What are the technical, structural and design implications for a home on a sloping site? Here, Homebuilding & Renovating offers some tips on costs, design and construction
A sloping site is both a problem and a gift. It will add complexity, and thus cost to the project, but the finished home is sure to be more interesting. These tips will help you understand the problems with sloping sites and how to overcome them. It will also introduce you to some design solutions.
This modern home has split levels creating visual impact both inside and out
1. Budget for additional costs from the outset
Sloping site homes often need reinforced suspended concrete floors, additional draining, stepped foundations, a pump and more complicated hard landscaping — and this all costs extra money. Unfortunately, there is no sliding scale to apply to sloping sites to help you work out the additional costs for every degree of slope. The best advice is to use detailed drawings and the help of an estimator or quantity surveyor to work out the costs of your project.
2. Cut and fill
To overcome the issues of building on a sloping site, some designs involve carving out a level plinth on which to build a home designed for a level site. The spoil cut away from the bank is then used to make up the levels on the lower edge.
The foundation costs are always going to increase due to the slope of the land and the requirement that the foundations should find original subsoil bearing. If the spoil is piled up against the lower or built up section of the new home then provision will have to be made for the oversite level within the building to be brought up to within 600mm of the proposed external soil level, in order to equalise the pressure on the walling. However, carting spoil away from a site is expensive and time consuming and its retention on site is a cost benefit, just so long as there is space to store it.
A level site was created for this home by cutting into the hillside
3. Consider drainage and sewers
If your site slopes down from a road in which the sewer is fairly shallow then you may have to think of using a pumped sewage system. This can add at least £2,000 to the drainage costs. However, there may be a corresponding saving due to the fact that the 50mm flexible pipe may well be cheaper to lay than a conventional drainage pipe. If your site slopes down from the road, within which the sewer is quite deep, then the slope may actually represent a saving in cost, as the resulting house drainage will not have to be as deep.
Sites which slope up from the road and sewer may seem more attractive so far as drainage is concerned, but if the slope is significant it might be necessary to install tumble bays within the manholes, so that the effluent can enter the sewer at a reasonable rate.
Surface and rainwater is also a consideration. Many local authorities will not allow surface water to go into the public sewers, and require that precautions are taken to ensure that surface water from your property does not flow down onto the road if your house sits above. Sloping down from the road means that surface water can collect around the base of the lower floor, or worse still, find its way into the garage. This may mean having to install a drainage channel to divert the water to soakaways.
4. Basements are not always a necessity
On a costing level a basement is always going to cost at least the same amount per square metre as any other part of the home, if not more. In ground with high water tables or in heavy clay, these costs and the sheer physical difficulties presented may make the choice unviable. However, if the lie of the land is such that there is no alternative to either a full or partial basement, then this can be the cost effective solution.
5. Do some research on retaining walls
If you build into the slope, the walls of your home may have to hold back considerable banks of ground — we call these retaining walls. Alternatively, you can carve out a level plinth, the surround of which will need retaining walls. Above 1,200mm in height these will have to be designed by an engineer.
In certain circumstances it may be cheaper, and visually more attractive, to construct a series of lower retaining walls with the ground stepped between them. An alternative is wire cages – known as Gabions – filled with stone, or interlocking concrete blocks that are subsequently filled with soil and planted, or left exposed for an industrial look.
6. Build on stilts
On steeply sloping land one solution is to build on a series of stilts or columns. This removes the need for extensive foundations and tanking. Moreover, it leaves the ground below exposed which you can then cover with plants (to hide the stilts), or use for storage. In certain situations it can be the cost effective solution and there is no reason why it cannot be employed with multiple level designs.
Stilts have made it possible to build a level home on this steeply sloping site
7. Try upside down living
As sloping sites often offer wonderful views, one way to take advantage of this is to reverse the accommodation, placing living areas on the top and bedrooms below. When it comes to your garage, it makes sense to have this on the same level as the road, but think carefully about how this is connected to sleeping quarters because you don’t want fumes in bedrooms.
Be aware that for every potential buyer who is excited by the individuality of the design, there are many who cannot accept departure from the norm. The housebuying public are incredibly conservative. They expect a natural progression of rooms. It may not devalue your home in real terms, but it will cut down the number of potential buyers and lengthen the time taken to sell.
8. Consider kerb appeal
All too often, homes built on sloping sites fall into the trap of providing purely functional accommodation and pay little heed to the need to maintain a good visual impact. Where the garage and entrance are on the ground floor, it can make the lower half of the house look boring and regiment so think about ways to break up the utilitarian frontage. Set garage doors back or beneath overhanging balconies to reduce their visual impact. Introduce doors as well as windows to upper floors and break up the front elevation by stepping parts back and introducing forward gable projections. Consider balconies and ask yourself whether your entrance has to be on the ground floor, or whether it may create more of a feature having it on the middle level with some stairs and a platform to one side.
Sites that slope away from the road suffer from being unable to advertise the full extent of their accommodation. What looks like a bungalow from the front may be a five bedroom house with several stories to the rear and potential buyers may opt for a property with more obvious kerb appeal. There is little you can do apart from positioning the home so that even the casual observer can see from the front that it extends downwards — and offer some indication of the hidden accommodation, such as through the use of rooflights.
9. Don’t forget about accessibility
Part M of the Building Regulations relating to disabled access can sometimes affect the design of a house on a sloping site. Externally, they require that access ramps for slopes up to 1 in 15 should not be longer than 10 metres, and those for gradients up to 1 in 10, no longer than 5 metres. Steeply sloping sites can, in the absence of a ramp, employ steps at least 900mm wide with a rise no greater than 150mm and a distance between landings of no more than 1,800mm. Additionally, if there are more than three risers, handrails must be provided to at least one side.
Internally the entrance floor must contain a WC accessible by wheelchair and here, the Regulations make no distinction between split level and flat site homes.
10. Make the most of changes in floor levels
On a sloping site, a split level floorplan is usually the most cost effective way to develop the site. Changes in level can help you define different areas in an open plan space and certainly add interest to a layout. However, multiple levels will limit the appeal of the property to households with elderly, disabled or young members, so think carefully about your needs and futureproofing.
Decking, terracing and even ponds have been built into this sloping garden
11. Use clever hard landscaping so that you don’t lose garden space
A garden that slopes away from the home can be lost so use raised decks and patios to create useable space. Raised wooden decks can be attractive and they can be constructed in such a way as to allow light to filter down to the windows of lower storeys. A garden that slopes up from the home is one that can be seen to an even greater degree than a flat site. It becomes a three dimensional garden that can be terraced so as to bring beauty to all levels of the home.