Manhole Covers: Choosing the Right One

However, a cracked or buckled manhole cover, whether it is made of ductile iron, galvanised steel or plastic should always be replaced as its loss of strength is sufficient to cause it to collapse, resulting in damage and injury.

If it’s a simple matter of replacing new for old, this is generally an easy task as a quick photograph and a few scribbled dimensions are all that is needed for a manhole cover professional to identify its replacement, but what if you need to upgrade it to a stronger or larger manhole cover? What if you need a manhole cover for an entirely new installation?

In this blog post, we will look at the different types of manhole covers, their sizes and load ratings, the materials they are made from and what they are used for.

What is a manhole cover?

This may sound like a pretty basic question, but it’s an important one as similar covers are used for different purposes. For example, a gully grate is a semi-open cover you will see at the side of the road, next to the kerb. Slots in the cover allow rainwater on the streets and pavements to run off into a storm drain and prevent flooding. Access chambers are similar to manhole covers but are smaller. These have various uses including gaining access to a water meter, using a fire hydrant or clearing a sewer blockage with a drain rod.

A manhole cover – like the name suggests – is used on a chamber that is large enough for a man (or woman) to enter the chamber. Primarily seen in sewer systems, manholes are also used for access to underground utilities such as water, electricity and telecommunications supply.

How do you measure a manhole cover size?

It’s a common mistake to assume the manhole cover is sized according to the outer dimensions of the cover or the frame. in fact, the manhole cover size relates to that of the clear opening – the smallest dimensions between the sides of the manhole cover’s inner rim.

Square and rectangular manhole covers are commonly manufactured in sizes ranging from 300x300mm to 1200x1200mm, while most circular manhole covers are either 450mm or 600mm in diameter.

It’s important that the manhole cover’s dimensions are at least equal to those of the manhole chamber, as while a larger cover can overlap the edges of the chamber, if it’s too small it probably won’t fit securely and may even fall into the chamber.

One reason why an oversized manhole cover may not be suitable is that some have reinforcement on the underside of the cover that extends below the level of the manhole cover frame. If this reinforcement touches the edge or sides of the manhole chamber it may cause the cover to fit incorrectly, so it’s better to match the manhole cover to the chamber exactly.

What is a manhole cover load rating?

Each manhole cover is rated according to the maximum load it can withstand, and this determines which manhole covers are suitable for any given situation, ranging from a lightweight cover situated in a garden or on a patio to an ultra-heavyweight cover in a dockyard or airport. Two systems are used to define the strength of a manhole cover: BS EN 124:2015 and FACTA.

BS EN 124:2015

BS EN 124:2015 is the British implementation of a European standard that divides manhole covers into groups that dictate the locations where they can be used and classes based on their static load capabilities.

separates products into classes based on a static load test, groups the locations where each class should be installed and specifies the minimum loading for each location. 

BS EN 124:2015 groups

• Group 1 – pedestrian access only
• Group 2 – car parks, driveways and pedestrian areas with only occasional vehicular access
• Group 3 – car parks, forecourts, industrial sites and areas with slow-moving traffic; highways (no more than 500mm from the kerb or 200mm into the verge), excluding motorways
• Group 4 – areas with vehicular access including carriageways, hard shoulders and pedestrian areas
• Group 5 – areas with high wheel loading such as loading areas, docks and aircraft pavements
• Group 6 — areas with particularly high wheel loading such as aircraft pavements

BS EN 124:2015 classes

• Class A15 – capable of withstanding a 15kN test load
• Class B125 – capable of withstanding a 125kN test load
• Class C250 – capable of withstanding a 250kN test load
• Class D400 – capable of withstanding a 400kN test load
• Class E600 – capable of withstanding a 600kN test load
• Class F900 – capable of withstanding a 900kN test load

When deciding on the right load class for your manhole cover it’s always best to over-specify as this will prevent unfortunate incidents if your calculations are slightly off.

FACTA

While BS EN 124 does offer ratings for steel manhole covers, some of its test procedures are considered to be inappropriate for steel. FACTA corrects this anomaly with a list of ratings that are specifically related to steel covers.

• FACTA A covers are only suitable for pedestrian areas with maximum wheel loads of 0.6 tonnes.
• FACTA AA covers are suitable for areas offering access to vehicles with maximum wheel loads of 1.5 tonnes. These are typically domestic driveways and very light industrial areas.
• FACTA AAA covers are suitable for service areas and light industrial areas where pallet trucks are used but not solid-tyre forklifts. They can withstand maximum wheel loads of 2.5 tonnes.
• FACTA B covers can withstand maximum wheel loads of 5.0 tonnes and are therefore suitable for pedestrian precincts, light commercial delivery and parking areas and light industrial areas where small solid-tyre forklifts are used.
• FACTA C covers are suitable for factories and industrial plants, commercial delivery and parking areas and industrial areas where solid-tyre forklifts and vehicles with a maximum wheel load of 6.5 tonnes operate.
• FACTA D covers are designed for use in heavy plant areas and service roads where heavy goods vehicles drive at no more than 20 mph. they are also suitable for industrial areas operating medium-duty forklifts with a maximum wheel load of 11.0 tonnes.
• FACTA E covers can withstand heavy, moving wheel loads of up to 16.0 tonnes. This makes them suitable for dockside and container storage areas where large, heavy-duty forklifts operate.
• FACTA F covers withstand wheel loads of up to 24 tonnes and are used in heavy plant and aircraft movement areas.

What are manhole covers made of?

BS EN 124:2015 also defines what manhole covers are made of:

• BS EN 124-2:2015 – cast and ductile iron
• BS EN 124-3:2015 – steel or aluminium alloys
• BS EN 124-4:2015 – steel reinforced concrete
• BS EN 124-5:2015 – composite materials
• BS EN 124-6:2015 – polypropylene (PP), polyethylene (PE) or unplasticised polyvinyl chloride (PVC-U)

What are the different materials used for?

Cast & Ductile Iron Manhole Covers

These are the strongest and most resilient manhole covers and will typically be used for all locations ranging from Group 3 to Group 6.

Galvanised Steel Manhole Covers

Lightweight, these are easily installed yet surprisingly strong. They are commonly used for domestic driveways where they are more than sufficient to cope with family cars and light commercial vehicles.

Galvanised Steel Recessed Manhole Covers

Galvanised steel manhole covers are also manufactured in a recessed design. The recess is deep and strong enough to hold block paviors, asphalt, stone and concrete slabs, wet-pour concrete or resin-bound aggregates, so recessed manhole covers are used to disguise a manhole in a paved area, patio or driveway.

Composite & Plastic Manhole Covers

These manhole covers are sometimes popular as an alternative to iron and steel as they have little scrap value and therefore present less of a target to thieves.

Why are some manhole covers round?

Although most manhole covers in the UK are square or rectangular, round manhole covers – more widely used in other countries – are becoming more popular.

One reason for this is they are stronger. The strength of a square or rectangular cover varies at different points of its surface depending on the distance between each point and the edge of the cover, whereas with a round manhole cover the strength is distributed more evenly.

Positioning a square or rectangular manhole cover close to a building or within a geometrically paved area requires careful positioning to avoid it being visually misaligned. A round manhole cover doesn’t present this problem.

Round manhole covers are also easier to handle. They can be rolled, rather than lifted, into position and be aligned with the manhole cover frame at any angle rather than first lining it up with one edge.

However, there are also advantages to having a square or rectangular manhole cover. When the cover is lifted, these will rest securely against the full edge of a frame, whereas a round manhole cover will only be supported at one small point. It can therefore become easily dislodged or roll to one side.

We hope you have found this information helpful and interesting. If you have any further questions, you are always welcome to call the friendly team of drainage experts at Drainfast on 01420 555600 or email [email protected].

Also, look out for more articles in our ongoing series of blog posts, bringing you useful information, insights, guides and tips on all things drainage!