Volume 4
Chapter 13 Foul & Surface Water Drainage
13.1. A house meets the tolerable standard if it has an effective system for the drainage and disposal of foul and surface water.
Introduction
13.2. This element of the tolerable standard requires every house to have a drainage system capable of managing and disposing of wastewater and rainwater. This ensures that the house remains watertight and assists in providing the occupants with a safe, hygienic environment.
13.3. This chapter provides guidance for assessors on how to judge if the systems for drainage and disposal are effective. The advice in this chapter should be used alongside an assessor's own experience and will help him/her to make sensible judgements. Assessors should also consider the advice given in this chapter in the context of guidance on other elements of the standard, including water closets, bath/shower and wash-hand basin, sink, and rising and penetrating damp.
Legislation
13.4. The tolerable standard was first defined in the Housing (Scotland) Act 1969 and has always included the requirement for a house to have an effective system of drainage of surface and foul water. The Housing (Scotland) Act 2006 does not change this.
13.5. Assessors should be aware of other legislation relating to the disposal of surface and foul water. We provide details on the Water Environment (Controlled Activities) (Scotland) Regulations 2005 at the end of this chapter.
Definitions
13.6. This chapter provides a more detailed description of the terminology used in this element of the standard:
13.7. Effective system for drainage and disposal: this refers to a fixed and permanent system that is capable of transferring surface and foul water from the point of collection to the point of disposal. To be effective, the system must be able to cope with the volume of water to be disposed of and transfer this to an appropriate point of disposal.
13.8. Foul water: this is the by-product of normal domestic activities, and includes all wastewater from toilets, sinks, baths, showers and wash-hand basins.
13.9. Surface water: this is rainwater that falls on the roof of the house, or on other surfaces around the house, such as driveways and paths.
13.10. The next part of this chapter gives advice for assessors on how to judge if a house has a system for drainage that meets the tolerable standard.
Making the assessment
13.11. The flow-chart below will help guide an assessor through the process:
13.12. An assessor should consider the following information when thinking about each of these questions:
Is there a system for drainage and disposal of foul and surface water?
13.13. An assessor should, wherever possible, look at the house's system for the drainage of surface water and consider if all the necessary parts are present. A typical drainage system will have gutters attached to the roof at the lowest ends of each slope. Each gutter will be fixed securely to the roof and fall ( i.e. have a downward gradient) towards a connecting down-pipe. Assessors should be aware that sometimes the down-pipe will be concealed within the structure of the house and not be visible. The down-pipe will be fixed securely to the house wall and continue from the gutter to at least ground level, where it will transfer the water to an appropriate drain, soakaway, or free-draining soil.
13.14. The system should be able to effectively manage the rainwater falling on the roof, and other surfaces, of the house. A house will normally be below tolerable standard where the system is unable to cope with the volume of water produced during normal rainfall conditions. Alterations to the building may have changed the system, or increased the roof area draining into the system so that it is no longer able to cope, or a system may have been inadequately designed or specified.
13.15. Assessors should look for evidence that the system may not be able to cope and use their experience to judge each case. The following indicators will help an assessor reach his/her decision:
- localised discoloured patches on the exterior walls of the house;
- penetrating damp affecting the interior of the house; and
- feedback from occupiers that the system overflows during normal levels of rainfall.
13.16. Assessors should be aware that while the presence of one of these indicators may indicate that the house could be below tolerable standard, this will not always be the case. The problem may be the result of a blockage which could be cleared easily, such as weeds or leaves. In these situations the house would not be below tolerable standard.
13.17. For foul water drainage, an assessor should, where possible, look at all elements of the foul water drainage system inside and outside the house to identify any defects. This means looking at any exposed pipes connecting to:
- toilets;
- sinks;
- wash-hand basins; and
- baths and showers.
13.18. An assessor should also consider whether the size and fall ( i.e. the downward gradient) of the pipe-work is sufficient to cope with the normal use of the facility or facilities connecting to them.
13.19. For both foul and surface water drainage, an assessor should look for any defects and/or inadequacies in the system that mean it is, as a whole, not effective. Minor defects, such as a loose or blocked gutter, or a crack in a down-pipe, will not normally mean the house is below tolerable standard. The system should be fit for purpose and no gutters or pipe-work should be broken, or damaged to such a degree that the system as a whole is not effective and beyond economic repair.
13.20. Symptoms of ineffective or failed systems could include seepage, discolouration of the ground, or smells. An assessor should investigate the source of these symptoms, especially if they are located close to the line of the pipe-work, or near trees or large shrubs whose roots may have caused damage to the system. Such symptoms are not conclusive evidence of an ineffective system; they may instead indicate the need for a repair to an otherwise suitable system.
13.21. Assessors should remember that, in some cases, it may be possible for them to monitor the performance of a drainage system over several months and in different weather conditions. This may provide them with additional information to inform their decision on whether a house meets the tolerable standard.
Does the system dispose of surface and foul water effectively?
13.22. The surface water drainage system will normally transfer rainwater from rooftops and other surfaces to a nearby storm drain. Storm drains carry rainwater to local rivers and streams where it enters the watercourse untreated. Some houses will have combined surface and foul water systems, and in such cases the surface water is disposed of in the same way as the foul water. Houses in some rural areas do not have access to storm drains, so other arrangements will be used instead, such as a soakaway. Disposal of surface water to land adjacent to the house in this way will not normally cause a house to be below tolerable standard, provided there is no ponding and the water drains away effectively.
13.23. Most houses will dispose of foul water to a public sewerage system. But, again, for some houses this is not possible. Alternative methods for disposing of foul water include septic tanks and private outfalls. Where the foul water is transferred to a septic tank, an assessor should check wherever possible that all pipe-work and connections are sound and not damaged. The septic tank should be properly maintained and there should be no evidence that the tank is leaking, such as ponding of foul water near the tank.
13.24. Occasionally, assessors may find that a house disposes of its foul water to a mass collection tank (sometimes referred to as cess-pits or cess-pools) located in the garden or neighbouring land. These differ from septic tanks in that the foul water lies untreated in the tank until it is emptied. A house that uses this type of system is below tolerable standard.
13.25. Private outfalls dispose of foul water to a nearby watercourse, such as a loch, river or stream. Some houses use sea out-falls, and assessors should check that the pipe disposes of the wastewater below the low-water mark. Disposal of sewage by private outfall is regulated by the Water Environment (Controlled Activities) (Scotland) Regulations 2005 and these are enforced by the Scottish Environment Protection Agency ( SEPA). If an assessor suspects that a private outfall is in breach of these regulations, he/she should contact SEPA directly.