Changing Levels in Domestic Gardens: Planning Rules, Drainage Risks & Legal Responsibilities
A topic that frequently crops up on Facebook and other social media is that of changing levels within a garden. Site or product specific queries cannot be answered via social media, especially those concerning damp proof levels and ‘same level’ floors matching interior and exterior heights.
There are two main issues with contentious and varying advice that appear almost daily. The first concerns general levels – or ‘soft landscaping’ regarding excavating ponds or foundations and spreading the spoil on site.
Looking first of all at soil changes. Assuming the site is not within a National Park or Area of Outstanding Natural Beauty, where regional rules and regulations may be relevant, changes of level should be treated in a horticultural manner, when it comes to preparing and spreading the spoil.
Taking the creation of a garden pond as an example, an area of (say) twenty square metres has been allocated for a liner pond. This will be excavated to an average depth of (say) 1200mm, with a surface area of (say) fifteen metres, providing a total of eighteen cubic metres – perhaps nearer twenty-two cube with the bulking factor.
The spoil will be in various grades; turf (perhaps), topsoil and subsoil which must be kept separate. The turf should be removed to the compost area, along with any other turf stripped from under the area that is proposed to spread the remainder of the soil. It is important that the spoil from the pool is not simply spread over other ground that may contain vegetation e.g. lawns or strimmed down rubbish, otherwise the ground may become susceptible to fungal problems. Similarly, you should not spread sub-soil on top of decent topsoil, otherwise the bacterial content of the soil may be upset.
The most important consideration when raising soil levels is to look beyond the site, and ascertain what affect you may be having on cross site surface water movement. Even if a garden appears ‘level’ with no cross falls, neighbouring gardens may well be at different levels, and you must avoid ‘trapping’ water that has been used to traversing the grounds, perhaps for some distance from your project, otherwise you risk flooding higher level sites and becoming liable for a Court claim for damages.
Much comment on social media arises from ‘constructing platforms’ such as decking and paving. ‘How high can I raise a deck level without Planning Permission?
Under The Town & Country Planning (General Permitted Development) Order 2015, Schedule 2, Part 1, Class A1 (k) a raised platform is anything higher than 30cm. This height is taken from the existing ground level, wherever it may be in the garden.
There are several reasons why this Order is so important to landscapers and designers. Taking decking for example, raising a deck is almost an essential, given that the timbers should be kept clear of the ground, even those deemed to be ‘ground level’. A ‘raised deck’ is usually designed to be 600mm high, with anything greater being subject to Regulations concerning
Health & Safety – handrails, bannisters, step heights etc. Raised decks will most certainly require a Planning Application to be made, with detailed drawings submitted to the planning office for approval. Although applying for permission is the responsibility of the customer, as the professional on site, you would held liable for any breaches of Planning, and for proceeding without written authorisation.
The primary reason for requiring permission is that of neighbour privacy. With the average fence height being 1.8m, even a deck of 30cm will reduce the height to only 1.5m, which may result in the neighbouring garden being overlooked. Certainly, at 600mm, you would have a clear view over the fence and likely to receive complaints.
The same comments may be addressed to raised platform hard landscaping features such as paving supported by a retaining wall, infilled with rubble, MOT Type 1 etc. Except that, unlike decking, walling and paving construction works will also impede the potential flow of surface water across a site, and care must be taken to ensure that any swale, ditch, gulley or obvious low areas in a garden are not altered to prevent that free movement.
Indeed, solid surfaces such as paving may well increase the volume of water being forced onto the lower ground, and consideration should be given to ensuring the site is de-watered, either through adequate soak-aways or land-drains taking the water off site (without obviously discharging it into next door)
Always check with the Planners before starting work!
