Easy specification
We provide design and technical support
Sample service
Request sample boards, panels and more
Fast quote
Receive a quote within one working day
Delivery excellence
Trust us to fulfil your order on time, every time
Technical

What are the differences between permeable and non-permeable paving?

mm
By Craig McBride
Technical Manager
6 min read

The key differences between permeable and non-permeable paving are in the way they handle the collection and dispersal of rainwater. Permeable paving allows rainwater to filter through its surface into the sub-base aggregate below, which is lined with a geotextile membrane. Here, the rainwater collects and, depending on the permeability of the sub-grade, either soaks slowly into the ground, or is held and then channelled through pipes into the watercourse or drainage system.  

In contrast, where non-permeable paving is laid, rainwater runs directly off its surface and is quickly directed, unfiltered, via road gullies and channels into the drainage system.  

The installation of both paving types requires, among others, ground excavation, preparation of a suitable sub-base, and the use of suitable kerbing. Water runs off non-permeable surfaces into the drainage system, whereas permeable paving consists of blocks that allow water to drain away through the joints between them into the sub-base below. 

Permeable paving, at large, does not need to be supported through the installation of pipes, manholes, road gullies, channels, and petrol interceptors needed to handle the volume of unfiltered surface water run-off from non-permeable surfaces. 

Permeable paving surfaces are used on projects that meet the regulatory Sustainable Drainage Systems (SuDS) requirements of the Flood Water Management Act1. 

The importance of employing a good SuDS strategy is highlighted by the damage that can be done by flooding events, and the cost of the disruption that such events cause. Flooding can result in loss of life, affect the health and wellbeing of those impacted, and cause public services, transportation, and businesses to be disrupted.  

The cost of the flooding varies depending on its severity, but the House of Commons February 2024 ‘Flood risk management and funding’2 briefing document estimates the winter flooding of 2019/20 to have cost around £333 million, and the winter 2015/16 floods around £1.6 billion.  

Effective use of hard landscaping products that can help with SuDS compliance, and contribute to better flood management, is good for the project, the wider community, and the local environment. 

permeable paving

What are the key aims of SuDS management and how can permeable paving help? 

SuDS is focussed on flood risk management, not flood defence, and its aims include: 

  • Storing rainwater run-off and releasing it slowly – known as ‘attenuation’  
  • Harvesting and using the rain close to where it falls, rather than allowing it to flow elsewhere creating increased volume of water and increasing the risk of flooding 
  • Allowing water to soak into the ground through infiltration 
  • Slowly transporting or conveying water on the surface  
  • Filtering out pollutants 
  • Allowing sediments to settle out by controlling the flow of the water 

Permeable paving is frequently used as part of a SuDS solution, due to its synergy with these above aims, as it can: 

  • Capture and store rainwater where it falls 
  • Release it slowly, often into the ground, or into the local drainage system 
  • Trap pollutants and sediments in the underlying stone layers  
  • Break down organic pollutants through naturally occurring micro-organisms in the sub-base  
  • Trap heavy metal pollutants as they become attached to the aggregate   
  • Effectively clean water before it is released back into the ground or water retention areas such as soakaways, filter strips, swales, and ponds 

Permeable paving is a popular choice across a wide variety of projects in the housing, education, retail, sports, leisure, and transport sectors for various reasons. 

 Aesthetics 

As well as providing an excellent addition to a SuDS strategy, permeable paving offers a wider choice of attractive colours and finishes when compared to other alternatives with permeable surfaces. Permeable paving can provide projects with more options to enhance the visual appeal of paving areas and match the desired overall project aesthetics.  

 Adaptable to ground conditions 

Permeable paving is a flexible option and is suitable for installation over any type of subgrade. Once the permeability of the subgrade has been tested, the build-up of the sub-base can be matched to the water permeability or infiltration properties of the ground below.  

 Suitable for any loading category 

The sub-base of permeable paving can also be designed and detailed to meet any category of loading – from domestic parking right through to heavy traffic scenarios carrying up to 1,000 heavy goods vehicles per week. 

 Can be specified in blue roofs 

Permeable paving is also suitable for projects where ground level drainage may be limited, and blue roofs have been specified. Permeable slabs or block paving can be used on a blue roof when installed onto a grit laying course and jointed with grit. This type of roof is designed to capture and restrict the flow of water from the roof to slow down the volume of water leaving the site. 

permeable paving

Benefits of permeable paving for adoptable roads 

Where projects may be potentially adopted by the local authority, discussions will take place around the SuDS measures employed, including the use of permeable paving. Objectives are often centred around the long-term effectiveness and ongoing maintenance requirements of the specified paving system. 

Permeable paving is typically designed to accommodate a one in one-hundred-year rainfall event. This exceeds the capacity required of more commonly used drainage options that utilise non-permeable paving. It reassures the local authority about the ability of permeable paving to cope with extreme weather events that could otherwise lead to flooding.  

Permeable paving surfaces require maintenance. It is worth considering that if maintenance is not carried out as recommended the effect on the drainage systems for non-permeable paving is likely to be much more severe. For example, gullies will lose around 75% of their efficiency when the sediment level approaches the maximum before it blocks completely. In comparison, permeable paving will remain effective even if it gets to a level of being 90% clogged. 

Protect the environment with our SuDS-ready range

Tobermore’s Hydropave permeable paving range allows you to create spectacular hard landscaping features with environmentally friendly products.

Where can I learn more about permeable paving solutions? 

Tobermore has extensive experience of supplying permeable paving to a variety of projects across the residential, commercial, and public realm sectors. 

Craig McBride, Tobermore’s Technical and Product Training Manager, comments:

“Our permeable paving rapidly removes rainwater from the hard surface upon which it falls, and then controls its release without the need to add surface gullies and drains. It is a simple and attractive way to provide flood protection for hard landscaping areas across large or small projects. It delivers a low maintenance, self-contained drainage system, working in harmony with its surroundings to provide a truly sustainable way to reduce flood risks on a project.”   

Tobermore offers permeable paving solutions in the form of the durable and hard-wearing Hydropave Pedesta, the aged, antique appearance of Hydropave Tegula, the natural granite appearance of Hydropave Fusion, and the ultra-smooth surface of Hydropave Shannon which is perfect for recreational areas where bikes, skateboards, and rollerblades will be used. 

If you would like to learn more about permeable paving, and how it works as a SuDS solution, we have a dedicated CPD available that you can request to be delivered in person or online. 

 

Set the scene with a Free Hard Landscape Proposal

Our HLP service is designed to simplify your decision making process by offering tailored solutions for your specific project needs.

mm

Craig McBride

Technical Manager
Craig is the Technical Manager at Tobermore. With over 26 years of experience in the paving and walling industry, he is responsible for ensuring that all technical requirements for our products are in line with the latest guidance and legislation. He also provides technical support and guidance to the wider business and our customers.

How can we help?

Request a Quote