Depending upon the layout of your home you may find that a mattress will fit - because it bends - but the foundation won't make a corner or go up a flight of stairs. In the same way that a king set always come with a 2-piece, split foundation, many people buying queen sets - and, occassionally, full sets - discover that they need a 2-piece foundation to make things work.
This is particularly true in:

• Cape Code design homes
• Older homes/farm houses
• Some apartments

You can get a split queen foundation, with a new set, at the time of purchase for a $50 upcharge. Wholesale Warehouse also stocks queen-size split box sets. Please note that split-full sets are a special order item.