EXTRA. NHBC s technical newsletter August 2002 Issue 24. This edition includes:

Transcription

1 NHBC s technical newsletter August 2002 Issue 24 This edition includes: New Contaminated Land Guideline Values The introduction of Soil Guideline Values. Approved Document H (Drainage and waste disposal) A summary of key changes. Reports on the condition of flues and appliances at completion Greater emphasis on testing. European Standards and CE Marking What are they and what do you need to do? EXTRA STANDARDS EXTRA 1

2 CONTENTS 2 New Contaminated Land Guideline Values 3 Approved Document H 4 And still on drainage 4 Clarification - Approved Document L and Robust Details 4 Reports on the condition of flues and appliances at completion 5 European Standards and CE Marking New Contaminated Land Guideline Values The contaminated land exposure assessment (CLEA) model, and four supporting contaminated land reports (CLR 7-10), were published by the Department for Environment, Food and Rural Affairs (DEFRA) and the Environment Agency in March this year. These provide a scientifically based framework for the assessment of risks to human health from land contamination. When dealing with potentially contaminated sites, the most important question is: does the concentration of contaminant X pose a significant risk to human health or the environment? The CLEA model and new soil guideline values (SGVs) will help to answer this question with respect to human health. SGVs represent 'intervention values' which indicate to an assessor that soil concentrations above this level could pose an unacceptable risk to the health of site users and that further investigation or remediation is required. The primary purpose of SGVs is to determine if the existing land use poses unacceptable risks to human health under Part IIA of the Environmental Protection Act This legislation requires local authorities to identify land, in its present use, within their areas, which they consider to be contaminated. However, the SGVs will also be used in the context of development control to inform judgement for safe development. SGVs for 7 contaminants have been published so far, with values for each of three typical land uses: residential, allotments and industrial/commercial. Values for a total of more than 50 contaminants are expected eventually, although this may take several years. As they are published, the SGVs will replace the ICRCL (The Department of the Environment Interdepartmental Committee on the Redevelopment of Contaminated Land 1987) values that were published for 17 contaminants encountered on many sites. In addition the reports contain toxicological data which set out the Tolerable Daily Intakes and Index Doses for contaminants to support the derivation of the SGVs. These publications are available from: Environment Agency R & D Dissemination Centre c/o WRc, Frankland Road, Swindon, Wilts SN5 8YF Tel: publications@wrcplc.co.uk or can be downloaded from the DEFRA web site at ACTION: NHBC will expect consultants to make use of the new values, as they are published, in association with the guidance contained in NHBC Standards Chapter 4.1 and the NHBC/EA document entitled Guidance for the Safe Development of Housing on Land Affected by Contamination. 2 STANDARDS EXTRA

3 Approved Document H (Drainage and waste disposal) This article summarises the key changes in the 2002 edition of Approved Document H (England & Wales). Drainage layouts The guidance in Part H may significantly affect the layouts of drains on your developments. The requirement for 150mm diameter drains where serving more than 10 properties is well known but the Building Regulations now require drains serving more than one property to be kept clear from areas where future extensions are likely. In addition, access points should be located in places where they are accessible and apparent for maintenance in an emergency. This could be highways, public open space, unfenced front gardens and shared or unfenced driveways but not rear gardens! This change could have a significant effect on the designs of drainage schemes for your future developments. The recently published DEFRA document Protocol on Design, Construction and Adoption of Sewers in England and Wales confirms that there is a need for developers and the sewerage undertaker to work in close liaison. The intention of the protocol is to prevent the proliferation of private sewers and consequent problems of maintenance and ownership associated with them. This can be achieved by harmonising the essential elements of design and construction of sewers contained in Approved Document H with the guidance in the 5th edition of Sewers for adoption. So the message here is consult with the sewerage undertaker in accordance with the protocol prior to working up drainage schemes for approval by the building control body. It would be prudent to review your schemes now to ensure compliance with Approved Document H and the DEFRA Protocol. Surcharging of drains Many incidents of sewer flooding are due to surcharge into basements. For low lying sites (where the ground level of the site or the level of the basement is below the level of the ground at the point where the drainage connects to the existing sewer) care should be taken to ensure that dwellings are not an increased risk due to flooding. The Building Regulations now address this issue by requiring anti-flood measures such as the provision of pumped drainage or anti-flood valves depending on the risk of surcharge. So how do house builders determine the risk of surcharge? The answer is to consult the sewerage undertaker. You need to consult the sewerage undertaker whenever you intend to develop a site that is low lying or the proposal incorporates a basement. The sewerage undertaker can advise on the risk of surcharge, which will help you to determine what measures are necessary to prevent flooding. Building over sewers The requirements for building over sewers have now been incorporated into the Building Regulations. It is important that you check the sewer maps held by the sewerage undertaker to determine the location of sewers on site. Make sure you advise the building control body whenever you intend to build (or underpin) over or near to (within 3m of the centre line) a drain, sewer or disposal main shown on the map of sewers. You should also consult the owner of that sewer or drain (normally the sewerage undertaker). Building control bodies will take the requirements of the sewerage undertaker into account prior to granting approval for the works. Again consultation is the key to avoiding costly unexpected changes to designs during the development programme. Rodent control With increasing development of brownfield sites so our attention has been turned by Building Regulations to the problems of rat infestation. So how do you know if a site is at risk and requires additional protection such as rodent barriers or intercepting traps? Ask the environmental health department of the local authority whether any special measures are required for the control of rodents. Let the building control body know the result of the consultation so they can take this into account when assessing drainage designs for compliance. Solid waste storage Although Building Regulations offer detailed guidance on refuse storage and siting, more emphasis is now given on the need to consult the waste collection authority to determine their requirements. The waste collection authority has powers to specify the number and type of receptacles to be used and the location where the waste should be placed for collection. So make sure you consult the waste collection authority prior to finalising your designs for approval by the building control authority. ACTION: The 2002 edition of Approved Document H of the Building Regulations introduces some new challenges. House builders should consult with the relevant statutory authorities to minimise the effect of these on your future developments. STANDARDS EXTRA 3

4 and still on drainage here is a problem which occurred because of the movement of shrinkable clay Highly plastic clays are able to swell or shrink by up to 150mm. It is therefore important to ensure that all elements of the house construction that may be subject to movement (including the drains and other services) are able to accommodate it without adverse effect. This picture, taken from underneath a house in Essex, shows the foul drain passing through the outside wall over the top of the ground beam. The rising ground has caused the foul drain to lift and crush against the mortar droppings that have fallen down the cavity. The combination of the backfall and the constricted bore has stopped the drain from working. The cost of rectifying the drainage problem alone on 12 properties on the development was in excess of 400,000. Points to consider: Is the cavity free of mortar droppings at the base of the wall? Is the fall of the drainage system sufficient to cater for likely differential movement in the pipe run? Is there room for pipework to move uniformly if it is likely to be subjected to heave or shrinkage? Does the construction allow for differential movement where it may occur? Clarification Approved Document L and Robust Details Standards Extra 23 (page 3) In Standards Extra 23 (page 3) we advised of changes to the NHBC Standards made to align them with the 2002 edition of Approved Document L "Conservation of fuel and power" (England and Wales) and the Robust Details document. The article stated that the Standards changes would be effective for all homes from 1 October This was incorrect. NHBC would like to clarify that the changes to the Standards to align with the 2002 edition of Approved Document L and Robust Details apply only in England and Wales to homes where required by the Building Control Approval. Reports on the condition of flues and appliances at completion The Government has asked building control bodies to obtain a report detailing the condition of flues and appliances at completion stage for each installation. All flues now need to be tested to ensure their integrity and, where an appliance has been installed, a spillage test needs to be carried out to confirm the safe operation of flue and appliance. Builders are responsible for ensuring these tests have been carried out and that a report is available for review by the building control body. Now is the time to give consideration to how you will comply. Speak to your specialist contractors and make sure they know what is expected. Consider where these reports will be held so that they can be easily retrieved when requested by the building control body. Remember that if a report is not available a Final Certificate cannot be authorised. ACTION: Builders should familiarise themselves with the changes to Part J and make sure that reports are available on site. STANDARDS EXTRA 4

5 European Standards and CE Marking What are European Standards? European Standards for products are now starting to take over from the British Standards we are all familiar and comfortable with. For instance, NHBC has already recognised the relevant European Standard for chipboard flooring. The reference to BS 5669 was changed some time ago to BS EN 312 and this is how the material should be ordered, including the new grade Type P5. As time goes on, more and more European Standards will replace British Standards and manufacturers, both in the UK and across the Channel, will be making their products to the new standards. What is CE Marking and what does it tell me? CE marking(see below) indicates that the product meets the minimum requirements to allow it to enter the European market. The technical requirements are set out in European standards and the information accompanying the CE marking provides the user with some basic technical details of the product. This information will be useful to building control bodies for building regulation purposes. Although the products have to satisfy type testing and factory production control requirements, these tasks do not always have to be done by a third party, so the CE marking should not be regarded as a quality mark. Do I have to use CE marked products? Products which have CE marking can be freely traded across Europe under European law. To do this, it has been necessary for all European countries to agree the content of each standard and this has led to many delays in their preparation. Over such a large geographical area, what is not critical to Mediterranean countries can be critical to countries like the UK further north. For example, roof tiles which may be suitable for frost free climates won t be suitable to withstand our winters. It is not necessary to use CE marked products. However, by using CE marked products of the correct grade or class it will help to satisfy the building control body because they are generally obliged to accept information accompanying the mark as being correct. It s worth mentioning that under the European rules only certain products can be CE marked Why do I have to change to the new system? Many manufacturers are international companies and will want to sell their products in the UK, Europe and possibly worldwide. It is inevitable that to sell products to the widest market, manufacturers will switch to the new European Standards. In fact, British Standards as we know them, won t exist. As part of European law, the UK will have to withdraw its national standard once a European Standard is published, subject to a transitional period where both will run in parallel. What do I need to do now? Keep yourself abreast of changes to Standards. Government agencies, BSI and manufacturers will all be providing information on the new regime. For those products which are critical for Building Regulation purposes check with manufacturers on whether they have changed to new European Standards. Check that any material or product has characteristics, which are equal to or better than the current Standard. This is not always as easy as it sounds because European Standards are written in performance terms whereas British Standards have generally been prescriptive. Although this concept is a different approach to standards making, it won t mean that products will change significantly from those we use today. Where can I obtain more information? The following websites have information on CE marking; The Office of the Deputy Prime Minister ( British Standards Institution ( Example of what the CE mark may tell you. 5 STANDARDS EXTRA

6 s & s Below are the answers to a selection of questions we have recently been asked in NHBC Technical. Drainage connections to pre-formed inspection chamber bases Where pre-formed inspection chamber bases are used, does the main channel entry connection have to be used in all instances or can connections be made using the branch connections? The entry connections should ensure no deposits can accumulate within the base where they can then lodge and cause blockages. To avoid a build up of solids the main channel entry connection should be used in all cases. Where two drains meet a base from different directions, the inspection chamber should be turned and swept bends used to connect one drain to the main channel. The other drain can be connected to a side entry as shown. Diagonal bracing to double hipped roof Is diagonal bracing needed on a double hipped roof? Hipped ends will tend to provide stability, and according to BS , Code of practice for trussed rafter roofs, hipped roofs do not require diagonal bracing if the length of the roof between the hip ends is less than 1.8m. Partial fill insulation to gable walls Where partial fill insulation is placed in the cavity but does not continue to the top of the gable wall, is a cavity tray needed? Installing a cavity tray with weepholes above is good practice. The cavity tray should not significantly weaken the gable. However, provided workmanship is acceptable and insulaton is adequately retained against the inner leaf so that there is a nominal 50mm clear cavity between the insulation and the outer leaf, a cavity tray is not needed. Insulation of extract ducting Should the duct from an extract fan running in the roof void be insulated to prevent condensation running back into the fan? Condensation could cause damage to the extract fan and condensation dripping from the fan could be a nuisance to the home owner. Therefore the duct should be insulated (placed under the roof insulation where practical). Alternatively, a condensation trap should be provided with pipework to the outside, laid to a fall. 6 NHBC Technical Buildmark House, Chiltern Avenue, Amersham, Bucks HP6 5AP Tel: Fax: technical@nhbc.co.uk HB /02