HOW TO: Dig Out Your Basement or Cellar

In Brooklyn, land of townhouses and row homes, most houses have cellars or English basements (either entirely or partially underground) that amount to a lot of unusable space.  These cellars used to be where coal was deposited and burned to keep the houses warm and they are usually unfinished with very low ceilings.  Our cellar had 6 foot ceilings, a thin slab of concrete floor and exposed rock foundation walls.  It was a dank and gross place to be, completely unusable and disgusting.  Here's how we made it into the space it is today.

1. Engage the services of an architect, contractor and a structural engineer.  When you are playing around with the foundation of your home you can never be too careful.  Having licensed people on board who have done this type of thing before can be the difference between great success and a total disaster.
2. Research local building codes to determine ceiling height requirements.  In our case, we had 6 foot ceilings and wanted 8 foot ceilings.  The cost of those extra two feet was huge, so we thought about reducing it to 7 feet, but later found out that the building code would not allow for 7 foot ceilings so we paid the cost to go to 8 feet.  Better to know sooner rather than later.
3. Determine the location and status of your foundation.  With our row house, the foundation didn't go much beyond those existing 6 foot walls.  In our case, we would need to underpin and support the foundation more.  We were given the choice to pay to underpin our (and both our neighbor's foundations) or to pour concrete around the perimeter of the foundation to create a ledge that would support the foundation.  The general rule of thumb is a 1:1 ratio of length to depth, so we opted for a two foot wide ledge to gain two feet of ceiling space.  Sure we would lose 4 feet of basement width, but we decided to leave the ledges exposed so they could be used for storage.   
4. Determine local building codes for underpinning.  In our case, the department of buildings required us to support the foundation in three foot long sections of concrete.  We had to stagger the sections and have each stagger inspected before proceeding.
5. Determine an entrance/exit path for concrete and dirt.  Since most Brooklyn basement have old coal shoots, we used opening along with a conveyor belt to get rocks and dirt out and concrete in.
6. Beware of rocks.  When you dig a few feet down you are bound to hit some rocks.  We had the good fortune of hitting a human sized piece of black granite.  Since you are in a cellar you cannot use explosives to break up the rock, so we used saws, drilling and good old fashioned chipping to get that rock out. 
7. Create a border for your support ledges.  We used decking and plywood to keep the ledges level and supported when the concrete was poured.  Later the plywood was removed. 
8. Dig Down to your desired depth, remove dirt and pour slab
9. Use a concrete sealer paint to paint the ledges - these could also be covered in sheetrock or pretty much any other material you desire.  But plain concrete is dirty and dusty.  
10. Arrange walls and doors and needed.  Then enjoy your new found ceiling height!

NOTE:  Pay close attention to where you house sit compared to the water table.  If your cellar is prone to flooding, think about installing a sump pump in the floor before you pour the slab.  This is much easier than going back later and doing it.