Foundations

Once the driveway was in a condition where it was usable attention turned to the foundations.

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The first job was to clear the area for which we were going to dig the foundations. This first area was going to be for the garage. A little care was needed around the kitchen drain as that will be staying for a while until the new kitchen is in place and then it will be decomissioned.

The intention was to end up with a finished floor level that was 300mm below that of the existing building. Calculating the depth of slab and insulation etc a depth for this dig was decided.

Problems:

After only a few minutes, three problems had become apparent.

  1. We had to dig 'across' the trench
  2. The existing building foundation was higher than we thought
  3. The kitchen drain would need some work

You may notice the tea and biscuits in the picture above, these were needed whilst we came up with a plan to address these issues.
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This picture illustrates our three problems.

The width and shape of the trench.

The existing foundation can be seen on the left and is about 100m higher than we hoped for.

The remains of the kitchen drain can be seen to the left of the far wall of earth.

Solutions:

The tea and biscuits did their work and after a while we had our solutions.

  1. 'We had to dig 'across' the trench.' - Not much we could do about this, as it was not possible to position the digger at the end of the trench it had to be dug from the side and this resulted in a much wider trench than would have been ideal. This, of course, means not only more concrete, but more spoil to deal with also.

  2. 'The existing building foundation was higher than we thought' - This area is for the garage floor slab and easier to work around it. The problem will come on the other side of the wall where we will need room below the finished floor level for the joists. We need to make sure the floor levels match so consideration needs to be given to both sides. One option would be to break out the top of the foundation to get the depth we need, but look at the picture and you'll see how thin that foundation is. Obviously when they did the underpinning they didn't bother with that bit of wall as the outhouse was in the way. The solution we came up with was to raise the finished floor level by 75mm which will give us scope to lap the garage slab over the existing concrete. The loss of this ceiling height will be addressed later when the interior work is done.

  3. 'The kitchen drain would need some work' - This drain will have a new section added before the concrete is poured. It is not a critical issue as the drain will not be in use for too long with luck.

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This picture shows the other end of the trench where it meets the existing house wall again.

That's a better depth of concrete under that wall, but it still is only half as much as we'll be putting under the new walls.

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Here's an overview of the completed trench.

The one down the right hand side is wider as it will also serve as a footing for the retaining wall as it runs alongside the garage.

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And how much spoil comes out of a hole like that?

This is how much.

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Although the building inspector said the clayboard was optional we decided (after several long discussions I have to add) that we would put it in. The reasoning being that as we were pouring a slab over this area if the clay did move it would have nowhere to expand to and it would be the safe option to give it an escape route. Under the suspended floor it will be a different matter as there's growing room for the clay there.

Here's the boards having been hastily added in the time it took for the first concrete truck to reverse down the road. The first couple of dumper truck loads of concrete have also been added.

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The first concrete truck was too long to get onto the drive, so we had to unload into the dumper and put it into the trench.

This one fitted onto the driveway fairly easily..... which after all is why we went to the trouble of doing it early in the process.

It was gratifying to note that the wheels of the concrete truck didn't even leave so much as a shallow groove on the driveway. All that hardcore was worth the effort.

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Two concrete loads went in (the second a lot easier than the first) and then the third arrived.

This was the first truck back again and so we had to use the dumper once more. Here's one of the last loads off the third truck going in.

Unfortunately there wasn't quite enough to get us up to our ideal level so there was a fair amount of discussion, and even more raking of wet concrete, whilst that issue was addressed. We're reasonably happy with the solution and this will all be sorted out when we start laying blocks anway.

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Just in case we forgot in the morning.

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Now the concrete has hardened we can put some temporary steps in to give us access to the back door again.

There's still a big drop, so we still need the reminder sign, but it is not as drastic a drop as it was before.

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Attention now turned to the foundations required at the rear of the building.

In order to facilitate these being poured a temporary roadway was constructed over the garage area. This is documented on the 'driveway' page.

The first job out the back has been to strip back the top soil from the garden. This picture shows the start of the process.

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Here the digger is being used to gather the soil into a heap and move it to the rear of the garden.

The top soil is being moved to allow the spoil that comes out of the footings to be spread on the garden and the top soil will then be replaced.

This should hopefully reduce the need for any more grab lorries to take spoil away and also allow the garden to be levelled to give us a flat lawn instead of one on a slope.

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This view shows where the spoil that came about from creating the temporary roadway over the garage area has been spread at the rear of the house.

The site foreman can been seen in the window ensuring this has been done properly!

This will be dug through again to put the footings for the rear part of the extension in. It was thought better to bring the ground level up here before digging the footings rather than have a lower level foundation that will need to be brought back to finished ground level in brick.

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As with the garage foundations we did not want to dig the trench and leave it open overnight.

This meant the only job we could do today was to take some time to lay out the locations of the footings and mark them on the ground. It took a couple of goes with the calculator to make sure everything was square and true and then when we'd all triple checked it, we were happy. We have marked the likely location of the water pipe, the depth of it is the final unknown, we'll see what happens tomorrow.

Tomorrow we'll dig the trench in the morning and get the concrete poured in the early afternoon.

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The day started well with the first sections of trench dug without any problems. The manhole you can see was on a drain run that was to be decomissioned so we dug through the pipes. We knew the testing part was still to come though as we had two futher drainage runs (which we knew the location of) and the water feed pipe (which we had a rough idea where it may be) to negotiate.

The water pipe was the biggest challenge to us personally, everyone else in the road had cut the pipe when digging their foundations, our mission was to not do that and be the only ones who hadn't.

This is also added to by the fact that the stop cock for the water supply is across the other side of the orchard by the road and it would take a bit of searching to locate it. As an added bonus turning this off stops the supply to the whole road. You can see the pipe in this picture, I'll tell you the story.....

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Information given to us by a neighbour was that the water pipe was around a metre below ground. We knew where the pipe went into the house, so we made our plans accordingly.

We were digging carefully around the drain you can see in this picture when we spotted the blue water pipe you can see above it.

This was not only a metre or so from the line we expected it to be on but was also quite close to the surface compared to our expectations. The fact it appeared to be a loop also made things more puzzling. We knew it must cross our outer trench somewhere else, probably where we expected it to be.

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When the loop of the pipe was discovered we had not started the inner trench. As we excavated around the drain pipe in that one we came across the run of water pipe you see in this picture placed in the same location as the drain.

Confident we had located the pipe in that trench we pressed on. It was at this point that the digger pulled up the metal pipe you see raised in the air above the trench. This was only 3 inches below the surface and was surround by concrete and hardcore. All agreed the digger driver had no chance of avoiding that!

Momentary panic ensued as we established that there was not water gushing out and the drips coming from the pipe was not too bad a result. We hadn't cut the supply, our mission was still on. What we had done though was crimp the pipe so there was no water getting into the house. This we didn't discover until we went to put the kettle on and had to cancel our tea breaks for the afternoon as a result.

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Back to the outer trench again and proceed with caution to try and find where the pipe crossed.

You can see it here a little beyond the drain pipe. It was about as far to the right of our expected location as the first one we discovered was to the left of it.

This bit of pipe was tugged by the digger, but apart from a small crimp, there was no damage.

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We now had a better understanding of where the pipe must cross the inner trench for the final time so went looking for it. Here you can see it behind the others and lower down the trench.

There was a bit of a puddle forming in the bottom of the trench that seemed to be rather too much to be caused by the drips we were seeing. We dug around the bent metal pipe and found that it was actually leaking rather more than we first thought. We hadn't created a fountain though, so not a major drama.

No time to fix it now anyway, the first concrete truck was due soon and we had a trench to finish.

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Here's a drawing showing the route the pipe took to enter the house.

Given that it crossed our trenches four times I'd say it was a job well done to only bend one bit.

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With the trench dug and the pipes and drains avoided we protected them and very shortly afterwards the first concrete truck arrived.

The first load had almost finished being poured when there was a 'flump' noise and we looked to see the side of the trench where the water pipe had been pulled had slipped in. A hurried re-direction of the concrete pour avoided the area and then we had to clear the trench as best we could before the next load arrived.

Four more concrete lorries came and a total of almost 30 cubic metres of concrete went into our hole.

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This picture shows the scene a few days later once the concrete had set.

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The next job on the foundations was to reduce the oversite down to the final level to provide the void under the floor joists.

This will also make it easier for the bricklayer when it comes time to put up the walls, so we cleared an area outside the footing to the same level to give him a consistent working position as well.

The pile of soil you can see in the background are the roots of the bamboo. These were dug out and will be pressure washed to remove the soil before the roots are sent away for composting and the soil is returned to the garden. We really didn't want to spread bits of bamboo root over the whole garden.