The most expensive proposal, costing about £75m over 20 years, is a minimum pipe size of 150 mm for private foul water sewers.
It has been introduced to reduce the number of blockages but, as the DETR estimates that 30% of foul water blockages that result in property flooding are actually caused by grease, the proposals also include a plan for grease separators to be fitted to discharges from small hot food premises.
This change is likely to hit small businesses hardest – for takeaway restaurants, the £4500 estimated cost per installation will be onerous. Space and location of the units will also need to be considered in what is usually very restricted kitchen space.
Worries about property flooding have also led to proposals for the use of pumping stations and anti-flooding valves in basements and low-lying areas. This would give buildings additional protection against both blockages and from the effects of combined rainwater and foul water sewers becoming overloaded. Other proposals include: more measures to protect against rats in drains, guidance on greywater recycling and recognition that low-flush WCs require a modified approach to pipework design.
The DETR says the inadequate maintenance of wastewater treatment systems and cesspools is a prime cause of pollution. It plans to address this by promoting awareness of the system. Notices describing the type and location of the treatment system and outlining maintenance procedures would be required in the building. However, as such notices rarely remain in place after the buildings' first redecoration, the impact of this measure may prove limited. Other proposed changes relate to guidance on alternative methods for waste treatment, such as reed beds, drainage fields and mounds and packaged treatment plants.
Although extensive, changes to the rainwater drainage section of the document will have little impact on the cost of installations. Rather, the new document offers more guidance, particularly on sustainability. Eaves drop systems – where gutters are not provided and rainwater is allowed to fall from the eaves directly to the ground – are included for the first time. This is likely to be welcomed by architects but consideration will need to be given to the possibility of water staining walls or entering the building, not to mention the need to ensure that rainwater can be dealt with at ground level.
If adopted, the new section H4 on building over drains and sewers will prohibit building and underpinning over sewers unless it can be demonstrated that this will not affect the maintenance or use of the sewer. The DETR says this reflects current best practice and, as such, claims that there will be minimal costs associated with the changes Another new section covers separate systems of drainage. This will clarify the requirement for buildings to have separate drainage systems for foul and surface water. This is important because surface water discharges to foul systems can lead to overflows from sewers and treatment works.
Currently named H4, and to be renamed section H6 under the new proposals, the part dealing with solid waste is being revised to take account of recycling and measures to reduce landfill. The changes that will have the biggest impact will be the requirement for separate storage areas for waste that can be recycled and waste that cannot, a proposed doubling in storage space for waste and restrictions on the slope and number of steps on routes to storage areas together with restrictions on their location. The government has calculated the cost of this to be £24m over 20 years but estimates the cost and environmental benefits to be much greater.
Part H: Drainage and waste disposalThis section deals with the design of above and below ground drainage, cesspools and tanks, rainwater drainage and refuse stores. A consultation on this document has just finished, with the revised version due later this year. The Approved Document:
- Provides guidance on above ground drainage including sanitary pipework.
It covers pipe size and water trap details, design recommendations for branch discharge pipes and stacks, ventilation recommendations for discharge stacks and details of stub stacks
- Gives details on below ground drainage including layout and pipe cover, design recommendations for rigid and flexible pipes, pipe sizes and gradients and provision for clearing blockages and the siting and construction of access points
- Gives information on cesspools including capacity, siting and construction
- Provides guidance on rainwater drainage including: gutter sizes, outlet sizes and materials suitable for use above ground; pipe sizes, gradients and materials for drainage below ground
- Details refuse storage for both domestic and non-domestic buildings including storage capacity and location.
Carl Harrop is a senior public health engineer at Buro Happold.