It depends on whether you own your property and have equity, whether you have payment breaks or are in arrears etc.
It comes down to your personal circumstances and what happens during the course of the IVA.
IVA started March 2011, Completed March 2016 and certificate issued 11 days after final payment. It was not always easy but then some of the best decisions aren't.
Reasons for extension will be detailed in the agreement you signed -- usually those mentioned above, the biggie being equity release. It is all in your paperwork.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014