As Tierra designs ltd is based in the hilly area of ‘the Chilterns’ most of our enquiries come from this area, predominately Berkhamsted and Tring. One type of garden we have to contend with frequently are those with sloping sites. Quite often we will be faced with a heavily sloping garden with a design brief of wanting as much flat space as possible. To achieve this can be an expensive exercise - with retaining walls, drainage solutions, and boundary reparations.
Over the years we feel we have created some really nice spaces in sloping gardens, and love doing so, but before discussing the ways of doing this in the most economical way possible, let’s talk about the problems these gardens bring. Just why are sloping sites so difficult - and expensive?
The trouble with trying to eek out the most amount of flat space in a sloping site, is that to create any flat area, there will be a certain amount of earth moving, and it will often have to be moved twice. Topsoil will need to be stripped off and stored, before digging out the subsoil to new levels… and then the topsoil returned to provide a flat area that can then be planted or turfed. Add to this any access issues that might make the use of a digger not possible, and you can start to see the labour costs rising.
The fact that a site is already sloping, also indicates that there may be access issues, for materials in and out of the garden. No-one wants to be lugging materials up, or down, a slippy slopy site. Couple this with the safety aspect of running machines in and out. Careful consideration in choice of materials is important at the initial design stage in order to keep labour costs low.
Rain water will naturally form micro channels and rivulets, through the soil and run under the surface of the sloping ground. You won’t necessarily know this is happening but as soon as you start cutting into a bank of sloping ground, if the weather is wet, you will start to see the water surface, and pool, in the area you had marked out for a nice flat lawn. Some sites are often worse than others due to soil type and conditions, but it is a factor often overlooked until the costs of the drainage solutions are realised. Careful consideration of these issues must be undertaken at an early stage in the design process, including how the proposed works might affect the neighbouring properties as well.
Creating flat areas running up to boundaries within a sloping site by design means changing the height of the ground adjacent to any existing boundary wall or fences. This ultimately means replacement of those existing boundaries to a more solid solution that is capable of retaining the land on one side of the boundary. Discussions with neighbours also need to be had at an early stage. The boundary that is in place may not be yours to change.
Often any retaining that needs to occur, has to be undertaken fully within your land thus reducing the space you were trying to gain. Another consideration is whether the works fall under planning law, and the party wall act – again early discussion and consideration is paramount.
Changing the level of ground around existing trees can cause issues, and should be kept to a minimum. This includes trees on, and off, your property. Raising the level of soil around a tree by as little as 10cm is enough to suffocate the surface roots of the tree, leading to its death. Again certain species will be more prone to soil agitation and movement than others.
On this site in Berkhamsted we reached out to arboricultural consultant Peacock Consulatancy to ascertain the level of works that could be undertaken near this Cedrus deodara. This resulted in an exclusion zone around the tree, which affected the end garden design.
Having discussed the problems associated with sloping gardens let us look at the ways we can create great usable spaces in these sites, and the ways that we can create these without blowing the budget.
“Realise there are certain things worth spending budget on, and things that are not. Why build a wall when you don’t need to build one. Try to always keep an eye on the ‘cost to benefit ratio’”
At the early design stage, it is really important that you outline the flat/level space that you need, rather than want. This is key, as it will allow you to concentrate the majority of the budget on facilitating the works to achieve this. Then the remaining space within the plot can be set aside for aesthetics, making the space you have created a wonderful place to be. No-one wants to sit on an exposed lawn surrounded by fences admiring the nothingness! But with careful planning, beautiful secluded spots can be created, enveloped by plants and trees.
By carefully positioning the level areas in places which maximise privacy, sun, shade, views etc, it is perfectly possible to take all the positives of the existing site, whilst minimising the amount of works. It is not always possible due to the above external factors, but it is best to try and position these areas away from the boundary, negating costly works to the fences and walls as previously mentioned.
In the creation of these areas we will have necessitated a certain amount of soil retaining required. It is time then to think about the materials used, and the ways in which labour can be kept low. The standard would be to build small walls to create terraced areas. Walls in their construction need concrete footings, again more labour and materials. We need to think about how these walls will age. Rendered finishes will not last the distance in the UK climate on a non-damp proofed wall. So again, more budget to create a wall that could be rendered. Bricks as a go to, work well, but again the time and materials send the budget up. Sleepers are often used but as we all know these will have a finite lifespan. They can be used but consideration must be taken for the work involved in their replacement.
Steel retaining sections being installed during the construction phase on this Harefield site.
For the last 15 years we have been using steel to great effect in sloping gardens. It has obvious benefits in that it looks good, weathers well, and can be fabricated off site, for a relatively quick installation. Retaining walls can be fitted in as little as a day. Using steel posts with timber sleepers slotted between, is another good and economical method in retaining soil. We know the sleepers will rot over time, but by using the steel posts the sleepers can be replaced easily down the line, much like slotting a fence panel between concrete fence posts.
Seen here on a project in Highgate, these small steel step risers create a nice level space above, and require minimal labour to install.
The use of Hardwood decking is a great way to create useable space in a heavily sloping garden. Surrounded by planting, deck areas can be linked with platforms that are easy to navigate, opening up the whole space. Hardwood rather than softwood decking should always be used as the maintenance is much less and offers less of a slipping hazard if looked after.
This heavily sloped site in Berkhamsted benefitted from hardwood platforms immersed in planting.
Having as discussed, kept the construction of retaining walls to a minimum we can then concentrate on the sloping ground in the areas between the level zones. Planting into slopes has many benefits. The roots of the plants act as great stabalisation for the soil, stopping it from migrating down the slope in wet weather. The extra height a slope can give offers some great advantages in creating additional cover from plants, enhancing the useable space dramatically. Lawn banks are a lovely way to create open space, offering children a place to run up and down. Wildflower banks are also aesthetically appealing and offer less maintenance than a lawn bank. Having these planted banks is also a great aid in managing water and drainage which can be an issue in sloping sites as highlighted above.
For the above reason also look at creating permeable surfaces where possible in the flat/level areas. Grit surfaces are good and economical. Hardwood decking is ideal for sloping sites as it drains well to the ground below.
This very steep bank in Rickmansworth was almost inaccessible before. By planting the entire bank and running timber steps up through the planting, a pleasant journey has been created up to the breeze hut.
By using Hardwood decking, as seen here in one of our Berkhamsted gardens, large usable spaces can be created without the need for major earthworks.
The garden design process is set out to consider all the above factors, and should lead to the construction of the most sympathetic and economical garden, individually tailored to the client. A list of your requirements for the garden is key, before you even consult a garden designer. The initial consultation with whichever garden designer you choose to approach is an ideal opportunity to discuss feasibility, costs, methodology, and all of the subjects covered in this particular entry!
Learn more about the design process with Tierra Designs Ltd on our Process page.