.

Where timber is weak and where it is strong

Wood-decay fungi need free water in the wood cells, which means a moisture content above 20–25%. This figure comes from the handbook of the USDA Forest Products Laboratory (FPL). Air-dried timber usually holds no more than 20% moisture, and at that level decay does not occur. The trouble is that water still finds its way into a frame, through a roof leak or condensation inside the wall. And according to the same FPL data, some wood-boring beetles will colonise timber with low moisture content as well.

The second problem is movement. Below the fibre saturation point (about 30% moisture), wood shrinks and swells. According to the Wood Handbook, it moves most along the growth rings, roughly half as much across them, and only 0.1–0.2% along the grain. If the timber was poorly dried, this shows up as gaps between members, cracks and loosened joints.

Under the right conditions, though, timber lasts for centuries, as the Wood Handbook chapter on biodeterioration states plainly. Wood is a poor conductor of heat, and light timber-frame houses cope well with earthquakes. The price is constant moisture control and protective treatment that has to be renewed over time.

Fire safety: G1 does not mean non-combustible

In Ukraine, the combustibility of building materials is determined under DSTU B V.2.7-19-95 (a Ukrainian national standard, identical to GOST 30244-94), and these groups are used by DBN V.1.1-7:2016 (Ukrainian state building codes on fire safety). Materials are divided into non-combustible (NG) and combustible. To qualify as NG, a sample in the test furnace may raise the temperature by no more than 50 °C, lose no more than 50% of its mass and burn with a flame for no longer than 10 seconds.

Combustible materials fall into four groups, G1 to G4. G1 is the best of them: flue gas temperature up to 135 °C, damage up to 65% of the length and up to 20% of the mass, and no self-sustained burning. So G1 means a material burns poorly and goes out on its own. It is not a “won’t burn” rating. HOMERS materials are rated fire class G1 (low combustibility under Ukrainian DSTU) and self-extinguish once the source of fire is removed.

Steel itself does not burn, but it loses strength when heated. According to SteelConstruction.info, hot-rolled steel at 550 °C keeps about 60% of its load-bearing capacity. Timber burns, but predictably: under Eurocode EN 1995-1-2, solid softwood chars at about 0.65 mm/min, and for a while the char layer protects the inner part of the cross-section. In a frame house with small-section studs, that reserve is smaller. Whichever option you choose, ask for the fire resistance test report for the whole wall, and not only the combustibility group of the insulation.

Earthquakes and wind

Seismic forces are proportional to a building’s mass, which gives light structures an advantage. Think Wood makes this argument for timber frames, and it applies equally to light steel panels. In Ukraine, building in seismic zones is governed by DBN V.1.1-12:2014, and the seismic intensity for a particular plot is taken from the general seismic zoning maps (LIGA:ZAKON on the changes to the codes, in Ukrainian).

The HOMERS structure was tested at NDIBK (Ukraine’s State Research Institute of Building Constructions), report No. 221-323/023/26 of April 2026: seismic resistance of 8 points on the intensity scale and a wind load of 400 kgf/m², or about 3.9 kPa. Wind loads in Ukraine are set by DBN V.1.2-2:2006 (Amendment No. 1, in Ukrainian). With a light house a lot depends on anchorage, so ask separately how the panels are fixed to the foundation.

Thermal bridges: timber has the edge, and steel can only win on detailing

The figures do not favour steel. The Wood Handbook gives softwood lumber a thermal conductivity of 0.10–0.14 W/(m·K), while steel is around 45 W/(m·K), several hundred times higher. A steel stud running through the insulation becomes a thermal bridge. Australia’s energy rating scheme NatHERS deals with this using thermal breaks and a continuous layer of insulation over the frame.

In a steel house, then, the way the junctions are built decides the result. HOMERS insulates with a continuous 200 mm shell of polyurethane foam (PUR) with no gaps, and the panels join with a labyrinth groove so there is no direct bridge between outside and inside air. The company states energy efficiency class A and compares PUR with mineral wool in frame walls: the wool settles over the years, and the studs form bridges. You can check this with a thermal camera, or with calculations for the junctions at corners, windows and the foundation. There is more detail on the technology page.

Weight, foundations and installation

A light house does not need a concrete slab. HOMERS sets its houses on ground screws (screw piles). The foundation goes in within 1–2 days with no concrete work, and you can build on a slope without levelling or in woodland without felling trees. The panels are made at the company’s factories to a CNC precision of ±0.5 mm; manufacturing takes about 30 days and installation 7–14 days. The structure withstands up to 10 assembly and disassembly cycles without losing strength, so the house can be moved. Surveying and site preparation are always paid for separately.

Maintenance, warranty and cost of ownership

HOMERS gives a 25-year warranty on the structure and writes it into the contract. For a typical timber modular house, the company’s own comparison puts the warranty at 3–5 years.

The cost of owning a house over 25 years involves more than the price per square metre. Work out these items separately:

• heating and cooling: the gap between class A and C–D (the HOMERS estimate for a typical frame with mineral wool) adds up every year;
• renewing protection: for timber that means preservatives, paint and pest inspections; for steel, checks on the cladding, sealants and fixings;
• the risk of repairs after a leak, since timber reacts to water more severely;
• the full budget: HOMERS model prices exclude installation, foundation and delivery, and utility connections are extra too.

Steel frame vs timber: a side-by-side comparison

Frequently asked questions

Does galvanised steel rust?

The zinc wears away gradually, and while some remains, the steel is protected even where it is scratched. The rate depends on the atmosphere: up to 0.7 µm a year in rural C2 areas and up to 2.1 µm in C3 towns and cities. Ask the manufacturer for the coating class (Z275, for example) and how the cut edges are protected.

If the materials are class G1, does that mean the house won’t burn?

No. G1 is the best of the four combustible groups; non-combustible materials are labelled NG. G1 means the material does not sustain burning on its own and goes out once the source of fire is removed.

Will a steel-frame house be cold?

Steel conducts heat hundreds of times better than timber, so it all depends on whether the insulation breaks the path of cold through the metal. HOMERS solves this with a continuous 200 mm PUR shell and labyrinth joints between the panels. You can check the result with a thermal camera.

How long does a timber-frame house last?

Timber that stays dry and protected from pests lasts for decades and longer. The risks start where water keeps getting into the structure. How long a particular house lasts depends on its design, installation and upkeep.

Does a steel prefab need a concrete foundation?

Not with HOMERS. The houses stand on ground screws, which take 1–2 days to install. Surveying and site preparation are paid for separately.

See the structure in person

The easiest way to compare is to walk into a house. A full-size Basilio stands in the HOMERS showroom at VDNH, Kyiv’s exhibition centre. The showroom is open on Saturdays and Sundays from 10:00 to 19:00, and on weekdays by appointment. If you would rather discuss your plot and a model first, request a consultation.