02 Key Issue 1

Question 1

What caused the drain to become defective?

Answer 1

This was unconfirmed as the excavations were not undertaken in the end, however I suspected it may have been a combination of extra load due to recent resurfacing of the area and roots from adjacent trees attacking the displaced joints

Question 2

What tests could you have undertaken to determine whether the drain was defective?

Answer 2

1. Visual inspection - lift inspection chamber cover and flush/run water to observe flow
2. Water test - insert bung into one end of the pipe run and fill up pipe to a certain level, observing whether the level reduces (thus indicating pipe is leaking)
3. Air test - bungs are placed at either end of a pipe branch (one connected to a pump), air is pumped into the pipe and the pressure monitored over a period of time to determine its watertightness

Question 3

What impact could the defective drain have had on the existing building?

Answer 3

Any change in ground water levels as a result of a leaking drain may have undermined the building’s foundations, however there was no evidence of movement in this case

Question 4

Did you need to consider any surrounding buildings before undertaking the excavations?

Answer 4

Had there have been any buildings within a closer proximity, I would have considered issuing a Notice of Adjacent Excavation under the Party Wall etc Act, however there were no structures within the required distance for such provisions to apply

Question 5

Would a building surveyor design drainage?

Answer 5

They can do, however they may seek further advice from a structural engineer or specialist drainage contractor

Question 6

Do you feel you are capable of assessing and designing drainage?

Answer 6

As the works in this case were localised and minor in complexity, I felt competent in its design by considering the appropriate guidance

Question 7

How did you design the drainage?

Answer 7

• Mainly using Approved Document H (Drainage and Waste Disposal) as a guide and the relevant British Standards it relates to
• I also used information from the CCTV survey report to identify the location and extent of the works that required designing
• For option 2, I also used BS EN 12056 to calculate the flow rate and therefore gradient required for the above ground drainage pipework

Question 8

What type of pipe was replaced and what did you replace it with?

Answer 8

The existing drain was vitrified clay pipework and I proposed the replace the defective section with clay pipe to match

Question 9

How would the new underground pipe have been connected to the existing pipe?

Answer 9

I specified the installation of adjustable couplings that contained adjustable collars at each end made from a durable rubber material that could be tightened by stainless steel ‘jubilee clips’ to connect the two sections of pipe in a line

Question 10

How did you specify the new build-up of the ground from the drainage to the surface?

Answer 10

I looked in Approved Document H and as I was specifying rigid pipework, it had to sit on 100mm of granular material (graded 5-10mm) up to half the depth of the pipe and then selected fill (free from stones >40mm and lumps of clay >100mm) 150mm above the top of the pipe, with the rest of the excavation backfilled as normal

Question 11

Does the bedding that sits around the underground drain need to be compacted?

Answer 11

Yes, a maximum compaction fraction of 0.3 was detailed in Approved Document H

Question 12

Was the defective pipe for foul water or surface water and why would this have an impact?

Answer 12

It was a combined drainage system receiving both foul and surface water, which may have had an impact when specifying the size of the pipework, however this was not a factor for this minor like-for-like repair

Question 13

In option 2, how would you have connected the new above ground drain to the existing SVP?

Answer 13

A section of the existing SVP would have been removed and replaced with a branch junction connector, providing a ‘T’ junction for the new pipework, all connected with adjustable couplings

Question 14

In option 2, to enable you to install more than one toilet, why could you not have used a shallower gradient?

Answer 14

• Using BS 12056, I calculated the flow rate of the new toilet and used this with Approved Document H to determine the required gradient
• As the flow rate would have been less than 1 l/s (even with 2 toilets installed), a 1:40 gradient was required
• I also spoke to a building control officer, who advised that due to the predicted low useage of the area, no less than a 1:40 gradient would have been suitable

Question 15

In option 2, what other options did you consider to allow for the installation of more than one toilet?

Answer 15

• I considered the use of a macerator pump, however the client was strongly against this due to previous maintenance issues on other projects as well as the amount of noise they generate
• I also considered ramping up to the area to allow a greater fall, however this was not practical due to the space restrictions

Question 16

What did you consider in terms of maintenance of the drainage system?

Answer 16

• Rodding points would have been installed in the above ground drainage at junctions
• Access to the underground pipework would have been gained via the existing inspection chamber and a rodding point on the new SVP branch junction if option 2 was chosen

Question 17

What methods are available for connecting uPVC pipework?

Answer 17

1. Solvent weld - stronger connection but not adaptable once connected
2. Push fit
3. Threaded (screw) fit

Question 18

How did you assess which drainage option was the most cost-effective?

Answer 18

I liaised with a QS who considered current market rates based on pricing guidance such as BCIS, as well as costs for similar work on recent projects

Question 19

What were the respective costs and lifespans of the different drainage options?

Answer 19

• The costs for lining, providing above ground pipework (along with relocating the external door) and fully replacing were all similar
• Most lining contractors offered 25-30 year warranties, whereas the expected life of brand new drainage was 50+ years

Question 20

How does the process of relining the drain work?

Answer 20

1. A polyethylene liner is impregnated with a 3-in-1 resin (resin, hardener and accelerator)
2. Liner is then fed into an air inverter, which inverts the liner whilst pushing it through the existing pipework
3. The resin then bonds itself to the inside of the pipework
4. An inflatable sleeve is then fed into the liner to pressurise it up against the inside surface of the pipe
5. Usually takes about 1.5 hours to cure, after which the inflatable sleeve is withdrawn and the new ‘pipe within a pipe’ is formed

Question 21

How was the CCTV survey commissioned?

Answer 21

They were appointed directly by my company, with their services being covered in my company’s own fee and with a back-to-back agreement in place, reflecting the terms of my company’s own appointment (e.g. level of PII, payment terms, exclusions etc.)

Question 22

Who took liability for the CCTV survey?

Answer 22

My company were responsible for the delivery and content of their submission

Question 23

You say replacing the drain would have had increased quality control due to building control involvement. Do you feel you would have not been able to provide this quality control yourself?

Answer 23

I would have provided quality control, however there would have been increased control due to an additional party who would have also had to provide a compliance certificate for the works

Question 24

Why do you feel the client would have selected option 2 had they not have been able to extend the end-users’ current tenancy?

Answer 24

I believe that due to the quality concerns and risk of future problems with the lining option, the client would have preferred not to take the risk and instead compromise on the number of toilets

Question 25

What legislation covered the scheduled monument?

Answer 25

Ancient Monuments and Archaeological Areas Act 1979

Question 26

What procedure did you follow in order to obtain scheduled monument consent?

Answer 26

I initially contacted Historic England and a conservation officer advised that I would need to submit a scheduled monument consent application form to determine whether we could proceed with the works

Question 27

What information did you include on the scheduled monument consent form?

Answer 27

1. Applicant details
2. Agent details
3. Owner of the monument details
4. Monument name, location and grid reference
5. Description of proposed work
6. Plans / drawings detailing the work
7. Any other relevant information
8. Signature
9. Ownership certificate (like in a planning application)

Question 28

What were the timescales involved in obtaining the scheduled monument consent?

Answer 28

I was told the decision would be made within 8 weeks

Question 29

Why did you advise the client that they only needed to extend the programme by two weeks?

Answer 29

Although the maximum timescale for scheduled monument consent is 8 weeks, the conservation officer advised he would be able to make a decision in a shorter period (approximately 4 weeks) - a 2 week extension was therefore all that was required to ensure consent was received before tendering

Question 30

Why could the drainage works not have been left until the end of the programme once the scheduled monument consent had been received?

Answer 30

The consent decision would have impacted the chosen layout option and due to the location of the dry rot works being undertaken at the same time, the main contractor needed to start working on the toilets first if the programme was to be met

Question 31

By trying to avoid the need for scheduled monument consent in option 2, would moving the door not have required any other consent that may have taken just as long?

Answer 31

• Yes, this would have needed planning permission, however I spoke with a planning officer who advised that this would not have been a problem and therefore I deemed this less of a risk than option 3
• If planning permission would have been rejected, we could have kept the door in-situ and not use it, as the fire officer was happy that the fire escape plan could be revised and managed sufficiently due to the occupancy and use of the building

Question 32

What would you have done if an item of historic importance was discovered?

Answer 32

A condition of the scheduled monument consent was that a conservation officer would need to be present during any excavations - I would have therefore been led by his advice as to future steps depending on the nature of the discovery, however I would inform the client immediately, who may have wished to employ an archaelogist for further advice