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What is this week's blog about?
In this week’s blog, we take a look at pitch fibre drains – a drainage defect that you may come across if you inspect residential properties for valuation or survey purposes.
This is relevant knowledge for the Inspection, Construction Technology & Environmental Services and Building Pathology technical competencies, for both Residential and Building Surveying pathway RICS APC candidates.
What are residential drains typically made of?
Drainage pipes are made of various materials, with the type of material used typically relating to the age of the property’s construction.
Older Victorian pipes are typically made of clay, which is a robust and durable material. They were typically laid into a trimmed trench (known as Class D) and many are still in good condition, over 100 years later.
Later pipes were made of materials such as cast iron, asbestos cement and pitch fibre (which we will focus on in this blog article). Pitch fibre, specifically, was commonly used in the 1940s-1970s, with a lifespan of circa 40 years – meaning that many systems now have significant defects or are failing.
Modern pipes, by comparison, are usually 110mm diameter, made of flexible plastic (uPVC) and should be bedded in small gravel or pea shingle, to prevent cracking. These are fairly cheap, can withstand pressure from the ground above (if laid on suitable bedding material) and are frost-resistant. Clay pipes are sometimes still used for commercial drainage pipes.
Do I have to inspect underground drainage systems?
Any residential surveyor providing a survey level one, two or three, under the RICS Home Survey Standard, needs to be aware of the relevant scope of inspection for underground drainage (Figure 1).
Figure 1 – Survey Levels and Underground Drainage Inspection
Survey level one
Inspection chamber covers should not be lifted and drains will not be inspected.
Survey level two
Accessible inspection chamber covers should be lifted and the drains visually inspected, if it is safe to do so and if no damage will be caused.
Survey level three
Accessible inspection chamber covers should be lifted, if safe to do so and if no damage will be caused. Normal operation of the drains will be visually observed, although this may be limited if a property is drained down and vacant. A surveyor may turn on taps and flush any toilets to do this.
What is pitch fibre?
Pitch fibre is an organic material, such as cellulose or wood, which is formed into a pipe then impregnated with bitumen or coal tar (and asbestos, in some cases). They are typically bedded on sand.
Pitch fibre pipes became popular as they were cheaper and lighter than traditional clay pipes.
On a survey level two or three, pitch fibre pipes can be visually identified by their black matt appearance (see Figure 2).
Figure 2 – Visual Identification of Pitch Fibre Drains
A big thanks must go to Matthew Gardiner MRICS of Sodbury Home Surveys for providing these images.
If pitch fibre drainage is suspected, then a CCTV drainage survey (see Figure 3) would be advisable to comment upon the condition of the pipework and wider drainage system. This will identify issues that cannot be observed on visual inspection of the inspection chamber alone.
Figure 3 – CCTV Drainage Image of a Pitch Fibre Drain
There are various issues relating to the use of pitch fibre drains, including:
Use of push fit joints (without any sealing ring) can allow root ingress into the pipework.
Lightweight material can be damaged easily by bricks or masonry. These were sometimes laid underneath the pipes for support.
Health & safety risk relating to potential asbestos used in the construction of the pipe, if it is disturbed, cut or removed.
Pitch fibre reacts with hot water, fat and oil over time – all things that are put down domestic drains. This can lead to blistering, distortion, blocking and collapse of the pipework.
Use of drain rods to clear blockages can actually further damage the pipework.
How can pitch fibre drain defects be remedied?
Pitch fibre drains which are in good condition should be monitored on a regular basis for blockages or issues (e.g., the pipework shown in Figure 3).
It is likely that at some point in the future that they will experience defects and serious issues.
If a defect is identified to a pitch fibre pipe upon further investigation or a CCTV drainage survey, then there are a number of remedial actions available:
Repair by re-rounding and re-lining (using a resin liner) of the existing pitch fibre pipes. This is a cheaper option and likely to extend the lifespan of the pipe by up to 40 years.
Replacement using a pipe bursting technique and replacement with a HDPE pipe.
Excavation and replacement with modern uPVC piping. This is both costly and disruptive.
Purchasers and homeowners should be aware that some building insurance policies may exclude cover for water leaks or damage to pitch fibre pipes. The Financial Ombudsman Service website provides further reading on this topic.
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N.b. Nothing in this article constitutes legal, professional or financial advice.