Leaky Buildings ï¿½ The Perfect Storm
A “perfect storm” is an expression that describes an event where a combination of circumstances will aggravate an otherwise benign situation.
Our perfect storm involved the use of materials prone to rotting, cultural changes which moved away from traditional building methods, poor building practices and lack of oversight and controls. This unfortunate combination has led to the very expensive mess which will be forever known as the era of the leaky building.
Definition of Leaky building
Leaky buildings are defined asï¿½those that both allow water to penetrate the building envelope or cladding system and that then hold the water in the wall cavity, where it may remain for some time. This results in the buildingï¿½s timber framing staying wet.
Timber Framing ï¿½ material of choice
The majority of New Zealand residential houses are built around a timber frame. This is an excellent building material which is ideally suited to local conditions. Itï¿½s a renewable resource and the material is flexible so will withstand substantial movement from high wind loads and earthquakes without breaking. The downside is that timber is susceptible to insect and fungal attack.
Wet rot (Coniophora puteana) is a fungus that attacks wet timber. Once established the affected timber becomes blackened in colour, as if scorched, it breaks into longitudinal cracks with the grain breaking into small cubes internally, frequently there is a skin of comparatively sound wood on the surface but underneath the timber will have lost its structural integrity.
The 4 Ds ï¿½ Deflection, Drainage, Drying & Durability
The traditional home building method recognises that some water would occasionally get past the outer cladding. The response is to provide three barriers between the outside elements and the protected frame. The first layer is the external cladding. The second layer is a cavity behind the cladding to drain water away and assists with ventilation. The third layer is the ï¿½builders paperï¿½ which has a two fold function in that it allows water vapour to escape from the inside assisting the framing to dry out but deflects moisture in its liquid state travelling for the other direction back into the cavity.
In the event that the worst happens and water does penetrate through to the framing, there is one final barrier. The timber itself may be chemically treated to resist insect and fungal attack. Chemical treatment of timbers are denoted by a hazard class which goes from H1
(never in contact with moisture) through to H5 (always contact with the ground or moisture). H3 contains fungicides and is commonly used for the exterior structural framing. Low risk internal framing is either untreated or H1
Moisture in older homes was eliminated through passive vents such as chimneys or through less than airtight cladding that provided a reasonable air exchange rate for a home. Although older homes typically did not have moisture problems, the down side is that they are often draughty and expensive to heat.
So what went wrong?
Modern construction methods placed more emphasis on energy efficiency and waterproofing than on water management or ventilation. They relied on a waterproof skin with sealed joints between panels, rather than on a second line of defence against moisture such as drain cavities in exterior walls, and ventilation. Demands for energy efficiency also require insulation, which further reduces the ability of the home to dry out. If the framing is put in wet, it tends to stay that way.
Like the ï¿½perfect stormï¿½ there were a number of causes acting in combination which lead to the leaky home problem.
1. The Building Act 1991 reduced controls and standards under the assumption that standards would be maintained by market forces.
2. The increased use of monolithic cladding systems had design features that compromise water management. Water management (rather than water-proofing) requires deflection (using eaves and flashings), drainage (using drainage cavities), drying (ventilation), and durability (treated timber).
3. Introduction of new building systems which some builders were unfamiliar with. Some insiders have also blamed the reduction of standards on the demise of the apprenticeship schemes.
4. Consumer preferences for more complex building forms which make them more difficult to waterproof.
5. In 1998 the New Zealand standard for Timber Treatment was changed to allow untreated timber for wall framing. Treated timber can also rot but is generally slower to do so than untreated. So from 1998 to 2004 a significant amount of framing used in houses was untreated.
6. Increased insulation resulting in reduced evaporation should moisture penetrate through to the structure.
7. Architectural design trends toward Mediterranean stylings which are more suited to hot dry climates and low pitched roofs without eaves.
The situation was addressed by the Building Act 2004 which in effect reintroduced and/or tightened up on controls.
Measuring Risk Factors & Initial Investigation
There are some simple practical steps that you can take to ascertain whether your home has a moisture problem.
Although numbers are reasonably significant, the percentage of the overall housing stock classified as being leaky buildings are relatively small. On the flip side maybe 30% of all homes will let some moisture penetrate around window flashings, etc. The important thing is that if there is a potential problem to identify and sort it out early.
A small number of keen owners now have annual moisture tests undertaken, but these are the exception rather than the rule. What we are recommending is situational awareness and if there are any suspicions, do get professional advice early.
We have set out a list of potential indicators and would suggest that, if your home has three of more risk factors, further investigation is recommended.
If there are signs of persistent mould on wall or ceiling linings, it is always an indicator of excess moisture. Mould needs water to survive. Some mould infestations may have a simple explanation such as poor bathroom ventilation, unflued gas heaters, steam from cooking activities, even leaking plumbing, etc. but all should be investigated thoroughly to assess the source of the moisture.
The Smell Test:
Some mould infestations are not visible and may be occurring unseen behind the wall, ceiling, or shower linings. However moulds have a distinct What he wrote in justin-bieber-news.info free games, but noted that he is going to give a concert in Argentina. smell.
Develop a basic risk profile.
In many buildings there may be no surface signs or discernible smell but the wet rot can be working away unseen behind the wall. Certain location and design features increase the risk of leaking.
You can undertake a simple risk analysis yourself by counting the number or level
of potential risk factors. These are as follows:
1. Your house has Monolithic cladding without cavity. These score much higher on the risk scale than other cladding types.
2. The house was built between 1991 and 2004.
3. Wind zone. These are classified as low, medium, high and very high. In Porirua the stronger winds tend to come from the north-west and south. The higher the wind speed the more likely that water can be forced into the structure.
4. Location. Is the house built up against a bank?
5. Number of storeys. The more storeys a house has the more wall area that will be exposed to the weather. Single storey homes score lowest.
6. Eaves. These shelter the cladding by deflecting a proportion of the water that may land on the wall surface. Wide eaves afford greater protection. Narrow or no eaves will provide the least protection and thus will attract a higher risk score.
7. Envelope complexity. Simple shaped buildings with a single cladding type are considered to be the lowest risk. Medium risk buildings are moderately complex incorporating angular or curved shapes and with no more than two cladding types. High risk buildings are described as complex angular or curved buildings with multiple cladding types.
8. Decks. These are a major cause of leaks. Some designs are more problematic than others:
a) Cantilevered decks where the supporting joists are continuous from the inside through the cladding to the outside of the building. These are difficult to seal where they penetrate the building envelope.
b) Decks that form the roof of a room below.
c) Insufficient step down between the interior floor level and the deck.
d) Deck holds water after the rain has stopped.
e) Poorly maintained deck surface.
f) Water penetration through solid balustrade fixings where these penetrate the waterproof deck surface.
9. Ground Clearance. No gap between the ground and bottom of the cladding. This can cause ground moisture to travel up into the framing through capillary action.
If there are obvious signs of moisture in the visual or smell test, or if your home scores high on the risk matrix, then you should definitely follow up with a professional moisture test.
Stage 1 Non Invasive Moisture Tests and Indicative Cost
The pros commonly use one of three methods:
1. Capacitance tests:
The operator holds a small meter (about the size of a TV remote) either to the interior wall lining or to the exterior. They 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 often misleading. Thus this type of testing has its limitations.
2. Resistance tests:
This is conducted with a small meter which has two sharp prongs which are inserted into the timber. This more direct testing can be used when the wood is exposed such as a basement where the sub floor framing is accessible. The moisture meter sends a small voltage into the piece of wood being tested. The voltage is conducted into the piece of wood through two very sharp pins. These pins are set a specific distance apart from each other and when the test button is pushed the meter can read the resistance between these two pins. The higher the moisture content the less resistance.
3. Thermal imaging:
The operator creates a thermal map of the property using infrared imaging. Areas of anomaly (cold spots) are then followed up using a capacitance or resistance test. It is claimed that thermal mapping assists the inspector to more accurately target areas of concern.
The following are indicative costs only and you need to contact a building inspection company for a quote.
For capacitance and resistence testing with report expect to pay around $150 per hour GST. Depending on the size of the house, for a mid range house of say 200 square metres in size budget on a job lasting 3-4 hours.
A similar test using thermal imaging, expect to pay around $695 GST.