We all know that most things expand when they get hotter – some things even expand when they get colder, just look at water and ice – this property is called thermal expansion. But what does this mean if you are planning on using steel, for example, in a construction project?
What is thermal expansion
Thermal expansion is the tendency of matter to change in volume – and length – in response to a change in temperature. When a substance is heated, its particles begin moving more, requiring a greater average separation between the particles and causing, therefore, a greater overall volume. The reverse is not true as, whilst heated metal will contract to its original length and volume once cooled, there is no independent contraction of metals due to lower temperatures. One of the most obvious exceptions to this type of behaviour is water, which actually expands at temperatures approaching zero degrees Celsius.
The difference between steel and wood for construction
Issues with thermal expansion in construction are mainly around the stability of steel framed – as opposed to wood framed – houses. Thermal expansion is measured as the degree of expansion divided by the change in temperature, this measure is called the material’s "coefficient of thermal expansion". For most materials there will be a different, and greater, coefficient of expansion for length as well as volume. This is why the expansion coefficient for length of very long, narrow steel constructs – such as railway lines – is important. One of the most common types of wood used for housing frame is pine. This wood has a coefficient of expansion for length of 5 x 10^-6 and the corresponding coefficient of steel is 12 x 10^-6. This does not seem to be a significant difference does it?
What does it really mean?
You can calculate for yourself how much a 1 metre – or 1,000mm – length of steel and the same length of pine would lengthen when exposed to a temperature increase of, for example, 10 degrees. Temperature is measured in degrees Kelvin for these types of calculations, so 10 degrees Celsius equals 283.15 degrees Kelvin. Simply multiply the coefficient by the temperature change by the length to get the change in length. For steel this is 0.000012 x 283.15 x 1000 which equals 3.3mm and for wood it is 0.000005 x 283.15 x 1000 which equals 1.4mm. Which is just as we thought, not a great deal of expansion and not much difference at all between the two materials for these lengths.
Steel in construction
So we now know that there is very little scope for temperature induced expansion and contraction in steel framed construction, and even less difference between steel and wood. Whether a steel frame is mechanically jointed or welded, in a properly constructed and insulated home, thermally induced movement and noise is no more likely than with timber. Steel framing expands and contracts at rates not too dissimilar from other materials, which means it is unlikely that there will be problems either during or following construction.
Steel homes are quiet inside
The exterior walls and ceiling of a steel framed house are filled with thick insulation, restricting outside noise. Wood, by comparison, is particularly sensitive to humidity and contracts as it dries, whereas a steel framed home doesn’t creak at all due to humidity variations. A steel housing frame is mechanically jointed and in a well-constructed and insulated home, thermal expansion is not an issue. Steel framing expands and contracts at rates very similar to the other materials used in building, which means it is unlikely that there will be noise or cornice cracking problems.
There is a lot of very technical information online about the thermal expansion of material like steel. Probably the easiest way to find out about any possible issues and how best to negate them, however, is to talk to your steel merchant or a steel fabricator.
Article Sourced from:
Yellow Pages. (2015, September). Things to Remember When Building with Steel. Yellowpages.com.au. https://www.yellowpages.com.au/articles/steel-supplies-and-merchants/things-to-remember-when-building-with-steel
