The Facts on Manhole Covers

Here we explain a few commonly asked questions about manhole covers.

Recessed manhole covers – how do they differ?

While conventional manhole covers are designed to fit flush with the surrounding surface, recessed manhole covers allow for infilling so the cover blends into its surroundings.

A screed cover is only deep enough to be filled with a layer of concrete screed, whereas a block pavior cover will need a deeper recess to accommodate the additional height of block paving or setts.

A recessed cover may also be used if a manhole is located in a resin-bound drive or a grassed area. Resin-bound aggregates require little depth, but grass will need sufficient room for root growth and to prevent grass from drying out too quickly.

What is a sealed cover and when is it used?       

A single sealed manhole cover is characterised by a single tongue-and-groove joint that creates an airtight seal between the cover and frame.  A single sealed manhole cover helps to prevent foul odours from escaping and water from entering the manhole.  Double sealed manhole covers feature an additional neoprene rubber seal which, providing there isn’t an accumulation of pressure in the manhole, is better at preventing gases and odours from escaping the manhole. For this reason, a double sealed manhole is often used for foul drainage manholes situated within buildings or enclosed spaces.

How do FACTA loadings differ from cover loadings? 

More commonly used for recessed covers. FACTA load test ratings are based on structural engineering calculations for fabricated covers which are normally restricted to use in 20mph speed limit areas (and therefore not subject to the same dynamic loads as cast iron covers).

Cover loadings are based on European Standard BS EN 124, which was the original method of rating the strength of a grating, manhole or access cover. This was revised in 2015 to include annexes that cover the various materials used for covers.

BS EN 124 calculates the dynamic vehicle loading for fast moving traffic, to ensure that it rates all material types against the highest possible installation requirements.

How do I select the correct manhole cover size?

Manhole covers are usually sized according to the clear opening size of the manhole, not those of the cover. This is so the cover will sit securely across the manhole.

It is always considered best practice to select a cover that is a good size match for the manhole.

• A cover that is too small may need additional work to the brickwork at the top of the manhole to ensure the cover is held securely in position and unlikely to become dislodged and fall into the manhole.
• While an oversized cover won’t need this extra work, it could potentially look too large for the location and be unnecessarily cumbersome if access to the manhole is required.

If you are unaccustomed to measuring manholes for covers, a call or email to the experts at Drainfast with the inside dimensions of your manhole (excluding the cover and frame) could save you an expensive and annoying mistake. Call them on 01730 774000 or email action@drainfast.co.uk for prompt, friendly advice and support from one of the UK’s leading providers of specialist drainage supplies and related products.