Exemption u/s 54

I am a CA Inter Student...

I learnt that to avail the exemption u/s 54 (Capital Gain), one should purchase a residential House Property (RHP) within 2 year of transfer (or, before 1 year of transfer) or construct the house property within 3 years pf transfer.

I have a doubt whether purchase of a RHP and then improving it (making additional floors) amounts to construction? 

Can I purchase a RHP  after 2 year (before 3 year) and reconstruct it and avail the same exemption?