Common Defects on Clay Drainage Systems
Displaced Or Misaligned Joints
Pipe bedding options were seldom considered for older systems, and the excavated soil was usually used for back-filling. There were some guidelines advising the use of more suitable materials that were dry or more finely ground, and the removal of bricks and masonry from the fill until there was a safe covering over the pipe-work. However, we do find cases where bricks and rocks have clearly damaged the system during the back-fill.
Even the slightest water loss from a joint can be detrimental to the system, as the water erodes and washes away the sub-soil that it relies on for structural support. The water loss undermines the next pipe, which moves and causes another defective joint, and so on…
If joints are stepped against the system’s flow, they present snagging points for solids to build up and form a block. Water is then pressured out of joints with even the slightest defect, which continues the deterioration process.
A system may start to block, then totally collapse, sometimes with no warning signs. There may also be issues such as subsidence to your property, as the result of years of water loss adjacent to the house foundations.
Fractured & Broken Clay Drains
As mentioned above, water loss from defective joints can lead to the erosion of the sub-soil supporting the pipe-work, leading to stress fractures, and the process goes on. Clay drainage systems also fracture and break for other reasons, such as a carelessly placed brick during back-filling, impact damage from the installation of a fence post or a new gas or water main.
Constant vehicle movement on the road or a driveway can affect drainage systems, and the simple process of rodding a drain can damage sharp bends or drop shafts. The defects can lead to eventual collapse, by allowing root ingress, and jagged pipe-work causes the build-up of solids until the sysem blocks.
Tree Root Ingress In Clay Pipes
One of the main causes of blockages to clay drainage systems in this pleasant green land is tree root ingress. Tree roots will penetrate mortar joints, particularly if there has been shrinkage in the curing process. They access the system through fractures and breaks in the pipe wall, and even modern systems will be prone to ingress if a suitable root barrier system is not used.
Disturbed ground such as back-filled drainage trenches make easy paths for roots, and condensation on the outer wall of pipes, or moisture from leaking joints, may attract roots looking for a good nutritious feed.
Very fine roots initially access the system through a defective joint or break, and once inside they fan out, reducing the internal bore of the pipe-work and causing solids to snag until the system blocks. Water loss is accelerated, also affecting further joints, and the ingress increases.
Well established tree root ingress will completely fill the internal bore of a system, and the fine roots that initially accessed the system grow into tap roots that break and fracture clay pipe collars.
Moisture Detection and The Importance of Property Inspection
Over the Christmas period, I was asked by two former Police colleagues to inspect properties they had purchased without Pre-Purchase Inspections. So I thought I would take this opportunity to point out how important is to have an inspection carried out on the property either by the Vendor or the Purchaser to identify any possible issues, and how the use of Moisture Meters and Thermal Imaging Cameras have their limits.
There are a large number of these devices being used in the industry. However, it would be unwise to rely solely on them, as their operation and interpretation is also dependent on the operator. They are tools to be used in conjunction with experience and knowledge of high risk areas. I have inspected houses where tests gave a low or normal moisture reading, only to find dry but rotten wall framing when the cladding was removed. These properties had leaked in the past then dried out, giving a false impression that the property did not have any water ingress problems.
My clients frequently ask whether my inspections use infra-red or moisture meters. Moisture Meters use radio frequencies to identify moisture in buildings. But contrary to public perception, Thermal Imaging (commonly referred to as infra-red) can also pick up moisture. Thermal Imaging identifies thermal temperature differences and can, in the right circumstances, assist with the identification of water ingress due to the thermal temperature difference between the exterior and interior of a building. Most devices used to identify moisture are generally non-invasive, while some can be used invasively with probes. I use a Trotec and a Protimeter device to identify moisture, and in some situations I recommend engaging the services of a proficient Thermal Imaging Camera Operator to assist with the identification of moisture ingress.
The property I inspected prior to Christmas had many high risk junctions due to design, construction and cladding types, and I found historic water ingress to several areas which had tested dry when using moisture meters. The person purchased the property but is aware of the issues it had.
My Inspection Reports have on every page "I want you to buy your dream home, the one with no surprises".
A property inspection is not a guarantee that all defects (and/or future defects) have been identified, but it is a lot safer, and once again I emphasize how important it is to have a Pre-Purchase Inspection carried out before purchasing a property.
Deflection, Drainage, Drying & Durability - December 2011
Predominantly the only houses that were required to have a cavity system prior to the Building Act 2004 being introduced were brick veneer.
Many of my reports refer to the lack of weep holes at the base of the bricks walls or the lack of vent holes at the top of brick walls. These must remain open to allow drainage and ventilation, I find in a lot of situations the weep have been buried or partially blocked with drives, footpaths or gardens.
Due to the leaky home era of building in this Country the 2004 Building Act identified what type of buildings are required to have a cavity system.
A risk matrix was introduced where a risk score is calculated on every wall of the house which would determine which wall required a cavity. The determining factors are width of soffits, how many storeys high the house is, design complexity, and cladding type to name a few. If the houses score over a certain number then a cavity system would be required.
Prior to the 2004 Building Act being introduced a large number of high risk face sealed cladding systems were installed directly onto wall framing.
If a cladding system failed then water gained direct access to the wall framing behind.
The combination of this and the use of untreated timber being used in house construction between 1995 & 2005 lead to thousands of houses leaking, rotting causing millions of dollars of damage. There are many cavity systems used in construction today, predominantly a cladding system would be on a 20mm system which does not allow the building wrap or insulation to touch the back of the cladding to form a bridge where water can access the wall framing.
Most systems used are called Acceptable Solutions under E2 External Moisture of the Building Act, some systems are called Alternative Solutions.
An Alternative Solution is where the Manufacturer has proven to the Local Territorial Authority that their product or system although falls outside the scope of the Act will perform to the required standard. Well I hope you have found this brief explanation as what a cavity system is.
Grant's Word on the REINZ's Warning for Buyers - November 2011
The Real Estate Institute warned buyers against using unlicensed inspectors and advised to use members of two professional industry bodies, The Institute of Building Surveyors and the Royal Institution of Chartered Surveyors.
The article also advised people should not buy a house without a professional written report and to only use the above registered members.
I do agree there are probably some average, and in some cases, poor pre-purchase inspection reports being completed by either untrained or unqualified pre purchase building inspectors but do not agree with just using the above bodies named above.
I am not a member of either body but have completed modules set down by The Institute of Building Surveyors, I am a trade qualified builder and was trained by another pre purchase inspector who has been carrying out inspections for over ten years. I know I am qualified to carry out pre purchase inspections to a high standard.
I advise people to carry out background research on the company they are engaging to carry out their pre purchase inspection.
Obtaining a low cost and in some cases an inadequate inspection may not identify the issues the property may have. The sale and purchase may go ahead but may leave the purchaser with potentially large costs to remediate problems the property has.
A pre purchase inspection is to give the purchaser an idea to the general condition of the property.
The property report is not a guarantee that all defects (and/or future defects) have been identified. The inspection is carried out solely on a visual basis. All efforts have been made to identify possible defects (and/or future defects). The property report is not a guarantee that the house meets all the requirements under the Building Act at the time of construction and/or under the Building Act at the time of inspection.
The purpose of the report is to identify areas of interest/concern, NOT to provide independent expert advice on specific elements and NOT to recommend solutions to faults identified. The purpose of the inspection is to provide an impartial, technically knowledgeable and visually thorough account of the properties general state being the next best step toward assisting a purchaser in determining the appropriateness of the purchase to their individual threshold for maintenance and repair.
No house is perfect and as long as the purchaser is aware of the issues the property has then that is all that can be asked from all the parties involved.
The phrase at the bottom of all my reports emphasises this, it says.
I want you to buy your dream home, the one with no surprises.
This is why I have a website for people to look at me, my qualifications and experience.
New Zealand is becoming more like The United States where people are now attempting to sue people, rightly or wrongly.
This is why I have chosen not to carry out inspections on monolithic house without a Report Conditions and Agreement of Service Contract.
I am competent to identify the issues a monolithic property has due to my experience and knowledge which has been increased by the weather tightness courses I have undertaken.
A pre purchase inspection is a visual one and cannot be expected to see behind the cladding of a property.
Being named in a Judicial Court process for a weather tightness claim regardless of whether you contributed to the claim is an expensive process. Parties involved with the property could include the Builder, Council, Real Estate Agent and the Pre Purchase Building Inspector regardless of whether they had any part to play in the problem with the property.
I encourage all potential clients to look at my website and Facebook to be happy they are getting a competent Building Inspector to carry out their inspection on what could be their biggest purchase of their lives.