ROOFING, CLADDING DRAINAGE & LANDSCAPING & INSULATION
This is backed up by other recent Government and local guidance such as the National Model Design Code, which says: “All schemes will be expected to follow national policy by achieving a 10% net gain in biodiversity. All new streets should include street trees.”
Tree maintenance requirement
MEETING NEW PLANNING REQUIREMENTS FOR TREES Extensive tree planting and retention of existing trees in developments, with provision for long-term maintenance, has just become a priority with new Government policies taking effect. Concrete block permeable paving offers an important opportunity to help satisfy these requirements with irrigation integrated with SuDS, hard surfaces and urban design – as the trade association Interpave explains. The latest requirements for trees in developments have been established in the July 2021 National Planning Policy Framework (NPPF) for England. The NPPF sets out what local planning authorities (LPAs) will require, when setting local
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policies and also considering planning applications for all developments. The NPPF states that: “Planning policies and decisions should ensure that new streets are treelined and that opportunities are taken to incorporate trees elsewhere in developments.”
However, measures need to be put in place to nurture and allow trees to mature, generally for decades, enabling them to actually deliver their real potential – including net-carbon storage, urban cooling through shading and evapotranspiration, biodiversity and public wellbeing. So, the NPPF also requires that “appropriate measures are in place to secure the long-term maintenance of newly-planted trees, and that existing trees are retained wherever possible”. Urban trees and paving have traditionally been seen as in conflict. But this is not the case, with concrete block permeable paving (CBPP) a key sustainable drainage (SuDS) technique to reduce flood risk and make cities more liveable. CBPP offers unique opportunities to collect, attenuate and treat rainwater runoff, removing pollutants before irrigating green infrastructure. Unlike conventional impermeable hard landscape materials, CBPP allows the same pattern of runoff transfer to the ground as natural vegetation, allowing water to reach tree and shrub roots, despite providing an attractive hard surface above. Local planning authorities now need to incorporate long-term tree maintenance measures in their planning consents and a straightforward spatial solution, such as permeable paving providing irrigation, offers a holistic multifunctional solution.
Beneficial relationship A recent Interpave case study (available via www.paving. org.uk) explored the 20year beneficial relationship between CBPP and trees at the Martlesham Park and Ride scheme. Here, concrete block permeable paving has operated efficiently with minimal maintenance amongst extensive tree planting without root disruption or other issues.
The benefits of CBPP for trees while retaining accessibility are recognised by the current Code of Practice for accessibility in the external environment, BS 8300-1:2018, which states that: “Tree grilles should be avoided. Smooth or paved permeable surfaces should be used wherever practicable.” Permeable paving can be laid level and still avoids puddles without the need for drainage gulleys. It provides a safe, firm, pothole-free surface for everyone – including wheelchair users and people pushing prams. Two decades of experience in the UK demonstrate the long-term performance of CBPP with minimal, if any, maintenance. CBPP generally comprises an upper layer of concrete blocks with permeable jointing and laying course, over a sub-base and other structural layers of permeable material for water storage. Interpave is currently exploring new ways of applying CBPP to optimise gradual supplies of water for tree irrigation at both levels, as well as effective interaction with tree planters and proprietary tree pit systems. Paving layouts are also being considered to maximise the permeable paving catchment area for tree irrigation, particularly outside the protective tree-canopy zone. Interpave would be pleased to hear from anyone considering integrating permeable paving and trees on projects (email: chris.hodson@paving.org.uk).
Low intervention retrofit Another important innovation, particularly for regeneration, is the retrofitting of CBPP as an overlay to existing, conventional road bases or other hard surfaces. These thin overlays create attractive, safe and sustainable shared surfaces. They can be particularly effective when used to supply a gradual flow of clean water horizontally into raingardens or bioretention areas with trees and other green infrastructure, via simple slot inlet/outlets, to store water for irrigation and biodiversity, as well as SuDS. Such lowintervention techniques enable transformation of the public realm in response to the raft of recent active travel, low traffic and open space initiatives.
