Considerations when seeking landscape adoption with Hampshire Highways

Following the publication of Hampshire County Council’s Section 38 Guidance for Developers, and supporting Technical Note for Trees, Landscape and Ecology, we have summarised the key design factors when designing soft landscapes on or within proximity to adoptable highways.

Whilst many of these requirements fall within the current best practice, there are some recommendations that will have an impact on the ability to maximise greening opportunities and biodiversity net gain, all of which help to create a strong sense of place.

It all Starts with a Soil Assessment

• Soils should be assessed prior to agreeing on planting to ascertain the soil structure, ph. levels and suitability to support the proposed planting palette.
• A soil scientist can ascertain to what extent topsoil and subsoil can be reused or remediated to avoid expensive imported material.
• Inform impact of roots on foundation design (shrinkable soils) to meet NHBC Standards.

Plan Early for Successful Tree Planting

  • Minimum root volume = 10sqm. (as roots tend to grow in the top 600mm this will require an area of 17sqm. In most street settings (where space is limited) this will require the root cell systems and agreement with the Highway Authority.
  • Min size – Extra Heavy Standard / planted at least 2 metres from back of kerb (footway or carriageway) / 2m clear stem (2.4 when next to cycleway).
  • A weldmesh guard should also be fitted where trees are planted into grass verges.
  • Underground guying is expected in areas with high footfall and traffic count. The stake and tie system is acceptable in grass verges, and other roads where the risk of vandalism is reduced.
  • A minimum distance of 5m between mature tree canopy and the light source will normally be required as a minimum. Given the unpredictable nature of tree growth (in urban conditions) this is difficult to predict 100% but the correct tree choice is fundamental to achieving tree cover through the streetscape.

Planting will need to be maintained by the Developer for an agreed period, usually a minimum of 36 months but this may be reduced to 12 months on some specific sites with prior approval with the HCC Arboricultural Team.

Shrub Planting

  • No shrubs planted within 0.5m of adopted footway / carriageway.
  • No shrubs that grow above 300 within visibility splays / 600mm elsewhere. Occasional vertical obstructions within visibility splays may be permitted provided that in combination they do not create a solid visual barrier.

Hedgerow Spacing

  • The ultimate spread of hedges should be 0.5m offset from footpath / carriageway. We assume the remaining gap will be planted with groundcovers or grass in-between.
  • Hedgerow shrubs should normally be planted in a double staggered row, 5 per metre.
  • Trees within hedgerows should be spaced at 10m centres / min 2m from footpath / carriageway.

Grass Guidance

  • Avoid grass against vertical structures (walls / Buildings / fencing). allow 200mm paving material or min 500mm planting bed.
  • Preference is to adopt slow growing ‘low maintenance’ grass areas with suggested mixes that offer some ecological value.
  • Wildflower areas will be considered where appropriate and through prior agreement only.

Following the above recommendations is likely to provide significantly more room for landscape than most developers typically allow for. We would encourage early engagement with decision-makers to ensure design aspirations are deliverable through the S38 technical stage. We have the skills to navigate through these challenges and provide the best outcomes for all parties.

Feel free to get in touch should you wish to discuss how we can assist you through the S38 landscape adoption process.

You can read the full guide here.