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BS 7913: 2013 - Guide to the Conservation of Historic Buildings

BS 7913 serves as the standard of Good Practise for works to older, traditional buildings.  It sets out standards for Building Surveys, and dispels the commonly held thinking about dampness in buildings.  It clearly shows that Rising Damp no longer has a place in surveys, and that intelligent diagnosis of the real reasons for dampness can follow a simple, inexpensive process.

In it's Foreword, Mike Brown, Chair IHBC comments "It serves as an accessible standard of good practice for works to older, traditional or valued buildings..... all regardless of levels of formal designation, controls or regulation."  He goes on to say:  "... this Standard is for non-specialist users as well as specialist conservation practicioners.  Its widespread recognition both as a British Standard and as a practicioner's manual is an especially important consideration today, especially as we see reductions in planning guidance."

The Standard is intended for those who own, use, occupy and manage historic buildings, the professional team's contractors and others employed to work on their behalf, and can be used by decision makers and funders.

I've put that last phrase in Bold for a reason.  One of the most frustrating parts of our job as Surveyors of old buildings is the fixed, intractible and often completely incorrect attitude of banks and building societies to problems with the property.   We encounter a standard phrase on a daily basis in valuation surveys "We require a timber and damp survey by a member of the Property Care Association."  This single phrase has been responsible for more damage to historic buildings in this country than a World War, and centuries of natural weathering.  With this British Standard comes the hope that finally a sea change in attitude is upon us.

If I have a criticism of the Standard, it is only because some of the words used may frighten the very people it is intended to reach - the ordinary man on the street who loves his Victorian terraced home, and wants to stop the damp industry injecting it.  He wants to instruct his local builder in how to undertake works.  Words such as Sustainability, Heritage management, Strategic and Conservation management plans - all are a little off putting when you just want to stop the bank insisting on damp treatments.  Every word of this Standard is essential - it sets out an holistic approach to assessing, managing and maintaining your 'Heritage Asset' - or Victorian semi.  If you read through the slightly awkward sections on strategic and operational management, you finally arrive at Section 6.2 - Condition surveys and inspections.

It is at this point that BS 7913 becomes a powerful tool for the surveyor, and his client alike.  Sections dealing with Structural Movement, Water and Moisture ingress, Fungal attack and Insect attack are all very specific in pointing out that the type, cause and extent of any issue must be professionally assessed.  The standard also stresses that environmental conditions are often the main cause of these issues, and that using the 'minimum intervention' principle, treatment is often as simple as increasing ventilation and reducing humidity.  Some quotes from Section 6.1 should illustrate my point:

"Dampness is often caused by external ground levels being higher than internal floor level, or the insertion of modern non-porous materials.  It might be possible to remedy these by improving drainage, or selective removal of non porous materials."

"The decay of timber in buildings is closely related to moisture levels.  High levels of moisture modify the composition of timber in a way that makes it more susceptible to insect and fungal attack.  The moisture content of timber should be kept below 20%.  It is not necessary to remove timber that has been affected by fungus, because fungus becomes inactive when the level of moisture is reduced.  In most cases, chemical treatment is unnecessary...."

Naturally members of the Property Care Association will be most upset to learn that millions of pounds worth of useless chemical treatment of timber in British Homes is considered unnecessary, and the Banks and Building Societies should take heed!

With regard to Insect attack, the Standard goes on to say:

"Investigation to establish the extent of damage to timber and to assess the level of impairment of structural strength should be carried out.  The principle objective should be to remove the sources of moisture.  Insecticidal treatment should only be used as a last resort as it can cause environmental damage and might require licenses for protected species.  Precautionary treatment should not be applied to unaffected timbers."

Many old roof structures are inhabited by bats.  These creatures eat phenomenal amounts of insects, and need to be encouraged.  Spraying toxic chemicals on roof timbers and membranes in bat roosting areas is strictly controlled, and almost never allowed.  I've seen countless examples of Property Care Association member companies routinely spraying toxic chemicals all over historic timbers in roof spaces clearly occupied by bats.

The Standard has this to say about Repointing:

"It should only be carried out when the mortar has deteriorated leaving voids that leave the wall vulnerable to water penetration, or when mortar is very soft.  Comprehensive repointing is rarely necessary.  It should be restricted to areas of need.  Mortar should be removed with unpowered hand tools; mechanical disc cutters should not be used for removing pointing in historic buildings.  Narrow joints are particularly difficult to repoint.... The use of hard cement mortars is rarely desirable as aggressive decay of masonry could result"

Further sections deal with good practise in the design of Alterations, focussing on reversibility where possible, Reinstatement - where a set of simple tests guides us through the justification and practicality of reinstating features that have been lost - as opposed to adding something because you think it looks like it should have been there.

I must stress that this is a Guide.  It is not a 400 page Handbook of Building Conservation.  It sets out guiding principles, and makes sensible suggestions.  It suggests the reader refers to relevant professional expertise where needed. Anyone involved in working with old buildings should have a copy.  More than that, they need to read it and work towards achieving its aims.

For us, that means that Banks and Building Societies, and valuation surveyors alike, need to take heed of the very specific guidance with reference to timber and damp.  Recommendation of unqualified chemical salesmen needs to stop.  Sensible professional advice should take over.

    Regulated by RICS