Guide to Conversion of Traditional Buildings

Section 3: Environment - Application of the environment standards: 3.1 Site preparation – harmful and dangerous substances

Mandatory Standard

Standard 3.1

Every building must be designed and constructed in such a way that there will not be a threat to the building or the health of people in or around the building due to the presence of harmful or dangerous substances.

Limitation:

This standard does not apply to the removal of unsuitable material, including turf, vegetable matter, wood, roots and topsoil on the site of a building (other than a dwelling) intended to have a life not exceeding the period specified in regulation 6.

3.1.1 Application of standard to conversions

In the case of conversions, as specified in regulation 4, the building as converted shall meet the requirements of this standard in so far as is reasonably practicable, and in no case be worse than before the conversion (regulation 12, schedule 6).

3.1.2 Commentary

There may be a view that this standard has little relevance to the conversion of a traditional building and that it is designed to deal with new developments on previously contaminated land. There are, however, a number of situations where the presence of harmful and dangerous substances can impact upon an existing building and its occupants. Examples of conversions where contaminants may be present are:

a) Where the previous use of the building allowed the possibility of spillage or release of contaminants such as chemicals, toxic metals, oils, asbestos and other hazardous fibres and particulates etc.

b) Where the building was previously used to house animals e.g. cattle byres.

c) When the fabric of the building contains harmful and dangerous materials such as asbestos, lead water pipes, historic lead-based paint etc.

d) Where there is contaminated land immediately adjacent to the building, which may be disturbed during the conversion, for example when installing surface water drainage to control moisture levels or flooding.

e) Where a pathway exists by which a contaminant can reach the building, for example, contaminated ground water from a pollutant source being directed to the building.

In addition, this standard also covers the treatment of the solum of buildings to prevent vegetable growth and evaporation of moisture from the ground. There is a requirement for any part of the underbuilding that is in contact with the ground, such as sloping ground, to be tanked. Further information is contained in Part 2, Section 3.4, Moisture from the ground, when dealing with this issue.

In the conversion of traditional buildings, this standard is a ‘reasonably practicable’ standard, which gives some flexibility as to how far it is implemented provided that the situation is no worse than before the conversion. This means it is possible that, for example, additional treatment of the solum may not be required. However, where there is an established risk to the building or to the health of people in and around it, remedial action will normally be required.

A site-specific risk assessment should be carried out where the history of the site indicates the possibility of contaminants being present.

3.1.3 Issues to be considered

Typical risks in the conversion of historic/traditional buildings

1. Harmful or dangerous substances

Where historic lead-based paint finishes are present there will be pressure to remove them and replace with modern, non-toxic paints – this may lead to a loss of an important historic decorative scheme.

Many traditional buildings have had systems installed that incorporate asbestos insulation. However, this is unlikely to be original to the building and its removal will not present a risk to the building if carried out in a properly controlled way. Note: if asbestos-containing material is found, the latest advice from Health and Safety Executive should be followed regarding removal or leaving in-situ. (refer to part 1, chapter 2.5.5 for further information).

Former farm steadings and stables, where animals have been housed, will be contaminated with faecal matter. The greatest risk is to hidden archaeology below the floor and in the ground surrounding the building when contaminated material is removed.

Treatment or removal of building fabric that has been impregnated with contaminants, especially porous materials, may lead to loss of historic fabric or unintended consequences for building performance where incompatible materials or processes are used.

Existing walls may be undermined and services disrupted by removal of contaminants up to 1m deep.

Animal urine can break down any plaster and may encourage mould growth, whilst pigeon / bat guano may be present in enclosed areas, such as roof spaces. Anthrax may be found in animal hair used in lath & plaster, while arsenic may be present in historic paints, wallpapers, and plasters. Lead oxide may also be present where lead has corroded, particularly on roofs and flashings.

2. Adjacent land and pathways

It is important to know if there is contaminated land immediately adjacent to a building, which may be disturbed during its conversion, for example when installing surface water drainage to control moisture levels or flooding. Existing pathways by which a contaminant can reach the building should be identified, for example, contaminated ground water from a pollutant source being directed towards the building.

3. Solum treatment

Treating the solum of a traditional building to raise its level to that of the adjoining ground can be disruptive to historic floors. Solum treatment can compromise moisture management through insufficient ventilation and drainage, increasing the risk of timber and stone decay.

3.1.4 Recommendations to meet the standard

Each site must be subject to site-specific risk assessment, which must consider the sensitivity of the intended use of the site. It is necessary to recognise the specific source(s), pathway(s) and receptor(s), and the extent of remedial treatment required to ensure that human health, the building and the wider environment are no longer at risk. In the case of housing, the risk assessment and nature of pollutant leakages will depend on the following factors and their relationship to the contaminant:

• the design and layout of the conversion,
• whether the site includes gardens and, if so, where they are situated,
• any harmful or dangerous materials which are particular to the conversion and the precautions that will be used in construction.

Points that should be considered to reduce risk to people and buildings prior to work commencing are:

• Local knowledge should be actively sought on the history of the site and surrounding area.
• The history of the site can provide insight into whether the site is contaminated and reference to current and historical OS maps and site plans can provide evidence of contaminants.
• A walk over the site can provide other valuable indications, including the type of vegetation (or lack thereof), any unusual smells or suspicious containers.
• A soil and site investigation may be considered if the desktop study and walk-through show possible contaminators (such as middens etc.).
• This standard requires a hazard identification and assessment to be carried out, for which a risk assessment specific to the site is required.
• The site should be considered as a pathway or receptor of contamination, and advice from the appropriate environmental guidance of the local authority should be sought on these risks to reduce risk when developing the site.
• A restoration plan (also known as a remediation or risk management plan) should be prepared for the contaminated site – refer to Planning Advice Note PAN 33, 2000, for further information.

Points that should be considered to reduce the risk to the occupants and the building during the conversion of a traditional building are:

• The type of contaminant defines the approach to its removal and/or treatment.
• Expert advice for remediation should be sought in cases where contamination has been found and specialists employed for the removal of the contaminants.
• If contamination is found during construction the verifier should be informed immediately.
• Contaminants in most cases should be removed by experts, and advice sought from the verifier in this regard.
• Licenses may have to be sought for removal of some contaminants.
• For buildings of greater cultural significance, the potential impact on the fabric or character of a building arising from any removal or treatment of contaminants should be included within any conservation plan for the building.

Treating the solum of older buildings to meet the recommendations of the standard may be destructive to traditionally constructed floors if they must be lifted to raise the solum level and treat the surface. However, unless there is evidence that the existing solum is a source of unacceptable dampness that is causing damage to the building, is a risk to the health of occupants, or is supporting vegetable growth (including fungal growth), the least damaging approach may be to leave the existing solum as it is. Where there is evidence of high moisture levels then the recommendations contained in Section 3.4, Moisture from the ground, should be followed.

3.1.5 Further reading

Additional guidance can be found at:

• BR 255 (1994), Performance of building materials on contaminated land.
• British Standards Institution (2017) BS 10175: 2011 + A2:2017, Investigation of potentially contaminated sites – Code of Practice.
• British Standards Institution (2020) BS 5390: 2015 + A1:2020, Code of practice for ground investigations.
• CIRIA (1995-97), Special publications 101-112, Remedial treatment of contaminated land, Vols I-XII.
• The Scottish Government (2000) Planning Advice Note 33: Development of contaminated land.