The full impact of changes three years ago to Part H - dealing with drainage and waste disposal - is only now being felt as housebuilders try to make better use of land and deliver high-density schemes. Nick Orman of the WRC Group explains

The last revision to Part H of the Building Regulations may have been three years ago, but some housebuilders are only just starting to feel the effects of the changes.

The changes to the drainage and waste disposal regulation are making an impact because housebuilders are now delivering different types of housing - namely the high-density schemes favoured by John Prescott and the authors of PPG3.

Complying with Part H is more challenging when homes are more tightly packed together. Traditionally drainage has been directed round the rear of properties so that external soil stacks could be hidden. The new styles of housing with their irregular layouts can block off the routes designers would normally use for drainage. Concerns over crime have also caused problems as housebuilders are now sealing off the rear of their properties, thwarting drainage designers as well as thieves.

It means designers now have to find new routes for foul water drainage, which don't contravene the latest changes to part H. Regarding the layout, the biggest constraints in the regulations are recommendations concerning the proximity of buildings and the accessibility to manholes and inspection chambers on sewers.

Sewers should be kept away from foundations wherever possible to reduce the impact of any leakage on the foundations and to allow excavation for repair to the drain without compromising the stability of the building. With buildings so close together, bringing a sewer through a narrow gap between buildings becomes extremely difficult.

When a blockage occurs on a sewer, the impact may be on one or a number of users who may be remote from the manhole or inspection chamber. In the past, when fences were low, it was possible to find the inspection chamber easily and since most houses were occupied throughout the day, permission could be obtained. Now 2 m high fences and walls make finding the inspection chamber without drawings very difficult, and obtaining permission to enter property can be impossible as householders are often absent during the working day.

Approved Document H1 recommends that: "Access points on sewers should be in places where they are accessible and apparent for use in an emergency." Highways, public open space, shared driveways and even unfenced front gardens are possible locations. However rear gardens enclosed by two metre high walls and gates simply are not.

The solution to both these problems is to treat each house separately and to bring all the connections out at the front of the property. This has been practice in Scotland for many years. Access for rodding can be from a gully at the rear, which can also act as a relief point in case of blockage. The result is a simpler, often shorter drainage layout that can discharge directly to a sewer at the front of the property.

For surface water drainage there is an additional constraint in that requirement H3 now requires surface water drainage to be through infiltration drainage whenever reasonably practicable. If pipes do have to be used then the layouts suggested above can be adopted.

Revisions to regulations have brought fresh challenges, but there are solutions that have been shown to work.

Key changes to Part H

Pipework layout

  • Manholes on sewers to be accessible
  • Proximity to buildings
  • Flood protection in low lying sites
  • Off-site drainage now has to be controlled
Surface water drainage

  • Surface water to infiltration systems if practical
  • Surface water to sewer as a last resort