Piles of fun for everyone

week 3

In talking to our neighbours about our extension plans, we discovered (thanks to the fact they've already built a small extension on their property) that the ground our houses were built on is what's called 'made up ground'. What this means is it was, at some point, reconsistuted either to fill levels or to reform an old industrial site. What does this mean for our grand plans, I hear you ask? It turns out it means we need to spend more money (yeah, OK, I could have guessed that) to have a special kind of foundation put in place on which to build the extension. From our investigations it seems that all of the properties in our area are built on piled foundations due to the nature of the ground.

What are piled foundations?

According to the awesome Design Buldings Wiki "Pile foundations are deep foundations. They are formed by long, slender, columnar elements typically made from steel or reinforced concrete, or sometimes timber.". Essentially the ground is unable to bear all of the load of the structure being placed on it with a standard shallow foundation, so you have to dig deeper to get enough support from the stronger ground beneath. The challenge is how far down do we need to go...

OK, what's the damage

We don't really know the answer to that just yet. The structural engineer is putting together a design for the pile and ring beam foundation (cost £450+VAT) which then goes to the builder who arranges for a piling contractor to do the work. We've been told the costs for this work can vary wildly between £2k and £10k, so we're budgeting for the worst case.

It also means we'll need to make sure we get a builder who can accommodate this (in all likelihood, they'll contract out the work), and expect it to add a little bit of time to the overall duration of the project as it's a level of complexity you don't get on a standard extension project.

In the grand scheme of things it might not be our biggest issue, but it's good to have caught this upfront before getting into the build and realising it would set things back a little. It also means we can spec the foundations ourselves wth the structural engineer and provide this to the builders to get an accurate, fixed price quote, rather than it beong something that eats into our contingency budget once we're underway.

Chalk another one up to 'you live and learn'!