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Weight Loading on a roof

Weight Loading on a roof.

It isn’t uncommon to be handed a specification where a new material is being specified to replace the original.

In most cases necessary investigation has been undertaken, and it has been concluded the roof is able to support the additional load. However there are instances we have seen, where this has been overlooked.

Weight loading on a roof structure is obviously very important and when roof coverings are being replaced it is essential that we make sure that, if we are specifying a change of material which will increase the load on the roof, we check that the existing structure can accommodate the increase in load.

This will usually involve employing a structural engineer. If necessary the structure may have to be strengthened, but if this is not possible, then we will have to consider another roof covering.

There are some misconceptions about the weights and loads of some roofing materials – so be careful. The most common is the belief that the heaviest roof tiles are concrete interlocking tiles. Heavy as they are, this is wrong.

Here are some examples which demonstrates this,

  • A Marley Eternite) Double Roman concrete interlocking tile weighs 47Kg/m2.
  • The same manufacture’s concrete plain tile weighs 73.8Kg/m2.
  • And their Acme plain clay tile weighs 64Kg/m2.

As you can see a plain tile is around 50% heavier.

Natural slates vary in weigh depending on their size and thickness. The most common size these days is 250 x 500mm and their weight is around 38Kg per m2. About half the weight of a plain tile and 25% lighter than a concrete interlocking tile.

A common mistake is to replace slates with an interlocking roof tile and, as you can, see this would increase the load on the roof by around 25%. Cembrit Jutland man-made slates weigh around 20Kg/m2

But the lightest material are pressed metal slates. Britmet, a UK manufacturer has a range of these products all of which weigh around 7Kg/m2.

It’s crucial therefore before specifying a change in covering to understand the weight load implications this may have, and the buildings capability of supporting this. Most reputable manufactures and contractors should be able to give you a good steer on the increase in weight load, and employing a structural engineer will ensure you know the new system will be safe to install.

As with all roof related matters, should you have any uncertainty about weight loading on a roof, and wish to discuss the project in more detail, our sales and estimating teams are always on hand to offer free professional advice and surveys.