► RELN | Risers

Add Pit Depth When Underground Pipework Sits Lower

Sometimes the problem isn't where the top of the pit finishes — it's where the pipe needs to enter below ground. When stormwater pipework sits deeper than a standard RELN pit comfortably accommodates, a compatible riser extends the chamber so the installation can reach the required connection depth without changing to an unrelated pit system.

That makes pit identification the first job, because RELN risers are matched to specific pit families. Industrial Shed currently carries risers for Series 300, Series 410, Series 450 & Series 600 pits. Start with RELN | Drainage & Pits when the pit itself is also required, or browse RELN when the project extends into other compatible drainage components.

Final surface height still matters, but it isn't the only reason depth becomes important. Pipe invert levels, excavation depth, pit series, surrounding works & future access all need to make sense together before another section is added to the chamber.

What Are RELN Risers?

RELN Risers are extension sections designed to increase the depth of compatible RELN drainage pits.

The current Industrial Shed collection contains four distinct options:

► Series 300 Riser – 250mm | 001004
► Series 410 Riser – 350mm | 001006
► Series 450 Riser – 300mm | 001093
► Series 600 Riser – 300mm | 001122

Each belongs to its nominated pit family rather than acting as a universal extension.

One important exception is Series 250. RELN states that Series 250 doesn't use the same dedicated riser approach; another Series 250 pit can be used with its base cut out where additional depth is required.

Why Choose RELN Risers?

Reaching deeper pipework can otherwise turn into an unnecessary redesign of an already suitable pit arrangement.

A correctly matched riser can help:

► Increase pit depth
► Reach deeper underground pipelines
► Retain the nominated RELN pit family
► Accommodate construction levels
► Support residential drainage alterations
► Extend larger commercial pits
► Keep underground connections within the chamber
► Preserve access from the finished surface

RELN specifically states that its Series 300 riser increases pit depth by 250mm so the pit can intersect with pipelines positioned deeper in the ground.

That point is worth separating from surface slope. RELN notes that the slope of the land doesn't determine whether the Series 300 riser is needed. Underground pipe depth does.

Common Applications

A driveway renovation provides a useful example. The existing stormwater route may need to pass beneath new construction at a level lower than the standard pit conveniently reaches. Rather than treating the visible grate height as the whole problem, the installer needs to reconcile the pipe connection below with the finished surface above.

Other situations can include:

► Deeper residential stormwater pipework
► Commercial drainage alterations
► New paved developments
► Car-park drainage installations
► Service-area drainage
► Property extensions
► Landscape drainage works
► Civil drainage projects using compatible RELN pits
► Replacement of existing pit arrangements where levels have changed

Commercial developments create a different challenge. A larger Series 410, 450 or 600 pit may need additional chamber depth because incoming or outgoing drainage has already been established deeper underground.

Property upgrades can be less predictable. Once old paving or concrete is removed, the installer may discover existing stormwater lines at a depth that wasn't obvious from the surface. Having the correct riser available can solve that dimensional problem without treating the complete drainage layout as disposable.

Product Selection Guide

Identify the Pit Series First

There is no useful shortcut around this step.

Before choosing a riser, determine whether the installation uses:

► Series 300
► Series 410
► Series 450
► Series 600

Then match the extension to that family.

A riser that adds the preferred amount of depth but belongs to the wrong pit family isn't the correct component.

Series 300 – The Residential & Light-Commercial Path

Series 300 is likely to be the familiar starting point for household surface-water drainage.

RELN's current Series 300 Traditional Pit has an external depth of approximately 325mm, while the Series 300 Deep Pit is approximately 450mm deep.

The compatible Series 300 riser adds 250mm.

This can become relevant when:

► Incoming pipework sits deeper
► Outgoing pipework needs a lower connection
► Existing site conditions require additional chamber depth
► A Series 300 installation needs to remain accessible from above

Before automatically adding a riser, compare the standard Series 300 & Series 300 Deep Pit configurations. The simplest suitable arrangement may depend on how much depth the installation actually requires.

Series 410 – When the Commercial Pit Needs More Reach?

The Series 410 riser is different from the other current products because it adds 350mm rather than 250mm or 300mm.

That makes measurement particularly important.

Potential considerations include:

► Commercial drainage layout
► Existing pipe invert
► Required connection point
► Excavation depth
► Finished surface level
► Maintenance access

Don't order by eye from the pit opening. Confirm that the chamber is Series 410 before selecting the corresponding 350mm riser.

Series 450 – Extending a Larger Commercial Pit

Larger drainage chambers bring more room below ground, but pipework can still dictate additional depth.

The Series 450 riser adds 300mm to the compatible pit arrangement.

It may be relevant where:

► Commercial pipework runs deeper
► Drainage routes intersect at different levels
► External works alter the required pit configuration
► A larger chamber needs to remain accessible at finished level

Where surrounding works form part of the installation, Building & Construction Supplies for Every Project can support the broader construction stage.

Series 600 – Add Depth to the Largest Current Riser Option

A Series 600 installation should be approached as its own drainage system rather than treated as an oversized Series 300.

The compatible Series 600 riser adds 300mm.

Before including one in the job, establish:

► Exact pit model
► Pipeline depth
► Required chamber depth
► Excavation allowance
► Surface treatment
► Access around the completed pit

Large components reward planning. Discovering the level calculation is wrong after excavation & surrounding work has progressed is far more disruptive than checking it before installation.

Don't Order a Series 250 Riser That Doesn't Exist

Series 250 is the exception worth remembering.

RELN states that where additional height is required with a Series 250 Traditional Pit, another Series 250 pit is used with its bottom cut out.

That differs from the dedicated:

► Series 300 riser
► Series 410 riser
► Series 450 riser
► Series 600 riser

Recognising that distinction prevents buyers searching for a dedicated Series 250 riser that isn't part of this range.

Measure From the Pipework Up

Looking down into an empty excavation can make depth surprisingly difficult to judge.

Establish known levels instead:

Determine the required pipe level.
Confirm the pit connection position.
Calculate the chamber depth needed.
Establish the finished surface height.

Select the pit & riser combination that reconciles those points.

Work from measurements rather than adding a riser simply because the pit appears shallow.

Don't Let Surface Slope Answer the Wrong Question

A sloping block can make it tempting to assume a deeper pit automatically needs a riser.

RELN specifically notes for its Series 300 product that the slope of the land has no effect on the need for the riser.

The important question is whether the pit needs additional depth to intersect the underground pipeline.

Surface fall controls how water approaches the drainage point; pipe depth controls what has to happen beneath it.

Compare a Deep Pit Before Adding Components

More parts aren't automatically a better installation.

For Series 300 work, compare the available pit depths before finalising the combination.

A standard Series 300 pit is approximately 325mm deep, while the Series 300 Deep Pit is approximately 450mm deep.

A 250mm riser then provides another depth option where required.

Calculate the target first & choose the simplest suitable configuration around it.

Consider the Grate Only After the Chamber Is Resolved

The component visible at ground level is only the top of the drainage assembly.

Once the pit family & depth are established, the grate or cover can be selected around the surface requirement.

For lighter domestic drainage, RELN | Plastic Grates provides compatible options across selected pit systems.

Where a galvanised steel surface is preferred, RELN | Galvanised Grates provides another path.

Get the chamber geometry right before spending time deciding what its top should look like.

Use the Cover to Suit the Purpose of the Pit

Not every extended pit needs to collect runoff directly through its top.

Where the chamber functions as an access or junction point rather than an open surface inlet, RELN | Pit Checker Plates can provide a relevant solid-cover comparison across compatible pit families.

Ask:

► Does water need to enter through the top?
► Is the pit primarily a junction?
► What traffic crosses the location?
► Is maintenance access required?
► Which cover belongs to the pit series?

Riser depth & cover type solve different parts of the same installation.

Allow for Pipe Connections

Extra chamber depth is useful because it changes where pipework can intersect the pit.

RELN's Traditional Pits are designed around horizontal pipework & can connect with 90mm & 100mm PVC pipe, with larger stormwater pipes accommodated by cutting the pit appropriately where specified.

RELN also advises using silicone to seal & secure PVC pipework to Traditional Pits.

Plan connection height before cutting the pit wall. A riser can't undo a pipe opening made at the wrong level.

Think About Multiple Pipe Levels

A junction pit may have more than one pipe entering or leaving the chamber.

When several runs meet, record:

► Incoming pipe sizes
► Incoming invert levels
► Outlet level
► Direction of each run
► Clearance between openings
► Required chamber depth

The lowest required connection may be the one that determines whether the riser belongs in the design.

Don't Confuse a Riser With a Drainage Outlet

Adding chamber depth doesn't solve a poor downstream route.

A riser changes the vertical dimension of the pit. It doesn't:

► Increase pipe fall by itself
► Clear a blocked downstream line
► Correct an undersized outlet
► Redirect runoff
► Replace proper stormwater design

If the water has nowhere suitable to discharge, a deeper chamber isn't the complete answer.

Check the Finished Surface Before Backfilling

Once paving, concrete or landscaping surrounds the pit, correcting an elevation mistake becomes considerably harder.

Before completing the surface, confirm:

► Pit is correctly positioned
► Riser is the correct series
► Required depth has been achieved
► Pipe connections are secure
► Grate or cover will finish at the intended level
► Maintenance access remains practical

Where concrete needs to be prepared or modified around existing drainage,  Concrete Cutting & Drilling Tools can support suitable site preparation.

Protect the Open Chamber During Construction

A deeper pit is also a larger place for construction debris to disappear.

While the grate or cover is removed, prevent:

► Concrete slurry
► Soil
► Aggregate
► Paving offcuts
► Packaging
► General site waste

from accumulating inside the chamber.

Clean the pit before commissioning rather than expecting the first heavy rainfall to move construction debris downstream.

Recheck Levels When a Project Changes?

Drainage calculations made before a landscaping variation may no longer match the finished job.

Revisit the pit arrangement when:

► Paving thickness changes
► Concrete levels move
► Pipe routes are altered
► Additional drainage lines are introduced
► Finished landscaping levels change

Spring Jobsite Prep Getting Your Gear Ready reflects the same practical habit of checking equipment & working areas before changing conditions expose unfinished problems.

Avoid Making a Small Level Error an Expensive One

Drainage components are usually cheaper than reopening finished concrete, paving or landscaping.

Confirming pit depth, riser compatibility & pipe levels before the surrounding work is completed can prevent unnecessary demolition later.

The Hidden Cost of 'I Can Get It Cheaper Online looks at the wider cost of a job once compatibility, downtime & rework are taken into account.

The right component is the one that lets the complete installation work as intended.

Expert Tips

► Take pipe-depth measurements before ordering the riser. The underground connection is the reason for adding depth.
► Write the pit series on the job list. Series 300, 410, 450 & 600 risers aren't universal extensions.
► Remember the Series 250 exception. RELN uses another Series 250 pit with the base cut out rather than a dedicated riser from this collection.
► Compare Series 300 Deep before automatically stacking components. A different pit depth may provide the cleaner arrangement.
► Mark intended pipe openings before cutting. Check every connection height against the final level calculation.
► Measure again after project variations. Changed paving, concrete or pipe routes can alter the required arrangement.
► Keep the chamber clean while it's open. A deeper pit can hide a surprising amount of construction debris.
► Confirm the grate or cover can still be removed. Additional depth shouldn't compromise future maintenance access.
► Record the completed configuration. Pit series, riser & cover details can save considerable identification work during future maintenance.

Good drainage work depends on details that disappear once the site is finished. Why Good Fasteners Matter More Than the Tool You Drive Them With carries the same lesson: small components deserve proper selection when the reliability of the completed job depends on them.