House on a Raft Foundation

This site is next door to me. And it's been interesting to see the building process unfold. No foundations approach. Straight on the clay. Interesting because there has been criticism from builders in Christchurch that this is an expensive approach. Don't think so... The site was scraped flat to clay. The a thin layer of scoria added....

You can see Lot 1 here - with its edges laid out on top of the scoria and clay. The sites were dug down a little - because they will be three stories high. So there's some retaining walls required and stormwater collection....

This is Lot 2 of this Devonport subdivision. You can see the wastewater pipes sticking up...

The wastewater pipes in close up. I scraped back the scoria. You can see how shallow they are just grooved into the clay. (I guess this is the one vulnerability - if the land moves - earthquake - then these down pipes would be snapped off where they enter the ground. Easy to fix I guess though... later...)

These polystyrene blocks - when they arrived - I thought: "great underfloor insulation..." But that's not what they are for. I guess all that PVC needs to go somewhere. Cheap space taker in foundations... First, black plastic sheeting goes down as you can see, and the blocks are ready for placement....

The plastic sheeting doesn't curl up the boundary boards. Just flat on the scoria... The waste water pipes have collars of polystrene around them....

Then the polystyrene blocks get put in position. You can see the spaces between. These will form the ribs which are the main strength of the foundation base....

The blocks are a precise distance apart - measured by these little black plastic spacers...

Then the steel gets added. A crucial part of the structure of the foundation which is a sort of raft. It can be tilted - eg by an earthquake - and then re-levelled. Hence the attraction for Christchurch...

The reinforcing is laid on top - placed on more black plastic spacers to give exact separation. And you can see reinforcing rod laid in the gaps between the blocks...

Then along comes Mr Concrete and pours it. I thought the blocks might want to float up, but the concrete gets poured on top first, then flows into the gaps, andf there is no tendency for them to float. All very perfect....

Then the building goes up. Like a rocket. No floor studs interestingly (on the ground floor)...

This pic gives an indication how the wood framing is fixed to the foundation... where metal girders are used - these are bolted to studs which appear to get drilled and set into the concrete....

This same view from outside... I will be interested in how the building is clad, and how rainwater runoff is managed...

But for now, I will content myself with trying to be a good planker inside. With a little help from my friends and a piece of 4 by 2....

Eventually got there. Got for the abs and the back muscles. Not sure that this is very good for you. But interesting...

Emily was a natural...