Driveways and Sustainable Drainage Systems.

by grosvenor on May 27, 2013

My report this week is concentrating on driveways and in particular our obligations under the Sustainable Drainage legislation and how does this legislation affect those who wish to install a new driveway on their property.

In brief the Sustainable Drainage legislation was introduced as a necessity to deal with the overloading of the public sewar caused by increased levels of storm water run off due in significant part to front gardens being made into driveways. Although a problem mainly associated with urban areas, the legislation applies to us all.

I essence the legislation now dictates that it is the property owners responsibility to cater for the storm water that falls on his / her ground. Therefore when considering a new driveway, even if you are replacing an existing one, your thoughts should include the what can we do with the rainwater that falls on it. It is also worth noting that in theory all new driveways will need planning consent – this is generally a paper exercise that will be signed off by planning officials but permits your plan for storm water control.

Many of the more popular driveways such as tarmac and block paving are not permeable and therefore create run off. In this instance there will need to be drainage channels installed to catch that water and feed it into an appropriately sized soak-away. the size will be determined by factors such as the permeability (how quickly water soaks in) to the soil and the quantity of the water to be catered for – affected by the area of collection. If you are on clay soils this can be quite a large item which as with all soak-aways will need to be sited 5m or more from the dwelling. In reality the practical solution may even be impossible to achieve in which case you will be seeking permission to allow water to enter the public sewar. If this is to be the case do remember to ensure you fit a water trap in the drain that feeds the sewar – you may create a wonderful drive but the smell will very much restrict your appreciation of it!!

Another approach which you may wish to consider is to not disturb the natural ability of your land to absorb the moisture which falls on it. This can be achieved using permeable paving solutions of which there are probably more than you think. The principle by which they all work is to make the driveway base material act as a giant soak-away by using materials that create natura voids within it means that rainwater fills those voids and slowly discharges the water into the soil over a longer period when the rain stops. The first on the list and certainly the most ecconomical solution is to specify a loose aggregate driveway. The old problem of loose shingle migrating just about everywhere other than on the drive surface remains but is really only a problem on smaller drives and ones where vehicles need to perform tight turns, so for the larger area with relatively straight access a shingle driveway should not be instantly dismissed. The migration issue is not helped by the fact that shingle by nature is a rounded stone which due to its shape naturally wants to roll. This is excentuated by the general mistake of putting too much on – allowing 15mm depth of 10mm shingle is about right; you can always add more! This can be overcome to a large extent by the use of grits and of great popularity now the decorative aggregate (be careful to choose one that is suitable for driveways). We at Grosvenor are finding that Granite chippings are the perfect answer to many clients driveway problems. Available in a variety of colours the 14mm stone is very angular which means it locks together to form an attractive, stable but fully permeable surface. The pictures below show driveways that Grosvenor have recenty constructed for clients in Haywards Heath and Horsham using silver grey granite chippings over a MOT type 1 base. The driveway shown in the right hand picture is on a particularly wet site. With the previous wet months really testing its integrity I am pleased to report it has performed exceptionally well.

Steer - May 2013  (2)                Gate Closed - May 2013

Other permeable driveway options include permeable block paving which by the way the sub-bases are constructed and by the use of speciall blocks create the permeability required.

Another option that we at Grosvenor particularly like is the recent development of a fully permeable resin bound driveway. The product consists of a 20mm layer of decorative grits (available in a number of colours) bonded to the surface of a base layer of bonded recyled car tyre chippings! The system provides all the practical benefits of a hard surface driveway, is aesthetically pleasing, is eco-friendly and fully SUDS compliant as well being virtually maintenance free. See our colleagues at www.sudscape.co.uk for examples of this product.

If you are considering a new or replacement driveway please visit our website www.grosvenor-lt.co.uk or please do contact me on 07932 081889 (Martin Blake).

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