Sandwich Panels – the advantage of incorporating the outer skin, inner skin and insulation in a single element

As the name suggests, a sandwich panel consists of a sandwich of concrete with a filling of insulation.  It has the advantage of incorporating the outer skin, inner skin and insulation in a single element.

The outer skin (or ‘wythe’ as Americans call it) is usually quite thin, in the order of 50 – 80mm.  The insulation is in the order of 80mm – 100mm thick depending on the required thermal performance and the inner layer may be anything from 100mm upward, depending on the size of the panel.  In use, the inner layer is the loadbearing one, with the insulation and the outer layer hanging off it.

The make-up of the panel also depends on the system being used to fasten the two layers together.  There are several systems available.  It is possible to make a sandwich by using ‘traditional’ reinforcement passing between the layers, however in practice, commercially available systems are used, and there are several such systems available.J&P

Stainless steel wire clips which go through the insulation. Stainless steel cylinders as well as clips; Resin-fibre pins on a regular grid.

There is a drawback with steel systems in that they create relatively rigid connections between the two layers at ‘strong points’. This means that differential movement due to the sun expanding the outer layer can set up quite high stresses. For this reason most steel systems limit the maximum size of the outer layer to 4.5m – 5m.  Beyond this, expansion joints must be provided.

By agreement with the precaster, it is possible to have the inner face suitable to be left exposed, or suitable for direct decoration,  The outer skin can be treated in the same way as single skin panels, including facing with natural stone or brick.  It must be remembered though that such panels can get quite heavy, and site cranage must be considered.

 ‘This information is provided in good faith. While every effort has been made to ensure that the contents are correct at the time of writing, details do change. Amendments will be made as and when necessary; blog/website users and readers are advised to check for the latest edition. J&P Building Systems Ltd is not liable for any inaccuracies in the information provided. All advice from Key2Concrete and J&P is intended for use in the UK only by those who will evaluate the significance and limitations of its contents and take responsibility for its use and application. No liability (including that for negligence) for any loss resulting from such advice or information is accepted’.

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