2 Diagnosis stage
The diagnosis stage is the investigative part of the remediation process, and Figure 7 shows how the early collection of general information contributes towards this stage
Further detail
Section 1: General information collection stage
This section outlines the diagnosis process for consultants. Remediation experience is essential for this diagnosis stage to ensure the adequacy of testing and assessment of evidence. Consultants may wish to engage the assistance of experienced remediation specialists to assist with this diagnosis. This will help ensure the reliance of conclusions on which subsequent remediation work for the project is based.
The following general aspects should be noted.
- Expertise
Remediation specialists should be experienced and show evidence of past involvement in successful remediation projects and possibly in training courses. (The New Zealand Institute of Building Surveyors offers specialist remediation training for members.) Other qualified specialist expertise is needed for timber and mould analysis, corrosion, structural issues, and other associated areas such as acoustics and fire protection.
- Destructive testing
The consultant should clearly establish with the owner the extent of inspection (refer to 'Types of surveys'), including any destructive testing, cladding removal and sampling required.
- Inspection equipment
Particular equipment is needed for activities such as gaining access to all areas of a building (including subfloor and roof spaces), photographic recording, moisture testing and opening up parts of the cladding. Ongoing testing and observation may also be needed for difficult-to-diagnose moisture problems.
- Health and safety
Building investigations can sometimes reveal decay of a severity that is threatening to the structure of critical building elements. This requires immediate engineering advice and action, such as temporary repairs, structural propping, closing off certain parts of the building and consulting with the BCA.
The removal of claddings or linings may reveal moulds that can pose health hazards to the repairers and occupants. Specialist advice is needed on mould identification, likely hazards and treatment.
Types of surveys
For practical purposes, the guide assumes two levels of surveys within the diagnosis stage, a general survey or a detailed survey. This is an artificial separation, because diagnosis work is a continuum in termsof the depth and detail involved in the investigation.
However, the concept of two levels is useful when considering the purposes of the initial investigationand the work that is likely to flow from the initial recommendations.
Further detail
Appendix 2: Timber rot and moulds
2.1 The diagnosis process
The diagnosis process follows an investigative methodology as shown in Figure 8.
It is a logical and ongoing process, designed to cause the minimum amount of damage to the building while at the same time providing a reasonable overall understanding of the likely causes of leaks and extent of damage.
Initial assumptions can change as further information is gathered and assessed. An open mind is needed in order to avoid drawing premature conclusions.
The scope of the investigation
A significant issue is the extent of appropriate investigation and reporting levels, dependent on the purpose and scope of the survey.
While this section concentrates on detailed diagnosis, less detailed surveys with limited scopes are sometimes called for and can be useful at the initial stages for deciding which parts of the building to survey in more detail and how invasive that survey needs to be (refer to 'A limited scope survey').
A limited scope survey
In a less detailed general survey, limited invasive moisture testing may be the extent of the inspection process necessary to fulfil the particular purposes of the evaluation.
(However, several sample cut-outs may be carried outto determine underlying construction details at critical junctions such as window jamb to sill junctions and inter-storey junctions.)
2.2 Steps in the diagnosis process
The diagnosis process in Figure 8 is described as follows.
2.2.1 Step 1: Visual investigation
From the owner's descriptions (and the consultant's analysis of risk factors), a visual examination of the building and its condition is undertaken. This inspection provides important clues on moisture problems, and can indicate the areas that require particular attention (refer to 'Signs of moisture presence').
However, the fact that there are no initial obvious signs of moisture should not deter an investigation, as leaks can be extremely advanced before symptoms appear.
Moisture levels in walls can build up over a long period, with occupants being unaware of any problem. There can also be multiple causes of water entry, and water can travel a long way from a point of entry before it is apparent.
Areas where moisture is evident and/or damage has already occurred are usually examined first. An experienced consultant, or their specialist adviser, also aims at this point to identify the probable leak source(s).
The overall standard of workmanship and current maintenance can also indicate potential moisture-related problems.
Other moisture sources
It is important that the survey includes an assessment of subfloor areas as these may be inadequately ventilated and damp.
Internal causes of moisture generation should also be noted (refer to 'Internal moisture').
Signs of moisture presence
(from external or internal moisture)
- Stained/rotting carpet, rusty fixings
- Mould and mildew growth
- Swelling of skirtings or other trim
- Sagging ceiling linings
- Sagging or uneven floor surfaces
- Lifting of vinyl floors
- Corrosion of fixings
- Water dripping from soffit
- Dark stains, paint bubbles
- Paint and substrate deterioration
- Musty smells, nail popping
- Cracks - type and location
- Efflorescence
Internal moisture
Signs of moisture inside a house may initially appear to indicate leaks, but instead result from other problems such as leaking plumbing or condensation resulting factors such as the:
- lack of adequate thermal insulation, and/or
- lack of adequate ventilation, combined with
- occupants' habits (eg, cooking, showering times, a house shut up during the day).
2.2.2 Step 2: Non-invasive testing
Visual observations are accompanied or followed by non-invasive moisture tests, using a moisture meter in capacitance mode. It is important to understand the limitations of capacitance mode testing (refer to 'Moisture meters').
The results of non-invasive testing should be compared with a known dry area that has been established as a 'control', with test results backed up by invasive testing and sample cut-outs at critical locations.
Apparently 'dry' buildings
Visual inspections and non-invasive testing often provide no initial evidence of leaking, while further investigation can reveal signs of severe moisture penetration. If circumstances prevent the use of invasive testing (eg, for a pre-purchase inspection), then the limitations and risks involved must be explained clearly to potential users of the information.
Selecting test locations
Evidence from visual inspections (including high-risk areas) is used to select moisture test locations.
Non-invasive testing is usually (and preferably) undertaken externally, because water accumulates or travels immediately behind the external cladding.
However, there may be instances when lack of access precludes external investigations,or where the external cladding material is not suitable for surface testing, in which case less reliable internal investigations are necessary(refer to 'Apparently 'dry' buildings').
Moisture meters
Moisture meters use changes in electrical properties in timber to provide an estimate of the moisture content.
The two common types of meters in use are the resistance meter and the capacitance meter (which can be purchased as a single meter with two modes).
Note - the results from both types must be compared with known dry locations as readings may be affected by hidden materials (metals and chemical preservatives).
Capacitance meters (non-invasive testing)
These are used on a surface, and measure an electrical property called the 'dielectric constant' and produce an electric field that can penetrate into the timber. Although the field can penetrate deep into the timber, the meter readings are biased to the surface moisture contents (so internal readings are frequently misleading).
Resistance meters (invasive testing)
These measure the flow of electricity between two pins inserted into the framing, where the timber acts as an electrical resistor between the pins. Different timber species and treatments have varying electrical resistance, so values shown on the meter will need to be adjusted to suit the species and the type of timber treatment.
2.2.3 Step 3: Invasive testing
Visual observations and non-invasive moisture tests are followed by invasive moisture tests with the meter in resistance mode (refer to 'Moisture Meters' above).
Selecting test locations
The evidence collected in previous steps is now used to select high-risk and other locations in the building for invasive moisture testing.
Further detail
Figure 3: Common areas of weathertightness risk
Control point
Establish equilibrium moisture levels by identifying areas likely to be dry (such as beneath eaves) to allow comparisons with other readings.
Material from drillings
Clues on timber condition can sometimes be gained from evaluating the timber extracted by drilling:
- dampness of timber and cladding
- softness and colour/consistency of drillings.
Dry but decayed
There can sometimes be areas of substantial decay without elevated moisture readings or obvious signs of decay. Examination and testing of drillings and/or cut-outs is needed to reveal the decay in this type of situation.
Further detail
Appendix 2: Timber rot and moulds
When the general level of elevated moisture levels is established, further invasive testing is needed to provide the likely sources of water entry, associated leak lines, areas of damage and points where water escapes to the outside. The aim here is to provide an overall picture of the moisture behaviour within walls.
Invasive moisture readings are easiest to follow if they are presented on a photograph or elevation as shown in Figure 9. This is referred to as 'moisture mapping'.
2.2.4 Step 4: Cut-outs and sampling
This involves cutting out sections of cladding at selected locations to confirm leak paths, causes and decay. It also allows samples of materials to be extracted and analysed for identification of timber treatment, decay and moulds (refer to 'Timber samples'). Although cut-outs can help to establish likely leak paths, the full extent of leaks will only be confirmed as areas of cladding are removed during repair work.
Where weathertightness defects are suspected, cut-outs may also be used to expose underlying components (for instance, a hidden inter-storey junction).
Repairing cut-outs
Consider how cut-outs will be temporarily or permanently weatherproofed once testing is complete (including using the assistance of a builder if necessary). If problems are revealed, permanent repair may wait for the later remedial work.
Timber samples
Samples for laboratory testing should be taken from exposed timber. Samples should be chosen according to the:
- dampness of timber and cladding
- softness and colour/consistency
- suspected decay during construction
- suspected past/present leaks.
Special drilling tools (incremental borers) are available to take timber samples.
2.2.5 Step 5: Identify leak sources
At this stage, evidence collected in the previous steps is used to help identify the reasons for moisture entry, the possible extent of timber damage, the likely leak paths, the initial sources and any other contributing defects (refer to 'Contributing defects').
Further checking and sample testing may be needed at this point in order to reach reliable conclusions, and the consultant should be prepared to revisit and test earlier assumptions.
Contributing defects
Leaks can be complex. While a leak may be tracked to its source, other weathertightness defects commonly contribute to the extent of moisture penetration (and consequent damage). All possible sources must therefore be checked. Examples are a:
- leaking parapet cap at the top of a wall, which has a horizontal junction further down that does not allow water to drain
- leaking window jamb above a non-draining sill.
Figure 10 shows how likely leak paths may be presented. This type of presentation may be repeated for all applicable elevations.
2.3 Diagnosis conclusions
2.3.1 Damage assessment
Figure 11 shows how the assessed likely extent of timber decay and damage may be illustrated.
Although this section focuses on identifying moisture entry and damage, investigations are likely to identify weathertightness defects that have not yet caused leaks or damage.
Assessment should therefore include predicting likely further damage if repair work is not undertaken (refer to 'Future risks').
Structural concerns
If there is any concern regarding the effects of timber decay on critical structural components, engineering advice must be sought and temporary measures taken to ensure safety.
Future risks
In certain situations, decisions will be needed as to whether defects that are not yet leaking are likely to allow future moisture entry if they are not upgraded. (The extent of timber treatment is critical for assessing possible consequences).
Further detail
Section 3.5: Repair priorities
Diagnosing mould and decay
The decay specialist
Ensure the testing is carried out by a recognised specialist in the field, as mould and timber analyses can involve different expertise.
In particular, timber analysis requires more specialised knowledge than plant pathology or mycology.
Identification of the degree of timber decay andthe type of moulds that may be present on framing, wraps and linings is a specialist task that requires laboratory testing.
Samples of moulds and suspected timber decay should be taken for laboratory analysis.
Further detail
Appendix 2: Timber rot and moulds
2.3.2 Identifying and repairing causes of leaks
The diagnosis now needs to provide a prognosis for the building envelope and to outline recommendations for repair. In order to forecast weathertightness and durability performance, the extent of damage and deterioration must be quantified, based on the level of any timber treatment and the assessment of damage discussed in 2.3.1 above (refer to 'Initial options for repairs').
The work required to repair damage and to make the building weathertight and durable must address both the symptoms of damage and the mechanisms of deterioration.
Further detail
Section 3.2: Current state of active defects
Initial options for repairs
Alternative remediation strategies are considered in detail during the design stage. However, initial options still need to be explored in order to provide an earlier outline scope of work for the remediation project. In broad terms, these options fall into three categories.
- Complete re-cladding of the building
- Targeted repairs
- Combination of re-cladding and targeted repairs
2.3.3 Costs
At the completion of the diagnosis work, the potential extent and likely severity of problems are known and broad approaches to repair have been identified. Although limited information is available, initial estimates must be prepared to allow project budgets to be established so that decisions can be made about the next steps in the remediation process (refer to 'Initial repair estimates').
However, it must be noted that the estimates will be based on experience with similar, completed repair work (therefore limiting the accuracy). The design work is yet to be done, and the full extent of the damage is yet to be revealed.
Further detail
Section 3.9.2: Estimates and budgets
Initial repair estimates
Allow for:
- all project costs including design, administration and consent fees etc (not just repair costs)
- upgrading where necessary to comply with the Building Code
- costs related to timing and disruption issues (including alternative accommodation if needed)
- remedial work to prevent potential damage.
2.4 Reporting
The level of reporting that is required depends on the objectives of the survey, and should be tailored according to the circumstances. A detailed survey will usually result in a detailed report, while general surveys are limited in scope and will lead to less detailed reports.
Further detail
Figure 7: The diagnosis stage
Recommendations
Whether general or detailed, the survey report needs to cover the specific brief, information collected, investigations undertaken, and results of those investigations. For a general survey, the recommendations would usually be at a broad advisory level, and could include the requirement for a detailed survey of the building.
The report that results from a detailed survey will not only include further detail, but also often be extended to cover a recommended scope of repairs and, most usefully, a preliminary estimate of cost for the remedial work.
Back to top