3 Design stage
Figure 12 summarises the overall design process that is considered and explored in this section.
Remediation work uses the results of the diagnosis process described in Section 2 to develop a detailed remediation proposal ready for tendering (refer to 'Starting point of design').
In simple situations, little further development will be needed, but in many cases the initial scope of work forms the beginning of a complex process of exploring options and priorities of repair work (to be discussed with the owner). Detailed design proposals can then be prepared for contracting and construction of the remedial work.
Starting point of design
At the start of design development, the consultant should have the following.
- Descriptions of known current defects
- Estimated extent of moisture penetration and deterioration
- Recommendations that provide a general outline of repair work
- Rough orders of cost for the scope of work
Interpreting diagnosis results
The consultant needs to interpret the diagnosis results to appreciate the significance of the underlying defects and risks. Further recommendations should be considered, as what might appear to be the most obvious methods of repair may not be the most appropriate (given the complexities commonly involved in moisture problems).
How does a defect allow water in?
It is important to understand this. The way a defect triggers leaks can be unexpected, depending on particular circumstances such as siting, orientation, construction, maintenance etc. Also, combinations of defects can work together, so fixing one defect may mean that others resurface later.
As well as quantifying the extent and severity of deterioration, any defects that have caused (or contributed toward) moisture damage should be identified in order to allow future risks to be evaluated (refer to 'How does a defect allow water in?').
'Active' and 'inactive' defects
Weathertightness defects have been separated in this section into two types, 'active' and 'inactive'. Active defects refer to those that are leaking at the time the assessment is undertaken (referred to as 'currently' leaking). In contrast, inactive defects are those not currently associated with elevated moisture levels or damage in the adjacent timber framing, although (depending on the circumstances) they may have leaked in the past or have potential to leak. Both types of defects are important when considering repair priorities
Section 3.5: Repair priorities
3.2 Current state of active defects
The most important defects are those that are currently leaking and these need to be considered carefully, in terms of their locations and type.
Active defects should be grouped into broad types so the nature and common characteristics of each type can be further considered (refer to 'Grouping defects').
An example of grouping could be:
- within the cladding itself
- windows and doors
- roof junctions
- apron flashings
- decks and balustrades
Figure 3: Common areas of weathertightness risk
Table 5: Common weathertightness defects
The specific locations of identified 'active' defects in the building should be studied, and their particular characteristics identified (eg, exposure, risk features etc).
Consider early options
Consultants should develop preliminary solutions for known 'active' defects, and options for achieving the same objective should be explored. Consideration should be given to various repairs in terms of costs, required maintenance and expected durability (refer to 'Initial sketch details').
Initial sketch details
Initial sketch details will be rough and exploratory as the first translation of descriptions into 3D forms.
However, they should still allow the assumptions used in the earlier preliminary estimates to be checked. Problems are also more likely to be identified when sketch details are explored.
3.3 Nature of active defects
The initial consideration of defects described above helps in understanding the defect mechanisms applying to a particular building, and helps to clarify remedial recommendations and options (refer to 'The nature of defects').
The nature of defects
To help consider options for repair, it is useful to classify defects into categories as follows.
- Systemic problems
- Limited problems
- Isolated problems
The decision of whether defects are isolated, limited or systemic is critical for establishing the appropriate repairs, and raises issues of future moisture problems, including potential moisture problems for wall areas that are currently dry.
Figure 13 shows how (depending on the particular circumstances) defects might be categorised.
3.3.1 Systemic defects
If defects are systemic throughout the building, the resulting remedial work is likely to be extensive. If the problem has led to moisture penetration, mould and decay may be established. In these instances, complete re-cladding of the building is likely to be necessary, along with extensive replacement of decayed timber framing and the installation of increased levels of weathertightness protection (such as cavities) to provide a future dry environment within walls.
However, some defects can take time for the building element to deteriorate sufficiently to cause extensive problems. Less drastic remedies could be appropriate in these circumstances.
In all cases, the level of existing timber treatment will be a critical factor in determining the likely consequences of leaking.
Table 1: Risk of leaks and consequences of failure
Nature of defects
Decide whether defects are systemic, limited or isolated, by considering whether there are:
- general cladding problems such as lack of control joints, sub-standard plaster etc.
- general component or location problems (eg, window flashings, base details, clearances, roof wall junctions repeated generally around the building)
- other areas with similar defective details
- similar locations/exposures
- isolated problems with limited application
- further investigations needed to confirm how widespread defects are.
At this point, further investigation could be necessary to reliably establish the extent of present timber damage. This may require additional survey work and laboratory testing.
Appendix 2: Timber rot and moulds
Need for re-cladding
Once current moisture penetration and deterioration is known, the next question is whether all walls need re-cladding or just limited areas. An important influence will be the level of timber treatment and other component problems noted during inspections.
It is likely that a systemic problem, together with a component problem (for instance, lack of control joints leading to cracking, combined with poorly flashed windows), will lead to re-cladding being the most cost-effective current or future solution.
Currently dry walls
If some walls are dry and undamaged, the consultant should investigate why this is in order to assess the risks of future moisture penetration. It may be that local protection (for instance, by roof overhangs) has delayed the onset of leaks and a defect may be remedied in time without the existing cladding having to be removed. In other cases, limited repairs may not be possible (refer to 'Dry but systemic defects').
'Dry' but systemic defects
Some types of systemic defects cannot be remedied without recladding.
A building may be currently dry on all walls, and yet require recladding in order to comply with the durability provisions of the Code.
Two examples of this are sub-standard solid plaster and inadequate backing sheets (eg, layout, material, thickness) behind flush finishes.
These types of defects may not yet be causing leaks, but are considered likely to deteriorate and leak in the future (based on experience of similar situations).
Other options for currently dry walls
At this stage, consultants should explore the options available for protecting dry walls despite the identified inactive defect(s). If moisture can be deflected away from the wall, the dry condition may then be extended.
Table 2: Reducing the risks
3.3.2 Limited defects
This category applies to those defects that are limited to discrete components or locations around the building. The problems identified during the diagnosis phase need to be put into the context of the specific building (refer to 'Limited defects').
These are associated with particular components (such as repeated defective window installations).
Common problems include areas such as cladding clearances, the bottom of apron flashings, roof to wall junctions, and some types of cladding base details.
Consider the following.
- Are there other general problems?
- Are other cladding details generally okay?
- Are there other similar defects/locations? If so, have they remained dry?
- Does further moisture testing need to be done on apparently dry walls?
- If dry, why have they remained dry? Will they remain dry in future and for how long?
3.3.3 Isolated defects
This category applies to isolated features of a building, such as decks, pergolas, special windows, chimney structures and the like. It may also apply to certain locations that do not apply elsewhere around the building (such as a limited section of wall).
Depending on their position within the building envelope, isolated defects are generally more amenable to targeted repairs (refer to 'Position of isolated problems').
Position of isolated problems
The extent of damage associated with isolated problems depends on where that particular feature is located within the building.
For example, a leaking deck-to-wall junction will have substantially greater impact on the surrounding wall for an upper floor deck (particularly if above living areas) than for a ground floor deck with a concrete foundation wall below it.
Similarly, defective wall-to-roof junctions of a dormer window will have greater consequences than defects in a curved-top ground floor window.
As is done with the other categories, a consultant will need to confirm that the particular defect is not repeated in locations elsewhere in the building. If it is, moisture levels and possible damage in those areas will need to be checked.
3.4 Potential for future damage
The likelihood of future deterioration is as important as current deterioration. Even if walls are currently dry, possible future problems must still be assessed to determine whether there is a reasonable expectation that the cladding (in its present form) will continue to keep the building dry (refer to 'Judgement').
It is important that consultants establish the potential for future moisture problems, because this will shape the timing, nature and eventual costs of the remediation measures that are required.
It is critical that consultants use their own knowledge and experience to infer known weathertightness problems, for example, from both:
1. the particular building
(a) construction details
(b) site conditions
2. other buildings
(a) similar details, claddings, risk features and so on
(b) similar site conditions.
Section 1: General information collection stage
Past and future maintenance
The level and quality of past maintenance may have impacted on the current condition of the building, but maintenance can be increased to possibly improve its weathertightness and assist in its future performance.
Hidden leaks and decay
Be aware that not all leaks or decay may have been identified in a survey and walls that appear to be 'dry' often have hidden moisture or decay problems.
The following scenarios use two buildings, one that seems to be leaking on some walls only, and one that is apparently dry.
3.4.1 Building leaking on some walls
It is important to understand why the same type of defects that are causing moisture problems on some walls, have not yet leaked onto other walls (refer to 'Why are some walls not leaking').
This understanding will help establish whether:
- mechanisms that are acting to deteriorate parts of the building will begin to do so on undamaged parts in the future (ie, inactive defects will become active)
- other mechanisms are in place that could cause problems or prevent problems
- the rate at which damage has occurred on leaking walls is likely to escalate.
Why are some walls not leaking?
Consider mitigating influences together with factors applying to dry areas such as:
- prevailing weather - rain, wind, sun
- site protection - site shelter from trees, slope, and other site features
- building protection (eg, eaves, canopies)
- variable workmanship
- ease of maintenance and inspection
- current maintenance - has this prevented problems to date?
- length of time walls have stayed dry
- risks of undetected leaks in future
- possible future movement in framing, and likely effects.
3.4.2 Apparently dry building
Building owners are becoming increasingly aware of the type of buildings and claddings that have in the past experienced moisture penetration and may be concerned about the condition of their building, regardless of any known moisture problems.
A general survey allows a consultant to prepare recommendations (including priorities, or the need for further investigation) to allow an owner to decide on (if any) repair work, maintenance, ongoing monitoring or further investigation should be undertaken (refer to 'Aims of general surveys').
If the results of a limited survey provide reasonable assurance that a building is currently dry and undamaged, the process followed from then on will be similar to that used for maintaining dry walls on a building that has some leaking walls. However, if the survey indicates a likelihood of significant moisture penetration and damage, a more detailed survey will be needed.
Aims of general surveys
The key aims of general surveys are to:
- verify current moisture levels using appropriate invasive moisture testing of locations in areas considered high risk
- identify high-risk areas and consider the detailing used in these locations, cutting out small sections of cladding at sample positions (such as a typical jamb-to-sill junction, inter-storey junctions etc) to establish likelihood of back flashings at high-risk junctions
- identify weathertightness defects that are likely to lead to future moisture problems, including mitigating influences such as shelter and drainage.
The discovery of moisture penetration should lead to a subsequent 'detailed' diagnosis.
Limitations of general surveys
General surveys may be used for apparently dry buildings, or in cases where the weathertightness compliance of a building is in doubt (such as for buildings referred to the Department for a determination).
An inspection process should be used in general surveys that provides sufficient evidence (when considered with information collected) to allow assessment of the ongoing weathertightness of the cladding systems. These inspections are less detailed than those usually undertaken on obviously leaking buildings, but still involve invasive moisture testing, sample cut-outs to inspect underlying construction and the identification of defects that could lead to future weathertightness problems.
Section 2.1: The diagnosis process
3.5 Repair priorities
The preceding sections explore ways of collecting, analysing and categorising information on a building, in order to understand both the current condition and the nature of possible future risks. The following section discusses how repair priorities are established.
3.5.1 Importance of remediation
While it may be ideal to remedy every identified defect in a building, a practical approach is needed to suit the particular circumstances (for instance, staging the repairs according to their priority). This involves considering the location and severity of the leaks and/or defects, with the likely consequences, keeping in mind that completed repair work must meet weathertightness and durability provisions of the Building Code.
One useful approach to establishing remediation priorities is to balance the level of risk of moisture penetration against the severity of the likely consequences (including health risks), should a leak occur. Table 1 illustrates one system that could be used to achieve this.
Risk analysis caution
Care must be taken when analysing risks. There must be a rational, recorded basis for establishing varying risk levels that can be explained as 'reasonable' in the circumstances of the particular building.
The categories within Table 1 are shown to illustrate the use of risk profiles to suit specific situations. Decisions on the priority of the repair work required will vary according to the particular building structure (for example, the level of timber treatment) and the cost-effectiveness of the repairs.
Table 1: Risk of leaks and consequences of failure
||Likely consequences (1)
||Severe and widespread
||Moderate or isolated severe
||Minor and isolated
|Leaking and degraded
|Some current leaking
|Highly likely to leak
|Leaks possible in future
Risk/consequence levels applied to a particular project might be classified as:
A Critical remedial work C Necessary remedial work E Low priority
B Urgent remedial work D Advisable remedial work
3.5.2 Repair priority
Critical work (Type A in Table 1)
Critical areas require immediate action to prevent further deterioration and to ensure safety. Temporary repairs, structural work or measures to protect the health of the occupants may be needed before the main remedial work can be carried out (refer to 'Moulds').
If timber decay could endanger critical structural elements, a structural engineer should review the condition and design any temporary propping required. Access to parts of the building may need to be restricted (for example, to decayed decks or support beams).
Further repairs can also be carried out to weather-proof moisture-affected areas temporarily until permanent repairs are completed.
Evidence of moulds requires immediate attention, and specialist laboratory tests are needed to confirm the type and extent, together with advice on actions required to protect the health of occupants and workers.
Appendix 2: Timber rot and moulds
Urgent/necessary work (Types B, C in Table 1)
For all necessary remedial works, outlined design proposals should be developed to a level suitable for owner consultation, and any estimated costs should be updated. These categories include permanent remedial proposals for Type A areas (to replace temporary repairs).
Advisable work (Type D in Table 1)
This category requires the most consideration and judgement. The advantages of risk reduction need to be balanced against likely consequences, subject to the repaired building meeting the requirements of the Building Code (refer to 'Advisable remedial work').
Advisable remedial work
Factors to be considered include the following.
- Existence and level of timber treatment
- Presence of active fungal growth
- Difficulty/costs (access, design style etc)
- Increase in vulnerability from cutting into an existing dry structure
- Whether work can be planned for later implementation without significant effect
- Whether any leaks would be obvious, or could remain undetected in future
- Whether the risks could be reduced with improved maintenance (within 'normal' reasonable expectations)
Low priority (Type E in Table 1)
This category is where details have been identified that do not meet current expectations, but where the risk (and likely consequences) of moisture entry is judged to be low.
In certain low and medium exposure conditions, specific combinations of exposure, wall construction, detailing and timber treatment may result in little or minimal damage, even if the wall construction is not ideal. In the unlikely event of a leak occurring, the consequences have been assessed as not likely to be severe or widespread, and comprehensive remediation may not be warranted.
The consultant must still ensure that recommended remedial work will result in an adequately weathertight, durable and Code-compliant building.
The possible risks associated with some low priority defects (and the likely consequences) need to be explained to an owner, who should also be made aware of preventative ongoing maintenance they should undertake (for instance, regular washing, maintaining sealants and coatings, cleaning gutters etc) and periodic monitoring of these areas.
Having established the varying levels of importance of remedial work required for the building, the consultant should then prepare a priority list of repairs and proposals, together with a preliminary estimate of costs for those repairs and proposals.
3.5.3 Staging of remediation work
At this point in the design development, the scheduling of work can be considered including the possibility of staging repairs over time (refer to 'Staging repairs').
It may be possible to stagger work, starting with the most damaged or risky areas. This allows repair costs to be spread, but extends disruption and will be costlier in the long run.
It may be possible to extend remedial work over longer periods for example, where repairs on low exposure walls are deferred for 5 to 10 years, if their condition is monitored.
Discuss any proposed repair programme with the BCA to clarify implications on the building consent.
The Act requires a code compliance certificate to be issued within 2 years of the consent. Unless the BCA grants an extension, separate consents will be needed if the remedial work takes too long, which will add to the overall costs.
Consider the following phasing of different types of the work.
- Immediate work to prevent further damage and ensure safety
- Short-term work for temporarily repaired areas, those likely to leak in the near future or with severe consequences if leaks were to occur
- Medium-term work to remedy defects with little immediate risk
- Longer-term work for areas with lower level risks and consequences, but where work is needed for longer term durability
Factors to consider
Primary factors to be considered include the following.
- Construction costs - the additional start-up costs with separate stages
- Risk of further damage - areas not repaired may continue to deteriorate
- Disruption - occupants will be disrupted for a longer period of time by noise, access, loss of use of areas, dust and other construction irritants
- Financing - different scenarios will require different realistic cash flow plans
- Property values - specialist advice should be sought on the impact of varying remedial scenarios on property values
Any future sale - deferred work may need to be declared as an area with known potential problems.
3.6 Design-related issues
The next part of the guide considers in further detail some of the associated design issues that have been mentioned in preceding sections. These matters will affect decisions and may limit options in many situations.
3.6.1 Reducing risks
The E2/AS1 risk matrix covers key weathertightness risk factors, and the guidance document External Moisture - A guide to using the risk matrix offers useful information and explanations of these factors.
Possible measures to improve weathertightness, such as those suggested in Table 2, that provide and maintain a dry environment, should be explored. These may prove more cost-effective than the installation of new cladding over a drained cavity.
The effect of shelter
The effect of rain on walls can be significant. Providing shelter minimises the effect of water penetration on walls. However, it is important to check timber treatment levels and current timber condition in these areas, because apparently sheltered walls may still be degrading.
Remediation options aiming to preserve currently dry walls can include providing shelter to individual details or to a whole wall. Many building envelopes are not clear-cut in terms of defining the remedial work required.
3.6.2 Visual effects
The change in a building's appearance could be the most obvious result of any remediation work, particularly if it involves alterations to cladding materials or other noticeable elements (such as the removal of enclosed decks, or the addition of eaves, canopies or enclosures in order to reduce the risk of moisture penetration).
If the remedial work aims to minimise changes to the look of the building, care should be taken to select profiles, materials and colours that complement or enhance the original design.
|Table 2: Reducing the risks
|E2/AS1 risk factors
||Possible risk reductions
||Add 'permanent' localised shelter(1)
|Roof/wall intersection design
||Limited protection of wall
|Increase roof overhangs
Change to side-fixed open balustrades (with no upstands)
If rafters exposed, clad soffits
||Extend eaves/verge widths
Add canopies to compensate for lack of eaves
Replace parapets with roof overhangs
Special windows (eg, box, bay, corner,
raked or curved tops)
|Simplify or reduce inter-cladding junctions
Remove or roof over
Alter to freestanding type
Replace with standard joinery
||Decks over living areas
Decks open underneath
Enclose the deck
Expose underside to allow drying of joists(1)
Improve access for monitoring
Separately support deck
|(1) Take care - some measures are effective only if they are retained as permanent features.
However, if the work is likely to result in major changes in appearance, professional design assistance is warranted as architects and experienced designers should be skilled in understanding and managing the consequences of potential visual impacts. The visual impact of remedial measures must be considered carefully as it has the potential to positively or negatively influence the value of the building.
Revising the image
Most repairs will require building consents which will then form part of the public records of a particular building.
It may be worth exploring the advantages of purposely revising a building's image, rather than returning it to the same external appearance as prior to the remediation work.
Figure 14 shows how the appearance of a building might be changed. The combination of changes in cladding, with a decrease in risk features, can substantially alter a building's appearance in a positive manner if repairs are skilfully executed. The resulting impact on the property's value could outweigh the initial costs of undertaking the work.
If design changes are made, itemisation of the applicable costs may be needed by the owner for future claims and/or arguments.
(Check with the legal advisor if applicable.)
Section 3.7: Other issues
3.6.3 Town planning considerations
It is common for buildings requiring extensive remedial work to have used the maximum building envelopes allowable in local town planning bylaws at the time of construction.
If building volumes of the original design were maximised, then the addition of protective weathertightness measures to a building can conflict with building envelope restrictions, as shown in Figure 15.
Envelope restrictions, repair options and possible cladding changes must be discussed with the local council early in the design process. Some councils may allow eaves and canopies to project into public space (eg, road reserves), but permission from neighbours is likely to be required for changes to other boundary areas.
3.7 Other issues
The following provides further detail on some of the issues mentioned in previous sections (such as cost-effectiveness, ongoing maintenance and strategies) that can affect repair decisions and may often limit remediation options.
Cost-effectiveness is key to certain remediation decisions, and judgement on what is important depends on the viewpoint of those involved and the timescale involved. A measure may not be cost-effective over the short term, but could be when considered on a longer-term basis.
Cost-effectiveness can be viewed differently by various stakeholders according to their financial and long-term interest in the building (refer to 'Cost-effectiveness viewpoints').
Alternatives may need to be developed (with costs and associated risks outlined for each) to allow owners to make informed choices.
Consultants must base advice to owners on the results of investigations, and not be party to any inadequate repair work (based on immediate short-term wishes).
While all remedial work must comply with the Building Code, a consultant should be aware of (and able to counter if necessary) other viewpoints.
Examples of different viewpoints include:
- an owner planning to sell
- an owner planning to remain long term
- a body corporate balancing wishes of the unit owners against responsibility to ensure ongoing weathertightness
- lending institutions financing remedial work or with mortgages over the building
- parties involved in the original design and construction of the building
- future buyers of the property
- consultants concerned about exposure in regard to possible future failure.
3.7.2 Ongoing maintenance
Ongoing maintenance for the building needs to be considered during remediation design. Normal maintenance of the building envelope increases the likelihood that elements will continue to perform over their intended service lives (and, at a minimum, fulfil the durability requirements of the Building Code). Inadequate maintenance increases the risk of degradation of the building envelope.
If any existing direct-fixed cladding is left in place, then maintenance is especially important for ensuring that these walls remain weathertight. When a wall relies on sealant joints, these must be inspected regularly and repaired as necessary.
Access for appropriate monitoring and maintenance is critical, and the design should provide for this. The levels of maintenance required by different components and wall claddings will vary, with some types being more 'forgiving' than others. Consultants should therefore consider the need for a maintenance plan for the building (refer to 'A maintenance plan').
Section 5.2.2 Maintenance and monitoring
A maintenance plan
Ideally, customised plans should be prepared that are tailored to suit the expertise of the person who will be undertaking the inspection and maintenance.
- a homeowner may need very specific guidance on the areas to inspect, what to look out for and the resulting maintenance actions
- a property manager on a multi-unit complex (or an untrained resident) may need guidance in the form of maintenance schedules
- an experienced professional should need little guidance.
The preparation of a maintenance schedule can ensure that current and future owners know what ongoing maintenance is necessary for preventing future weathertightness problems.
3.8 Alternative strategies
Remediation design starts with defining requirements, and previous sections have discussed various analyses and factors that should be considered as part of the process.
This can lead the consultant to consider using alternative approaches for remediation involving different levels of initial construction cost, maintenance costs and weathertightness risks (refer to 'The design stage').
The design stage
In remediation projects, basic design parameters of orientation, form and layout are pre-existing. The design stage is essentially one of design development.
Some owners may find it hard to see the value in this stage of the process, instead wishing to focus on proceeding directly to stopping the building from leaking.
3.8.1 Sketch options
If any options change the appearance of the building significantly, these should be illustrated so an owner is aware of what the visual impact will be from different choices.
Sketch options need to be developed to a level suitable for owner consultation. Relative costs should also be prepared so owners can consider the proposed remediation options in an informed way.
3.8.2 Implications of alternate strategies
Table 3 summarises some common remediation strategies that are used, including their impact on performance and their limitations. A remediation project can involve combinations of strategies, with the choice of strategy influencing costs and risks for future weathertightness performance.
3.9 Choosing a strategy
A remediation strategy should be chosen in consultation with the owner. When presenting information, the consultant should clearly identify any issues and provide advice on them.
The consultant should explain the varying levels of risk associated with repair alternatives and guide owners so that risks, costs, cash flow, appearance, durability, disruption (including costs of relocation, if necessary) and other factors are balanced. Implications on future maintenance needs, and any deferred remedial work should also be presented to the owner (refer to 'Approval time').
The remediation strategy or plan should reflect the integration of all repair requirements for the building; it should establish priorities and describe alternative approaches - while still ensuring the minimum requirements of the Building Code are met.
Owners may need considerable time to review and consider their position, particularly if the required remediation is extensive and costly.
The time required for a multi-unit complex will vary according to the number of owners involved, and a body corporate is likely to need time to formulate special resolutions and payment schedules.
The availability of finance may need to be investigated before choices can be made. While it is important that the owners do not make commitments without knowing that finance will be available, raising funds is time-consuming and can delay the remediation process.
3.9.1 Project programming
Different remediation strategies involve different timescales, and it is important that these are explained to the owner. Once a strategy is chosen, the consultant should prepare an outline project schedule that shows the main activities in both the pre-construction and construction phases. This is useful for owners, as it provides them with key decision dates and a timeline on what funds will need to be raised (refer to 'Outline programme').
While details will become more certain as the project develops, an outline programme is important in setting out the steps and general timescales involved. Owners should understand that some flexibility is needed as some parts of remediation work cannot be reliably predicted until the cladding is removed.
This shows the time needed for all stages of the project including:
- preparation of drawings and specifications
- obtaining of building consents
- selecting suitable building contractors
- obtaining contract prices
- completing contract formalities
- undertaking construction work.
If the building is to remain occupied during construction work, the programme will need to allow for this. Inconvenience or health and safety issues may require occupants to vacate all or parts of the building at particular times, with the work phased to suit.
Table 3: Implications of alternative measures
3.9.2 Estimates and budgets
The chances of finding unanticipated conditions are higher when the full extent of the damage is not apparent until the building is opened up during construction. Carefully prepared estimates, with appropriate contingency and provisional allowances, can help to cater for this uncertainty (refer to 'Quantifiable/non-quantifiable elements').
Some costs can be well defined and estimated reliably once the remediation design is complete, but those associated with timber decay and damage are difficult to estimate accurately until the framing is exposed. These costs are covered by provisional allowances that are used for reimbursing materials and labour costs.
Section 4.3.4: Contract payments
Time and cost overruns
Because of the nature of remedial work, unforeseen situations (including original, non-compliant work) often occur, and are discovered only when cladding is removed. This can result in delays and extra costs.
Over- or under-estimating
Understating costs can result in owners committing themselves to a remediation project they cannot pay for. Over-estimating, however, can result in owners delaying or not proceeding with necessary repairs.
Tenders will be a combination of lump sums and provisional allowances, depending on the nature of the items and work involved.
Lump sums can be set for quantifiable elements such as:
- project specific requirements, scaffolding etc
- cladding removal
- window removal and reinstallation
- installation of a new cladding system
- replacement of interior floor coverings
- replacement of interior fittings.
Provisional allowances (based on estimated quantities) are likely to be needed for such items as:
- timber replacement
- interior lining repair and replacement
- work required to services
- original substandard work revealed
- other unforeseen conditions.
All costs need to be included within the remediation project budget including associated fees, relocation and storage costs for occupants, security, insurances and so on.
As well as unanticipated conditions, cost and time overruns can result from unrealistic expectations and inadequate budgets. It is essential for the owner that the consultant creates a realistic project budget that accurately reflects probable costs.
Consultants must also advise owners of the level of uncertainty applicable to cost estimates at each stage of the design process, and explain to owners how the estimate plus contingency combine to give a 'worst case' cost estimate for the project. (refer to 'Contingency funds').
Table 4 illustrates how an overall project budget can vary over the course of the remediation process.
An 'owners contingency' fund for unforeseen or unexpected problems should be included in a project budget.
The amount should reflect the high side of the accuracy range at each stage of the remediation process, and, by doing so, will therefore reduce from the earliest diagnosis stage to the tender stage.
For example (depending on the particular project), at the condition assessment stage, the contingency fund may be 50 percent, at preliminary design stage 30 percent, at contract documentation stage 25 percent and during construction it may be 20 percent.
3.10 Developing the sketch design
The selected remediation strategy should now be developed as necessary to allow a preliminary assessment of costs to be prepared. This step may sometimes be omitted if the earlier design work has been developed sufficiently to allow reliable estimates to be prepared (depending on project size and complexity).
While work on simpler, detached house projects can probably proceed directly to the preparation of working drawings, further design work is likely to be needed for complex, multi-unit developments. This can improve the reliability of the project estimate (over those drawings used when alternative strategies were explored and presented to the client).
|Table 4: Project budgets over time
||Progression through the stages of the remediation process
||Completion of diagnosis stage
||Remediation strategy selected
||Completion of contract documents
|Level of information
Outline scope of work
More detailed design
Other issues identified
(or estimate) accepted
|Basis of estimates
||Historic from previous
available for estimating
|Full details available
||Based on accepted bid
||Owner's contingency could be plus or minus
could be plus or minus
could be plus or minus
|Accuracy should improve
(say 20 percent
Shows overall magnitude
Allows decisions on next steps to take
|Allows finance to be sought
Allows finance to be secured
Can plan cash flow
|Monitor during construction
to avoid surprises
Building consent authority requirements
If these have not been done earlier, discussions with the local BCA or council should take place regarding building consent requirements, the level of BCA inspections that will be needed during construction, any quality assurance requirements, Code compliance or other issues relevant to the project (refer to 'Compliance issues').
Issues to consider for a remediation project include plans/requirements for:
- building/resource consents
- planned staging of work
- alternative solutions or E2/AS1 details
- quality assurance requirements
- variations to consent drawings
- minor repair work
- any upgrading needed for other current Code requirements (eg, fire)
- other Code clause issues
- health and safety issues (including the disposal of hazardous wastes).
3.11 Contract documentation
At this stage of the process, the remediation strategy and proposed design will have been agreed upon and the cost estimates updated.
The next step is the preparation of working drawings that, together with specification and pricing information, will form the contract documents (refer to 'Contract documents').
The following section considers the development of working drawings and the 'technical' specifications. Other (non-technical) documentation required for a contract is discussed as part of the construction stage.
Section 4: Contracts and construction stage
The contract documents consist of the legal agreement between the owner and contractor (usually a standard format), together with the following documents.
The building consent documents
- Scope of the works
- Working drawings
- Other BCA requirements
- Pricing information. (provisional allowance, sums etc)
- Any notices to tenderers issued
These outline the site plan, floor plans, elevations and sections, and should:
- indicate the overall scope of the work
- show interfaces between remedial work and existing unchanged areas
- identify locations of components
- reference drawings of details.
These should detail the:
- locations of materials and components
- relationship to adjacent construction
- profiles of existing components
- clear delineation of existing versus new construction and details.
3.11.1 Working drawings
Although the working drawings form part of the submission for a building consent, their primary function is to provide enough information to allow the contractor to perform the repair work in accordance with the contract requirements and the Building Code. The drawings must identify and locate all materials, components and assemblies that require repair and indicate the extent of the necessary work. Further detailed information is provided in the specifications (refer to 'Detail drawings').
While changing design decisions can impact on construction costs, it may be necessary to reassess some earlier decisions if new issues arise during detailing (this may also be necessary during construction, as unexpected conditions are exposed).
Section 4.4.3: Contract changes and uncertainties
The design of details
Remediation work is obviously limited by the existing construction, many repair details may vary from those included in E2/AS1. However, the Acceptable Solution can provide guidance and benchmarking of expected performance.
The weathertightness principles underpinning E2/AS1 provide a good starting point for designing remediation details to suit the particular circumstances (refer to 'Details').
External moisture - An introduction to weathertightness design principles
A BCA will need to be satisfied that the proposed repair details are Code compliant. A designer must justify the weathertightness of proposals when they are developed into construction drawings and included in the building consent application.
This guide is primarily intended to be a guide to the process involved in remediation projects, and does not provide prescriptive solutions for repair.
Effects on other requirements
If direct-fixed claddings are to be replaced with a cavity-based system, bracing, insulation values, acoustics and fire-ratings are likely to be affected. Any changes must be catered for within the new construction details.
Most repair details need to be designed to suit the specific circumstances of the building, but the principles underlying E2/AS1 should still be followed. There is little point in following a detail that was used in the original construction, when a lack of performance has been demonstrated (always remember that a dry environment must be created).
Good Practice Guides
Current BRANZ Ltd Good Practice Guides should be consulted for detailed information and practical advice on appropriate details (many are alternative solutions). Some guides list defects, causes and repairs, which can be useful for diagnosing and detailing remedial work.
Consultants should ensure that the most up-to-date manufacturer's recommendations are followed during the installation of components or cladding.
The manufacturer should also be consulted for advice on maintaining and prolonging the durability of existing claddings or components.
Upgrading existing work
Sometimes, existing construction has inadequate fire ratings and bracing. This is often not apparent until revealed during remedial work.
If obvious before then, upgrading these elements should be included as part of the contract documentation, with specialist advice obtained as necessary.
3.11.2 Technical specifications
Technical specifications complement working drawings and provide details about the quality of materials and components, compliance with standards, workmanship and any approved suppliers of materials or components. As for other construction work, documentation for remedial projects should be specific to the remediation workrather than relying on general specifications.
Other general (non-technical) aspects of tender documents and contracts are discussed in the following section.
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Section 4: Contracts and construction stage