1099-S for sale of a small fraction of lot on which my house sits

I sold a 1 foot swath of my 40 foot wide lot for "X" dollars.  (This land is added to the size of the adjacent lot which will allow a new house to be built there).  The use of the house which is my permanent address is unaffected because I received an easement for exclusive use.  How do I determine the cost basis for this sale?  Would it be the 1/40 of the land portion of the original purchase price of the house (i.e house and land)?  Also, TurboTax is not set up to handle a real estate sale like this and so treats this sale as equivalent to the sale of a house. The end result is that I owe no tax on nearly 100% of the proceeds.  Does this make sense?