syne

The more I read the less likely it seems to be a good idea to do it this way, especially as there's no ground issue to do so. Looks like a strip it is..

Fair, maybe, maybe not I would start by breaking it down. How much will it cost you to do the bits you can; fence down, muck away and all that, don't forget to count your £/ hours as that's part of their price. Then add the cost of the footings; (the concrete, the blocks, pipes and bits n bobs, the digger, the calcs if your having them done.) Then your left with the cost of the stone and the cost of the labour... Does the remaining price seem fair?

hi, Self builder here (as much as possible anyway) based in s yorks, and currently working on an extension. so, hope you all can tolerate the intrusion with silly ideas and endless questions..

sorry, The extension is 6x6m so 36m2 and the adjoining garage is approx 7x7, but with a taper so it works out about 34m2 Deferential movement, well that's a issue my SE can hopefully remove from the equation. I much prefer the icf to blocks and when combined with the slab takes (pretty much) all the cold bridging out of the equation, not to mention the speed factor. Price wise the raft is looking to be similar in cost, the icf similar also. I'm just not sold on the idea of an insulated raft for a garage floor, seems like overkill.

I've begun the process of designing an extension and an fairly certain I'm going to have an insulated raft with icf walls. This will be adjoining a (likely strip foundation) cavity wall house. I've had a quote from isoquick for the raft approx 6m² but I'm not sure if it's worth extending this to cover the garage floor? It would essentially double the price, but the alternative is going to create a strip & Insulated raft & strip or raft monstrosity combo. Is it going to lead to problems? should I just swollow the extra cost even though its going to be a waste of resources and is an insulated raft even suitable for a garage floor? The upside I suppose, is that if the raft is continuing then it simplifies things and if someone decides they need another huge room downstairs in the future the prep will have been done....

So am I correct in thinking just like 'a rising tide raises all boats' - 'a ground movement, moves all foundations'? If a sips extension on an icf was attached to a brick house on a strip found - would the disparity in building weights create a different raise/movement amount between the two building types? ie the heavier brick house creates more resistance/moves less Or do they both pose an insignificance resistance and the ground moves them both by the amount the ground decides to move? When you say "A ICF raft founded at the same depth as the original found" I presume you mean the top, So the bottom of the new raft would sit level with the top of the old?