Why you need to project manage your extension

Hips improved so water directed away. Felt repaired / replaced where the hole was.

Hips improved so water directed away. Felt repaired / replaced where the hole was.

I wish I had read this before extending my home, but as I am writing from personal experience that would have been impossible. This guide could be called “A case study of cowboy builders at work and how disaster was averted”.

Several things went wrong for us during this extension. I did not really highlight them on the daily updates, although the keen reader will certainly spot the tell tale signs of trouble being afoot.

What this taught me is that you should always take an active role in managing your build. Even if you get good builders in, still check progress daily and do not be afraid to check credentials. Ensure that professionals are used throughout the build.

What went wrong?

My builders were recommended to me. They came as a pair, a builder with 20 years experience and his labourer, and another builder of similar age and his labourer. I was informed when hiring them that they could do the entire build, including the plumbing, electrics, roof …. everything!

As somebody who knew nothing about building whatsoever before it started, this did not sound in any way unusual. However, things first went wrong when they installed the electrics and the plumbing.


2013-08-16 16.11.46

Electrics running along the floor and a very dodgy mains water pipe. Even had a bit of hose at the end, which they said they were going to replace. All plumbing was removed.

The only electrical work in the new extension was to extend an electric circuit and a single ceiling light. At the time this came under Part P of building regulations so had to be designed, installed and tested by a qualified electrician, but that is no longer the case.

My builder installed all the electrics himself, telling me that he had been doing it for 20 years and the only reason he was not qualified was because he did not want to pay the £3000 to get the certificate. However, his method of wiring, although satisfactory, was far from ideal.

Ideally, he should have run all the cables up the walls and across the ceiling, and chased the cables properly into the walls with a protective cover. Instead they went down to the floor and around. This may look OK, but there are two main issues with this.

First, there is no “safe zone” where the cables first come into the room and then down to the floor. Although this is in an area we would never need to drill a hole, there is a risk that one day somebody will do just that. They will hit live cable instead of a metal plate.

Second, the cables run under the second damp membrane layer, although above the first on the edges (and the whole floor is on the damp course and with air bricks under). But there is a small risk of dampness getting to the cable and rotting it (although pvc is pretty durable) and also risk of rising damp coming up the cable.

I had an independent electrician test this all and he said it was OK, but not ideal. I asked him off the record what he would do in my situation, and he admitted he would just leave it as it is. If a problem ever arose it would trip the fuse and you would then re-do the electrics in the room.

The second thing with the electrics is the ceiling light. The builder ran the ceiling light from the old outside light. This seems sensible. However, the outside light was spurred off the mains for the extractor fan in the utility. We had this removed, and almost had that cable taken out completely by our electrician when the kitchen was being done (I hired an electrician and plumber to do the new kitchen). This means that today we can turn off the living room light by switching off the “extractor” switching in the utility. A little silly!


The builder was also proud of his plumbing skills, and his labourer was also an apprentice plumber and then worked as an assistant to a plumber for a few years. That should make you feel confident?

All of their plumbing was terrible. First, for the outside tap they simple extended the pipe from the old wall and under the floor of the new extension. This means mains water running under the living room. If there is a problem, the whole living room needs to be torn up. This alone is not a huge problem, but the builder used “push fit” plastic fittings. Specifically, they used John Guest’s Speedfit.

Second, the new radiator was first plumbed direct from the old one using 10 mm plastic pipe. It failed to heat the radiator up. So they then removed the old radiator (I decided we did not need it, and it made more room for my bookcase) and replaced the pipes with 15 mm, copper pipes which were connected using push fit.

There is nothing wrong with push fit when it is done properly, although most plumbers consider them a “DIY” solution. However, push fit needs to be installed correctly.

The John Guest Speedfit website says that all fittings should always be placed within inspection boxes so that they can be checked and replaced. This means that any fittings which go under a concrete floor should be boxed in with a (usually) wooden plywood lid, before the concrete screed is laid.

Copper pipes over the top of the insulation with no protection from the concrete, and not inspection boxes.

Copper pipes over the top of the insulation with no protection from the concrete, and not inspection boxes.

Also, and the inspection box solves this too, the pipes should be allowed to move. So you should never concrete them in completely (not even if chased into a wall). Over time the expansion and contraction of the copper will wear down the plastic fittings, resulting in a leak. And this will be a leak under concrete with no access. Solution – dig up your living room floor!

Finally, copper corrodes when in contact with concrete, so needs to be fully protected. Denso tape is often used. The builders had no intention of using this.

dodgy plumbing with push fit

The builder’s attempt at protecting the main water copper pipe from the concrete. Note, this is the outside tap under full mains pressure, running underneath our sofa. Those plastic fittings will probably last 12 months at most in these conditions.

The builders were intended to just pour concrete over all the fittings and the bare copper pipe.

Luckily my wife checked the fittings the night before the screed was due to arrive. It was already leaking! So I contacted a plumber friend, and he came around at 5.30am the following morning to check it. He told me to halt the build so that he could do the job properly. He saved us, no doubt about that!

My plumber removed the outside tap pipe completely and re-routed it through the utility wall towards the drive. Short distance, all proper fittings, nothing where it cannot be serviced.

Pipes plumbed behind the radiator

Pipes plumbed behind the radiator and beneath the Celotex insulation

The radiator plumbing was replaced with plastic pipes, but a single pipe running from the main 15 mm copper pipe all the way to the radiator. The pipe also ran under the floor insulation and was then chased up the wall behind the radiator, all out of contact with concrete and out of sight.

If we were not watching the build and taking notes we would never have known what problems were potentially ahead of us. The fact that the pipes were already leaking on the day the screed was coming is highly concerning. But remember, they were builders, not plumbers!

discarded plumbing

The roof

The actual construct of the roof, the steel, the timber and how it connected to the house, is fine. However, the flat roof, the felt cover and the lead flashing was all pretty poor.

We had a lot of rain in the winter of 2013 /14. Every time it rained I made a point of sitting in the living room and looking carefully. No sign of water anywhere. Good!

Well, good until just before Christmas 2013. On once evening when the rain was coming down really heavily I noticed some water dripping down through the soffit. It was below one of the roof windows, so I concluded that the water must have been coming through there.

leaking roof water in through hips

This shows where the water was getting in through the hips,

I contacted the builder by SMS and he replied “there is no way water can get in around the roof window so I would say it is drifting under from fascia, not a problem”.

Note, he did not inspect it, he just guessed that it was not a problem. However, there were no internal leaks, so all was well.

Well, until one day in the new year. The rain was driving towards the house and I sat by the French doors watching the rain and sipping tea. I got up to go back to work (I work from home, which is how I managed to keep a beady eye on everything) and promptly swore. There was a pool of water at the base on the old French door. Water was visible running down the door frame and it was wet all above the frame too. The roof was leaking.

leaking roof cowboy builder

A pool of water indoors. A perfect way to cool your toes on a hot summer’s day!

I phoned the builder, and no answer. I sent message to the builder. Never got a reply.

I called a roofer to look and he diagnosed the problems. He did this not by guessing, but by removing the flashing where the water was getting into the house, and also removing tiles all around the area were water was getting down to the soffit.

There were five main problems with the roof. The roofer asked me, “did they have an apprentice roofer do this?” and I replied, “the builder did it”. “Oh”, was his response, “no wonder”.

The problems with the roof:

1. Although the roof was flat, water was pooling in a few spots. One spot was near the leak. This pooled water could then be blown towards the house, as it was when the rain was driving.

2. The felt on the roof hardly extended up on the join with the house. It went up a couple of centimetres at most.

3. The flashing was poorly placed and not chased into the wall, so water hitting the bricks would run down under the flashing (making it pointless).

4. The “hips” of the roof were higher than the flat roof. This allowed water the seep into the mortar for the hips and run down the felt under the tiles. Normally this would not result in the leak I saw coming out of the soffit, but there was a hole in the felt! The roofer described this hole as “about this size of a cigarette burn”. Both the builder and his son who did the roof were chain smokers!

5. There we too few stones on the roof, and of the wrong type. Good quality stones for a flat roof act as another layer of insulation, they quieten the sound of rain, reflect the sun and also stop puddles forming.

Hips improved so water directed away. Felt repaired / replaced where the hole was.

Hips improved so water directed away. Felt repaired / replaced where the hole was.

My roofer repaired the roof, and touch wood, it is all OK now. He removed the stones, added a new thick layer of roofing tar and lots of new stones. He added a strip of felt that went up the wall, to a height of under the window cill. The flashing was chased into the brick work. On the hips, felt was added to guide the water away from the mortar. He also made the mortar super smooth to reduce erosion etc. from rain, moss and other stuff that gets in rough finishes. And some new felt.

new roof stones on cowboy builders roof

New stones on the roof. The roof was also levelled so no pooling. Recent rain showed that all worked well.

Flashing before and after. Flashing now chased into the brickwork so water cannot get in.

Flashing before and after. Flashing now chased into the brickwork so water cannot get in.


That that is three jobs which the builders should have got in experts for: electrics, plumbing and roofing.

It all cost me more money. I paid £70 for the electrics inspection, £160 for the plumbing and £400 for the roof repairs.

To their credit my builders did get in a plasterer. But I think the real reason for that is because they were hoping to get the job finished quickly – the plasterer worked all weekend just before the final week.

How to avoid an extension nightmare!

To avoid this, ask your builder if they will be bringing in qualified traders to do tasks such as electrics, plumbing, roofing, window installation etc. Some jobs are best done by experts who do nothing but this all day, every day.

I actually chose my builders partly because they said they would do everything. I thought that was better, to have them on site every day doing the work themselves. Another builder quoted a similar price and called himself a “project manager” and said to me that he would need to get together a team of tradesmen. That put me off. In hindsight, I should probably have gone with him.

Of course, not all specialists are good. I hired an electrician and a plumber for the kitchen. The electrician was excellent, very pleased with the job, and a fair price.

The plumbers on the other hand, were appalling. They left a mess, broke a tile in the bathroom, broke a brick, did not chase the pipes into the wall properly in the kitchen, flooded the kitchen, destroyed plasterboard rather than cutting it out. They really did not take their job seriously. The person who sold the job to me, the head plumber, was hardly there; the two remaining spent half the time bickering and the other half smashing my house up, or flooding it. I will never use them again, even if they are the last plumbers on earth and a burst pipe is causing my entire house to drown under 20 m of water (I’ll open the door).

Final top tip: If you are getting an extension done, read up on building practices, photograph the work as you go and do not be afraid to ask people their advice. Post photos on forums, ask friends that are in the know. Do not assume everything is OK.

In an ideal world all builders would take pride in their work and also know when to get others in to do jobs. Unfortunately, some are too proud to ask for help and too ignorant to know when they need it.

More like this in the Planning and Design section

  5 comments for “Why you need to project manage your extension

  1. March 4, 2014 at 7:29 am

    Are you naming the builders in question so others are pre warned?

  2. Jon
    March 4, 2014 at 8:07 am

    Not publicly, it’s not worth the trouble it can cause. But if you are getting some work done by all means ask me if the names are familiar. They are not builders who are easy to find. They do not have websites or online profiles. They did come recommended but unfortunately the previous client now too has a problem that only appeared six months later!

  3. Karl
    February 26, 2017 at 2:44 pm

    Hi Jon

    Can you recommend decent builders. We are extending and totally refurbishing our ground floor flat with new bathrooms, kitchen and plumbing & wiring.

    We are in London SW13.



  4. Jon
    March 8, 2017 at 8:31 pm

    Sorry Karl, I do not know any in the SW13 area.

  5. Brian W
    November 20, 2017 at 3:20 pm

    Many thanks for the benefit of your experience and your advice. Will be most helpful in my own upcoming project !!

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