Case studies

self build basement concrete waterproof self build basement formwork shuttering wall form self build basement drainage membrane self build basement concrete waterproof consultancy self build basement concrete waterproof supervision training
Concrete additives to make your work easier and better Formwork accessories to make your results waterproof and flat Budget external drainage membrane Consultancy and advice On site supervision and training


Self Build Basement Case Studies

Anyone in business knows that the things you didn't think about are the reasons you fail.

Anyone who built a basement knows the things he didn't think about and the things he forgot and the ways he thought he would save money are the reasons he had a leak, wasted money, can't have everything he wanted.

And without experience there will always be things you try but regret, things you didn't think about and things you forgot.

In my experience there are two main causes of this:
  1. You cannot be on the shovel, be using the saw, be screwing up the formwork yourself - as well as look ahead. It is only one or the other.

  2. You hadn't done it before so you didn't know.
waterproof concrete basement and pool
I am Phil Sacre. I was a trainee land surveyor, then 6 years in the Royal Engineers (learning civils) and many years on big construction sites as the site engineer. All that experience before I built a domestic basement.

12 years ago I knew more about how to build a basement than the average Joe. In the 12 years since I have learned 100 times as much. I only called myself an expert recently.

That means I was still making mistakes when I knew 1,000 times as much as you might know now. One way or another, it will be very wise of you to buy £6,000 or so of goods, training, supervision and advice from me so that you have access to my experience throughout.

You will no doubt come across many people giving you contradictory advice. But mostly their way will be explained only as the way they always do it (or else the way they get more money from you).
waterproof concrete basement and pool

I have tried every way suggested to me. So when I tell you how to do it I can always explain why and why my way is better.

I am still learning, though very slowly nowadays. If you want to learn quickly on your own you are going to make the very expensive mistakes I made years ago.

  1. You can be on the shovel, be using the saw, be screwing up the formwork yourself - if you pay me to look ahead for you, to be on site Supervising. You do one and I do the other.

  2. I have done it before and I know.
waterproof concrete basement and pool

A few mistakes, made by others, to avoid yourself.
  1. Getting planning permission for the front of the new house to be in the same place as the house you will knock down - but not getting the old house surveyed first.

  2. Not organising building control or latent defects insurance before you knock the previous house down or even before you start work.

  3. Getting fined by the Health and Safety Executive for not providing proper welfare facilities. Don't forget the F10 either. The HSE is very fond of turning up on basement projects and issuing fines.

  4. Not getting a good soil investigation.
waterproof concrete basement and pool
  1. Not studying the CDM 2015 Regulations and how they apply to you. (They apply to everyone so they do apply to you).
  1. Not thinking about who you need to build or help you build.

  2. Not having anyone competent to keep an eye on all the labour all the time.

  3. Not doing any basic research to understand the materials you will use if you are in charge, for instance the different ways to buy and have concrete delivered; what men can lift and what requires a crane.

  4. Saving money. More money is wasted experimenting than for any other reason.
waterproof concrete basement and pool

10. Using ICF.

ICFs vary in all but three highly problematic ways.

First. They are made of polystyrene. If you fill a polystyrene form with 30 cubic metres of concrete you are putting in about 70 tonnes of liquid in just a few hours. It is too much. ICFs burst, bend, curve and stretch.

When I used ICF I was selling it and making good money. But when I began promising to have my client's best interests at heart I had to stop using it. Until then my basements all stretched here and there, leaned over here and there and just weren't right.

Second. You don't take ICF off and that means you don't know if you left voids in the concrete.

A leak found before you finish is repaired in minutes for pennies. But if the leak doesn't come to light till after someone lives in the new dwelling, it costs a fortune ripping everything off the walls and replacing carpets.

Third. They rely on the ties through the centre for all their strength. If you cut a tie, for instance to get past a floor, then you have to support the ICF with timber. But you cannot screw the timber to the polystyrene, so it is very difficult to make it strong enough.
this polystyrene ICF spread even after the concrete was setting

this polystyrene ICF spread even after the concrete was setting
void waterproof basement

1. In many ways this will always be my favourite case study.

The client was sensible, capable, friendly and wise. He made his money as a welder and by clearing blocked drains. So he was already very, very good at business and two trades. He experimented wisely after discussing his ideas with friends.

This basement, in early 2013, was the first time we used the resin rods and timber formwork instead of ICF. It all worked as double sided formwork and as single sided formwork fixed into underpinning as well.

Some of this client's comments at the time were: This is crackin', it's so strong, I'm delighted with this, you know I'm really excited I'm loving it.

derby waterproof basement slab ready

  derby waterproof basement customer

When we finished the basement he took me for a fine dining all you can eat Indian. By then we were, and still are, firm friends.

  waterproof basement window

derby waterproof basement scaffold and steps

  derby waterproof basement wall form

  derby waterproof basement wall form second side

  derby waterproof basement front wall ready

  derby waterproof basement pokering concrete

Here you see the extension is finished. The basement is bigger than the extension extending under the small patio at this end.

derby waterproof basement finished
  In the large photo just above you see how the concrete was stepped around the window to create ledges for brickwork that would not let water past the window frame. Below you see the finished detail.

basement window well

An interesting comparison opportunity arose during July 2014.

On July 19th, Ockbrook in Derbyshire and the A52 alongside had a deluge so great the locals thought that 200mm of rain seemed to have fallen in about 90 minutes. All traffic came to a halt for an hour and roads were running like rivers.

By then we were helping another family in the same village build two basements on one plot. Before choosing us, the second self builders visited the first basement we had helped build the year before, less than a mile away.

Their second excavation had been left on the Friday with all the steel fixed and cleaned and the 300mm high formwork in place and checked. But in this photo taken on the Monday after the rain the formwork is floating and the water is more than 300mm deep.

  By then the first basement (above) was finished. This is it. During the heavy rain this basement had a river running down their drive right beside it. We took both these photos within an hour of each other. No water showed itself on the inside anywhere.

waterproof concrete flood plain   waterproof concrete flood plain

We helped build both basements with concrete waterproofing additive and FRP rods and nuts. Not only is all the concrete proven to be waterproof in the worst possible conditions but neither did any joint leak.

2. Self builders who paid the price not getting a full and proper soil investigation.

There are countless ways to go wrong in ways that would not have happened had the client got a thorough soil investigation report beforehand. There are many cases where basements did not go ahead because of what the soil investigation found.

These are the lucky and wise clients who found out in good time that they could not afford to go ahead. Otherwise they would go ahead and run out of money before they finished, sometimes before the area was safe again.
Newspapers report seemingly every year basement projects where people died and basements that collapse and the house above or the neighbour collapses as well. Add to that list the basement excavations that lead to road closures and neighbouring house walls that crack. Constructing a basement is always potentially dangerous. But some are always going to be dangerous without the right precautions, which might be piling the perimeter or dewatering the ground. You just won't know unless you get a thorough soil investigation.

This is so important that one of our Basement Expert web pages is dedicated to the topic. There is a list of some firms that do this work and their contact numbers near the end.
The Basement Expert Ltd full web page about getting a soil investigation.

3. Self builders with a new basement in their back garden.

Willesden Green, London NW10.
This self builder, also an experienced developer, extended and renovated a house to be his own future home.

He adopted Value Engineering a long time ago, so his occasional workforce is his regular gang. He pays them all fairly plus some bonus after developed properties are sold. They are loyal, turning down other work when he wants them.

Value Engineering is where you and your workforce are one team. You all listen to each other. You reward them with a share of the money they save you.

The difference, you will find, is that they enjoy working with you. They don't let you down in case you replace them.

But you won't find such good people immediately. When you do you hang on to them.

They came to see us on another project. Their excavation was already complete before they asked us to visit. Primarily this was just a waterproof concrete customer, however the issues he faced are interesting enough to discuss.

First some photos.

This is how it was when we arrived for the first time. He was incredibly lucky that the London Clay is almost to the surface. More often London Clay is topped with silt and local fill. The clay might be strong but the silt and fill cause difficulties.

Notice how difficult it is to get the digger out when you don't have space for a slope.

waterproof basement build london clay
  We do not know how he got his spoil out or how it was taken away.

Though it looks as though he demolished something at the side, perhaps a garage, took out all the spoil, then started his side extension before the basement was finished.

waterproof basement side access for excation

concrete compressive strength report to BS EN 12390 3 concrete permeability report to BS EN 12390 8  
The photo above was taken some time after our first visit, probably when the basement floor slab was poured because you can see we have made 5 test cubes. 2 are tested for strength and 3 for impermeability. Both to BS EN 12390. Compressive strength is part 3 and impermeability is part 8.

We have had many tests carried out over the years. Every cube passed.

Click on either image to the right to see two original test certificates.

Now that he could no longer get concrete down the side of the house he had to get the concrete over it. A 52m boom pump costs a lot of money and it is not good at going slow.

But had he still had a gap down the side of the house he would have been tempted to run a line of pipes to the rear. This is OK for floors but not for walls, because the pipes full of concrete are too heavy to move around.

basement concrete pump over house
  This photo is a different job. If you use a line pump instead of a boom pump, you have to knock off lengths of pipe and add lengths of pipes as you go round and round filling the walls.

It is very slow and very hard work. It is also very difficult because concrete is still spilling out when you try to clean ends to join them together.

using a line pump

Please bear in mind, as you read this case study, that they thought they knew best. We just turned up for concreting. Any decisions had already been made without us by them.

You can see a sun pipe in there. Very nice. But now that the concreting is above the outside ground level they are relying only on the insulation to form the edge of the roof slab. It didn't break but it did bend, wasting concrete they had to gun off later.

concrete top ceiling roof to basement
  But what we would have told them not to do, but what their structural engineer designed and building control approved, was the use of steel beams.

As beams they are fine. But what we have found is that the ends get cold and cause condensation inside. Also, unless the ends have plenty of concrete over them, water gets in from the earth under the beam and into the basement.

incorporating a steel beam in a roof over a basement

Any roof over a basement that needs to keep the weather out should be in reinforced waterproof concrete monolithically with the basement beneath.

This basement was very deep because most of the floor area is to be a swimming pool.

waterproof concrete basement with pool
  But when I popped in 2 years later he still hadn't got the pool finished.

waterproof concrete basement light tubes

Swimming Pools. Swimming pool equipment costs a lot and the space needed for swimming pool equipment can be considerable. So you should investigate these with pool companies before setting your heart on a pool in your basement.

Consider Endless Pools as well. Factory made units are popular and much easier if they are on your basement floor instead of sunk even lower.

4. Building up to the sides of your plot.

You cannot have your neighbour falling in to your hole and as a rule you need to give them notice under the Party Wall Act.

Which is why you usually end up with concrete piles down the side.

basement full width of garden

Piling is a lot of money and it requires a lot of space. Pile design requires a soil report.

Building a basement the full width of your garden adds a lot more cost to the basic cost of a basement. And the extra work has to be by specialists, so the self builder cannot do it cheaply. (Though you might consider underpinning or an underpinning-type approach).

Note as well that piles go in crookedly. A wall made of 300mm diameter piles will be about 450mm wide when you take the best front line.

5. Building against the public highway

waterproof concrete basement and pool

Actually we were the basement contractor to a private client when we created the basement for his house extension. Protecting the public highway from collapse was always the priority.

The client's brother (himself a developer and landlord) who acted as project manager for the works provided us with this reference.

"To whom it may concern.
We have been working with Basement Expert Ltd and Phil Sacre on a rather tricky basement job in Esher where the retaining wall was on the pavement line. Phil was ever present on the job and handled the difficulties professionally and effectively throughout. Despite payments upfront we never felt that he was taking advantage of us rather he just got on with the job. His technical expertise is second to none and we always felt we were getting the best possible solutions to the issues we encountered.
We have no hesitation in recommending Basement Expert Ltd and Phil Sacre and we will most certainly be using them again.
Please feel free to contact the undersigned for further information."

Obviously we cannot inundate this person with unsolicited messages from every prospective enquirer, but his details are available.

6. Wet rooms in basements.

You have 3 choices.
  1. No wet rooms.

  2. Wet rooms and Saniflow-type pumps.

  3. Wet rooms and below basement sump and pump.
2 costs barely any more than 1.

3 costs a huge amount in comparison. Typically in the tens of thousands of pounds.

From left to right you see a condensing tumble dryer, a washing machine and a Saniflow pump unit.

You can have Saniflow toilets, sinks and showers as well.

The Saniflow pump unit, other makes are available, takes all the water up from the basement to foul drainage somewhere above.
  Saniflow in a basement

Here you get something of an idea of the work involved putting drainage beneath your basement slab.

foul drainage under a basement   Bear in mind that when you put your pipes in trenches that the ends that turn up into the basement have to be positioned mm perfect if you are to carry a toilet bowl down put it on the pipe and find that it lines up with the wall behind it perfectly.

It is not easy.

But much, much, much worse, as a rule, is the fact that when you dig the extra hole for a tank, possibly another 3m (10 feet) deeper than the basement itself, you often find water.

foul drainage tank for a basement   And that water does not want to let you get a flimsy fibre glass tank, that cost you a small fortune, in easily.

Here someone (not us, but a waterproofing additive and FRP rod customer) gave up because the tank got damaged in the process of trying to push it down. They should have created the hole for the tank in the same way as the basement. Piles and waterproof concrete.
  basement foul drainage difficulties

Here are some of the reasons the basements we built do not leak, at all, anything, not even a drip.

Years ago, construction quality mattered and all parties worked together to get the outcome the Client desired. But that changed 25 years ago with the coming of Design and Build and complex contracts - both used to increase profit at the expense of quality.

We have revived the old levels of care but with the most modern materials.

If you build your own basement you have the opportunity to make sure everyone does their work well and you don't have to do anything twice.

  1. We scabble and clean every joint.

  2. We form walls without kickers and we don't use threaded rods that leave holes - the two most common causes of leaks.

  3. We pour the walls in two half heights so that all the concrete can be placed and compacted properly.

  4. We make sure that the slurry to line the concrete pump pipes never goes in the work.

  5. We make sure that every waterproof concrete pour is supervised.
Details that make all the difference.

In these photos you see our fibreglass FRP threaded rods and nuts that control the wall width and hold the sides together. They take the weight of the concrete while the timber triangles hold the formwork straight and upright and form the support for our scaffold.

waterproof concrete basement slurry basement underpinning blinding

we took the best of ICF and improved it

basement for a structural engineer  
The rods get cut off flush when they are finished with leaving no holes to repair.

FRP rod cut flush

And no leaks.

This basement had 80mm of water poured in with a hose to make sure none escaped before it was backfilled. You can see that no water is getting out through the joint.

cotswolds basement slab   The rods and nuts can be used with hired in systems as well.

But you will usually need a crane of some sort if you hire in kit.

Both to move it and to load the truck when you return it.

Window wells, outside staircase, external drainage.

All are easily included.

This basement is painted and wired. Nothing else. The washing machine and tumble dryer are down there with the water pumped away with a Saniflow unit.

Otherwise there is no heating, minimal but some ventilation, and the basement is adequately warm and dry for storage.

He told us during the Winter that it is always about 10°C.
  self build basement house


self build basement concrete waterproof self build basement formwork shuttering wall form self build basement drainage membrane self build basement concrete waterproof consultancy self build basement concrete waterproof supervision training
Concrete additives to make your work easier and better Formwork accessories to make your results waterproof and flat Budget external drainage membrane Consultancy and advice On site supervision and training


Case studies