Replacing a broken manhole cover can be a confusing business. Follow these few simple steps to improve your understanding of what is required and allow you to make an informed choice about what and where to buy.
As manhole covers (sometimes known as inspection chamber covers) age, they tend to become brittle due to continued exposure to the elements. Eventually they will break, particularly if they are made of cast iron. A broken cover allows drain odours to escape from the underground drainage system and it poses a danger to pedestrians and vehicles, so it needs to replaced as a matter of urgency.
When buying replacement covers, there are two key factors to consider – size and loading capacity.
Size
Manhole Covers are generally classified by their “clear opening” size – that is the size of the opening that they are made to cover. As any broken cover is almost certain to have been in place for a number of years, it is very unlikely that a replacement cover will fit into the original frame. For this reason all manhole covers are supplied with frames. The old frame will need to be removed by chipping away the surrounding concrete. When this task is complete, you can clearly the see the size of the opening that is to be covered. Two measurements are required, length and width. It is usually best to take these measurements in millimetres, although most reputable manhole cover suppliers will show the measurement in both metric and imperial sizes.
Loading Capacity
For safety reasons it is crucial that the replacement cover is fit for the purpose that is intended, and this is generally down to the area that the cover is to be fitted over, and the type of traffic that will be using that area.
If no car or commercial vehicle can ever come into contact with the manhole cover, then a 2.5 tonne pedestrian cover will suffice. This will generally be found in patios or garden areas. If the cover is in a driveway that is to be used by cars, a 5 Tonne cover should be used as a minimum. A 5 tonne cover will support a slow moving wheel load of 1.25 tonnes.
If a van or small commercial vehicle is likely to use the area, the load rating should be increased to 10 or 17 tonnes, which will support slow moving wheel loads of 2.5 or 4.25 tonnes respectively.
For commercial delivery access and pedestrian precincts, it is recommended that a 25 tonne cover is fitted, as this will support a slow moving wheel load of 6.25 tonnes.
For areas where articulated lorries may be found, a 38 tonne manhole cover should be fitted. Forklifts exert an even greater strain on manhole covers due to their relatively small tyres, so it always best to check with your supplier before installing a manhole cover in an area used by this type of vehicle.
Installation
Once the correct manhole cover and frame has been sourced it should be installed by a builder or other capable person. The frame should be bedded in concrete (the actual amount of concrete will vary depending upon the weight and load capacity of the cover), and levelled appropriately. The concrete should be allowed to cure fully for at least 72 hours before any weight is put on to the cover.
Further information about manhole covers can be found on the Drainage Sales website.
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