Basic Comparison

• Simply stated, shiplap, milled lumber consists of simple interlocking pieces, where the top and bottom of each board is milled with a rabbet joint to form an attractive wood siding. On the other hand, tongue and groove boards are cut so that the tongue of one piece fits into the groove of the adjacent piece in an interlocking method.
  
  

Advantages of Tongue and Groove

• Tongue and groove siding fits together to do a better job of keeping the elements out of the house than shiplap. This enables the workman to install the siding in either a vertical or horizontal manner, though horizontal is more common. Tongue and groove siding tends to lay flatter against the building.
  
  

Advantages of Shiplap

• Shiplap is cheaper than tongue and groove, but it requires a bit more work on the carpenter to get the rows to lay flat against the building in a waterproof fashion. Also, if not installed properly, shiplap is more likely to warp and leak than its counterpart. However, a correctly installed exterior of shiplap siding has a finished appearance that appeals to many homeowners.