Cellar extension.

[123everton]

My house has a cellar, but it's only about 5 ft 6 deep, it is easy to gain access to the whole underneath of the house.
I'd like to extend the depth of the cellar and make it the full size of the house.
I know that I'd require plans and planning permission, but I was thinking would the cheapest option be to build 9 inch square pillars and then use steel rsjs to support the floor were it meets the gable and the interior walls.
Having inserted these pillars build another 4 inch wall inside of it and then dig out the rest.
This I'm hoping would avoid the need for underpinning as the ground beneath the gable would be undisturbed, the downside is that I'd lose just over two foot in the size of the cellar but for what I'd gain it'd be worth it.

[Mr Veritas]

The first thing you need to get yourself is a Structural Engineer,to advise you IF the scheme is feasible,and how it can be done.
Then you need an architect to plan it out for you.
If you do not have these,then you are asking for serious danger in playing about in the cellar of a house,especially if it is terraced or semi~detached.
Also if you do not consult with the two persons above,when (if you CAN achieve it yourself)your building works may not be "signed off" by the Councuil Buildings Officer.
There is a lot more to this that you seem to think.
Doing this sort of this sort of thing off your own bat can be dangerous and very expensive.