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A touch of the flue

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technical & practice: Revisions to Approved Documents Parts H and J - combustion appliances and drainage - come into effect this month

Building Regulations Approved Document Part J, Combustion Appliances and Fuel Storage Systems, is an update of the 2000 version, entitled Heat Producing Appliances.

It includes completely new sections relating to oil-burning appliances and liquid fuel storage and supply, making the document five times thicker and adding a substantial series of appendices on checklists, calculations, key dimensions and means of compliance.

The booklet is a much-improved version of the previous document, and it makes you wonder what has happened in the past two years to give rise to such substantial changes - presumably Part L. But given the rumours about upgrades to Part L, maybe this is a sign of things to come - a rolling programme of constantly updated regulatory guidance, from publication to consultation to amendment.

With increased air-tightness requirements imposed on building designers, it is essential that sufficient controlled combustion ventilation is allowed to permeate the building to aid combustion and to carry fumes away. Therefore this document must be read in conjunction with Part F, Ventilation.

Oil and water

Part J begins with six pages of definitions to clarify the terms used throughout, as compared with the old document, which did not bother to define any terms at all. Keying the definitions into the updated Part B Fire Safety, risk assessments and selfcertification schemes, it outlines the definition of issues from 'non-combustible materials' to 'a boundary' (see table to diagram 3.4, page 43).

The section on liquid fuel storage usefully combines information from Part B and clearly defines the terms of reference, although it does talk of 'fire resistance in terms of insulation, integrity and stability', whereas stability tends to no longer be a reference point, being generally designated in Part B as the 'loadbearing capacity'.

The revised regulations have substantially improved their explanations and illustrations. However, in diagram 4.2, flues are shown as 600mm from the top light of a window. Unless the window is only 600mm high, which it clearly is not in the drawing, then it does not comply with the note on the same page that stipulates that a flue 'terminal should be at least 300mm from a combustible material, ie window frame'. This is a minor point, but it is amazing that confusing drawings still get through to publication.

Drain timetable

The new Approved Document Part H, Drainage and Waste Disposal, comes with a delightfully titled companion volume, Protocol on Design, Construction and Adoption of Sewers in England and Wales, published by DTLR, DEFRA (Department of Environment, Food and Rural Affairs), Welsh Assembly Government, House Builders' Federation and Water UK (an organisation representing all UK water suppliers and waste water operators).

This sister document is intended to work as a point of harmonisation for private and public foul drain systems 'to prevent the proliferation of private sewers and the problems of ownership and maintenance associated with them'.

This does not tackle the reasons why developers often prefer to lay private drains and minimise the adoptable connections, and the document is far from being substantial.

However, at the very least it does provide a checklist, and it references relevant clauses in the Approved Document to look out for. Sewers for Adoption, 5th edition, is still the main point of reference.

Section H4 addresses the erection, extension or underpinning of buildings over, or in the vicinity of, drains and sewers shown on the maps of sewers. It recommends that a Building Notice will not suffice for such work and that full plans will be required.

The document begins with a few concessions. Baths and showers now only require 50mm deep traps instead of 75mm, and WCs discharging directly to a drain need only be 1.3m from crown to invert, instead of 1.5m.

Hide and seek Once again the document is substantially larger than the previous edition (twice the size) and many changes are hidden in the detail of the text.

The DETR has consistently omitted to identify the changes between the pre-existing regulation and the new, leaving architects with the laborious, and often hopeless, task of finding changes out for themselves. For example, in diagram 3, 'Branch connections', the diagram looks identical to the well-referenced diagram in the old document, but on closer inspection, you find that the falls from a WC to a stack have been changed.

The new slope alters from 9mm/m minimum to 18mm/m minimum - double the slope with definite implications for WC layouts. See also table 2 - 'Common branch discharge pipes (unventilated)' on page 9.

The section on foul drainage is very much clearer with cross-sectional drawings, much more detailed 'limits of cover tables', manhole dimensions and spacing, and access recommendations.

While discouraging the use of cesspools as a solution of last resort, the new document examines in some detail the design and construction as well as the practical implications of septic tank drainage fields. Obviously influenced by recent debates about water table contamination, flood levels and deleterious effects on plant life, section H2 provides a neat synopsis of the issues and ways to avoid the problems. Using unusually welldrafted cross sections, this section identifies various methods, from drainage mounds to reed beds.

Plain drains

Section H3 takes the 'sustainable' approach further and applies it to rainwater systems. The original Building Regulation stipulated that the system should allow rainwater to be carried from the roof of a building 'to a sewer, a soakaway, a watercourse'. The new regulations seem to reverse those priorities.

The document suggests a design rainfall intensity of 0.021 litres/sec for eaves gutters and has amended the multiplication factors in table 1 'calculation of drained area' - (it used to be, 'calculation of area drained' in the original document). It also examines syphonic roof drainage systems, while the section on drainage of paved areas looks at pervious paving and free drainage. General guidance is given for soakaways, swales, filter basins and detention ponds.

All in all, these booklets are significant improvements on the previous guides; better designed, well laid out and substantially illustrated as well as having more detailed text. Let's hope that by the time we have located all the minor adjustments for ourselves, it will not be time for the next update to drop through the letter box.


Building Regulations Approved Document Part H: Drainage and Waste Disposal, 2002, DETR

Building Regulations Approved Document Part J: Combustion Appliances and Fuel Storage Systems 2002, DETR

Building Research Establishment Soakaway Design software (BRESOAK), priced £150 (including PDF formats of BRE Digest 365 Soakaway Design), is available from csc@bre. co. uk Note: further to reference in Robust Details (AJ 28.2.02), we note that the new edition of Thermal insulation: avoiding risks is now available

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