The wife wants to build an extension (additional kitchen and bedroom) onto the side of our house but I've seen a few in our mooban that have fell away from the house after a few years (and a few others which seem fine). Any suggestions how to ensure the extension stays upright and attached to the house? Is it related to how deep they pile or number of piles or both? There's also not much room for a big piling rig. Anyone know a good contractor with experience of this? I don't mind paying more if the job is done properly. Or is it simply crazy to consider extending an existing house built on this swamp.

The usual reason for an extension sinking is settlement and more often than not because the foundation has not been taken down to the depth and tied into the existing.

Thus you get differential settlement house and extension falling at their oen rate and then the killer here....the ground heave.

You notice they have this crass idea to build up land with clay. When it getd wet you have trouble. The extension will break its own back.

My advice would be to dig well below the fill probably 1.5m if virgin ground can be found. Break and rebar tie a new foundation to it.

Remember an extensuon exerts as much pressure per metre run as the house itself.

If you can bolt on a steel channel vertically with tie bars then the new walls can be bonded in likr glue.

Most importantly find someone who knows what they are doing and not someone who says mai pen rai at every question you pose.

Agree with Eyecatcher I have actually had a falling-away small bathroom on grandma's house underpinned and it worked, and just filled the growing one inch gap.

I explained to the builder to do it in alternate sections and it's worked out....that's up-country.

Trouble is as Eyecatcher hints tying the two structures together is still a bit dodgy unless foundation identical it can overstrain somewhere or other.....but should likely be ok and not too much sweat if a hairline crack need filling once in a Blue moon.....just not like grandma's one inch gaping chasm (her bathroom was also added as an afterthought.)

Bangkok area....you need deep footings/piling?

One or two storey?

One thing comes to mind, you may in any case keep it light as possible using thermalite (lightweight) blown concrete blocks and perhaps sheet roofing....if you think "asbestos" sheets look naff you can get a top brand of metal sheeting guaranteed a very long time and it's even lighter and so is the roof framing. Make sure it has insulating foil glued underneath at manufacture to reduce heat and rain noise....it works quite well if you don't buy cheap.

I'll also add thermalite blocks properly done can support a metal roof without reinforced concrete columns incorporated so more weight saved.

Edited November 23, 201411 yr by cheeryble

Yes, Bangkok area, two storey. It's a Land & House mooban, deep piled (I think) with those lightweight bricks. The previous owner built a one storey maids room extension which fell away about 2 inches at the top, one of the first things we did was knock it down. I'm really cautious about this extension as I don't want to end up knocking that down as well.

The rear area will not have been piled so you will need to pile before building. Some Asian builder's have a comical way of piling (but I supposed it works)

http://m.youtube.com/watch?v=FB2uHnztADU

Hello Guys. I am in the same situation you were in. I am extending the back part of the house. I have 2 options given by the contractor.. 

1. Independent piling foundation which is not tied to the existing foundation. 

 

2. Additional piling that will be tied to the existing foundation.

 

From the post above I under 2nd option is advised so that the house and extension "sinks" at the same rate. Is my understanding correct?

Were it me:

 

The portion of the addition next to the existing, I would tie to the existing footings/piles.

 

The portion of the addition opposite of the existing I would have an independent piling foundation.