Method statement covering the independent surveying for timber decay, damp problems and other latent defects together with the specification of remedial works

1 Introduction

Independent, professional surveying and specification is required in order to ensure cost effective repair and refurbishment of buildings. This is also necessary to minimise the risk of damp or decay problems occurring after refurbishment. The methods to be employed in providing such a service are described below. These are based on the results of a 5 year DTI funded research and development project undertaken by H+R in co-operation with the Building Research Establishment and the Scottish Institute of Wood Science together with other European partners. H+R have over 30 years experience in this field and are market leaders in providing these services

2 Survey

2.1 Identification Of Existing Damp And Decay Problems Affecting Timber Or Other Building Materials

2.1.1 Building defects

The building should be inspected to identify existing building defects allowing water penetration into the structure or allowing moisture to accumulate in the structure. This should include the identification of any significant rising or penetrating damp. Any structures vulnerable to damp and decay, currently or in the past, should then be identified using this information. Findings should be recorded

2.1.2 Structural decay

All materials to be retained on refurbishment should be assessed for structurally significant decay. Specialist technology should be used, as necessary, to determine the condition of wall ties, larger section timbers or timbers built into masonry. These include the use of special drills to determine the extent of decay deep in structures and materials. Materials found to have been vulnerable to decay in the past, in 2.1.1 above, should be inspected in detail; in particular the bearing ends of roof trusses, floor joists, lintels and wall plates and non-timber elements such as wall ties, brickwork, masonry, leadwork and pointing. Findings should be recorded

2.1.3 Timber decay organisms

Vulnerable structures should be examined in detail for evidence of current or past infection by organisms able to cause timber decay. Specially trained 'Rothound' dry rot search dogs may be used for this purpose. The infections found should be identified and their potential for causing past or further decay should be assessed and recorded. In particular, the viability of any infections and whether they are live or dead should be determined

2.1.4 Identification of moisture distribution

The moisture distribution in the structure should be determined so as to identify any materials that have accumulated a significant amount of moisture due to building defects in the past. Those materials that have accumulated enough moisture to allow damp and decay problems to develop during or after refurbishment should be inspected. An assessment should be made of the moisture content and condition of the fabric; in particular of damp masonry and large section timbers such as lintels and truss ends. Specialist technology should be used, as necessary, to investigate the affected structures, and the findings should be recorded

2.1.5 Identification of latent defects

The findings in sections 2.1.1 to 2.1.4 above should be assessed in conjunction with the refurbishment proposals for end use and the proposed level and frequency of maintenance. The design team should then be advised of possible latent building defects that could increase the risk of damp and decay problems developing in new or refurbished structures during or after refurbishment

2.2 SPECIFICATION OF REMEDIAL WORKS

2.2.1 Structurally decayed timbers

Recommendations should be given for the replacement of structurally decayed timbers identified at 2.1.2 above. Recommendations should be given to the structural engineer to allow the design of appropriate repairs to partially decayed timbers where cost effective, or where these must be retained for historic reasons

2.2.2 Timbers or other materials vulnerable to decay during or after refurbishment

Recommendations should be given for the replacement of timbers or other materials vulnerable to further decay identified as in 2.1.3, 2.1.4 and 2.1.5 above. Generally, timbers vulnerable to decay should be replaced with non-timber elements or with new timbers, isolated from damp or potentially damp masonry with a suitable damp-proof material or air gap. Consideration should be given to the use of chemical remedial treatments, where cost effective, for the short term protection they may provide. This can only be determined after a full assessment as set out in 2.1. Chemical remedial treatments should not be relied upon to provide long term protection to vulnerable timbers. Wherever possible, the aim should be to detail the structure so that it is protected from decay even if water penetration occurs during or after refurbishment

2.2.3 Building details

Recommendations should be given for the refurbishment and re-detailing of the building so as to minimise the risk of water penetration or the accumulation of moisture in the structure after refurbishment. The correct detailing of roof and ground drainage systems is important. Ventilation of structural voids and the avoidance of the inappropriate use of impermeable materials will reduce the risk of interstitial condensation. The aim of the recommendations should be to make the structure 'fail safe', wherever possible, in conjunction with 2.2.2 above, and maintainable given the intended occupancy

2.2.4 Structural drying

Recommendations should be given to allow the long term drying of damp structures during and after refurbishment. This will prevent these acting as 'moisture reservoirs' which could cause damp and decay in the future. This should be done by the informed use of detailing as in 2.2.3 above

2.2.5 Rising and penetrating damp

Recommendations should be given for the control of any rising and penetrating damp identified in 2.1.1, 2.1.4 and 2.1.5 above. This should be by the use of fail safe robust techniques aimed at preventing the cause and by controlling rather than concealing the symptoms of damp. In particular, recommendations should be given for the repair of defective damp-proof courses or ground and surface drainage systems

2.3 Inspection of Remedial Works

2.3.1 Approval of proposed methodology

Samples of methods to be used in carrying out remedial works recommended by H+R are to be approved by the H+R consultants and agreed with the supervising officer on site. In particular, timber and masonry repairs

2.3.2 Inspection during works

Remedial works specified, as recommended in 2.2 above, should be inspected by the H+R consultants, the clerk of works or other appropriate building professionals as instructed by H+R. The inspections should be carried out prior to closing up of areas or the application of finishes so that all reasonable steps can be taken to ensure works are carried out as specified

2.3.3 Inspection on completion

On completion, remedial works specified, as recommended in 2.2 above, should be inspected by the H+R consultants who will take all reasonable steps to satisfy themselves that works have been carried out, as specified in 2.2 above, and that works will be effective in preventing the damp and decay problems identified in 2.1 above. Any failures to carry out works as specified in 2.2 above, should be recorded so that appropriate risk management measures can be taken, for example, insurance and maintenance provisions

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