How tall are double deck trailers?
In the mid-2000s, both double deck trailers and lifting deck trailers were built up to 4.88m (16'); however, that limit has been pushed in recent years and Don-Bur now regularly build up to 4.92m (16'2") and, on rare occasion, 4.95m (16'3").
A derogation exists in the UK which means that overall height is not considered when complying with construction and use regulations. This means that UK manufacturers can build trailers to any height. The practical restriction is bridge height.
Unmarked bridges in the UK should be 16'6" (5.0292m) or greater. Any bridge that does not have this clearance should have the clearance clearly indicated. All public highways (including dual carriageways and motorways) have a standard minimum clearance of 16'6" or greater.
However, across mainland Europe, there is a strict maximum height limit of 4.0m, which significantly restricts what is possible in terms of double deck design. In these cases, careful consideration is needed to achieve usable aperture heights on both decks, and compromises may be required depending on the load type.
What About Minimum Heights?
While most double deck trailers aim to maximise available height within legal or practical limits, it's worth noting that there’s no fixed minimum height for a double deck. The overall height is really only limited by the aperture height required on each deck to suit the intended load.
In cases where headroom isn't a concern – such as side loading by forklift – it's possible to significantly reduce the trailer's overall height. This is typically achieved by fitting smaller wheels to lower the main deck, thereby maximising available aperture within a reduced overall height.
For example, a step frame trailer at just 4.0 metres high can offer a main deck height of only 880mm, giving a total internal aperture of 3.033m – roughly 1.5m per deck. While such a configuration may not be ideal for manual loading due to restricted headroom, it can be perfectly suited to forklift operations or automated systems where personnel access isn't required.
In some specialist cases, it’s even possible to go lower. A trailer design incorporating independent suspension and boxed wheel arches can achieve a main deck height as low as 250mm. Within a 4.0m overall height, this allows for a total aperture of 3.663m, giving approximately 1.831m of clearance per deck – significantly improving usable space without exceeding European height limits.
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